Abstracts are listed in alphabetical order by surname (family name) of the primary author. Authors whose names appear with more than one paper are identified biographically in one paper, and referenced in the other(s). Speakers are indicated by an asterix. More than one asterix indicates poster presentation by several authors.

Abstracts and biographies were sent to primary authors for proof-reading. They have also been proof-read in part by Ibrahim A. Al-Jallal, Richard D. Chimblo, Ronald B. Clark, Joshua D. Cocker, John Filatoff, Dennis J. Fyfe, Geraint W. Hughes, Panos G. Kelamis, Daniel A. Nietupski, Rex C. Price, Arnold M. Rivett and Hasan S. Talu from Saudi Aramco, and Peter J.R. Nederlof from PDO.

Some authors could not be contacted to provide photographs.

Abstracts should be referenced as:

Author(s) 1996. Title of Abstract. Presented at the 2nd Middle East Geosciences Conference GEO’96. GeoArabia: Middle East Petroleum Geosciences (Abstract), v. 1, no. 1, p. X.

Application of Source Rock Maturity Studies in Basin Thermal History. Example: Lower and Middle Cretaceous Formations of Kuwait

Abdullah, Fowzia H.A.*

Kuwait University

and Robert R.F. Kinghorn

Imperial College, UK

A correlation was made between theoretical and experimental maturity levels to investigate the thermal history of the area. Rock samples of Lower and Middle Cretaceous age were collected from four well locations in Kuwait. Maturity was measured using the following parameters: thermal alteration index TAI, vitrinite reflectance and pyrolysis thermal parameters. A comparison of the different parameters indicates that oil generation starts at a depth of 3,050 ± 305 meters (10,000 ± 1,000 feet). The input for the theoretical TTI index calculation were taken from well logs. The results indicate an overestimated maturity level (depth of oil generation = 2,530 ± 90 meters, 8,300 ± 300 feet). This might indicate that the amount of heat received by these sediments was not constant during time and was lower than present day situation by 5 to 7°C per kilometer as indicated by the TTI calculation. This change in geothermal gradient with time cannot be related directly to plate tectonic movement in the area. It might be a result of local geologic changes. Many geologists related the anticlines in the area around the Gulf to be a result of epirogenic movement. The possible explanation is an upward migration of salt rocks with time that formed the broad elongated domes of the studied fields. As the salt approaches the surface with time the geothermal gradient increased.

Fowzia H.A. Abdullah is an Assistant Professor in the Geology Department of Kuwait University since 1993. She worked as a teaching assistant for three years at Kuwait University. Fowzia joined the Environmental Protection Department in Kuwait as a researcher for two years. She has a BSc in Geology and a MSc in Petroleum Geology from Kuwait University. She obtained her PhD and DIC from Imperial College, London University in 1993 in Petroleum Geology.

Robert R.F. Kinghorn is currently a Lecturer in the Geology Department of Imperial College, University of London. He has over 25 years experience in teaching and research, principally in organic geochemistry, the formation of oil and gas and basin modeling. He is the author of a book and several papers on these subjects and has undertaken overseas lecture tours. He has a BSc in Chemistry from Edinburgh University, a BA in Geology from the Open University and PhD from London University.

Geographical Information System (GIS) and Remote Sensing in the Exploration Environment

Abel, Roger D.* and W. Mark Tuttle

Petroleum Development Oman (PDO)

Geographical Information System (GIS) technology and Remote Sensing have been implemented in Petroleum Development Oman (PDO) within the Exploration Topographic Department in support of various applications over the previous two years. This paper discusses the approach adopted by PDO, the techniques used, and the benefits to the business. The primary uses for GIS technology within exploration are in providing users with simple access to corporate attribute data via a uniform map-based interface, in providing the means to carry out data quality control, spatial analysis, and mapping. Initially GIS technology had been implemented with applications linking to the corporate well database, to prospect and lead databases for portfolio management, and to seismic 2-D and 3-D location and interpretation data. Particularly for personnel new to the PDO environment, GIS provides a tool for users to become quickly familiar with the available corporate data and for managers to analyze data in a way not previously possible. This paper will demonstrate how the implementation of GIS in combination with the development of homogenous corporate databases is leading to an improvement in data quality, in wider use of common datasets, and better decision making.

Since January 1994, PDO has used digital satellite images of the earth in support of hydrocarbon exploration activities. Specific applications of these methods to exploration processes include mapping of surface sedimentation and near-surface geological features for identification of 3-D seismic velocity anomalies resulting from incorrect application of statics corrections, identification of difficult and hazardous areas in support of planning seismic acquisition surveys, and assessment of environmental impact resulting from geophysical prospecting. This paper will review various techniques and methods of enhancing multispectral and multitemporal image data, and show specific examples of their application to petroleum exploration.

Roger D. Abel is currently a Topographer with Shell International Petroleum Company with assignments in New Zealand, Holland and Oman. Roger also worked with Gardline Surveys, UK as Hydrographic Surveyor, primarily in the North Sea from 1980 to 1982 and with Plowman, Craven and Associates as Land Surveyor between 1978 and 1980. Roger holds a BSc (Honors) in Land Surveying Sciences.

W. Mark Tuttle graduated in 1983 with a Diploma in Engineering and in 1988 received his BSc in Geodetic Engineering. He has ten year cummulative experience in surveying and mapping within the service and oil industries. Mark is a member of the Association of Professional Engineers, Geologists and Geophysicists of Canada and the Association of Canada Land Surveyors.

Characterization of the Upper Arab-D Reservoir, Abqaiq Field, Saudi Arabia

Abu-Ali, Mahdi A.*, Abdullah S. Al-Shamsi, Tarek A. Bin-Afif and George A. Grover

Saudi Aramco

The Upper Arab-D, or Zone-1 reservoir represents a significant but little produced interval within the larger Arab-D reservoir at Abqaiq Field. The Arab-D is divided into 3 main reservoir zones with Zones-2 and 3 contributing most of the oil production. The Upper Arab-D is less than 30 feet thick, consists of a basal low-porosity dolomite to dolomitic limestone, a medial high energy skeletal-peloidal grainstone/packstone reservoir facies, and an upper unit of interbedded dolomudstones, cryptalgalaminates and nodular-to-bedded anhydrites that generally grades upwards into massive anhydrite. Open hole logs indicate high oil saturations, but flow meters reveal little to no contribution from Zone-1, regardless of completion type in vertical wells. This necessitates development of Zone-1 via long-radius (>1,000 feet lateral section) and short radius (<1,000 feet) horizontal wells to deplete recoverable oil, and to avoid contribution of water from Zone-2.

Successful development of the Upper Arab-D requires detailed characterization, correlation and mapping of the basal dolomite unit, containing very thin (1 to 2 feet) impermeable beds within it. These beds are important in preventing cross-flow of water from Zone-2, but are beyond the resolution level of open-hole logs. Porosity-permeability transforms from core analysis data coupled with petrographic data have enhanced the ability to predict and map the impermeable beds in non-cored wells. Porosity and permeability maps based on minimum cut-off porosity values, and aerial distribution of the basal dolomite unit are providing the necessary geologic control for horizontal well placement. This will optimize depletion of recoverable hydrocarbon, using both long- and short-radius horizontal drilling technology, from the Upper Arab-D reservoir at Abqaiq Field.

Mahdi A. Abu-Ali has been with Saudi Aramco for 11 years in R&D, exploration and recently reservoir development. His areas of interest include reservoir characterization and modeling, basin analysis, hydrocarbon generation and migration, and oil-source rock correlations. Mahdi is affiliated with the AAPG, ACS and EAOG. He holds a BSc in Industrial Chemistry from King Fahd University of Petroleum and Minerals and a MSc in Geochemistry from the Colorado School of Mines, USA.

Abdullah S. Al-Shamsi received his BSc in Geology from King Fahd University of Petroleum and Minerals, Saudi Arabia in 1989. After graduation he joined Saudi Aramco and worked as a carbonate Geologist in Ghawar field studying the Arab-D reservoir using cores and thin sections. In 1994 he went to Canada to work with Chevron Canada Resources on a training assignment for nine months. Now Abdullah is working on 3-D seismic interpretation in Abqaiq field.

Tarek A. Bin-Afif has been employed by Saudi Aramco since his graduation from King Fahd University of Petroleum and Minerals in 1978 with a BSc degree in Geology. For the past four years, he has been involved in updating geologic models in northern Ghawar and Abqaiq fields in support of reservoir management and simulation.

George A. Grover is a Reservoir Geologist in the Geological Department at Saudi Aramco. George was previously a Research Geologist with Chevron Petroleum Technology Company, La Habra, California (1985-1990), and an Exploration Geologist with Gulf Oil Company, Texas (1981-1985). He holds a PhD in Geology (1981) from Virginia Tech.

Application of Computer Technology to a Geologic Mapping Study in Saudi Arabia

Al-Amer, Abdullah I., Brian E. Gratto* and Mohammed A. Waheed

Saudi Aramco

Advances in computer applications that facilitate mapping, correlation and cross-sections provide an efficient method in studying regional geology. To achieve the goal of providing an accurate geologic framework to support field development, drilling operations and reservoir studies, this paper describes the applications and methods used to re-correlate the Pre-Neogene to Upper Cretaceous interval in some oil fields of Saudi Arabia. The project consisted of collecting shallow log data and loading it into a cross-section package (Pre/Mier), which was then used as a project database to interactively enter new picks or review and revise the existing picks. Data was extracted from Pre/Mier and loaded to a mainframe database (M204) where existing routines allowed ZMapPlus to provide preliminary isopachs. Pre/Mier was then utilized to re-examine and correct erroneous data that had been highlighted on these isopachs. Changes were then reloaded to the mainframe database. The final set of integrated isopachs and structure maps was completed using the point gridding algorithm, a True Vertical Thickness Macro, two seismic reference maps, and the interactive editor in ZMapPlus. Stratamodel/GTM was then used to visualize these grids to gain a better understanding of the influence of the Pre-Aruma Unconformity and stratigraphic variations within the interval studied. This approach yielded some insight into the structural history of the major oil fields and met the goals of providing an accurate suite of maps to support drilling operations and as a basis for further reservoir studies.

Abdullah I. Al-Amer completed his BSc in Geology (1984) from King Saud University, Riyadh. He is a member of the Dhahran Geological Society and has worked for Saudi Aramco since 1984. His work included assignments in exploration, hydrology, well-site, geo-technical services and an overseas project with Texaco in 1991. He is currently a Senior Geologist in the Northern Area Reservoir Geology Division, Saudi Aramco.

Brian E. Gratto received his BSc in Geology from Queens University in 1977. He worked for Saudi Aramco from 1982 to 1990 and rejoined the company after earning a MMath (Computer Science) degree from the University of Waterloo in 1993. He is a member of the AAPG, DGS, and is currently a Geologic Specialist supporting computerization of mapping, cross sections and 3-D modeling in the Geology Department of Saudi Aramco.

Mohammed A. Waheed graduated in Geology from Osmania University, India in 1963. Mohammed has 28 years work experience and has worked in the Exploration Department of a major oil company in Canada from 1967 to 1981. He joined Saudi Aramco in 1982, and since 1985, his work includes regional geology, stratigraphic modeling, reservoir studies and training of Saudi professionals. Mohammed is currently a Senior Staff Geologist working in the northern offshore areas of the company. He is an active member of the AAPG and DGS.

Permo-Carboniferous Glaciogenic Deposits, Al-Khlata Formation, Oman: An Outcrop Study

Al-Belushi, Juma D.*, K.W. Glennie and Brian P.J. Williams

University of Aberdeen, Scotland

The Al-Khlata Formation is an oil-bearing reservoir in Oman. Its origin during the Late Paleozoic Gondwana glaciation in the southern part of the Arabian Peninsula is demonstrated by the glaciogenic deposits of the formation in Oman. Outcrops of the Al-Khlata Formation occur in a belt parallel to the Huqf fold axis, the best outcrops being found in the two wadis, Al-Khlata North and South. In the southern wadi, glacial deposits rest directly on northeast-southwest trending striated dolomites of the Precambrian Khufai Formation. Overlying the striated dolomites is a 6 meter thick grey, sandy and poorly sorted diamictite (tillite). The basal tillite unit is overlain by a sequence of conglomerates and pebbly sandstones. The paleocurrent of the conglomeratic unit was towards the northeast.

In Wadi Al-Khlata North, the Khufai dolomites are not striated where exposed. The sequence of the Al-Khlata Formation is approximately 10 meters thick and consists of a mixture of polymict diamictites, conglomerates, pebbly sandstones, sandstones and siltstones. Detailed correlation between the two wadis is not possible though the basal tillite unit is common to both.

Further north, the quality of the outcrops becomes very poor where they form low hills of a deflation surface caused by extensive weathering partly by associated sabkha conditions. The direction of ice movement has been interpreted by some workers to be from southwest to northeast based mainly on foreset directions in the sands overlying the striated pavement; however, it is stepped down erosionally to the southwest, which implies ice flow from northeast to southwest.

Juma D. Al-Belushi is currently a final year PhD student at the University of Aberdeen working on the HC-producing glaciogenic sediments (Permo-Carboniferous) of Oman and Australia. He has been employed by Petroleum Development Oman since 1992 as an Exploration Geologist. Juma is a member of the AAPG and SPE and has participated in many international conferences. He has a MSc in Petroleum Geology from the University of Aberdeen and is scheduled to graduate with a PhD in October, 1996.

K.W. Glennie received his BSc and MSc degrees from Edinburgh University. He then spent the next 32 years as an Exploration Geologist with Shell, working in New Zealand, Canada, Nepal, Oman, Iran and Turkey before spending 15 years on the North Sea geology based in London. He retired from Shell in 1987, and he is an Honorary Lecturer at Aberdeen University, spending part of each year since 1990 working on the desert of south-eastern Arabia and maintaining his interest in the Oman Mountains. He is a member of the AAPG and Geological Society of London, Edinburgh, Aberdeen and The Netherlands.

Brian P.J. Williams obtained a BSc (Honors) in Geology and a PhD in Sedimentology from the University of Wales. From 1964 to 1970 he worked as a Postdoctoral Research Fellow at the University of Ottawa, Research Fellow at the University of Wales, and a Senior Hydrogeologist for the Water Resources board in Reading. From 1970 onwards Brian was a Lecturer, Senior Lecturer and Reader in Sedimentology in the Department of Geology, University of Bristol. In 1988, Brian became Professor in Petroleum Geology at the University of Aberdeen where he is the director of the MSc course in Petroleum Geology. His current research interests include hydrocarbon reservoirs in Australia, Canada, Texas and the North Sea; non-marine clastic sedimentology and basin analysis. Brian is a member of the Institute of Petroleum, SPE, PESGB, AAPG, Society for Sedimentary Geology, International Association of Sedimentologists and the Geological Society of London.

FMI as a Tool to Optimize Horizontal Well Completions in Waterflood Carbonate Reservoirs

Al-Busaidi, Rashid S.

Petroleum Development Oman

The intensive horizontal drilling campaign at Petroleum Development Oman has had significant economical and technical merits. However, drawbacks were also apparent particularly with respect to early and unexpected water breakthrough i.e. not related to the bottom water sweep. This phenomenon was noticed in two of the carbonate fields of north Oman (Yibal and Lekhwair). To study this behavior, FMI logs were run in over 10 horizontal wells in each field. The objectives were to identify fracture systems and their lateral trends, occurence of fault related fractures, facies variations and sedimentary features.

The FMI logs indicated the presence of open and cemented high density fractured zones with most of the fractures oriented in line with the patterns of faults as interpreted from 3-D seismic. The FMI image pointed out a penetration of different electrofacies boundaries which are due to sedimentological variations; moreover, vugs and pyrite nodules have been identified. Based on these results it is concluded that the presence of fractures is the the primary cause of early water breakthrough. In general, wells where the FMI results were used to select the completion intervals (i.e. avoidance of perforating of fractured intervals) showed better production performance (i.e. lower watercut). High density fractured zones, in most cases, indicate the existence of fault(s). Some of these faults are below the seismic resolution.

Rashid S. Al-Busaidi is currently a Production Geologist with Petroleum Development Oman. He has 6 years of petroleum engineering and drilling experience. Rashid received a BSc in Geology from Yarmouk University.

Optimization of Horizontal Wells in a Complex Carbonate Reservoir, Onshore Abu Dhabi

Al-Deeb, Maged A.A.*, Waddah T. Al-Hanai

Abu Dhabi Company for Onshore Oil Operations (ADCO) and

Mahmood Akbar

Schlumberger, UAE

The development of highly heterogeneous carbonate reservoirs has been a big challenge to the oil industry for years. The problem is further aggravated when it comes to the complex reservoirs of a high API oil. Extensive efforts and planning are required to extract the oil from these reservoirs. This paper discusses how to boost the oil production from a highly heterogeneous reservoir, onshore Abu Dhabi. The formation is mainly comprised of dolomitic limestone with matrix and rock porosity distributed randomly in the form of patches of varying sizes. The porous areas of the formation are separated from each other either partially or completely by dense nodules or cemented areas of limestone.

Due to the erratic production behaviour of the vertical wells, some horizontal wells were planned. The first two horizontal wells in this reservoir could not achieve better production rates than the vertical wells. Therefore, a strategy was formulated to investigate the reason why the first two horizontal wells did not perform as expected and moreover, to design the trajectories for future horizontal wells. The downhole imagery, well logs and cores from five vertical and two horizontal wells revealed the occurrence of fractures in the Simsima carbonates. The highest fracture density was observed in one of the vertical wells drilled in the crestal area of the field. In contrast, the first two horizontal wells, also placed in the crestal region, intersected just a few small fractures.

The fracture analysis suggested a dominance of northeast-southwest striking longitudinal fractures in the anticline. Therefore, guided with the findings of the study, the locations and kick-off directions and trajectories for subsequent horizontal wells were accordingly planned. The first horizontal well drilled in light of the study results, produced ten times more than the previously drilled vertical and horizontal wells.

Maged A.A. Al-Deeb is a Lead Reservoir Geologist with ADCO. He has 20 years of industry experience, 6 with Gulf of Suez Petroleum Company, Egypt. His interests include carbonate reservoir characterization, fracture reservoir, core analysis and data integration. For the past 7 years, he has been involved in horizontal drilling projects. He has a BSc in Geology from Al Azhar University, Cairo, Egypt.

Waddah T. Al-Hanai holds a BSc in Chemistry from the University of Beirut, Lebanon, a MSc in Physics from Marquette University, USA and a PhD in Fluid Mechanics in Porous Media from the University of Bordeaux, France. His work experiences include reservoir engineering which involves supervising simulation and study works. His fields of interest are mathematical formulation of the physics of two-phase flow and development of upscahng methods.

Mahmood Akbar is a Division Geologist with Schlumberger Middle East. He joined Schlumberger in 1985 as District Geologist for Pakistan until 1992 when he became Division Geologist for the Oman-Pakistan Division. Since 1993, Mahmood has been with Schlumberger Dubai. He received BSc and MSc degrees in Applied Geology in 1983 and 1985 respectively, from the University of Punjab.

The Challenge of Interpreting 3-D Seismic Over Shaybah Field

Al-Faraj, Mohammed N.*, Michael D. Ferguson and Ibrahim A. Al-Ghamdi

Saudi Aramco

The giant Shaybah Field, situated in the northeast region of the Rub Al-Khali desert in Saudi Arabia, was discovered in 1968. 2-D seismic and well control were used at the time to delineate the field. With development of the field now likely to commence in the near future, an ambitious 3-D seismic program was launched in 1993 in order to synthesize a detailed picture of the geology encompassing the hydrocarbon accumulation in the field.

Over 120 million seismic traces, covering an area of about 1,100 square kilometers were acquired in a rough terrain consisting in its entirety of flat sabkhas and high sand dunes. The mountainous sand dunes, reaching as high as 200 meters at times, posed a severe static problem; up to 180 milliseconds of time corrections were often applied to the seismic traces in order to resolve sand-related static effects.

In addition to complex topography, the 3-D structural interpretation had to overcome sub-surface problems related to lithofacies and biofacies distributions. First, the lithology of the gas-capped oil reservoir consists predominantly of carbonates, overlain by denser, compacted shale. The decrease in density at the reservoir level relative to that of the sealing shale creates an imaging problem: namely, a weak reflection at the top of the reservoir. Second, and probably of utmost seriousness, is the mapping of an undulating reservoir surface resulting from the presence of carbonate rudist buildups, which also results in the top of the reservoir not conforming to its base.

Mohammed N. Al-Faraj received a BSc in Electrical Engineering from the University of Wisconsin Milwaukee in 1983, and MSc and PhD in Geophysics from The Colorado School of Mines in 1987 and 1993, respectively. From 1983 to 1984 Mohammed worked as a Project Engineer for SCECO in Saudi Arabia. Since 1984, he has been with Saudi Aramco. His interests include seismic data processing, reservoir characterization, and working on multi-disciplinary teams. He is a member of the SEG and EAEG.

Michael D. Ferguson received his BA in Geology from the University of South Florida in 1977. From 1977 to 1981 he worked as a Geophysical Engineer with Geophysical Services International in Saudi Arabia. In 1981, Michael joined Aramco Overseas Company as an Exploration Geophysicist based in Croydon. Since 1982, he has been with Saudi Aramco as an Exploration Geophysicist in Interpretation in Dhahran. His interests include 3-D seismic workstation interpretation, seismic data processing and reservoir characterization.

Ibrahim A. Al-Ghamdi is an Exploration Geologist working with the Exploration Organization in Saudi Aramco since 1985. He has worked in area exploration, reservoir geology and wellsite. Ibrahim also worked in special projects including reservoir modeling with EPRCO in 1989. Most of his work concentrated on carbonates of the Jurassic and the Cretaceous of Arabia. He is interested in carbonates, artificial intelligence, sequence stratigraphy, geostatistics and field geology.

Deterministic Versus Stochastic Approaches in Reservoir Characterization: A Review

Al-Fares, Mohammad H.* and Panos G. Kelamis

Saudi Aramco

Two distinct approaches in reservoir characterization are identified. The first approach employs “deterministic” methods which rely on theoretical relationships between the reservoir model parameters and the data observed. A deterministic model in this approach is estimated by simulating its response so that it matches the measured data. The simulation part requires a physical relation to be known so that a synthetic response for a given model can be generated. Mapping acoustic impedances from post-stack seismic amplitude data belongs to this category. This approach, however, can be limited by our understanding of the underlying physics relating the reservoir model parameters to the data observed. The second approach employs “stochastic” methods, which capitalize on the statistical properties of the model/data directly rather than the theoretical relationship between the two. They can generate multiple equiprobable realizations of a single parameter along with its uncertainty distribution. Kriging techniques belong to this category in which a variogram is used to quantify spatial correlation and variability of a property as a function of distance and direction. The use of the two approaches of deterministic and stochastic modeling is evaluated with geological, geophysical and engineering data and a proposed third approach is investigated by combining the two.

Mohammad H. Al-Fares has been with Saudi Aramco as Research Geophysicist since 1984. He obtained his PhD from the University of Southern California in 1992. Mohammad is a member of the SEG and EAEG. He is professionally interested in Inverse Problem Theory and Reservoir Geophysics. He holds a US Patent for his innovative seismic inversion technique.

Panos G. Kelamis holds a BSc (Honors) in Physics from the University of Athens, Greece (1977), MSc and DIC in Geophysics from Imperial College, London and a PhD in Geophysics from the University of Alberta, Canada (1982). He worked with Western Geophysical in Houston and Dome Petroleum in Calgary. Panos joined the Geophysical R&D Division of Saudi Aramco in 1985 where he is currently Head of Field Development. He is a member of the SEG, EAEG and is the SEG Representative for Africa and the Middle East.

Hydrocarbon Potential of Iraq

Al-Gailani, Mohammad B.

GeoDesign Limited, UK

Iraq is one of the most exciting oil exploration opportunities in the Middle East. Hydrocarbon reserves are enormous, estimated at around 150-200 billion barrels. The remaining potential is at least as large with vast areas of around 150,000 square kilometers still waiting to be explored.

There are over 526 known structures delineated and only 125 (24%) are known to have been drilled. Out of the 125 drilled structures over 90 are proven field discoveries but only 30 fields have been partially developed. Most of the current developed reservoirs lie in the Tertiary, Upper and Middle Cretaceous. New discoveries have been made in the Lower Cretaceous (Yamama), Jurassic (Najmah and Sargelu), Triassic (Butmah and Kurra Chine), Permian (Chia Zairi), Carboniferous (Ga'ara), Silurian (Akkas) and Ordovician (Khabour) reservoirs. There are 47 known reservoirs, ranging from Ordovician to Miocene. The most common reservoir is the Zubair Sandstone which is present in over 27 fields. The majority of the fields consist of stacked reservoirs reaching up to ten pay zones in the giant Majnoon field where only the Lower Cretaceous has been reached. Deeper prospects are still awaiting drilling and testing. Over 30 to 40% of proven Iraqi oil reserves lie within a few thousand feet. More than 60% of the remaining discovered reserves lie within 10,000 feet. The finding cost of oil is probably the lowest in the world. The current cost is estimated at around 50 cents per barrel. The drilling success rate is the highest in the world and varies between 1 in 2 in the Mesopotamian basin and up to 1 in 4 in the western and northwestern areas.

Mohammad B. Al-Gailani is currently Managing Director of GeoDesign Limited, a consultancy office based in London specializing in databases of the Middle East. He graduated from Baghdad University in 1972 with a BSc in Geology and worked briefly for the Iraqi National Oil Company in Baghdad. He won a scholarship in 1973 for Post-Graduate studies in Petroleum Geology where he obtained his MSc in 1974 from the University of Aberdeen and then a PhD and DIC in January 1979 from Imperial College, London. Mohammad worked as an independent Consultant in the Middle East and the Parana Basin in South America. He has published several papers on diagenesis and reservoir characteristics at unconformities. He has been an active member of the AAPG since 1973 and the Petroleum Exploration Society of Great Britain.

Early Evaluation of Potential Hydrocarbon Zones in Abu Dhabi Wells by Using Mud Log Data and Gas Ratios

Al-Habshi, Abdulrahman S.*

Abu Dhabi National Oil Company (ADNOC)

Michael Redmond* and Philip M. Soar

Gearhart Middle East, UAE

Mud Logs provide total hydrocarbon and chromatographic analysis of light hydrocarbons (Methane to Pentane, C-1 to C-5) released during the drilling process, measured at the header tank. The primary requirement is to obtain relative measurements of the gas content of the mud returning from the well.

A number of Industry Standard Gas ratios of the light hydrocarbons produced were calculated and integrated with other relevant parameters such as wireline logs, drilling and geological data to locate zones of interest which require further evaluation and production testing to determine hydrocarbon fluids and reservoir boundaries during the drilling of the wells.

Previously, zones of interest were analyzed on a point-by-point basis, if at all. Recent advances in computerized acquisition and interpretation of gas data has improved the quality of data available so that it is now possible to apply these calculations over complete intervals, or the well, in near real-time.

In this paper, several examples are shown from Abu Dhabi Cretaceous, Jurassic and Upper Permian reservoir sections to demonstrate successful delineation of porosity and fluid content by application of qualitative and semi-quantitative gas ratios. Further examples are shown from previously drilled wells where this technique could aid future successful evaluation of wells during drilling.

Abdulrahman S. Al-Habshi is currently Supervisor of OPCOS Areas Geology with Abu Dhabi National Oil Company (ADNOC), Abu Dhabi, UAE. He has 23 years of experience in geology of which six and a half years were with the French company BRGM, Jeddah, Saudi Arabia, four and a half years with the Petroleum Department, Abu Dhabi, UAE and 12 years with ADNOC, Abu Dhabi. Abdulrahman is a member of the SEE and SPE societies. He obtained his BSc in Geology from Baghdad University in 1971.

Michael Redmond is General Manager of Gearhart Middle East Ltd. in Abu Dhabi. He has 15 years experience in the oil industry in northwest Europe and the Middle East including managerial positions in the geological and engineering service companies in the Middle East for the past 10 years. He is a Fellow of the Geological Society of London, and a member of the AAPG, SPE, SEE, IMWDS, and holds a BSc in Geology from Imperial College, University of London.

Philip M. Soar is the Operations Manager with Gearhart Middle East Ltd., Abu Dhabi. He has 16 years experience in the oil industry in northwest Europe, Australia, North America and North Africa, and has worked on exploration and development drilling projects in the Middle East for the past 9 years. He is a member of the SPE, SEE and IMWDS, and holds a BSc in Geology from the University College of South Wales, Cardiff.

The Occurence of Devonian Sediments in the Eastern Ghawar Area, and their Exploratory and Stratigraphic Implications

Al-Hajri, Sa'id A.*, Lawrence E., Wender, John Filatoff and A. Kent Norton

Saudi Aramco

Historically, strata of Latest Devonian age (Famennian) have never been identified in the Kingdom of Saudi Arabia. However, recent deep gas exploratory drilling at the Harmaliyah structure, located east of Ghawar oil field has proved for the first time the existence of strata of this age. This new phase of exploratory drilling activity in the Eastern Ghawar Area is focused on the early Middle Devonian Jauf Formation. The Devonian is missing on the crest of Ghawar as a result of uplift and erosion associated with the Hercynian Orogeny of Late Carboniferous age. Drilling on the eastern flanks of Ghawar, as well as low relief structures such as Harmaliyah, however, has penetrated a fully preserved Devonian section.

Based on palynological evidence and the recovery of palynomorphs belonging to the Retispora lepidophyta zone, Late Famennian age is assigned to the upper part of the Jubah Formation. Furthermore, high resolution biostratigraphic correlation with the standard zonation of south-western Europe indicates that part of this section belongs to the LE biozone of Streel et al. (1987), and the pusilites-lepidophyta biozone of Richardson and McGregor (1986). The existence of this previously unrecognized section further validates the flank play concept and confirms that Devonian strata are preserved on the flanks of high-relief Hercynian structures such as Ghawar.

Sa'id A. Al-Hajri is a Biostratigrapher with Saudi Aramco. He holds a BSc in Geology from King Fahd University of Petroleum and Minerals and MSc in Geosciences from Penn State University. In 1992, he received the “Highest Technical Contribution Award” from Saudi Aramco. Sa 'id is a member of CIMP, AASP, BMS and DGS, and has published several papers on geological and palynological subjects.

Lawrence E. Wender is a Geological Consultant with Saudi Aramco in Dhahran. He was previously with Mobil Oil Corporation and has 17 years of oil industry experience. He is currently Team Leader of the Ghawar Pre-Khuff Gas Project. Lawrence holds a MSc in Geology from the University of Utah.

John Filatoff is a Palynologist with Saudi Aramco‘s Geological R&D Division where his activities, since joining in 1992, have focused mainly on Tertiary Red Sea and Paleozoic deep-gas exploration. John has some 25 years of oil-industry experience, primarily in Australia, but also in Iran and Venezuela. He holds BSc and PhD degrees in Geology from the Universities of Queensland and Western Australia, respectively. He is a member of the Dhahran Geological Society, Geological Society of Australia and the Petroleum Exploration Society of Australia, as well as a number of specialist palynological societies, viz. AASP, CIMP and PPAA.

A. Kent Norton is currently an Explorationist for Saudi Aramco‘s Area Exploration Department where he has worked since 1991. He previously worked for Saudi Aramco‘s Geophysical and Geological Departments from 1979 to 1985. Kent received a BSc in Geology from the University of California, Davis in 1979 and a MSc in Geology from Northern Arizona University in 1990. He is a member of the AAPG and the DGS.

Geological Intepretation of the Shuttle Imaging Radar SIR-C/X-SAR Data of Saudi Arabia

Al-Hinai, Khattab G.*, Abdallah E. Dabbagh, Weston C. Gardner and Muhammad Asif Khan

King Fahd University of Petroleum and Minerals, Saudi Arabia

The Space Shuttle Endeavour, carrying Shuttle Imaging Radar (SIR-C/X-SAR), imaged selected parts of the Earth during the two missions in April and October, 1994. The SIR instrument acquired remote sensing data in L, C, and X bands. The main objective of the experiment was to assess the utility of radar imagery for multiple mapping and environmental applications. The Research Institute, King Fahd University of Petroleum and Minerals, participated in the NASA Science Plan to evaluate the Shuttle Imaging Radar data for paleo-drainage and geologic mapping.

The geologic interpretation of the L-band image strips over the Arabian Peninsula has revealed faults, folds, joints, basalt flows (harrats) and stream drainage patterns which are not clearly visible on other remote sensing images (Landsat and SPOT) and are not shown on existing geologic maps. By virtue of its shadowing and shallow sand penetration capability and sensitivity to terrain textural factors, the radar images complement and enhance other remote sensing data to provide a new and unique view of the Earth‘s surface.

Khattab G. Al-Hinai is the Manager of the Remote Sensing Center, Acting Manager for the Division of Geology and Minerals at the Research Institute and an Associate Professor in the Earth Science Department of the King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. Khattab received a PhD in Remote Sensing-Geology from Imperial College in 1988 and a MSc and BSc in Geology and Engineering Geology, respectively, from the American University of Beirut. He joined the Research Institute in 1980 as a member of the Division of Geology and Minerals. He has been involved with several funded and in-house projects pertaining to sand dynamics, sand control, engineering geology and remote sensing. Khattab participated in the development of laboratories, manpower and research programs in the division. He is the author of numerous research papers and has participated in writing and editing many technical reports for the Research Institute.

Abdallah E. Dabbagh is the Director of the Research Institute, KFUPM. He completed his BSc in Geology in 1968 from the American University of Beirut and PhD in Geology in 1975 from the University of North Carolina. Following his PhD, he was appointed Visiting Lecturer in Princeton University for one year. Since then, he joined the academic ranks at KFUPM. Abdallah‘s primary activity is in the management of research, but he is strongly interested in the transfer, application and adaptation of modern technology with specific emphasis on environmental applications of remote sensing and utilization of radar imagery. He has received several scientific awards including the King Faisal medal in 1985. He was on the Board of Directors of Saudi Aramco from 1989 to 1996. He was appointed to three National Committees, and has served as a representative of Saudi Arabia at numerous international energy and environmental conferences and panels.

Weston C. Gardner is a Senior Research Scientist in the Division of Geology and Minerals at the Research Institute of KFUPM. Most of his professional career was with Mobil Oil during some 38 years of employment as a Petroleum Explorationist and Research Geologist. In 1971 he received his PhD from Northwestern University, USA. He has long been involved in the geological interpretation of airphoto and space images. He has taught courses in both Remote Sensing and Petroleum Geology at Trisakti University in Jakarta, Sultan Qaboos University in Oman and KFUPM in Dhahran. He is currently completing a geological interpretation of some 50,0 kilometers of SIR-C radar strips of the Arabian Peninsula, recorded in April and October 1994 from the NASA space shuttle Endeavor.

Muhammad Asif Khan is a Research Specialist in the Remote Sensing Center, Geology and Minerals Division. He completed his BSc and MSc from Punjab University, Pakistan in 1969 and 1971, respectively. He obtained another MSc degree in Remote Sensing and Digital Image Processing from University of Tennessee, USA in 1981. At KFUPM, he has been associated with the establishment of the Remote Sensing Center and has contributed to numerous client funded research projects requiring the utilization of remote sensing data. He participated in several international programs to evaluate the applications potential of future generations of remote sensors (SIR-C/X-SAR, JERS-1, and ADEOS) for earth resources mapping and environmental monitoring. He is the author of numerous research papers and technical reports. His research interests include remote sensing applications, digital image processing and geographic information systems.

Characterizing Fractured Reservoirs in the Arabian Gulf

Al-Husseini, Moujahed I.*

Gulf PetroLink, Bahrain

Jean Letouzey* and Marie-Christine Cacas*

Institut François du Pétrole, France

The Precambrian Basement of the Arabian Plate consists of a regional system of horsts and grabens which initially formed during the Infracambrian. The horsts are mostly north-south trending basement blocks while the grabens are filled by Infracambrian evaporites. The major oil fields in the graben regions are salt domes, whereas the fields which correspond to the horst blocks are basement-controlled. The latter group of fields are generally truncated by northwest-southeast or northeast-southwest trending faults.

The structural development of the Gulf fields occurred during periods when important regional stresses were applied by extended large-scale tectonic episodes. These periods are associated with four major tectonic events: (1) Infracambrian Intra-continental Extension; (2) Late Paleozoic Hercynian Orogeny; (3) Triassic Extension associated with the Zagros Rift System; and (4) Late Cretaceous to Present Zagros Orogeny.

Detailed fault and fracture models of reservoirs in the Gulf Region are developed by combining: (1) orientation and structural growth history of the fields relative to the regional paleo- and current stress fields; (2) fault interpretations from 2-D and 3-D seismic; (3) micro-fracture analysis from well logs and cores; (4) field studies of fractured outcrops; and (5) analogue modeling.

Moujahed I. Al-Husseini founded Gulf PetroLink in 1993, a consultancy aimed at transferring technology to the Middle East petroleum industry. Moujahed was previously Exploration Manager for Saudi Aramco. He received his BSc in Engineering Science from King Fahd University of Petroleum and Minerals (1971), MSc in Operations Research from Stanford University (1972), PhD in Earth Sciences from Brown University (1975) and Program for Management Development from Harvard University (1987). Moujahed is a member of the AAPG, SEG, EAEG and SPE. He is the Editor-in-Chief of GeoArabia and has published over 20 geoscience papers.

Geo'94 Available:

Gulf PetroLink

P.O. Box 20393, Manama, Bahrain

Tel: (973) 214 881

Fax: (973) 214 475

Geo'94

Middle East Petroleum Geosciences

Edited by Moujahed I. Al-Husseini

78 papers presented at Geo'94

Conference, Bahrain

April 25-27, 1994.

2 Volumes, 939 pages,

color throughout, hardbound

Available: AAPG Bookstore

P.O. Box 979,

Tulsa, OK 74101-0979

USA

Fax: (918) 560 2652

Tel: (918) 584 2555

Jean Letouzey has been with the Institut François du Pétrole since 1971. He is Deputy Manager of the Geology and Geochemistry Department. He received his MSc in Geology and PhD in Geophysics from the University of Paris in 1969 and he graduated in Geology and Geophysics from Ecole Nationale Supérieure des Pétroles et Moteurs in 1971. Jean is a member of the AFTP and AAPG and is particularly interested in basin studies and tectonics.

Marie-Christine Cacas joined the Institut François du Pétrole in 1990 and is presently in charge of reservoir fracturation modeling. She graduated from Ecole Nationale Supérieure d'Hydrolique de Grenoble in 1985 and received her PhD from Ecole Nationale Supérieure des Mines de Paris in 1989. She is particularly interested in rock fracturation and reservoir modeling.

The Development of Improved Reservoir Facies Beneath Dolomitizing Tidal Channels/Embayments: A Useful Tool for Reservoir Prediction in the Khuff Formation

Al-Jallal, Ibrahim A.

Saudi Aramco

Recent studies of the Khuff Formation in the Ghawar field of Saudi Arabia indicate that most of the reservoir facies are diagenetically controlled. The primary porosity of grainstones in the Khuff Formation has been affected by dolomitization, cementation or leaching. One of the most interesting observations during these studies is that the dolomitization process preserved, and sometimes enhanced, the primary porosity of the common subtidally deposited carbonate sands. The intensity of dolomitization increases with proximity to the overlying bioclastic wackestone - packstone facies interpreted to be of tidal channels/embayment deposits. These channels/embayments acted as continuous conduits for Mg-rich fluids sourced mainly by sea water, which were concentrated inland by evaporation. These fluids percolated downward and continuously dolomitized the rock beneath thus inhibiting the precipitation of anhydrite cements. This process preserved the original primary interparticle porosity and sometimes enhanced it with the addition of intercrysalline porosity between crystals within grains. This process resulted in high porosity and permeability at these localities.

In formations similar to the Khuff where shallowing-upward cycles occur, this relationship provides a potentially useful tool to assist reservoir geologists in their search for new reservoirs and additional reserves.

Ibrahim A. Al-Jallal is currently Chief Geologist in the Geological R&D, Exploration in Saudi Aramco. He received his BSc from the University of King Saud, Riyadh in 1973, a MSc from Western Michigan University, USA in 1979, and PhD in Petroleum Geology from Imperial College, University of London in 1990. His work experience involved well site operation, reservoir development, prediction and layering and depositional modeling. Ibrahim is the author of company reports on the Arab D and Khuff formations. His PhD dissertation was on the Khuff Formation‘s deposition, diagenesis and reservoir prediction in Ghawar field, Saudi Arabia. He recently extended this study regionally to include all of the Gulf States. Ibrahim is a member of the Editorial Advisory Board of GeoArabia.

The Role of Hydrogeology in Petroleum Development Oman

Al-Lamki, Mohamed S.S.*, Arafa M.A. Al-Harthy and Jos M.J. Terken

Petroleum Development Oman (PDO)

Hydrogeology has been studied in PDO since the early eighties. Initally, attention was focused on issues related to water supply and disposal. Increasingly, however, hydrogeology has provided an insight into the effect of salinity on oil saturation measurements and sub-surface temperature variations due to hydrodynamic flow. In south Oman, water is flowing in three main levels: the Cenozoic carbonates of the Umm Er Radhuma Formation and the clastics of the Paleozoic Haushi and Haima aquifers. The aquifer flow pattern is from the Qara Mountains in the south to the Umm as Samim sabkha in the north. Although impermeable strata are expected to isolate the different aquifer systems, salinity profiles and radiocarbon age-dating indicate that locally faults may breach the strata, thus allowing flow to take place across formations. As a result, aquifer water has become less saline and hence more resistive, masking the presence of the overlying oil on electric logs. On the basis of salinity data, water resistivities (Rw) have been mapped and the use of an Rw database has resulted in more accurate measurements of oil saturations. In the Marmul northwest field, for example, these corrections led to significant reserve additions as hydrocarbon saturations were increased from 30 to 70%. Present-day hydrodynamic cells are also clearly reflected by sub-surface temperature variations. Integration of the modeling results with other geological and paleoclimatic information has allowed the reconstruction of the thermal history of the South Oman Salt Basin and the prediction of oil quality for prospect evaluation.

Mohamed S.S. Al-Lamki is currently working as Hydrogeolgist with the Regional Studies Team of PDO. He holds a BSc from Straffordshire University and a MSc in Hydrogeology from University College London. Mohamed has worked in seismic processing, seismic interpretation and operations geology.

Arafa M.A. Al-Harthy is currently working as Production Geologist with PDO. He is involved with geological and operational aspects in petroleum engineering environment. Arafa is also working on a study to formulate Qarn Alam Area Water Management Plan.

Jos M.J. Terken (see Loosveld et al., p. 51)

Reservoir Characterization of the Ahmadi “Ab Zone”, Bahrain Field

Al-Madani, Adel A. and Yahya M. Al-Ansari*

Bahrain National Oil Company (BANOCO)

This study reveals that production of the Middle Cretaceous Ahmadi (Ab Zone) in Bahrain field is controlled by facies distribution. The Ahmadi (Ab Zone) sediments are comprised of a decimeter to meter bedded succession of shale and argillaceous and clean limestone. Lithofacies identified include, argillaceous bioclastic wackestone/packstone, bioclastic wackestone/packstone and bioclastic packstone. The bioclastic lithofacies contain the best reservoir characteristics with porosity and permeability ranging up to 22.3% and 3.0 mD respectively.

The methodology for predicting the bioclastic packstone facies from uncored wells requires an integration of wireline logs (both deterministic and probabilistic techniques) and core data.

Variations in production rates of Ahmadi (Ab Zone) may be attributed to one or more of the following: differences in permeability associated textural variations in the micritic matrix and the degree of diagenetic leaching of macrofossils, variation in the degree of hydrothermal leaching associated with the proximity of faults, proximity to faults and gas injectors that may be providing pressure support through the Ahmadi (Ab Zone).

Adel A. Al-Madani received his BSc in Geology from Ain Shams University in 1976. He joined BANOCO in April, 1977 as a Trainee Geologist and from 1979 to 1990 he worked as Explorationist in onshore and offshore areas. In 1991 Adel was assigned to work in the Bahrain field and he is currently working as Head Development Geologist.

Yahya M. Al-Ansari is a graduate of Geology from Qatar University (1993). He is currently working as a Development Geologist with Bahrain National Oil Company and is involved in reservoir characterization and formation evaluation research.

Synthetic Time-Velocity Pair Curves

Al-Nahwi, Hashim M.*, Adil A. Al-Khelaiwi James A. Richard, Lloyd W. Long and Arnold M. Rivett

Saudi Aramco

Saudi Aramco‘s processing database contains stacking time-velocity curves for thousands of lines in the Kingdom. In central and eastern Saudi Arabia there are lines spaced 10 kilometers apart or closer throughout current prospects. The velocity control already developed for these neighboring lines can be used to make processing easier.

A methodology was developed using time slice velocity mapping, which allows production of time-velocity data volumes for areas of interest. When new seismic lines are programmed, their survey coordinates are used to produce synthetic time-velocity pair data sets at appropriate locations. Newly shot seismic lines are stacked with these synthetic time-velocity curves.

Saudi Aramco‘s seismic data processing division has found that using these synthetic time-velocity curves reduces the effort needed for velocity analysis of infill seismic lines. This process is helping to produce a better product with less effort.

Hashim M. Al-Nahwi has worked for Saudi Aramco for 18 years in exploration. He holds a BSc in Geophysics from the University of New Mexico. Hashim worked for several years in the Depthing/Mapping Unit of the Geophysical Technology Division and has become concerned with the production and uses of velocity maps which are used in the depthing of 2-D seismic data.

Adil A. Al-Khelaiwi, Chief Geophysicist of Geophysical Technology Division, Saudi Aramco, has a BSc from the University of Liverpool. He has held several supervisory positions in the Geophysical Department. These assignments have enriched his experience in the seismic method from acquisition to reservoir characterization. Adil is a member of the SEG and DGS.

Arnold M. Rivett (see Rivett et al., p. 184)

James A. Richard is currently a Geophysicist with Saudi Aramco in the Depthing/Mapping Unit of the Geophysical Technology Division. He has 18 years of exploration experience: 13 years working in North America, and 5 in Saudi Arabia. He holds a BSc in Geology from Colorado State University and is a member of the SEG, RMAG, AAPG, and DGS.

Lloyd W. Long is currently a Geophysical Systems Analyst with Saudi Aramco. He has 17 years experience as a systems analyst, 13 of which are in the petroleum industry. Lloyd also has 7 years field experience working on seismic crews in North America and Saudi Arabia. He holds a BSc degree in Geology and Physics from Eastern Washington University and a MBA from Washington State University.

Completion Optimization of Horizontal Wells (Effect of Length, Diameter, Well Position and Perforation Scenario)

Al-Qahtani, Abdullah M.

Saudi Aramco

Due to their high production performance horizontal wells have become an established method for recovering oil and gas. A major uncertainty however, is whether the productivity of these wells will increase with increasing horizontal length. In horizontal wells drilled in high permeability reservoirs where a small pressure draw-down is needed to initiate flow in the horizontal section, the frictional losses in the horizontal section may be comparable to the pressure draw-down. As a result, the deliverability of the well is restricted. In this study, the in-flow and out-flow performances of the horizontal well are combined to predict its overall performance. That is accomplished by using a computer program that couples a theoretical solution of the productivity index to a multi-phase flow model in the horizontal section of the well. Different well completion scenarios and lengths were examined. The preliminary results of this study are: (1) in a 4-1/2 inch casing horizontal section, the increase of well length and perforation percentage does not yield a substantial increase in production; (2) in a well drilled in a high permeability zone, the frictional losses could be of the same magnitude of the pressure draw-down across the perforation rendering the end of the well unproductive; (3) different wells with different completion scenarios may perform similarly implying that the completion can be optimized to get the best performance; and (4) 2,000 feet of horizontal section length appears to be an optimum length.

Abdullah M. Al-Qahtani is a Production Engineer with Saudi Aramco where he has worked in different departments. He has conducted his MSc research on the evaluation of horizontal wells. Abdullah obtained his BSc and MSc from King Fahd University of Petroleum and Minerals, Saudi Arabia.

New Insights into Regional Correlation and Sedimentology, Arab Formation (Upper Jurassic), Offshore Abu Dhabi

Al-Silwadi, Mohammad S.*, ADNOC

Anthony Kirkham, ADCO

Michael D. Simmons,

University of Aberdeen

and Bryan N. Twombley, Ditton Petrographic

(See paper by Al-Silwadi et al., p. 6-27)

The Use of Geologic Models in Building the Stratigraphic Framework and Influencing Attribute Interpolation in the Hawtah Trend

Al-Sulami, Khalil H.*, Christian J. Heine and James R. Wilkins

Saudi Aramco

The two important steps in the 3-D geologic modeling process are: (1) building the stratigraphic framework; and (2) attribute interpolation. Improvements in hardware and software have significantly increased our ability to quality control both of these steps through visualization. In central Arabia, the stratigraphic framework is built by adding re-constructed layer isopach maps up from a key structure map, as indicated by the geologic model. This ensures the correct geometry of the geologic layers is preserved in building the geologic framework. The angular unconformity at the Base Khuff is represented by a truncation surface (grid) which removes the cells or portion of cells above the truncation surface while maintaining the proper depositional geometry for attribute interpolation. These surfaces are built using 2-D mapping software, any irregularities in the stratigraphic framework can be detected using logical operations. Any corrections can then be made to the surfaces prior to moving into the 3-D modeling software.

In addition to the stratigraphic framework, sequence specific sand distribution templates were used to influence the distribution of porosity. Net to gross surfaces were converted to porosity surfaces in the 2-D mapping software package using balanced translation curves. These porosity templates are now used to “condition” the porosity interpolation. This can be done within the 3-D modeling software or outside using a geostatistical routine that accepts conditioning templates.

Khalil H. Al-Sulami holds a MSc in Geology from King Fahd University of Petroleum and Minerals (KFUPM). He has been with Saudi Aramco for 14 years and has been involved in oil exploration, seismic interpretation and prospect evaluation for the past 5 years. Khalil is currently working on geological modeling.

Christian J. Heine received his MSc in Geology from the University of Tennessee in 1982 and a MSc in Petroleum Engineering from Tulane University in 1990. Christian was Associate Professor at Tulane University from 1990 to 1991, and worked with Mobil Oil from 1982 to 1990. He joined Saudi Aramco in 1991. Christian is a member of the AAPG and DGS.

James R. Wilkins received his BSc in Geology from the University of Southern Colorado. He worked as a Geologist for Western Geophysical Company under contract to Aramco between 1981 and 1986. He is currently working as Geologist with Saudi Aramco with emphasis on geological computer applications. James' work involves 3-D mapping and modeling and reservoir characterization.

Pseudo VSP Data Generation: Field Data Example from the Middle East

Ala'i, Riaz* and C.P.A. Wapenaar

Delft University of Technology, The Netherlands

The transformation of surface measurements into pseudo VSP data is a very useful tool in the interpretation of seismic data. It adds a depth dimension to seismic data and gives insight into the entire wave propagation through the subsurface.

In this paper we present the generation of pseudo VSP data from a dataset from the Middle East. One of the aims is the verification and update of the macro sub-surface model, by making use of inconsistencies of multi-source and offset pseudo VSPs together with the behavior of non-causalities (two-way schemes). Pseudo VSP data is generated for various borehole/detector configurations. The comparison of the pseudo VSP with the real VSP and well data improves the integration of surface seismics and well information. Due to acquisition difference between the real VSP and the surface data, the pseudo VSP has a lower frequency band than the real VSP. After proper pre-processing (including a thorough study of the sources and detectors used in both situations), the pseudo VSP may have a better signal-to-noise ratio. In practical situations both VSPs may enhance each other significantly. Now the fundamental importance in the pseudo VSP generation technique is that we can walk away from the well with optimally determined matching parameters at the well and extend our geological knowledge in all lateral directions (reservoir characterization). The absence of tube noise in pseudo VSP data is an added advantage over real VSP data. The presentation of VSP data in one-way time allows a better identification of P and S-waves. Using reciprocity, a multi-source pseudo VSP equals a multi-focus Common Focus Point (CFP) gather.

Riaz Alái received his MSc in Electrical Engineering specializing in Control Engineering from Delft University of Technology(DUT) in 1991. He is currently a PhD candidate at DUT working on a PhD research project on the generation of pseudo borehole data from seismic surface measurements. This project is part of the international DELPHI (DELft PHilosophy on Inversion) Consortium at DUT Center for Technical Geoscience (CTG), Faculty of Applied Physics, Laboratory of Seismic and Acoustics. He is affiliated with the SEG and EAEG. His areas of professional interest include wave theory and VSP processing.

C.P.A. Wapenaar received his MSc in 1981 and his PhD (cum laude) in 1986 from Delft University of Technology, both in Applied Physics. In 1986 he received the Shell Study Award. From 1987 to 1991 he worked at DUT as a Senior Research Fellow on behalf of the Royal Dutch Academy of Sciences (KNAW). In that same period he was Associate Editor for Geophysical Prospecting. From 1987 to 1993 he has been a Consultant for Jason Geosystems B.V. and Delft Geophysical B.V. He is currently Associate Professor at DUT, where he leads a consortium research project on elastic seismic data processing (Delphi). His main interests are wave theory and seismic processing. He is a member of SEG, EAEG and ASA.

3-D Seismic in Transition Areas, A Case History

Ali, Omar S.M., Abu Dhabi Company for Onshore Oil Operations (ADCO)

Atef A. Ebed*, Abu Dhabi National Oil Company (ADNOC)

Michael Fleming, Western Geophysical, UK and Ismail B. Haggag, Western Geophysical, UAE

Transition zones and tidal belts represent the toughest prospects for seismic exploration worldwide. Many prospective hydrocarbon reserves crossing these areas between onshore and offshore are still not well defined. Utmost flexibility and versatility of methods and techniques are required when the seismic exploration is projected to cross areas with water depth less than 1 meter, small islands, reefs, coastal swamps and beaches. Advances in 3-D seismic acquisition technology and processing methodology have again encouraged activities in these challenging areas. In 1994, ADCO in collaboration with ADNOC started to acquire one of the largest 3-D shallow marine surveys in the world, approximately 2,000 square kilometers, in the western area of Abu Dhabi. The survey is being acquired by Western Geophysical. The survey area presents a typical example of the transition zones where we have: (1) rapid changes from sand to very soft unpredictable sabkha onshore, to a very hard, coral, rocky surface underneath the water; (2) changes in water depth of about one to two meters affected by semi-diurnal tides; (3) large variations in sea bottom topography and sediments; (4) the very high salinity of water; (5) the desire to protect the environment: plant life including Mangrove trees and various species of animal life; and (6) the coastal areas are marked by extensive areas of shallow water with some deeper channels, swamps and reefs.

The objectives of the 3-D sesimic survey are: (1) to detect and define the extent and geometry of subtle faults at the reservoir level which might act as fluid barriers; and (2) predict and better understand the reservoir properties, such as porosity and lithology. The 3-D acquisition parameters such as bin size, fold coverage, source parameters and swath geometry were selected in such a way as to achieve the following: (1) high resolution seismic data; (2) regular offset distribution within each bin; (3) minimum azimuthal variation; and (4) optimum match between land, shallow marine and offsore seismic data.

This paper involves the planning procedure and describes a series of solutions used in 3-D seismic acquisition and processing for such hazardous shallow marine areas.

Omar S.M. Ali received a BSc in Geology from Cairo University. Omar has 30 years experience in geophysical prospecting with G.P.C. Egypt; Sonatrach, Algeria; and ADCO, Abu Dhabi.

Atef A. Ebed is currently a Senior Geophysicist with ADNOC. He has 25 years of experience in seismic exploration, of which 3 years were with GPC in Egypt, 12 years as Seismic Data Analyst with SSC in different processing centers worldwide and more than 10 years as Senior Geophysicist with the Exploration Division at ADNOC. Atef received his BSc in Physics and Geology from Alexandria University in 1969, Post-Graduate Diploma in Geophysics from Alexandria University in 1971 and a PhD in Seismic from Bucuresti University in 1978. He is a member of the EAGE and SEE.

Michael Fleming holds a BSc in Physics from Warwick and a MSc in Material Physics from Bristol. His work experiences include Processing Center Manager, Supervisor, Land Technology Group in Western Research, Houston, and Resident Manager in Saudi Arabia. He is currently the Area Geophysicist with EAME Land, London.

Ismail B. Haggag received his BSc in Applied Physics from Ainshams University, Cairo in 1970, MSc in 1975 and PhD in Geophysics from Karlsrahe University, Germany. He has been working with Western Geophysical, Abu Dhabi as Area Geophysicist since 1985. He started as Acquisition Geophysicist with Western in 1980 and was transferred to the London Processing Centre as Processing Analyst in 1984. Ismail is a member of the SEG, EAEG and the SEE. He is professionally interested in acquisition and processing of shear waves.

Standard 3-D Models to Serve the Industry

Aminzadeh, Fred

Unocal, Texas, USA

This paper gives an update on the results and status of the 3-D SEG/EAEG Modeling (SEM) Project. The project goal has been to design two 3-D models, salt and overthrust, and simulate realistic 3-D surveys through numerical calculations. They may be used for survey design, testing and validating different processing methods, interpretation of 3-D seismic, better understanding of wave propagation through complex media, training and benchmarking computer hardware and software.

So far, about 1,000 terabyte of data has been generated completing Phase A and Phase B and a portion of the Phase C of the project. “Classic Data Sets” containing subsets of calculations conducted for Phase A and B have been defined. These data sets will be made available to the general public. Plans for additional calculations of about 2 terabyte are underway. Many groups have already begun using and testing the data sets for various applications. These data sets are expected to improve the current 3-D processing methods and help reduce exploration and production cost.

Salt and overthrust structures offer two major challenging opportunities in the petroleum industry. The models generated under this project highlight the specific complications involved in these types of play, with the capabilities and limitations of the 3-D seismic data in each case. The whole industry and academic institutions will have access to a common data set enabling geoscientists to further fine tune their processing and interpretation tools in a consistent manner. These models and their legacies will be with us for many years to come.

Fred Aminzadeh is with Unocal‘s Geotechnology Group in Sugar Land, Texas and an Adjunct Professor in the Geology/Geophysics Department of Rice University. He received his PhD from the University of Southern California in 1979. Fred has done extensive work in seismic modeling, reservoir characterization and geophysical signal processing. He serves as Chairman of the Society of Exploration Geophysicists' research committee, and co-chairs the SEG/EAEG 3-D modeling sub-committee.

Basin Resource Development: Forecasting on the Basis of Risk Analysis

Anissimov, Leonid A.

Saratov State University, Russia

The role of risk management in exploration increases in mature hydrocarbon provinces, where numerous existing fields form the basis for statistical analyses. The classification and quantification of basin parameters (earthquakes, booked reserves, discoveries, etc.) allows the construction of dynamic models. These models are built on risk analysis and on the theory of queues and have been tested in several sedimentary basins including the North Sea, Indonesia, the Volga-Ural province and West Siberia. Analysis of these basins shows that certain statistical relationships exist, which permit the forecasting of undiscovered resources and the evaluation of human activity on the natural basin parameter distribution. Risk management in exploration may be very effective for the Middle East basins with their large number of oil and gas fields.

Leonid A. Anissimov is currently Head of the Hydrogeology and Engineering Geology Department, Saratov State University, Russia. He has 32 years of petroleum, geochemistry and environmental research experience at the Volgograd Research Petroleum Institute and Saratov State University. Leonid is a member of the Ecology and Civil Engineering Academies. He has a Doctor of Science in Geochemistry and Professorship in Water Problems.

Targeting Infill Wells in the Densely Fractured Lekhwair Field, Oman

Arnott, Stuart K.* and John N.M. van Wunnik

Petroleum Development Oman

The oil bearing reservoirs of the Lekhwair field in Oman consist of a low-permeability chalky limestone. These have been waterflooded since 1992 by a 200 well development project. On the crest, the reservoir is developed by a vertical inverted 9-spot pattern. On the low relief flanks, horizontal wells are employed. It soon became apparent that the reservoirs were more faulted and fractured than anticipated and early water breakthrough occurred in many producers (20%). Intensive efforts were successful in improving the mapping of the fault and fracture network and in identifying unswept reserves. Extensive use was made of FMI/S logs in horizontal wells, correlation of production attributes such as water cut, produced water salinity and gross production rates and production history matching with numerical simulation models.

To improve future oil recovery further infilling is required. However, the above simple evaluation methods are too coarse for reliable well targeting. A cost effective method to obtain the required targeting refinement is based on horizontal appraisal wells and FMI/S logs in these wells. The resulting data, in combination with the “coarse” maps, allow an area as large as 1,000 by 500 meters to be mapped sufficiently well to target successful infill vertical wells. The horizontal appraisal well is targeted in the most productive layer and pays for itself. A number of field examples illustrate the success of this method.

Stuart K. Arnott is currently Production Geologist for Petroleum Development Oman, working on the Lekhwair field. He previously worked for Shell in Holland and Britoil in the UK. He has a PhD in Seismology from Durham University and a BSc in Physics/Geology from the University of Glasgow.

John N.M. van Wunnik is currently Reservoir Engineer with PDO. He has 14 years of petroleum industry experience of which 10 years were with Shell‘s Exploration and Production laboratory in The Netherlands and 4 years with PDO. He is an SPE member and has published several papers on reservoir engineering subjects. John received his PhD in Physics from the University of Amsterdam.

Aspects of Operation Geology in Horizontal Drilling

Asada, Jiro*, Walid K. Najia, Nozomi Fujita

Zakum Development Company (ZADCO), U.A.E.

and Philip S. Leighton

Topaz Consultants Ltd., Scotland, UK

Horizontal activity in ZADCO‘s offshore fields of Abu Dhabi started in 1989, and continues to be an integral and extensive part of ZADCO‘s drilling program. To date, 70 horizontal wells including single-lateral multi-layered and multi-lateral multi-layered step profiles have been drilled. Geological practice in horizontal drilling has become more involved in directional engineering aspects. Geologists at site are fully in charge of steering a well, once it has entered a target reservoir. Thus, the integration of geology and directional engineering concerns have become a necessary standard practice in horizontal drilling program.

To achieve this, geologists have developed better knowledge of directional engineering principles and directional engineers become more aware of geological uncertainty. The geological operation for horizontal well requires a unique approach, more oriented towards directional engineering aspects.

This paper considers ZADCO‘s current standard geological practice for horizontal drilling, highlighting aspects of both office and site work. The role of well site geology in development drilling has been revitalized and enhanced as horizontal wells have become increasingly complex.

Jiro Asada is currently Reservoir Geologist with ZADCO. He joined the petroleum industry with Japan Oil Development Company in 1982. Jiro had been involved in horizontal drilling from the first offshore horizontal well in the region as Operation Geologist in ZADCO from 1987 to 1993. He gained a BSc in Geology from Shinshu University, Japan in 1982.

Walid K. Najia is currently Lead Log Analyst with ZADCO seconded from Abu Dhabi National Oil Company. He was Lead Operation Geologist with ZADCO from 1988 to 1992. He was involved in planning, supervision and following up of multi-lateral horizontal wells. He has 20 years of various petroleum industry experience in the region. He received a BSc in Geology from Punjab University. Pakistan in 1972. He was awarded a MSc in Petroleum and Structural Geology from Punjab University in 1974.

Nozomi Fujita is currently Operation Geologist with ZADCO. His activity is focused on the latest multi-lateral/multi-layered horizontal drilling. He joined the industry with Japan Oil Development Company in 1985. He received a BSc in Geology from Tokai University, Japan in 1985.

Philip S. Leighton is currently contracted to ARCO QATAR to supervise geological operations. He was Consulting Geologist with ZADCO from 1993 to 1995. He gained a BSc in Geology from the University of St. Andrews, Scotland in 1979 and joined the industry in 1980. He was awarded a MSc in Geology from the University of St. Andrews in 1985. In 1990 he co-founded TOPAZ Consultants Ltd. as an independent geological/environmental consultancy company.

Exploration Applications Developed from a Large Geophysical Database, Historical Review 1965-1995

Attewell, Peter*

Geophysical Service Inc. Saudi Arabia Ltd. and

Lloyd W. Long

Saudi Aramco

Since the first days of seismic exploration Saudi Aramco has committed an increasingly large volumes of geophysical data to database storage. These data include seismic survey X-Y coordinates, seismic time data, stacking velocities, well velocity surveys, uphole T-D picks, processing datum and residual statics, and the near surface model used for the initial stacked section. Other data kept in permanent digital form outside the corporate database include the “seismic reference datum”, near surface “frozen velocity models”, gravity and magnetic measurements, seismic tapes, film and report archives, and results from amplitude versus offset studies and various inversion depthing procedures.

This wealth of information helps geophysicists tackle a variety of problems by providing the data to back-up current hypotheses. Generalized “status maps and charts” can be periodically updated; flexible program applications can be written to examine the data statistically or in reduced form. This generates a large “value added” component to be realized from the existing data. Correlating different aspects of the data can help in cost reduction by targeting additional data acquisition more efficiently.

The historical development of the various database sets are described from a user‘s perspective. Logical database design with reference to the start-up of 3-D seismic recording are reviewed. Problems and advantages of transition from a central repository to today‘s more fragmented form are discussed together with the issues of physical file maintenance, data integrity and primary data retrieval for use in vendor applications. Anticipated future developments are reviewed including the planned need for POSC compliance.

Peter Attewell is currently with Geophysical Services Inc., Saudi Arabia. He has 25 years of exploration experience including work on the southern North Sea gas fields, and many years of involvement with Saudi Arabian data. Peter received his BSc in Geology from Imperial College, London and is a member of the Petroleum Exploration Society of Great Britain and the SEG.

Lloyd W. Long (see Al-Nahwi et al., p. 108-109)

Inverted Basins in Northeast Egypt: Geology and Hydrocarbon Prospectivities

Ayyad, Maher H.*

British Gas, Egypt

and Adel A. Sehim

Cairo University, Egypt

Observations of surface geology, integrated with seismic and well data, in Northern Sinai, revealed magnificent examples of inverted basins. The northern shelf of the Arabo-Nubian Massif experienced major extensional deformation throughout most of the Mesozoic time. A series of down-to-the-north tilted fault blocks, aligned in northeast-southwest trending sub-parallel fracture lines, have consequently developed. Syntectonic deposition throughout the Triassic, Jurassic and Early Cretaceous steadily steepened block tilting and formed half graben sub-basins. Basin axes run alongside the main active faults where vertical displacements progressively increase with depth. These sub-basins are on trend with the Palmyra-Sinjar troughs in Syria and Abul Gharadiq basin in the Western Desert of Egypt (i.e. Syrian Arc Trend). By Mid-Cretaceous, differential movements between Eurasian and African plates sent compressional forces into the passive margin of Sinai. The transmitted stresses triggered the older extensional fault trends to re-activate in reversed direction. Throughout the Late Cretaceous to Oligocene, the basin fills underwent strong inversion uplift along the same bounding faults. The inverted basins now form the huge doubly plunging surface anticlines and the large offshore structures. These anticlines are asymmetric in shape and somehow reflect mirror images of the original sub-basins. Such depositional and structuring systems provided unique sites for hydrocarbon generation and accumulation. During basin development cyclic sedimentation regimes (partly restricted, paralic to open shallow-deep marine) prevailed and lead to the deposition of organic-rich mature source and reservoir quality rocks as well as sealing interbeds. Timing of hydrocarbon generation and expulsion relative to structuring and stratigraphic entrapment is an ideal fit. Proven hydrocarbon reserves were established along this structural trend from Abul Gharadiq basin in the Western Desert and offshore north Sinai, Egypt through Palmyra and Sinjar foldbelts in Syria to the world class great Arabian basin to the east and southeast.

Maher H. Ayyad is the Exploration Technical Supervisor of British Gas, Egypt. He has 25 years of industry experience, 23 with Unocal Corporation at various international locations (Australia, Indonesia, Singapore, Egypt, Netherlands and Syria) and 2 years with British Gas, Egypt. He is a Certified Petroleum Geologist member of the AAPG and has published several papers on geological and geophysical subjects. He has a BSc and a MSc in Geology from Assyut and Ain Shams Universities and is presently preparing his PhD at Cairo University, of which this paper represents a part.

Adel A. Sehim is Assistant Professor at Cairo University, Egypt. He has 13 years experience in different fields of geology, particularly the application of structural geology in industry and research. He published 11 papers on structural subjects. He has a PhD from Cairo University.

Sequence Stratigraphic Modeling of Lower Thamama Group in East Onshore Abu Dhabi, U.A.E.

Aziz, Sabah K.* and Mohamed M. Abd El-Sattar

Abu Dhabi National Oil Company (ADNOC)

The early Cretaceous Lower Thamama section in East Abu Dhabi is deposited during the Berriasian-Valanginian time. The section is represented by a thick carbonate succession composed dominantly of limestone and dolomite reaching more than 1,100 feet in thickness. The section is deposited in a marine setting ranging from shallow peritidal environment to relatively deeper shelf basin with well-developed prograding shelfal sediments near the margins.

An integrated approach utilizing sequence stratigraphy analysis, bio-lithostratigraphy and electric log data revealed the presence of three sequences (Sequence I, II & III) and two shelf edges within the lower Thamama section in East Abu Dhabi. These sequences were found to prograde and become progressively younger toward the east (basinward) with their shelf edges trending in a north northwest-south southeast direction.

Excellent reservoir development are found to be associated with the shelf edges of these sequences, particularly within the oblique/sigmoidal types of clinoforms, whereas potential source rocks are expected to be developed basinward.

Recent exploration activities proved the presence of commercial hydrocarbon accumulation within the Lower Thamama sequences in East Abu Dhabi.

Sabah K. Aziz is a Senior Review Geologist with Abu Dhabi National Oil Company (ADNOC) in UAE. He has 20 years of experience in the field of exploration Geology in UAE. He holds a BSc in Geology from Baghdad University.

Mohamed M. Abd El-Sattar is a Senior Exploration Geologist with Abu Dhabi National Oil Company (ADNOC), UAE. He has 21 years of petroleum and exploration experience in the Middle East, of which 11 years were with Gulf of Suez Petroleum Co., Egypt. He holds a BSc and MSc in Geology from Ain Shams University, Egypt. He is a member of many professional societies and has published several papers on structural geology and basin evaluation.

7th ADIPEC Exhibition & Conference

13-16 October 1996

Abu Dhabi International Exhibition Centre

P.O. Box 5346, Abu Dhabi, United Arab Emirates

Tel: (971-2) 446 900, Fax: (971-2) 446 135

Qatar, Alkhalij Field: A Diagenetic Trap in the Mishrif Formation

Balusseau, Bernard*

Elf Petroleum Qatar and

Mamdouh Z. El-Demerdash

Qatar General Petroleum Corporation (QGPC)

Alkhalij oil field is located about 110 kilometers off the eastern coast of Qatar, on Block 6 granted to Elf Petroleum Qatar in 1989. The prospect has been defined as the extent, on a large (130 square kilometers) but limited tract, of an intra-Mishrif seismic horizon (H2) interpreted as the occurrence of a porous limestone body at the top of the Mishrif Formation (Cenomanian). No significant vertical closure is present in this area which dips gently towards the southeast. This reservoir was assumed to be sealed laterally by truncation and/or facies change and capped by Laffan transgressive shales. The discovery well ALK 1, drilled in 1991, struck a 41 meter oil column at the top of the Mishrif and tested 1,600 barrels of oil per day on a 1/2″ choke. The extent of the field has been determined by drilling six appraisal and delineation wells together with seismic reprocessing. All of the five wells drilled within the extent of the H2 seismic marker found the oil bearing reservoir and thus confirmed the validity of the seismic concept. The reservoir is originally composed of inner shelf mudstones to packstones strongly weathered during a continental exposure which took place prior to the Laffan transgression (Coniacian to Santonian). Weathering dramatically improves the reservoir permeability and thus controls the extent of this diagenetic trap.

Bernard Balusseau is currently Exploration Manager with Elf Petroleum Qatar. He has 16 years of petroleum and exploration experience. He joined Elf Aquitaine Group in 1980 and has worked in Tunisia, Italy, France and Qatar.

Mamdouh Z. El-Demerdash received his BSc in Geology in 1974 from Alexandria University, and in the same year joined GUPCO, where he held the head position in Geologic Operations, Exploitation, North Gulf of Suez Exploration District Geology and Acting Manager and Regional Geology. Mamdouh received his MSc and PhD degrees in Petroleum Geology from Cairo University during his tenure with GUPCO. In 1989 he joined QGPC as Senior Exploration Geologist and in July 1993, he was appointed as Head of Exploration.

Fast Pre-stack Migration Using Equivalent Offsets and Common Scatter Point Gathers

Bancroft, John C.

University of Calgary, Canada

A new method of pre-stack migration is presented that runs one hundred times faster than similar methods. The new method includes pre-stack migration gathers for accurate velocity analysis. Conventional processing requires two time shifting steps of normal moveout (NMO) and post-stack migration. These two time-shifting processes may be merged into one process using an NMO-Kirchhoff migration operator that combines the source-receiver offset with the migration offset to give a new equivalent offset. More complex forms of the equivalent offset are based on pre-stack migration principles.

Samples in each input trace are assigned an equivalent offset then copied into a bin of a common scatter point (CSP) gather, and repeated for each migrated trace. No time shifting of the data is required. The fold in each offset bin may be in the tens for 2-D and in the thousands for 3-D. Each CSP gather may be scaled and filtered similar to CMP gathers with conventional algorithms. The combined effects of high fold and large offsets aid in focusing the energy for accurate velocity analysis. Pre-stack migration is completed by conventional NMO and stacking.

The tremendous speed increase is a consequence of applying NMO in one operation to all the traces gathered into one bin of the CSP gather. Other advantages allow migration from rugged surface topologies, evaluation of azimuthal velocity variations, and the possibility of statics evaluated before NMO. The presentation includes examples of CSP gathers, velocity analysis panels, and complete pre-stack migrations of modeled and real 2-D and 3-D data. Examples of P-P and P-SV converted wave processing will also be included.

John C. Bancroft is Senior Research Geophysicist with the CREWES project at the University of Calgary. He has worked in the field of signal and seismic processing for 24 years and has specialized in migration for 15 of those years. John has developed and written an extensive range of software that includes most migration algorithms, modeling, 3-D processing, and basic seismic processing including surface consistent analysis. He is an SEG instructor and has received the Best Paper Awards at CSEG and SEG meetings. He has a BSc and MSc from the University of Calgary and a PhD from Brigham Young University.

Stochastic Modeling of Subseismic Faults

Belfield, William C.

ARCO Exploration and Production Technology, USA

Faults below seismic resolution and fractures can be important components of a reservoir description because of their potential impacts on primary or secondary recovery. In attempting to understand the statistics of these systems, there is a growing concensus that fault and fracture networks exhibit statistical similarity over a large range of scale. This observation implies that power-law statistics are necessary to characterize these systems. In addition to results from 3-D seismic interpretation illustrating power-law behavior of fault displacement and length, data from horizontal wellbores in naturally fractured reservoirs clearly indicate scaling characteristics of aperture and spacing. There is a general understanding of how to extrapolate displacement and fault length to smaller scales, but less agreement pertaining to the spatial distribution of subseismic faults.

Recent approaches to modeling spatial distribution of subseismic faults or fractures utilize either ad-hoc assumptions about proximity to seismic faults or attempt to use a spatial characterization based on box-counting. Study of horizontal well fracture data indicates that fractures occur over a large range of scale. This observation suggests that fractures are space-filling (present everywhere) and the exponent measured by box-counting should be an integer. Non-integer values reported in the literature reflect the inability to measure and record small faults or fractures. Consequently, box-counting provides little useful information. To model subseismic fault spatial distribution, I assume that the scaling characteristics of fracture spacing, recognized in horizontal wells and based on resolution, is also applicable to faults.

William C. Belfield is a Senior Principal Research Geologist with the Reservoir Research and Technical Service group at ARCO. He works primarily in the description and characterization of natural fracturing and faulting in reservoirs. His degrees in Earth Science are from State University of New York at Stony Brook. William is a member of SPE and AGU.

SEG

International Exposition

& 66th Annual Meeting

10-15 November 1996

Denver, Colorado

Seeking Low Relief Structures, An Original Approach Applied in West Central Oman

Benkara-Mostefa, Cherif, Cyril Saint-Andre*, Eric de Bazelaire and Marc Girard

Elf Aquitaine Production, France

Today low relief structures are the main objectives associated with conventional plays in the Middle East. Up to now the imaging of such structures has failed because seismic reflections are hampered by strong energy multiples generated by near surface high velocity layers. The result is a reverberating seismic environment where it is difficult to separate real events and multiples when processing the data. Elf has developed a new multiple removal process, based on inversion, which requires very specific acquisition parameters. The success of the technique is based on the fact that high resolution acquisition allows separation of real events and multiples in a curvature-time domain and then enhances multiple removal. This original integrated approach has been applied with success to the last seismic survey acquired in the Butabul concession, onshore West Central Oman.

Cherif Benkara-Mostefa is Exploration Manager in Oman with Elf. He has 15 years of exploration and petroleum industry experience with the company. Cherif has a MSc and DEA of Geology from Grenoble University.

Cyril Saint-Andre is a Processing Geophysicist with Elf. His industry experience includes 4 years as Geophysicist with Elf where he is in charge of land/marine processing and supervision. Cyril has an Engineering degree from the Engineer Science Institute of Clermont II University. His areas of professional interest include seismic and signal processing.

Eric de Bazelaire is Scientific Advisor with Elf. He has 15 years of petroleum and exploration industry experience with Elf, following 11 years of research in optics at the Ecole Polytechnique and GESSY Laboratories. Eric is a member of the SEG, EAEG, SFP and SFO. He has an Engineering degree from Ecole Supérieure d'Optique and a PhD in Physics. His areas of professional interest include optics, signal processing and geophysics.

Marc Girard is an Acquisition Supervisor with Elf Aquitaine Production. He has 13 years of exploration experience with Elf where he is involved in the supervision of 2-D and 3-D land acquisitions worldwide. He has a MSc in Geophysics from ENSPM. His areas of professional interest include seismic acquisition and signal analysis.

AAPG INTERNATIONAL

CONFERENCE & EXHIBITION

7-10 September 1997

Vienna

“East Meets West”

Petroleum Development Oman Gas Exploration Unlocks Major Reserves

Bichsel, Matthias F.*, Andrew W. Wood and Anthony Mozetic

Petroleum Development Oman (PDO)

Since 1985, Petroleum Development Oman has been exploring for gas on behalf of the Government of Oman under a ten-year agreement signed in June 1984. The aim of the one-rig program was to find additional non-associated gas reserves (3 Trillion Cubic Feet) to meet domestic energy requirements for a minimum of 40 years, for which the available reserves (5.6 TCF) at that time were insufficient. Initial results of the campaign, which principally targeted the Permian Khuff Formation, were disappointing, analogues to the major accumulations of the Arabian Gulf failing to materialize. During the second half of the program, therefore, the strategy was revised to address the prospectivity of higher risk/higher reward plays recognized at greater depths.

Well Saih Nihayda-24, drilled in 1989, found gas/condensate-bearing reservoirs in Cambro-Ordovician sandstones of the Andam Formation below 4,000 meters. This discovery, in a seismically poorly defined anticline, sparked an intensive effort of 2-D, and later 3-D, long cable seismic acquisition. This led in 1991 to additional major gas/condensate finds in Saih Rawl and Barik, and a dedicated two-year two-rig appraisal campaign has since proven up sufficient reserves to support a Liquified Natural Gas export scheme.

The ten-year program has more than tripled Oman‘s non-associated gas expected reserves to some 22 TCF, exceeding the target more than five-fold. Significant potential for further gas discoveries identified in both north and south Oman provides encouragement for continued successful gas exploration in the future.

Matthias F. Bichsel is currently Exploration Director with Petroleum Development Oman (PDO). He has 15 years of industry experience gained with Shell International. Matthias has worked in various capacities in Bangladesh, Oman, Canada, Indonesia and The Netherlands. He holds a PhD in Earth Sciences from the University of Basle, Switzerland and is a member of the AAPG.

Andrew W. Wood is currently working with Shell International in London as Corporate Adviser. Prior to that, he was Exploration Director of Petroleum Development Oman from 1992 to 1995. Andrew has 17 years of industry experience with Shell, gained in various assignments in Europe, Africa and the Middle East. He holds a PhD from Oxford University and is a member of the AAPG.

Anthony Mozetic is joined Shell in 1970. After postings in Holland, UK, Nigeria and Norway he moved to Oman in 1989 as Exploration Team Leader of Petroleum Development Oman‘s gas team. Anthony, who holds a MSc in Geology, left PDO in 1995 to take up an assignment as Chief Geologist with Shell China.

ARABIAN OIL & GAS '96 CONFERENCE: OPPORTUNITIES & TECHNOLOGIES

15-17 September 1996

Oman International Exhibition Centre

Exploration Data Recovery, Archiving and Workstation Loading

Blake, Nicholas* and Charles J.M. Hewlett

Lynx Information Systems, UK

This paper focuses on solutions to the access and storage problems faced by seismic interpreters wishing to use a mixture of both new (perhaps 3-D) and old (perhaps 2-D) seismic data on a workstation. Access problems include lack of digital data, variations in processing across surveys, and inaccurate or missing location data. Such problems can be remedied by the appropriate scanning, vectorizing, reprocessing and data reconciliation methods. Exploration data storage still largely relies on warehouses full of magnetic tapes and paper data, with all the attendant problems of maintenance and access. Both tapes and paper are usually deteriorating rapidly and are always difficult to locate. CD-ROMs, D2s and other mass storage devices can overcome these problems by providing the facility to store all of this data in a digital form. Once converted it is possible to access this digital archive using universally recognized software standards and inexpensive hardware. Seismic profiles and well logs for example can be retrieved from a wide variety of hardware platforms using existing software, reviewed and then extracted quickly and efficiently and converted directly into workstation-ready format. Four case histories are reviewed to show how this integrated approach of data capture, archiving and retrieval can be used successfully in a real exploration environment to add value to any exploration data.

Nicholas Blake is currently Business Development Manager with Lynx. He received his BSc in Earth Science from the Open University in 1977. Between 1977 and 1986 Nicholas worked for SDP International where he was Vice President, Processing. Prior to joining Lynx, he was Consultant Operations Geophysicist in Australasia. He is a member of the PESGB, CSEG and ASEG.

Charles J.M. Hewlett received his BSc in Natural Science from Oxford in 1967 and a PhD from the University of London, Royal School of Mines in 1973. Between 1974-1980, Charles was Manager, Technical Support Group with Western Geophysical and was Geophysical Consultant until 1991. Charles is presently the Managing Director of Lynx. He has written various papers and is a member of the SEG and PESGB.

Practical Methodology for Interactively Modeling 2-D and 3-D Refraction Statics

Bremkamp, Stephen W.*, Stephen C. Kellogg, Cameron M. Luck and Peter C. Green

Saudi Aramco

In the industry‘s quest for finding new reserves while reducing exploration risk, it is often the case that the extent to which they are able to accurately define the near surface is directly related to success or failure. The geophysicist must be able to model near surface structure and overburden velocity to obtain a seismic section which accurately depicts the sub-surface. We have developed a methodology to model the near surface for large 2-D grids as well as 3-D volumes. We model either the refractor elevation or overburden velocity: when modeling one, the other instantly changes and statics are calculated. Modeling is now a cooperative effort between the geologist and the geophysicist, because any near surface information can be put into the model.

This technique is fast. It is feasible to construct and test an areal model over a prospect in a single day. Input to the program may be from any refraction analysis package which supplies delay times and refractor velocities. Graphical 3-D displays and color contours of surface elevation, refractor elevation, refractor velocity, overburden velocity, delay times, statics and seismic data (2-D) are instantly available. This technique has been used successfully for numerous 2-D and 3-D land surveys acquired over several oil fields and prospects in Saudi Arabia. Near surface complexities include solution collapses, sand dunes and escarpments with as much as three hundred feet of vertical relief.

Stephen W. Bremkamp is a graduate of Colorado School of Mines with a BSc in Geophysics. He worked for 10 years with Western Geophysical and has been with the Saudi Arabian Oil Company for the last six years.

Stephen C. Kellogg has a BSc in Physics. He has 16 years experience in processing and interpretation. Stephen began his career with Mobil Corporation and spent 5 years with Placid Oil where most of his work centered on international projects, including Zambia, Thailand, and Turkey. He has worked in Algeria and for the past four years has been with Saudi Aramco.

Cameron M. Luck graduated from the University of Calgary with a BSc in Geophysics in 1984. Between 1984 and 1991 Cameron worked with CGG, Calgary, as a Processing Geophysicist. Since 1991, he has been with Saudi Aramco.

Peter C. Green is currently Processing Geophysicist with Saudi Aramco. He received a BSc in Geological Engineering. He worked for two years with Digicon Geophysical. Prior to joining Saudi Aramco in 1990, Peter worked with Tensor Geophysical for 4 years in Egypt. He is a member of the EAEG and SPE.

Impact of Cemented Zones Associated with Stylolites in Jurassic Carbonate Reservoirs: An Example from the Smackover Formation, Jay Field, Florida

Broomhall, Robert W., Linda W. Corwin*, Ronald M. Saidikowski and J. Noel Wooten

Exxon Production Research Company, USA

Stylolites can be an important geologic feature affecting reservoir quality and, consequently, reservoir management, in many large carbonate reservoirs. Cemented zones associated with stylolites occuring in the apparently continuous, high porosity of the Upper Smackover at Jay Field are the probable source of thin horizontal barriers/baffles to vertical flow that have been suspected since early days of production and supported by subsequent full-field simulation modeling. These cemented zones vary from a few millimeters to several centimeters thick and were often missed during routine core plug sampling. Mini-permeameter analysis has been used to document the decreased permeability adjacent to the stylolites. A stochastic 3-D geologic model was constructed of the distribution of stylolites and cemented zones. The model honors: (1) their frequency distribution observed in core both by lithology (limestone and dolomite) and by sequence stratigraphic layer, and (2) their location in cored wells. The stylolite/cement model, together with geostatistical porosity and permeability models, provided the reservoir properties required for input into simulation models. Simulations were run on models both with and without the cemented zones to: (1) determine what impact the cemented zones have on field performance, and (2) examine operating strategies for the miscible nitrogen flood that was initiated in Jay Field in 1981. Results show that incremental oil recoveries from the miscible flood are higher for cases where the vertical communication is reduced due to the presence of the cemented zones. The exact value assumed for the vertical permeability of a cemented zone (0.001 md or 0.01 md) has minimal impact on the incremental recovery.

Robert W. Broomhall is a Senior Research Specialist with Exxon Production Research Company in Houston, Texas. He is currently involved in the application of geostatistical as well as classical geologic methods to the construction of 3-D numerical models of geologic parameters. He has 17 years experience in production operations and major pool studies in three major petroleum basins (Arabian, Permian, Western Canadian). Robert has a BSc in Geology from the University of Florida and a MSc from Northern Arizona University.

Linda W. Corwin is a Senior Research Specialist with Exxon Production Research Company in Houston, Texas. Her experience is in geologic reservoir description and construction of geologic 3-D numerical models. During the last 15 years, her areas of study have included Ghawar and Abqaiq Fields in Saudi Arabia, Prudhoe Bay Field in Alaska and, most recently, Jay Field in Florida. Linda has BSc and MSc degrees in Geology from Baylor University.

Ronald M. Saidikowski is a Research Associate with Exxon Production Research Company in Houston, Texas, where he has worked for 20 years as a Reservoir Engineer. The majority of that time has been spent in the area of miscible enhanced oil recovery, with an emphasis on simulation. He holds a BSc in Chemical Engineering from Northwestern University and a MSc in Computer Science and a PhD in Chemical Engineering from the University of Wisconsin.

J. Noel Wooten is an Engineering Technologist with Exxon Production Research Company in Houston, Texas. He has 29 years experience in geological support. He is currently involved in 2-D and 3-D geostatistical modeling of various fields around the world.

Survey Evaluation and Design Together with Quantified Quality Assurance: An Integrated Approach to Seismic Exploration

Brown, Gordon*, Lloyd G. Peardon and Ian R. Scott

Geco-Prakla, UK

Survey Evaluation and Design (SED) of 3-D surveys has allowed seismic exploration to proceed with added confidence of successful results. By careful analysis of survey objectives and the estimation of achievable results from existing real data, surveys are now routinely planned so that a successful conclusion can be assured. The backbone to our pre-survey analysis has been built around methods designed to quantify data quality. This we term as the Quantified Quality Assurance (QQA) method. In this paper we describe results obtained from a number of seismic surveys which benefited from the combined SED and QQA methods. We demonstrate the predictions of data quality prior to data acquisition and compare these to results achieved after the final 3-D migrated volume has been produced.

The QQA method involves the statistical separation of any seismic data into quality attributes combined with the calibration with borehole data. The attributes include measures of noise content, wavelet quality and resolution estimates, while the borehole calibration includes the confidence of the surface seismic to the underlying reflectivity sequence together with phase and amplitude characteristics. A derived geophysical model can be used to build an acquisition model in order to predict the QQA values for the new acquisition. These predicted values can then be used for Geophysical Acceptance Criteria for monitoring acquisition quality and the same methods can be applied throughout the processing phase. Thus data quality is monitored continuously up to the delivery of the final product.

Gordon Brown is currently Manager of Survey Evaluation and Design with Geco-Prakla based in Gatwick, UK and has 20 years experience in seismic exploration. Prior to joining Geco-Prakla as an Interpreter in 1985, he was Headquarters Geophysicist for 5 years with the National Coal Board, UK. He holds BSc and MSc degrees in Physics and Geophysics, and is a member of the EAEG. Gordon has presented at numerous conferences and has published papers on geological and geophysical topics in “First Break” and “Marine and Petroleum Geology”.

Lloyd G. Peardon is currently Manager of Geosupport with Geco-Prakla. He began his career as a Research Geophysicist and worked with Britoil from 1981 to 1988. He joined Seismograph Service (SSL) in 1988 as Research Manager. In 1993 he spent a year with Schlumberger Cambridge Research Center as a Research Program Leader before returning to Geco-Prakla, Gatwick to head the Geosupport team. Lloyd holds a BSc in Mathematics and a MSc in Digital Signal Analysis from Portsmouth University.

Ian R. Scott is currently a Technical Supervisor with Geco-Prakla‘s Geosupport Group which actively supports all the product lines within Geco-Prakla. Ian has 15 years experience in seismic processing, survey design and software development. He is a member of both geophysical and geological international professional societies. He graduated in Geology and Geophysics from Imperial College, London.

VIENNA '97 AAPG

International Conference & Exhibition

7-10 September 1997

TWO ORAL SESSIONS

on MIDDLE EAST

Petroleum Geology of the Middle East

Middle East Geosciences Geo'96

ABSTRACT DEADLINE

15 OCTOBER 1996

Stratigraphy and Palynofacies Character of Organic-rich Sediments in Precambrian Sandstone in Southeast Sirte Basin

Bu-Argoub, Fawzi M.* and Bindra Thusu

Arabian Gulf Oil Company, Libya

Recent advances in high resolution biostratigraphy permit the recognition of four episodes of organic-rich shale deposition in several relatively small but tectonically silled basins in Precambrian sandstone in the southeast Sirte Basin: (a) a lacustrine-lagoonal shale (Scythian-Ladinian) interbedded with the Amal sandstone, is a syn-rift deposit, and contains kerogen types 2 and 3; (b) a non-marine, lacustrine shale (Neocomian-Barremian) interbedded with the Sarir sandstone was deposited in a half graben (silled basin), and is dominantly composed of terrestrial kerogen types 2 and 3; (c) a brackish-lagoonal variegated shale member (Barremian-Aptian), interbedded with the Nubian sandstone, was deposited in a deep graben and contains kerogen types 1, 2 and 3; and (d) a highly complex and poorly studied Cenomanian-Turonian shale, associated with the Busat Formation, transgressive and Maragh sandstones deposited in shallow marginal marine environment, is composed of kerogen types 1, 2 and 3. The development of these organic-rich shales correspond to worldwide sea-level rises. However, the abundance of kerogen types 2 and 3 in all these shales demonstrates the dominant input of locally derived terrestrial plant detritus in the basins. These organic-shales are rich in total organic matter and have potential to locally generate waxy oil.

Fawzi M. Bu-Argoub is currently Head of the Geological Laboratory at the Arabian Gulf Oil Company, Libya. He has 10 years experience in the petroleum industry. He is a member of several international professional societies and has published several papers on the palynofacies and biostratigraphy of the Sirte Basin and Cyrenaica in eastern Libya. He has a BSc from Garyounis University Benghazi, a Diploma in Micropaleontology from University College London and a MSc in Micropaleontology from the University of London.

Bindra Thusu is currently Geological Adviser with the Arabian Gulf Oil Company, Libya and is Research Fellow at the University College London. He has published 35 papers related to petroleum geology and biostratigraphy of Libya, Canada, Norway and USA. He has a MSc from the University of Alberta, Canada and a PhD from the University of Bristol, UK. Bindra is a member of several international professional societies.

Structural Elements of Onshore Kuwait

Carman, George J.

Kuwait Oil Company

Megasequence boundaries in sediments of the Dibdibba Basin (~8,000 meters thick) define regional dip as 0.5° to 1.5° northeast with individual structural elements reflecting northerly and northwesterly trends. The dominant structural element is the north-south trending Kuwait Arch with Greater Burgan oilfields in crestal 100 to 500 km2 anticlinal closures and 10 to 50 km2 satellite closures on the western flank and northern axial trace. The Kra-Al Maru and Dibdibba features (like the Mutriba Structure) trend northwest and separate the Kuwait Arch from the Salmi Platform.

Structure and stratigraphic thinning of late Jurassic and younger strata indicates structural growth since ~155 million years before present (Ma) with Recent overprints; regional data infers Hercynian structural events. Extension, contraction, inversion and possibly halokinetic mechanisms occur. The Burgan-Magwa Graben has a northwest trend re-activated during the Cretaceous. The Mishrif Unconformity removed more than 250 meters of sediment during maximum uplift ~90 Ma. Other unconformities are likely at less than 5 Ma (top Dibdibba), ~30 Ma (top Dammam), ~155 Ma (intra-Najmah) and ~350 Ma (Carboniferous).

Subvertical normal faults, some possibly deep crustal, generally throw less than 50 meters and occasionally occur in swarms; the majority displace strata below the Mishrif Unconformity whilst rare faults reach near-surface. Reverse faults are interpreted on seismic (~255 meters throw) and in one well (~30 meters throw). The Minagish and Umm Gudair structures occur enechelon between the Burgan and Kra-Al Maru trends. Branching faults with small throws in the Bahrah-Raudhatain region suggest transverse movements. The principal maximum stress field orientation is 040°-050° consistent with regional trends.

George J. Carman has 12 years experience with major oil companies working on exploration, development and unitisation projects in the North Sea, Alaska, Australasia, Kuwait and 10 years with independent companies. His PhD research developed a new play concept in Papua New Guinea. George is interested in technological developments and their applications to petroleum geology and integrated projects involving multidisciplinary research organizations. He has published over 20 papers on surveying, stratigraphy, structure and field descriptions.

Interactive 3-D Near-Surface Modeling with Uphole Surveys and Refraction Analysis: A Case History

Carvill, Charles V.

Western Geophysical, USA and

Darko Tufekcic*

Western Geophysical, UAE

Nowhere is the accuracy of static corrections as critical as in the Middle East, where large oil fields are associated with subtle structure. The goal of 3-D near-surface modeling is improved static corrections through construction of a velocity and depth model that is consistent with all known near-surface information. This paper describes a near-surface modeling project for a large 3-D survey in the Middle East involving an extensive uphole survey program and refraction analysis of reflection records. The project illustrates an effective use of a generalpurpose, interactive program for mapping, visualization, and analysis of spatial data.

For this survey, 1,700 uphole surveys varying in depth from 30 to 100 meters were acquired. The first step of the modeling process was the importation and quality control of the interpreted uphole surveys. All uphole locations, layer thickness, velocities, and hole depths were checked and, as necessary, corrected. We then constructed an “uphole Earth model” consistent with this uphole data to a depth of 100 meters, i.e., the depth of the deepest holes.

Next, delay times for an horizon deeper than the uphole control were produced through refraction analysis of the Vibroseis first arrival data. Then, using a “delay time stripping” technique, the uphole Earth model was extended and integrated with these delay times forming a “final Earth model”. By incorporating the uphole information, the final Earth model largely resolves the ambiguity between velocity and depth. Finally, static corrections were computed for the final Earth model and applied to the 3-D reflection data.

Charles V. Carvill received a BSc in Geophysical Engineering from the Colorado School of Mines in 1978. After several years in seismic processing, he joined the Research and Development Group at Western Geophysical as a Research Geophysicist. Charles currently specializes in statics processing issues and is a member of the EAEG and SEG.

Darko Tufekcic is Manager of the Western Geophysical Exploration Technology Center, Abu Dhabi. He has 35 years of exploration and petroleum industry experience of which 5 years were with Zagreb University, 14 years with INA-Oil Industry, Zagreb, and 16 years with Western Geophysical. He has been involved in a broad range of exploration activities in many areas of the world and has published a dozen papers on geophysical and petroleum exploration. Darko has BSc and MSc degrees in Geophysics and Geology from the University of Zagreb.

Continuous Permeability Determination with Stoneley Waves and Multiprobe Wireline Formation Testing

Cassell, Bruce R.* and Fikri J. Kuchuk

Schlumberger Technical Services, U.A.E.

Permeability is crucial for estimating producibility and simulating reservoir behavior. One of the methods of obtaining continuous in-situ fluid mobility is by using the slowness and energy of Stoneley waves from the dipole sonic tool (DSI). The other means of determining mobility is by using the multiprobe wireline formation tester (MDT). This tool provides the capability of conducting controlled local production and interference tests along the openhole wellbore. It can be set repeatedly at different locations in a single trip and the formation can be probed in detail through pressure transients using a multiprobe configuration consisting of a sink (production) and three observation probes. In layered formations, this configuration combined with high-resolution wellbore images, permits the direct determination of both horizontal and vertical permeabilities on an individual layer basis. However, empirical porosity-permeability transforms using openhole logs as well as wellbore images may not always suggest the best multiprobe locations to be tested and the probes could be set against tight zones which may not flow. Unsuccessful settings cost money and may compromise a number of possible good test locations due to operational limits. By combining the DSI and MDT in one logging run we are able to define optimum test locations for the MDT by direct analysis of the effect of fluid mobility on Stoneley wave energy. To demonstrate the validity of the technique, we compare results from Stoneley wave and MDT analyses in a Middle East carbonate reservoir.

Bruce R. Cassell graduated in Geophysics from the University of Karlsruhe in 1979. He holds a PhD in Geophysics from the University of Cambridge (1982). His work experiences are Research Geophysicist with Western Geophysical until 1985, Chief Geophysicist for Europe with Schlumberger (1985-1987). He was Division Geophysicist for North-Continental Europe until 1990, Wireline Marketing Manager for Central and Eastern Europe until 1993, and then Chief Geophysicist for the Middle East and India. Since 1995 he is Wireline Marketing Manager for Schlumberger for Oman and Pakistan. He is a member of the SEG, EAEG, SPE and SPWLA.

Fikri J. Kuchuk has a MSc from Technical University of Istanbul and a MSc and PhD from Stanford University. Before joining Schlum-berger in 1982, Fikri worked on reservoir performance and well testing for Sohio Petroleum Company. Since then he has been assigned to Schlumberger Doll Research and, since 1994, he has been Chief Reservoir Engineer for the Middle East and India. He has published more than fifty papers on fluid flow in porous media.

Production Geology of the Safah Oil Field, Sultanate of Oman

Cleveland, Michael N.*, Gerard J. McGann and Hsiu Kuo Chen

Occidental of Oman Inc., Oman

A multi-disciplinary approach involving geology, reservoir engineering and geophysics is used to assess and manage the Shu'aiba reservoir of the Safah field in Oman. Techniques which are currently in use for field management include 3-D seismic acquisition, “slice” mapping, mapping of production and pressure data, borehole image logging and reservoir simulation.

Recently acquired 3-D seismic data suggests that faults in the field are few and of small displacement. The irregular surface at the top of the Shu'aiba reservoir, previously considered to reflect faulting, is now recognized as depositional topography developed on a shallow carbonate shelf with local rudist build-ups.

Slice mapping has been used to better describe the stratigraphically complicated reservoir. This methodology allows a detailed reservoir description including incorporation of horizontal well data and core data. These maps permit careful placement of new horizontal wells so as to avoid local, discontinuous tight limestones. They also serve as input for reservoir simulation.

Production and pressure maps show anomalous well behavior such as high gas-oil ratios. Borehole image logs in horizontal wells permit evaluation of reservoir heterogeneities such as fractures and lateral facies changes. Heterogeneities are investigated through analysis of petrophysical and engineering data to help understand and avoid future problems. Methods to maximize recovery which are currently under consideration are redistribution of gas injection and infill horizontal drilling.

Michael N. Cleveland is currently Chief Production Geologist with Occidental of Oman in Muscat. He has 18 years of oil industry experience in Asia, Latin America and the Middle East with Occidental, Cities Service and Dresser Atlas. He has authored a number of geological papers and is a member of the AAPG and SPWLA. He holds BSc and MSc degrees in Geology from Stanford and Rice Universities, respectively.

Gerard J. McGann (see McGann et al., p. 168)

Hsiu Kuo Chen is Senior Engineering Adviser with Occidental of Oman in Muscat, where he works in reservoir management and field development. Prior to this, he worked with Occidental Petroleum (Caledonia) Ltd., Occidental Research Corp., Phillips Petroleum Co., and Chinese Petroleum Corp. He has 24 years of oil industry experience. He holds a BSc in Mining Engineering from Cheng Kung University and MSc and PhD degrees in Petroleum Engineering from Stanford University.

ARABIAN OIL & GAS '96 CONFERENCE: OPPORTUNITIES & TECHNOLOGIES

15-17 September 1996

Oman International Exhibition Centre

An Overview of the Hydrocarbon Potential of the Paleozoic Petroleum System of the Middle East

Cole, Gary A.*

BHP Petroleum, Inc., USA

and Richard J. Drozd

Westport Technology Center International, USA

The Paleozoic petroleum system of the Middle East contains one of the best organic-rich, oil-prone source rocks found worldwide, the black clastic marine shales located at the base of the Silurian. These shales represent a widespread marine transgression, have a characteristic hot gamma-ray curve, are organic-rich (intervals with >10% TOC and oil-prone), and are responsible for charging structures from Jordan to Oman. Oil-oil and oil-source correlations have definitively found that the Silurian basal shales are the source of these oils. The source rock type is similar throughout the Middle East, and the oils expelled from the basal Silurian marine shales are sweet, light crudes (low sulfur and metals).

The main controlling factor on oil distribution is the burial history reconstructions across the Middle East. The geological history and the timing of generation and expulsion are key aspects for understanding the emplacement of hydrocarbons within the Paleozoic petroleum system. In the northern part of the Middle East, hydrocarbon generation and expulsion occurred mostly during Paleozoic time. Due to this “old expulsion”, most of the expelled hydrocarbons have been lost through time. Those areas that are prospective contain mostly gas (Iraq to northeastern Saudi Arabia), and some minor oil (Jordan and northwestern Saudi Arabia). The mature source kitchen was extensive and expelled large volumes of hydrocarbons during the Devonian period, but present-day field sizes are relatively small and potential exploration risk is high. In the central and southern parts of the Middle East (central Saudi Arabia to Oman), the burial history was more favorable for hydrocarbon expulsion and entrapment. The regional source kitchens in these areas expelled hydrocarbons during the Mesozoic through Tertiary. Because these hydrocarbons were expelled more recently (“young expulsion”) and post trap formation, large fields have been found recently, particularly in central Arabia, and exploration risk is lower.

Gary A. Cole is presently the Principal Geochemist for BHP Petroleum, Inc. in Houston, Texas, following a year as a Consulting Petroleum Geochemist with Westport Technology Center International. Prior to joining WTCI, he was employed at Saudi Aramco for 3 years from 1991 to 1994, and at BP Exploration from 1981 to 1991. Gary received his MSc in Geology from Southern Illinois University at Carbondale in the US. Gary has published numerous scientific papers in the fields of coal geology and petroleum geochemistry and has received several professional awards during his career.

Richard J. Drozd earned his PhD in Physics from Washington University, St. Louis, in 1974, and a BSc in Physics and Mathematics in 1966 from the University of Wisconsin. Richard has twenty years experience in research and management within the petroleum industry with Gulf Oil, Standard Oil, and British Petroleum. He is now with the IIT Research Institute. His specialties include interpretation of isotopic analyses of gases, seeps and oils; applications of geochemistry to problems in the development and production of petroleum; and statistical treatment of geochemical data. He is author of nine papers covering exploration geochemistry and basin studies.

Improving Reservoir Management with Complex Well Architectures

Corlay, Philippe*, Dan Bossie-Codreanu, Jean-Claude Sabathier and Eric R. Delamaide

Institut François du Pétrole, France

After 20 years of research and pilot applications, horizontal wells are currently widely used, becoming more and more a matter of standard procedure. Furthermore, new developments in deviated drilling technology start to strongly modify concepts about well architecture. The new techniques of lateral arms, cluster wells or extended reach drilling can improve reservoir management giving economical access to new reserves, optimizing marginal or mature fields. This paper shows how complex well architecture can improve oil production through a judicious placement accounting for the heterogeneities of the reservoir as well as the drive mechanisms involved. Production can be optimized by monitoring the different sections within a well architecture thus prolonging the life of the well. Potential applications for Middle East reservoir conditions are reviewed. The appealing potential use of complex well architecture for characterization purposes at an early stage of development is also introduced. An identification of the types of well architectures which could optimize pertinent data to be used by geostatistical models is presented. Methods of data acquisition within those complex well architectures are shown and new avenues in this field of research investigated. A new characterization methodology based on hard data acquisition and geostatistical methods is proposed.

Philippe Corlay is Coordinator of Advanced and Integrated Reservoir Studies at IFP with 14 years experience in reservoir engineering mainly in the domain of IOR applications and horizontal wells. Before joining IFP in 1986, he worked for 4 years as a Reservoir Engineer with Beicip-Franlab. Philippe holds a MSc degree in Civil Engineering from HEI, Lille, and a post-graduate degree in Petroleum Engineering from ENSPM, Rueil, France.

Dan Bossie-Codreanu is a Research Reservoir Engineer at IFP. His main interests are IOR applications, reservoir characterization and reservoir engineering. Before joining IFP he worked for Geostock and Beicip-Franlab. Dan holds a BSc in Petroleum Engineering from Texas Tech. University.

Jean-Claude Sabathier is Associate Director of Research at IFP in charge of the coordination of projects on reservoir characterization. Before joining IFP in 1993, he was scientific manager of Beicip-Franlab for 22 years, in charge of the supervision of the Reservoir Group. He was also attached to the Ministry of Industry, France, as an expert on French oil and gas supplies. Jean-Claude holds a MSc degree in Aeronautical Engineering from ENSAE, Paris and a post graduate degree in Petroleum Engineering from ENSPM, Rueil, France.

Eric R. Delamaide is a Research Reservoir Engineer with Institut François du Pétrole (IFP). His main areas of interest are reservoir engineering, EOR and drilling. Eric holds a BSc in Mining Engi neering from the ENSM, St. Erienne and a post graduate degree in Petroleum Engineering from ENSPM, Rueil, France.

The Upper Jurassic Stratigraphic Plays in East Abu Dhabi, U.A.E.

Darwish, Abdel Rahman R.*, Mohamed M. Abd El-Sattar and Sabah K. Aziz

Abu Dhabi National Oil Company (ADNOC)

The Upper Jurassic sedimentary section in East Abu Dhabi represents a major sequence (about 2,000 feet) of thick limestone with minor dolomite.

This sequence, which is dated Oxfordian to Tithonian, is unconformably overlain by the Habshan Formation of Lower Cretaceous (Berriasian) and underlain by the Araej Formation of Middle Jurassic. The Upper Jurassic section was deposited over an extensive carbonate ramp platform. Several depositional environments with different facies were recognized. The subsidence, eustatic sea level and tectonic movements in the area created an intrashelf basin in west Abu Dhabi, whereas shallow shelfal sediments were deposited in the east.

Sequence stratigaphic analysis, lithofacies description and depositional environments modeling revealed the presence of two main stratigraphic plays, the Asab Oolites and Hanifa reservoir within the Upper Jurassic section of East Abu Dhabi. Commercial hydrocarbons have been discovered in both reservoirs in about seven structures in the area.

The paper will discuss the stratigraphic plays, entrapment mechanism, reservoir developments and hydrocarbon potential of the Upper Jurassic section in East Abu Dhabi.

Abdel Rahman R. Darwish is a Senior Geologist with the Abu Dhabi National Oil Company (ADNOC) in the Exploration Division. Prior to joining ADNOC in 1980, Abdel Rahman was with National Oil Corporation (NOC) in Libya from 1975 to 1980. Abdel Rahman received his BSc in Geology from the Cairo University in 1974. He is affiliated with the SEE.

Mohamed M. Abd El-Sattar and Sabah K. Aziz (see Aziz and Abd El-Sattar, p. 115)

7th ADIPEC Exhibition & Conference

13-16 October 1996

Abu Dhabi International Exhibition Centre

Reservoir Modeling and Simulation of a Middle Eastern Carbonate Reservoir

Davis, Darrell W.*, Mike J. Sibley, James V. Bent, Jr. and Ben Wang

Texaco, Inc., USA

Over 600 million barrels of oil have been produced from a carbonate reservoir on the Arabian Peninsula. The dominant lithologies are grain-rich Lower Cretaceous limestones. Primary and secondary porosity types are present. A major, post-structural, stratigraphically cross-cutting, diagenetic barrier to fluid flow has been identified. By restricting aquifer support, significant production induced pressure depletion has occurred above this nearly horizontal barrier, resulting in a pressure differential exceeding 800 pounds per square inch at the field center.

The reservoir has been modeled for reservoir management and pressure maintenance purposes. The 3-D model has been subdivided into 25 flow units, which reflect the architecture of the major flow and barrier units. These units reflect both depositional and diagenetic history, and are defined on the basis of cross-disciplinary data. Among these data are core and thin sections, core analyses, seismic, isotope, open-hole logs, TDTs, RFTs, field pressure surveys, oil and water production data and production tests.

Through reservoir simulation of the geologic model, an excellent production and pressure (lateral and vertical) match of the field was obtained. Prediction cases for a variety of reservoir management scenarios were modeled. Reserve estimates have been modified, additional infill drilling opportunities have been identified, extension drilling is planned, and a pressure maintenance program is being developed and optimized.

Darrell W. Davis holds a BSc in Mechanical Engineering from the University of Houston. He is a Senior Reservoir Engineer at Saudi Arabian Texaco‘s Al-Zour (Mina Saud) office in Kuwait. He has over 15 years experience in production and reservoir studies, and has recently focused upon the design of secondary and tertiary recovery projects. He is currently active in reservoir modeling and field development of reservoirs in the Partitioned Neutral Zone of Saudi Arabia and Kuwait.

Mike J. Sibley holds a MSc in Geology from the University of Georgia. He is a Senior Geoscientist at Texaco‘s Exploration and Production Technology Department in Houston, Texas. He is currently active in exploration, development, and reservoir modeling activities for Saudi Arabian Texaco.

James V. Bent, Jr. holds a MSc in Geology from Stanford University. He is a Senior Reservoir Geologist at Texaco‘s Exploration and Production Technology Department in Houston, Texas. He has over 10 years experience in reservoir characterization and reservoir management. His research interests include carbonate sedimentology, petrophysics, mapping and flow unit modeling.

Ben Wang holds a PhD in Petroleum Engineering from the University of Texas at Austin. He is a Senior Reservoir Engineer at Timan Pechora Co. (a joint-venture company of Texaco, Exxon, Amoco and Norsk Hydro to develop Russian oil fields). He has 17 years extensive experience in reservoir simulations, reserve evaluations, EOR, coalbed methane production and horizontal well applications.

Use of Permanent Downhole Geophones as a Tool for Reservoir Behavior Characterization

Deflandre, Jean-Pierre D.*, Jean O. Laurent, Pierre-Claude Layotte

Institut François du Pétrole, France

Frédéric M. Huguet and François Verdier

Gaz de France, France

Downhole geophones have been developed for use in a permanent way (several years) in producing oil or gas wells. These geophones were designed to be installed between the casing and the tubing and can be adapted to different well completions.

Such geophones are suitable for two types of applications: microseismic monitoring and 4-D seismic measurements. Installing 3-component permanent geophones close to the reservoir level enables the recording of microseismic events of very small magnitude (less than -1). The data obtained make it possible to locate the mechanically active zones associated with fluid injection or withdrawal. For 4-D seismic measurements, these downhole geophones enable the easy setting of multi-azimuthal borehole seismic to locate, in a repeatable way, the displacement of the gas bubble limits in the instrumented wellbore vicinity.

These two applications have been successfully used in two different background gas storage reservoirs since 1991. Results obtained at the first site were used to improve the technology of the arrays. At the second site, one well has been instrumented for three years. Comments concerning the results obtained for each case will be developed.

Jean-Pierre D. Deflandre received a degree in Physics from the University of Paris in 1979 and a graduate engineering degree in Physics and Instrumentation from the Conservatoire National des Arts et Métiers, Paris, in 1987. He joined IFP in 1979. Jean-Pierre was first involved in thermal EOR laboratory measurements. Now, as a Research Scientist, he is mainly in charge of microseismic monitoring interpretation at the Rock Mechanics Department of the Applied Mechanics Division. He is a member of the SPE, SAID (French Chapter of the SPWLA) and AFTP.

Jean O. Laurent received an engineering degree from the Ecole Centrale de Paris in 1962 and a graduate geophysics engineering degree from the Ecole Nationale Supérieure du Pétrole in 1963. Jean joined IFP in 1965 and worked for many years on land and marine seismic equipment projects including hydrophones, streamers, marine and land sources. He is now in charge of a borehole seismic tool research project. He is a member of the SEG and EAGE.

Pierre-Claude Layotte received his licence in Physics from the University of Paris and a graduate geophysics engineering degree from the Ecole Nationale Supérieure du Pétrole in 1957. In 1960, he joined the experimental land seismic crew at IFP. Starting in 1963 Pierre-Claude headed the experimental seismic crew for many years, working on various research assignments dealing with acquisition techniques improvement, design of land seismic sources and use of shear waves in VSP and surface seismic. He is currently in charge of seismic data processing and interpretation with IFP and Associate Professor at ENSPM. He is a member of the SEG and EAGE.

Frédéric M. Huguet received an engineering degree from the Ecole Nationale Supérieure de Géologie and a graduate geophysics and geology engineering degree from the Ecole Nationale Supérieure du Pétrole. He joined Gaz de France in 1991 and worked as a Geologist with the Geophysical and Geological Service. He is mainly in charge of geological and geophysical studies concerning underground gas storage facilities as a specialist in reservoir geophysics. He is a member of the EAGE.

François Verdier received an engineering degree from the Ecole Nationale Supérieure de Géologie and a graduate geophysics engineering degree from the Ecole Nationale Supérieure du Pétrole and the Ecole d'Application des Techniques Gazières. He joined Gaz de France in 1975 and worked with the Geophysical and Geological Service. He is now the head of this service. His main expertise concerns geophysical and geological studies on underground gas storage facilities in France and abroad. He is a member of the Association Françoise des Techniciens du Pétrole, Association des Techniques Gazières and EAGE.

Nile Delta Prospective Province, Economics and Exploration Management

Deibis, Said Y.

Western Desert Operating Petroleum Company, Egypt

During the last thirty years, the exploration activities covering the Nile Delta of Egypt have yielded several gas discoveries. The estimated recoverable reserves are 15 trillion cubic feet of gas and the prospective area, north of the central Neogene hinge line, covers about 100,000 square kilometers. Exploration activities have revealed that the sedimentary sequence is very thick, of which the Tertiary rocks may exceed 20,000 feet of clastics. These sediments are characterized by the presence of not only the generating source rocks but also the reservoir sands at appreciable depths to drill, and have remarkably good petrophysical properties. The integrated tectonics of the area, within the regional tectonic framework of northern Egypt, coupled with the contemporaneous depositional elements, have created several entrapment conditions for gas accumulation. Geographically, the Nile Delta province occupies a strategic place close to a highly gas consuming market in the Middle East and southern Europe. In these countries the demands are expected to double within the coming decade. This paper elaborates on the economics of exploration and potential reserves of this province. The paper also discusses how the development of discoveries can be effectively implemented by reducing geological and economic risks.

Said Y. Deibis is presently the Exploration Manager and Board Director of the Western Desert Operating Petroleum Company (WEPCO). He has 35 years of petroleum operation experience, of which 8 years with Belayim Petroleum Company, Cairo, 3 years with Phillips Petroleum Company, Alexandria and 24 years with WEPCO, Alexandria. He is a member of several petroleum exploration and production societies and has published several papers on the Geology, Petroleum and Economics potential of Gulf of Suez, Western Desert and Nile Delta, Egypt. He has a BSc in Geology and Chemistry from the Faculty of Science, Alexandria, Egypt.

Geostatistical Model for North Ain Dar Pilot, Ghawar Reservoir, Saudi Arabia: An Improved Reservoir Simulation Model

Douglas, John L.* and Members of Ain Dar - Shedgum Modeling Team

Saudi Aramco

The North Ain Dar 3-D geocellular model consists of geostatistical models for lithofacies, porosity and permeability for a portion of the Jurassic Arab-D reservoir of Ghawar Field, Saudi Arabia. The reservoir consists of a series of shallow water carbonate shelf sediments and is subdivided into 10 time-stratigraphic slices on the basis of core descriptions and gamma/porosity log correlations. The North Ain Dar model includes an electrofacies model and electrofacies-dependent porosity and permeability models. Sequential Indicator Simulations were used to create the electrofacies and porosity models. Cloud Transform Simulations were used to generate permeability models. Advantages of the geo-statistical modeling approach used here include: (1) porosity and permeability models are constrained by the electrofacies model, i.e., by the distribution of reservoir rock types; (2) patterns of spatial correlation and variability present in well log and core data are built into the models; (3) data extremes are preserved and are incorporated into the model. These are critical when it comes to determining fluid flow patterns in the reservoir. Comparison of model permeability (Kh) with production data Kh indicates that the stratigraphic boundaries used in the model generally coincide with shifts in fluid flow indicated by flowmeter data and therefore represent reasonable flow unit boundaries. Further, model permeability and production estimated permeability are correlated on a Kh basis, in terms of vertical patterns of distribution and cumulative Kh values at well locations. This agreement between model and well test Kh improves on previous, deterministic models of the Arab D reservoir and indicates that the modeling approach used in North Ain Dar should be applicable to other portions of the Ghawar reservoir.

John L. Douglas received a BSc degree from McGill University, Canada, and a PhD in Geology from Memorial University of New foundland, Canada. Between 1984 and 1991 he worked in Calgary, Alberta for the Research Laboratories of Texaco, Canada Resources, and ESSO Canada Resources. John, ‘s principal respon sibility during this time was to provide geological support in the area of reservoir modeling to reservoir engineering and development geology groups. John is currently a member of the Southern Area Reservoir Geology Group of Saudi/Aramco. His professional interests include reservoir description and modeling and the application of geostatistical methods to the spatial distribution of geological data.

From Frontier Exploration to LNG: Integrating Regional Studies and Modern Technologies to Formulate Upstream Strategies in Yemen

Duval, Bernard C.*, Jean-François Dervieux

Total, France

and Thibault de Cizancourt

Total, Yemen

The paper illustrates the formulation of exploration strategies applied to two areas of Yemen, with varying degrees of risk: rank wildcat in the East Shabwa Area1, and intensive exploration in the Marib Area2. Commercial oil and gas discoveries were made in Mesozoic grabens of these areas, respectively, parts of the Wadi Sarr and Wadi Ain Basins and the Marib-Jawf Basin.

Firstly, the petroleum systems in both areas are characterized by Marine Type 2 source rocks of Kimmeridgian age, deposited at the time of maximum Late Jurassic transgression, with fairly high potential (SPI values: 6 to 13 tons hydrocarbon per square meter).

Secondly, vertical migration drainage is important in both cases, although with some lateral component, particularly in the Marib Basin. High impedance is characteristic of the latter, due to the presence of thick Portlandian salt formation on top of the Alif fluvio-deltaic sand reservoirs. In contrast, a low impedance system is observed in the Shabwa Area, where the oil is found in Barremian-Aptian sands, making the relative timing of migration and faulting critical to entrapment. The success ratios recorded during the different exploration phases reflect the risk levels applicable to the various play-types.

The contribution of modern technologies, among which sequence stratigraphy and wireline log imagery (in establishing a reservoir geological model), biomarker source characterization and maturity histories are described. Particular emphasis is placed on the use of satellite imagery and digital elevation models to prepare seismic surveys in extremely rugged high relief canyonland, correlate shallow and deep structural features and make preliminary studies of pipeline routes with minimum field operations.

Appraisal is in progress on East Shabwa, development is planned in Jannah, as well as participation in an LNG project in the Marib-Jawf Province.

Bernard C. Duval graduated from Ecole Polytechnique, Paris, Universities of Grenoble and Dijon, Ecole Nationale Supérieure du Petrole et des Moteurs (ENSPM). He was employed by Total between 1958 and 1995 and his assignments included Libya, Venezuela, Canada (VP Exploration-Production, North America). Bernard has been Senior Vice President Exploration of Total since 1985, in charge of worldwide exploration programs, strategies and negotiations. He is currently Associate Professor at ENSPM. He is a recipient of AAPG Distinguished Achievement Award (International), 1995, and a 1995 to 1996 AAPG Distinguished Lecturer.

Jean-François Dervieux graduated from Ecole Spéciale des Travaux Publics, Paris. He was a Surveyor Engineer with Total between 1980 and 1986. During this period, Jean-François did field work in Sudan, Gabon, Abu Dhabi and Algeria and was seconded to Zakum Development Company where he carried out radiopositioning and geotechnical surveys. Since 1986 as a Geophysicist, he specialized in satellite imagery, remote sensing applications and gravity and magnetic geophysics.

Thibault de Cizancourt graduated from the University of Clermont-Ferrand with a Master‘s degree in Physics and Ecole Nationale Supérieure du Pétrole et des Moteurs, Rueil, France. He was employed with Total since 1974 and his assignments included UK, Argentina, Tunisia and Egypt as a Geophysicist, then Chief Geophysicist. Thibault has been Exploration Manager of Total Yemen during the last 3 years and is now working at the Head Office in the Field Studies Department.

3-D Survey Design: Symmetric vs. Asymmetric Split Spreads

Egan, Mark S.

Geophysical Service Inc. Saudi Arabia Ltd., Saudi Arabia

Although the CMP fold coverage in a 3-D survey might appear to be adequate, it is not always guaranteed that a boundary will be properly imaged in the final processed section. Imaging routines rely on summation of the traveltime surfaces associated with many rays. These surfaces constructively interfere at the location of the reflection thereby creating the image. The point of caution here is that an improperly designed 3-D survey can be lacking in the specific surfaces required to produce the image. Dangerous dip and azimuth combinations can especially arise in surveys that use asymmetrical split spreads. This is a pertinent point in the Middle East since issues such as multiples and ground roll, not imaging, have dominated the process of 3-D survey design in the past. The realization now that faults and fracture systems can play major roles in the development of Middle East fields has led to a more careful analysis of the recording geometries used there. Specifically this study shows via simple modeling how the results in 3-D DMO sections vary as a function of spread symmetry, spread width, shooting direction and dip.

Mark S. Egan is an Area Geophysicist for Geophysical Service Inc. Saudi Arabia Ltd. (part of Geco-Prakla/Schlumberger). He has worked for GSISA and/or its parent companies for 20 years. In 1975, Mark received a BSc in Physics from Duquesne University in Pittsburgh, Pennsylvania. In 1978, he received a MSc in Acoustics from the University of Houston, and in 1988, he received a PhD in Geophysics also from the University of Houston.

Structural Analysis of Faults, Fractures and In-situ Stress and their Roles in Controlling Reservoir Dynamics of an Onshore Field, Abu Dhabi, UAE

El-Shazly, Salah E.*, S. Al-Matrooshi, Neil Young

Abu Dhabi Company for Onshore Oil Operations (ADCO)

and Mahmoud Akbar

Schlumberger, Saudi Arabia

Development of any hydrocarbon field is very dependent upon accurate delineation of its structural grain both at smaller and larger scales. Reservoir compartmentalization is very much controlled by smaller faults which sometimes are difficult to see and interpret correctly from both 2-D and 3-D seismicdata. However, such minor faults have been interpreted precisely in one of the Abu Dhabi oil fields (Field “A”) using borehole imagery and well log data from nineteen wells. The sealing nature of fault planes was determined primarily on the basis of visual examination of the downhole images. The findings were later confirmed by reservoir pressure data.

Minor-scale structural features, like fractures, can play a vital role in enhancing the permeability of reservoirs with variable matrix permeability like the Thamama. Therefore, an attempt was made to characterize the fractures in terms of their morphology and origin. Three types of processes were identified as the causes of stresses: fault, overburden and folding related stresses which eventually fractured not only the tight carbonates but also the porous carbonates of the Thamama in field “A”.

The results of the study are being employed in conjunction with 3-D seismic to refine the structural model of the field. The fault and fracture data have helped to explain the anomalies in pressure and production data of the Thamama reservoir in field “A”.

Salah El-Shazly is a Lead Reservoir Geologist with ADCO. He has 17 years of experience in exploration and production geology, 13 years of which were with Gulf of Suez Petroleum Company. He holds a BSc and MSc in Petroleum Geology from Ain Shams University, Cairo, Egypt. He has presented and published several technical papers in the EGPC Petroleum Exploration and Production Conference (Cairo, 1990 and 1994) and in the AAPG Conference (Dallas, 1991 and Nice, 1995). He is an active member of the AAPG and SEE (Society of Explorationists in the Emirates).

Salem Al-Matrooshi is a Lead Reservoir Geologist with ADCO. He has 7 years experience in exploration and production geology. He holds a BSc in Geology from UAE University, Al Ain. He has participated in multi disciplinary studies on different fields in onshore Abu Dhabi. He is an active member of the AAPG.

Neil Young is currently a Senior Reservoir Geologist with ADCO on secondment from BP Exploration. Neil joined BP in 1980 as a Petroleum Engineer, working on North Sea fields. He was also seconded to QGPC for 3 years followed by 7 years in reservoir engineering on the North Sea. He graduated from Heriot-Watt University with a BSc in Mechanical Engineering.

Mahmoud Akbar (see Al-Deeb et al., p. 100)

Dealiasing DMO: A Practical Technique to Process Data with Irregular Acquisition Geometry

Ferber, Ralf

Schlumberger-Geco-Prakla, UK

Irregular acquisition geometry is inevitable due to obstacles and cable feathering in 3-D marine surveys, widely spaced ocean bottom cables, and access limitations in 3-D land surveys. Such irregularities degrade the fidelity of reflectors' image and wavelet. Reservoir characterization based on seismic attributes, inverted acoustic impedance, and AVO analysis, is very sensitive to degraded amplitude and phase. The footprint of the acquisition geometry may lead to incorrect interpretation unless it is properly handled in the processing. Dealiasing DMO is a constrained inversion method that finds the optimal model to fit given data, using forward and transpose modeling to iteratively minimize the misfit of the model to the data. The method produces high quality images even in the presence of considerable geometry irregularities that would require in-fill surveys with other processing techniques. Applied in offset ranges the method benefits pre-stack analysis such as velocity and AVO analysis after pre-stack migration. The dealiasing inversion requires significantly more computing and I/O resources than DMO processing. However, the technique is now practical on modern parallel computers.

Ralf Ferber is currently Senior Research Geophysicist with Scllumberger-Geco-Prakla, UK He has 10 years work experience in 3-D seismic data processing. Ralf is a member of the EAEG.

Advanced Seismic Data Interpretation for Carbonate Targets Based on Optimized Processing Techniques

Fischer, Klaus C.*, Ulrich Möller

Schlumberger GeoQuest, Germany

and Roland Marschall

Schlumberger-Geco-Prakla, Germany

The Shu'aiba Formation represents one of the most prolific hydrocarbon reservoirs in Abu Dhabi. The remaining potential is believed to be related to subtle structural and stratigraphic traps. New developments in exploration geophysics like pre-stack depth migration integrating processing and interpretation form a powerful tool for improved development of existing oil fields and for identification of new oil fields. In general the processing is comprised of three phases (depending on the local validity/violation of the zero-offset-condition): Phase A:

Standard processing sequence up to final DMO stack and migration including calibration using elastic instead of plane-wave synthetic. The interpretation team generates a first macro model of the velocity field. Phase B: Post stack depth domain: the velocity field is checked and updated using the wavefront method. The new macro model forms the basis for post-stack depth migration, which is reinterpreted by the interpretation team in order to generate the final macro model required for Phase C. Phase C: Pre-stack depth-domain: the pre-stack depth migration is subject to final interpretation and due to the irregular surface of the Shu'aiba Formation, should form the basis for AVO. Further steps are L1 deconvolution followed by Born inversion, which is essential for generation of a high resolution lithological model. The procedure is presented using a 2-D seismic line, which was subjected to detailed interpretation (seismic sequence and facies analysis) of the Shu'aiba Formation. The final result is a detailed lithological model which is verified by applying elastic forward modeling. The results are to be used as input in reservoir modeling and geostatistical evaluations in order to take into account reservoir heterogeneities being important for prospect evaluation.

Klaus C. Fischer joined the Seismic Interpretation Service Group of Schlumberger GeoQuest in 1985. Since 1993 he has been the Manager of the Seismic Interpretation Services Group. He studied Geology at the University of Stuttgart and received a Diploma in Geology from RWTH Aachen in 1983. Klaus is professionally woriingin areas such as seismic stratigraphy and basin evaluation. He is affiliated with the EAEG and AAPG

Ulrich Möller joined the Seismic Interpretation Service Group of Schlumberger GeoQuest in 1990. He is currently a Senior Seismic Interpreter. Between 1987 and 1989, Ulrich was an Assistant at the Institute for Petroleum Geology at the Technical University Clausthal. He obtained a Diploma in Geology from the Technical University Clausthal in 1987. Ulrich is professionally working in areas such as seismic stratigraphy and basin evaluation. He is affiliated with the AAPG

Roland Marschall has been with Geco-Praila since 1967. He is currently the Chief Geophysicist Land Data Acquisition with Geco-Prakla in Hannover, Germany. Roland graduated from Montan University Leoben with a Diploma in Engineering in 1966 and a PhD in 1975. In 1990 he obtained full Professorship at Ruhr University Bochum. He is affiliated with the EAEG, SEG and DGG and is interested in seismic data acquisition, processing and interpretation.

Intensive Exploration in the Euphrates Graben, Syria

François, Denis *

Elf Hydrocarbures Syrie and

Wasif Al Youssef

Syrian Petroleum Company, Syria

The combination of extensive 3-D seismic surveys, field development, sedimentological and geochemical studies has resulted in an accurate definition of the petroleum system of the Euphrates Graben. This combination of techniques has resulted in the discovery of several hydrocarbon accumulations with a success ratio of 50%.

Denis François is the Exploration Manager in Elf Hydrocarbures Syrie. He has 15 years of oil exploration experience with Elf in Morocco, Angola, Congo, France and Syria. He graduated from the Ecole Nationale Supérieure des Petroles et des Moteurs of the French Petroleum Institute (IFP) and has a MSc in Geology from Lyon I University.

Wasif Al Youssef is the Director of the Exploration Department, Syrian Petroleum Company, since 1988. Since 1972 he has held the positions of Director, Service-Contract Department; Director, Petroleum Studies Department; and as Chief of Petroleum Reservoir Engineering. Wasif received his Diploma-Engineering degree in Petroleum Geology in 1972, and his Doctorate in Petroleum Engineering in 1993 from the Institute for Geology of Energy and Exploitation of Combustible Resources. Wasif has participated in numerous energy-related conferences as a speaker. He is a member of the Renewable Energy Resources Committee at the Read University, London.

Palynostratigraphic Zonation, Sedimentation History Reconstruction and Hydrocarbon Potential of the Paleozoic Sediments of Northwest Arabian Peninsula and their Equivalent in Algeria and Western Libya

Futyan, Abda R.I.* and Adil H. Jawzi

Futyan Jawzi and Associates, UK

Oil and gas deposits were recently discovered in the Paleozoic basins of Saudi Arabia, western Iraq, Jordan, Syria and southeast Turkey. These and the petroliferous Paleozoic basins of North Africa were part of the same Paleozoic mega-basin and shared similar geological, sedimentation and tectonic history.

Detailed palynostratigraphic analysis of a large number of well samples (mainly from Jordan) established seven regionally mappable palynological time zones for the Cambrian-Ordovician sediments, eight for the Silurian, ten for the Carboniferous and four for the Permian. The Devonian sediments are eroded from most of northwest Arabian Peninsula. Paleoenvironmental reconstruction, lithofacies, thickness and lateral distribution maps were produced for the established 30 palynological zones. Similar analysis of a larger number of well samples (mainly from Algeria) established over 50 regionally mappable palynological time zones (Cambrian-Carboniferous).

The main producing reservoirs in Arabia are the Cambrian sandstones, Upper Ordovician and Upper Silurian sandstone, Lower Carboniferous carbonates and sandstones, and Lower Permian sandstones. Major source rocks are present within the Middle Cambrian and several horizons within the Ordovician, Silurian and Carboniferous sediments. The main producing reservoirs in North Africa are the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Triassic sandstones. Major source rocks are present within the Ordovician, Silurian and Carboniferous sediments.

In this paper, the stratigraphy, sedimentation history, potential reservoirs and source rocks in Algeria and western Libya and Arabian basins will be illustrated and correlated. The present day distribution of the oil and gas fields and the hydrocarbon potential of some Paleozoic plays in Jordan will also be discussed and illustrated.

Abda R.I. Futyan is currently the Managing Director of FJA International Petroleum Consultancy based in Llandudno, Wales. He has 33 years experience in petroleum exploration. Abda previously worked for Natural Resources Authority in Jordan, for Saudi Aramco, PDO, Oman and between 1973 and 1989 with Robertson Research. He has a PhD in Biostratigraphy and a MSc in Petroleum Reservoir Engineering from London University.

Adil H. Jawzi is currently the Director of FJA International Petroleum Consultancy, based in Llandudno, Wales. He has 25 years experience in petroleum exploration. He previously worked for Iraq National Oil Company and Robertson Research between 1978 and 1989. Adil has a BSc (Hons) in Geology from London University.

Seismic Processing Issues in the Design of 3-D Surveys

Galbraith, James M.

Seismic Image Software Ltd., Canada

3-D seismic data are processed through a series of steps typically; statics, NMO, DMO, Stack and Migration.

For refraction statics we must ensure that both shallow and deep refractors are adequately sampled. Modeling by bins using typical velocities is performed to ensure adequate offset sampling and range for velocity analysis.

Straight line geometries are uncoupled for reflection statics solutions. Statics coupling can be ensured by breaking up the regularity of the geometry or by using smoothers in the structure term leaving long wavelength errors.

Weighted DMO fold in each bin can be calculated for a specific time and velocity. In the presence of dip the DMO response may be calculated for each bin. Examples of such DMO responses from different geometries show severe phase and amplitude changes indicating that such dipping targets if really present would show strong geometry imprinting. Random and coherent noise will be attenuated by CMP stacking provided there is a good mix of offsets in each bin. The full fold area must allow for the migration aperture. Migrating a portion of a diffraction gives some fraction of the correct energy. Not quite full-fold traces may be acceptable for bins near the edge of the survey.

In conclusion, survey geometry affects seismic processing. Offset distribution is the major factor in creating geometry “imprints” on the data, although azimuth plays a significant role in statics calculations. As 3-D designers, we must ensure the most even mix of offsets possible - if necessary by moving and/or adding shot points.

James M. Galbraith received his BSc (Honors) in Mathematical Physics from the University of Edinburgh in 1967. He is presently the President of Seismic Image Software, Canada. Mike served as President of Veritas Software Ltd. (1984-1987), Programming Manager of Veritas Seismic Ltd. (1975-1984), Programming Manager of R.B. Cruz and Associates Ltd. (1971-1975), and Research Assistant of the British Gas Council (1968-1970). His areas of interest include design of 3-D seismic surveys, computer interfaces for enhanced understanding and productivity in survey design and seismic data processing, front-end seismic processing techniques and algorithms and imaging techniques. Mike is a member of the SEG, EAEG, AAPG, CSEG, DGS, ASEG, PESGB, IEEE and APEGGA.

1996 AAPG ANNUAL CONVENTION

19-22 May

San Diego Convention Center

Block 4, Shabwa Basin, Yemen: The Structural Control on Sedimentation in a Mesozoic Rift Basin and Its Impact on Hydrocarbon Distribution

Gerdes, Keith D.*, Gurdip Sahota and Joseph Brannan

Nimir Energy Services Limited, UK

Abdullah Hassan and Mohammed Barahim

Nimir Ayad, Yemen

Block 4 lies in a central position within the Shabwa rift and includes a major transfer zone and the western flank of a central basin high within its boundaries. Most sediments in such a setting are axially transported and hence the effect of localized topography on sedimentation cannot be discerned. The predominance of carbonate lithologies in the Jurassic rift sequences in Block 4 illustrate that siliciclastic input in the block was restricted to discrete depositional events. Seismic and well data from Block 4 therefore provide a unique opportunity to map and model the interaction of tectonics and sedimentation in a central location within the rift. Recently, 1,600 kilometers of 80-fold seismic data were acquired in Block 4 and three exploration wells drilled. The data were augmented by the previously existing well and seismic database. Detailed structural and seismostratigraphic mapping of this data reveal the major structural elements and seismic sequences within the block. Depth conversion of surfaces correlated with major sequence boundaries provides a suite of maps which demonstrate the relationship between structure and deposition in Block 4. Transfer zones and sediment entry points are identified and their influence on both structure and rift sedimentation illustrated. Mapping of evaporite sequences show the control of pre-existing structures on halokinesis. Finally, seismo-stratigraphic mapping of the Cretaceous sequences demonstrates the channelling of prograding sequences by halokinetic features. The implications of this relationship between tectonics and sediment deposition for the generation and distribution of hydrocarbons is discussed.

Keith D. Gerdes has been Geophysical Manager at Nimir Energy Services Limited since 1992. He has 12 years experience in the oil industry, initially in production geoscience with Shell International. In 1986 he joined BP International and the Basin Studies Group reviewing new venture opportunities in Europe, Africa, Middle and Far East. He also contributed to and led in house courses in seismic stratigraphy and carbonate exploration. He holds a BSc in Geology and Geophysicsfrom Durham University, UK and a PhD in Geophysics from University College Swansea, Wales. He is a member of the AAPG, AGU and PESGB.

Gurdip Sahota (see Sahota et al., p. 186)

Joseph Brannan is an Exploration Geologist with 14 years experience in the oil industry. He joined BP from university in 1982 and spent years working in a number of hydrocarbon provinces. His major areas of activity included the North Sea, North Slope of Alaska, PNG, South America and the Middle East. He joined Nimir Energy Services Limited in 1992, and since then his major area of interest has been Yemen. Currently he is responsible for exploration interests in the Middle East and the North African region. Joseph holds a BSc from Glasgow University and a DPhil from Oxford University. He is a fellow of the Geological Society and a member of PESGB.

Abdullah Hassan is a Geologist with the Ministry of Oil and Mineral Resources (MOMR), Yemen. He is currently on secondment to Nimir Petroleum Company where he has been working as a Geologist since 1991. Abdullah worked on the West Ayad field with MOMR between 1984-1991. He graduated from Bucharest University, Romania in 1984 with a MSc in Geology.

Mohammed Barahim is a Geophysicist with the Ministry of Oil and Mineral Resources (MOMR), Yemen. He is currently on secondment to Nimir Petroleum Company where he has been working as a Geophysicist since He worked for the Yemen Company for Investment in Oil and Minerals for 2 years and also for the MOMR for 2 years. He graduated from the Mining Academy in Freiberg, Germany in 1985 with a degree in Geophysics.

Spatial Patterns of Porosity/Permeability Using Simulated Annealing Method

Ghori, Saleem G.

King Fahd University of Petroleum and Minerals, Saudi Arabia

The simulated annealing method (SAM) has been a successful reservoir characterization tool in geostatistics. This paper presents an application of SAM to simulate rock properties of carbonate reservoirs in Saudi Arabia.

The method was applied to a carbonate reservoir in Saudi Arabia consisting of well log porosity in 131 wells. A two component objective function was minimized. The components of the objective function were the experimental variogram and the pairs involved in at least one conditioning (known) datum. Several images of the porosity values were generated. These were also compared with the images obtained from the Gaussian sequential simulation method (GSS). Results show that SAM is superior to the GSS method in the sense that experimental variograms are reproduced exactly. The spatial patterns of porosity are more realistic and represent the true variability of the reservoir rock. The use of the conditioning point in the minimization of the objective function reduces the discontinuity of images near the wellbore with known data.

The simulated annealing method was also applied and tested on an exhaustive minipermeameter measured permeability data set obtained from a rock sample. The data from a tracer flow experiment was also used in the SAM. The method was used in the conditional simulation, assuming some of the known permeability data. The conditional fields are then used in the simulation of a miscible tracer flow through the sample rock and compared with the actual tracer concentration curve. Results show that the exact experimental variogram was reproduced. It is possible to reproduce tracer output curves by using it as the objective function in the SAM.

Saleem G. Ghori received his BSc in Petroleum Engineering from the University of Engineering and Technology, Lahore, Pakistan. He received his MSc and PhD from the New Mexico Institute of Mining and Technology, USA, both in Petroleum Engineering. After graduation in 1992, he worked as a Research Associate in the Petroleum Engineering Department of the University of Texas at Austin. Saleem joined the Research Institute at King Fahd University of Petroleum and Minerals in November, 1993. His research interests are geostatistics, reservoir flow simulation, tracer technology and parallel processing computers. He is a member of the SPE.

Deriving Permeability Transforms for Reservoir Simulation Models: A Practical Example

Gidman, June*

Chevron Petroleum Technology Company, USA

and Dennis J. Fischer

Cabinda Gulf Oil Company Ltd., Angola

Simulation is an important tool for reservoir management. Populating the simulation grid with structure, porosity, permeability, and saturation data is one of its technical challenges. Ofthese variables permeability is particularly problematic. Currently there are no logging tools that provide generally acceptable measures of permeability. Instead, most often core data are used to derive a correlation-based porosity/permeability transform. While there is commonly some relationship between porosity and permeability, this relationship is rarely sufficient by itself to adequately predict permeability. We take various approaches to predicting permeability, based on core and log data. Core and log data must first be quality controlled and depth matched. Since porosity is an important component of most transforms, it is essential that porosity derived from log interpretation compares well to porosity from core. We find that permeability predictions based on a combination of regression and model-based techniques most often provide the best results. There is generally some fine tuning to take into account V shale, fluid content (gas, oil, or water), reservoir lithology, and borehole rugosity. Our assessment of the best transforms is made by comparison of core and log data on depth plots. The calculated data are subsequently input to geostatistical modeling, scale-up, history matching, and reservoir simulation. The transforms are specific to the reservoir studied, but the approaches can be applied to other fields where there are core and log data.

June Gidman is a Geologist with Chevron. She has 17 years of experience, with 4 in BP, 3 in Union Texas, and 10 in Chevron. She is involved with the SCA and has published on core handling core to log data integration and reservoir geology. June received her BSc in Geology (Honors) from Leicester Uriversity and a PhD from Liverpool University.

Dennis J. Fischer is Chief Development Geologist with Cabinda. He has 13 years of petroleum in research, operations, formation evaluation, exploration and development. Dennis is a member of the AAPG, SPWLA, SPE, and has published on formation evaluation and reservoir characterization. He has a BSc in Geology/Geophysics and a MSc in Mining Engineering, from the University of Wisconsin.

Using Borehole Profiles or Structural Cross-Sections with Geological Images

Gozoren, Tarik I.* and Khaled A. Al-Bassam

Saudi Aramco

A geological cross-section or a simple well-borehole profile can be significantly improved for better reservoir characterization when displayed with sub-surface geological images. 2-D computer generated geological images are easily generated and are independently used to enhance reservoir interpretation. This study presents a simplified model-overlay procedure and its common applications for several Saudi Aramco reservoirs. Geological images consist of either well-to-well lithofacies distribution, seismic sections or reservoir property distributions. Any one of these, or combination of two can be overlaid on a standard structural correlation panel. Correlation panels are created by applying a scaled well spacing option at the top of the reservoir. Top and bottom penetrations are the target boundaries for image overlays. An identical procedure is applied for the simple well borehole profile displays. Accuracy should be maintained by transforming all cross-sections and overlays using a specified projection system and geodetic datum. This study, however, applies a geometric-N degree polynomial -transformation determined by the Least-Square Fit method.

Tarik I. Gozoren is System Analyst of the Geologic Application Services Division of Saudi Aramco. He has 23 years experience in geological and exploration applications. Tarik received his BSc and MSc degrees in Geological Engineering from Istanbul Technical University.

Khaled A. Al-Bassam is Administrator of the Geologic Application Services Division of Saudi Aramco. Khaled has 13 years experience in geological and exploration applications. He received his BSc in Civil Engineering from King Fahd University of Petroleum and Minerals.

Three-Dimensional, Carbonate and Siliciclastic, Forward Modeling

Granjeon, Didier H.*, Philippe R. Joseph,

Institut Français du Pétrole, France

François Guillocheau and Cecile D. Robin,

Rennes University, France

A three-dimensional stratigraphic forward model has been built at IFP to simulate geometries and lithologies of coastal environments, e.g., coastal plain, shoreface and upper offshore in a high-resolution sequence stratigraphic framework. The model is based on an improved diffusion equation, result of the coupling of mass conservation with production and transport relations for carbonate and/or siliciclastic sediments. The model can be used in two different ways. Firstly, it allows to quantify the relative influence of key parameters such as eustasy, subsidence and sediment supply on the basin-infill architecture. Secondly, applied on subsurface studies, an inverse method is used to fit the simulation to the available well data. When this match is achieved, modeling improves and validates the sedimentological correlation scheme and helps to better predict the extension of sedimentary bodies in exploration and appraisal studies when few wells are available. The model has been successfully applied on two field studies: the Lower Cretaceous mixed carbonate-siliciclastic formation (total simulated duration = 10 million years) of Paris Basin, France at a regional scale (160 x 200 square kilometers), and the Campanian siliciclastic formation (total simulated duration = 100,000 years) of San Juan Basin, USA at a reservoir scale (10 x 20 square kilometers). These applications validate the principles used in the model and provide a quantitative tool for better understanding the carbonate and siliciclastic filling of a basin.

Didier H. Granjeon is a Geologist in the Production Geology Group at Institut Français du Pétrole (IFP), Rueil-Malmaison. His research interests are in geosciences and deterministic approach applied to 3-D basin modeling. He holds a Civil Engineer‘s degree in Geology from Ecole des Mines de Paris and a PhD in Geology from Rennes University, France.

Philippe R. Joseph is a Senior Geologist in the Production Geology Group in Institut Français du Pétrole (IFP), Rueh-Malmaison. His research interests are in the combination of deterministic and stochastic techniques for 3-D sedimentological modeling of reservoir bodies. He holds a Civil Engineer‘s degree and a PhD in Geology from Ecole des Mines de Paris, France.

François Guillocheau is Head of High Resolution Sequence Stratigraphic Project at Rennes University. His research interests are in facies sedimentology, genetic stratigraphy, and comprehension of sedimentary record from a reservoir to a basin scale. He holds a PhD in Geology from Brest University, France and a These d'Etat from Strasbourg University, France.

Cecile D. Robin is a Geologist in the Sedimentary Group at Rennes University, France. Her research interests are in stratigraphic record of basin deformation and in sedimentary and tectonic evolution of Paris basin. She holds a Civü Engineer‘s degree and a MSc in Geosciences from Ecole de Geologie de Nancy, France and a PhD in Geology from Rennes University, France.

The Rangefront Fault of Northern Oman and its Effect on the Hydrocarbon Potential of the Gulf of Oman Basin

Hanna, Samir S.*,

Sultan Qaboos University, Oman and

David W. Rodgers,

Idaho State University, USA

The Late Cretaceous period in Oman was dominated by a well-documented thrust tectonic regime which involved the emplacement of the Semail ophiolite. Subsequent post-orogenic extension and exhumation created the modern Oman Mountains. Major fault zones which flank the mountains contain numerous kinematic indicators that record a polygenetic movement history. Detailed study of the northern rangefront fault indicates a dominant top-to-the-north-northeast slip direction, with as much as several kilometers of slip, along normal and oblique faults. Associated volcanic rocks (undersaturated alkali olivine basalt with fresh mantle nodules) suggest extension was deep-seated. The rangefront fault and associated structures must have influenced the sedimentation of the offshore hinterland Tertiary basin in the Gulf of Oman. Shales of the Eocene Rus (Rusayl) Formation are a potential hydrocarbon source and the overlying nummulitic Eocene limestones of the Dammam (Seeb) Formation and Oligocene Mam reefs (Azmari of Iran) form a potential reservoir. An overlying thick Neogene sequence should be sufficient to locate source rocks in the oil window. A model involving dip and oblique slip along faults of this hinterland basin suggests that potential large-scale traps may exist.

Samir S. Hanna received his BSc and MSc from Assyut University, Egypt, and a PhD on Tectonics of the Welsh and Irish Hercynian Orogeny from Swansea, UK He has been actively pursuing research on Oman since 1982. He worked in Swansea University, UK and consulted for Amoco International for about 6 years on the tectonics of Oman and UAE. Samir is currently an Associate Professor at Sultan Qaboos University, Oman where he has been working for eight years. He has written a book on the Geology of Oman, pubhshed in 1995.

David W. Rodgers received his BSc from Carleton College, USA, and a PhD on Hinterland Tectonics of the Sevier Orogenic Belt from Stanford University, USA. He has taught at Idaho State University since 1985 and currently serves as Department Head. His two areas of active research are hinterland tectonics of fold-thrust belts and crustal extension near hotspots. David received a 1994 Fulbright Scholarship to Sultan Qaboos University, Oman, where he taught classes and conducted research in structure and tectonics.

3-D Seismic Acquisition Experience in Saudi Arabia

Hastings-James, Richard* and Kamal M. Al-Yahya

Saudi Aramco

Saudi Aramco has acquired over 5,000 square kilometers of land 3-D seismic data over large fields in Saudi Arabia. Acquisition parameters have evolved considerably since the inception of the program as new technology has become available and experience has been gained. Currently data is acquired with crews having the capability of efficiently recording well in excess of 1,200 channels per crew at folds ranging up to 288 into 25 x 25 meter bins. 3-D seismic data from these fields will be used to illustrate the sensitivity of the data quality to changes in various acquisition parameters. The impact of parameter variation on crew production rates will be presented.

Richard Hastings-James is currently Geophysical Consultant with Saudi Aramco. He has 16 years of exploration industry experience, 12 of which were with Amoco Production Company in Canada, Houston and various locations throughout Africa and the Middle East. Prior to that, he was an Associate Professor at the Technical University of Nova Scotia, Canada. He has been with the Geophysical Operations Division of Saudi Aramco since 1992. Richard has a BEng degree in Electrical Engineering from the Technical University of Nova Scotia and a PhD from Trinity College, Cambridge. He is a member of the SEG and Dhahran Geological Society.

Kamal M. Al-Yahya has a BSc in Physics (1980) from King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia, a MSc in Engineering Geosciences (1983) from the University of California, Berkeley, and a PhD in Geophysics (1987) from Stanford University. Currently he is serving as Chief Geophysicist, Geophysical Operations, Saudi Aramco. His areas of interest include signal processing, integrated reservoir studies and data acquisition. He is a member of the SEG, EAEG and Dhahran Geological Society.

New Possibilities in Airborne Gravimetry: State-of-the-Art 1996

Hein, Guenter W.

Institute of Geodesy and Navigation, University FAF Munich, Germany

This paper reviews the progress in airborne gravimetry. After defining the role of airborne gravity measurements in geodesy and exploration geophysics, solved, open and critical problems are discussed in consideration of the various error sources. With the advent of satellite measurements to the Global Positioning System (GPS) scalar airborne gravimetry techniques have now reached a level where under favorable conditions accuracies of 1 to 3 milliGals (mGal) over wavelengths of 3 to 5 kilometers can be achieved. The approach as well as available hardware and software are presented. Prospects are discussed to reach accuracies of 1.0 mGal over 1.0 kilometer wavelength and better. Possible strategies are outlined in detail: (a) using modifications and a fine tuning of existing airborne gravity meters; (b) using inertial platform as well as strapdown system for scalar and vector gravimetry; and (c) to develop a ballistic airborne gravity gradiometer.

Günter W. Hein is currently Full Professor and Director of the Institute of Geodesy and Navigation at the University FAF Munich. He was President of the Special Study Group “Airborne Gravimetry” of the International Association of Geodesy (IAG) between 1991 and 1995. His major areas of research are in high-precision kinematic GPS positioning as well as in the integration of GPS satellite observations with other sensors like inertial navigation systems for various applications on land, marine and aviation, in particular with respect to navigation, guidance, attitude determination and gravity field recovery.

Advances in LWD Technology Permit Wireline Replacement in Horizontal Development Wells

Heysse, Dale R.* and Charles E. Jackson

Halliburton Energy Services, USA

Measurement-while-drilling (MWD) technology has steadily improved during the past 15 years. Early MWD was limited to gamma ray and directional measurements, which provided enough data to correlate with other wells. Later, resistivity logging-while-drilling (LWD) also became accepted as equivalent or superior to wireline resistivity.

However, complete replacement of wireline logs by LWD has been limited by a number of factors. First, some wells require special formation evaluation methods, including high-resolution borehole imaging and wireline formation sampling (sidewall cores and formation tests), and these are not yet available as LWD.

In addition, the acceptance of LWD density and neutron porosity logs has been slow, as many operators have found the LWD version to be inferior to wireline. The quality of LWD density and neutron logs is primarily limited by the inability to completely press LWD tools against the borehole wall and thus eliminate standoff. Modeling, lab tests, and field experience show that one inch of standoff can shift the neutron porosity by 5 porosity units, and the density measurement by 0.40 gram per cubic centimeter (approximately 25 porosity units). Only lately has the LWD technology improved to the point where the standoff can be measured, and most standoff can be prevented from affecting the measurements.

Finally, many formation evaluation programs require borehole-compensated sonic logs. This is especially true where advanced 3-D seismic methods are employed in reservoir management. The LWD sonic tool has recently become available to the industry. The development of advanced LWD density-neutron tools and borehole-compensated sonic tools means that more operators can replace wireline logs with LWD logs without sacrificing measurement quality. This is particularly attractive in horizontal development wells, where wireline tools must be run on drillpipe or coiled tubing. In many development drilling situations, the formation evaluation program is reduced and special methods, such as borehole imaging formation sampling, are not required. Thus, horizontal development wells may be excellent candidates for wireline log replacement by quad-combo LWD logs (resistivity, density, neutron and sonic).

This paper will present case histories where wireline logs were partly or completely replaced by LWD, and will include an economic justification for wireline replacement. In addition, the paper will present LWD resistivity, density, neutron porosity, and sonic logs which operators judged acceptable for wireline log replacement.

Dale R. Heysse is a LWD Global Advisor for Halliburton at the Houston Technology Center. He has a BSc and MSc in Physics from Moorhead State University, Minnesota and Washington University, Missouri, respectively. In the past 13 years Dale has held various field engineering, field operations, and interpretation development positions in wireline logging and LWD. He is a member of the SPE, SPWLA, and International MWD Society.

Charles E. Jackson is a LWD Global Advisor for Halliburton at the Houston Technology Center. In his position, he works on a wide variety of interpretation and petrophysical problems including environmental corrections for LWD and wireline tools, formation evaluation, and new applications for LWD services. Charles received a BSc in Electrical Engineering from the University of Oklahoma in 1975. After graduation, he joined Schlumberger Well Services, where he worked as a Field Engineer and Log Analyst. In 1982, he joined Gearhart Industries and went to work in the Interpretation Development Group in 1984 where he worked with interpretation methods, and interpretation software.

From Exploration to Development: Microbial Surveys Target Hydrocarbon Microseepage

Hitzman, Daniel C.*, James D. Tucker and Brooks A. Rountree

Geo-Microbial Technologies, Inc., USA

The measurement of hydrocarbon microseepage by microbial surveys targets exploration prospects and provides enhanced reservoir characterization. Light hydrocarbon gases migrate upward from buried reservoirs reaching the shallow soil environment along microseepage pathways. The light hydrocarbons are utilized by specific suites of micro-organisms which are very sensitive to the presence of hydrocarbon gases. The Microbial Oil Survey Technique (MOST) was developed to identify surface gas microseepage.

MOST has successfully identified hydrocarbon microseepage anomalies for broad reconnaisance surveys covering thousands of square kilometers to smaller surveys designed for individual exploratory well ranking and evaluation. MOST has successfully predicted commercial production prior to drilling in comprehensive wildcat well surveys. A new production technology known as Microbial Reservoir Characterization (MRC) integrates MOST with development geology and engineering data for an enhanced identification of subsurface reservoir fabrics. Where a reservoir is in communication with producing wells, microseepage is altered along pressure pathways streaming to production wells. In these cases, microseepage is essentially shut down and lower concentrations of gases reach the surface environment. Where the reservoir is not in communication with producing wells, microseepage continues to escape to the surface. For mature reservoirs, MRC monitors subsurface fluid withdrawal patterns at the surface by defining microseepage signatures which identify by-passed production, reservoir heterogeneity characteristics, and potential offset well locations. Microbial microseepage targets the distribution of hydrocarbon traps, maps the continuity (compartments) of a reservoir, and locates areas prone to higher quality reserves.

Daniel C. Hitzman graduated with a BA in Geology from Carleton College and founded Geo-Microbial Technologies, Inc. (GMT) in 1985. Daniel coordinates GMT‘s worldwide petroleum exploration and production services, as well as petroleum microbiology R&D programs. He is also a member of the AAPG, SEPM, APGE, AEG, TGS, SPE and TMS.

James D. Tucker is the Director of Geosciences for Geo-Microbial Technologies, Inc. (GMT) since 1991. He previously worked for various Mobil minerals and oil and gas groups. James holds a MSc in Geochemistry from the Colorado School of Mines. He is a member of the APGE.

Brooks A. Rountree is a Geologist for Geo-Microbial Technologies, Inc. (GMT) since 1991 and has worked for Sullivan and Company and Apache Corporation in Tulsa, Oklahoma. Brooks has a BSc in Geology and Psychology from Oklahoma State University. He is a member of TGS.

The Role of Structural Inversion in the Development of Diapirs in the Southeast Arabian Gulf

Hooper, Robert J.*, Ian R. Baron, Craig M. Murphy and Shaun Perkins

Conoco Inc., USA

Advances in seismic data-processing combined with new insights into salt tectonics derived from scaled analog- and numerical-model studies and advances in computer-aided restoration and visualization, prompt a re-evaluation of the development of salt-related structures in the southeast Arabian Gulf. In this paper we discuss a variety of salt-related structures including low amplitude salt-rollers, salt walls, and surface piercements. We discuss the origins of the structures, and suggest, by comparison with experimental data, that though physically very different, the structures may have a common origin. Understanding diapir development is a complex 4-D problem because the mode of piercement can change not only along trend but also through time. The cause of the deformation can rarely be determined within the bounds of a local survey area and needs to be viewed from a regional perspective. Widespread diapirism occurred throughout the southeast Arabian Gulf in the early Mesozoic. The tectonic regime at that time was broadly extensional on the trailing southern margin of Tethys. This tectonic regime changed fundamentally in the late Mesozoic and Tertiary. Data from the southeast Arabian Gulf reveal a major period of diapir growth in the late Mesozoic during the deposition of the Mishrif and Ilam formations. This event corresponds in time to contractional events associated with the emplacement of the allochthons in Oman. A second major growth period occurred during the Oligo-Miocene following the deposition of the Asmari Formation and corresponds to the Tertiary Zagros orogeny.

We envisage a developmental history where diapiric growth was initiated by thin-skinned brittle extension during the Paleozoic/early Mesozoic. The salt diapirs represented weak points within the sedimentary cover they intruded. Contractional deformation during the late Mesozoic/Tertiary was preferentially partitioned into the diapirs, squeezing the diapir-stems and adding “tectonic pressure” to the natural buoyant pressure within the diapirs. The net effect was rejuvenation of the diapirs. Salt-related structures in the southeast Arabian Gulf were not driven by salt movement but developed as a simple “reaction” to early thin-skinned extension and subsequent contraction of the overburden.

Robert J. Hooper has been with Conoco in the capacity of Senior Research Scientist since 1991. His primary function is to serve as a consultant to worldwide exploration groups on matters of structural geology, the interpretation of structures in seismic data, and regional tectonics. He is also involved in research into structural development in a wide variety of tectonic settings, and monitors several external research programs. Prior to joining Conoco, he was an Assistant Professor at the University of South Florida between 1984 and 1991. He received a PhD in Geology from the University of South Carolina in 1986. Robert is a member of GSA and The Geological Society of London.

Ian R. Baron is the Regional Coordinator for the Middle East Region with Conoco, Inc. Apart from a brief spell working in the North Sea and Australia, most of his career has been spent working on the Middle East and he has worked with Conoco‘s Mideast New Ventures Group since 1990. He obtained a BSc (Honors) in Geology from the University of Manchester in 1977. Ian is a member of the AAPG and the Geological Society of London.

Craig M. Murphy is a Geological Advisor in Conoco‘s Advance Exploration Group, where he is responsible for basin analysis and technical evaluation of new venture opportunities. His primary area of study since 1991 has been the Middle East. Craig received BSc and MSc degrees in Geology from Northern Illinois University and a MBA from Houston Baptist University. He is a member of the AAPG and SEG.

Shaun Perkins is a Geologist in Conoco‘s Advance Exploration Group, based in Houston, where he is responsible for basin analysis and technical evaluation of new venture opportunities. His recent work has largely focused on the Middle East but he has also been involved in projects in Venezuela, Russia, and Southeast Asia. Shaun obtained a BSc (Honors) from the University of Leicester in 1978. He is a member of the Geological Society of London and the AAPG.

Bitumen in Petroleum Reservoir Detection, Origin and Distribution

Huc, Alain-Yves* and Bernard Y. Carpentier

Institut François du Pétrole (IFP), France

Beside producible oil and gas, petroleum reservoirs often host bitumens. These bitumens, ranging from highly viscous oil to solid organics, can affect the whole reservoir or discrete intervals referred as “tar mats” (at Oil/Water contacts or within the oil leg and the water leg) and occur in many fields in the Middle East. Such bitumen occurrences adversely alter reservoir properties and can not be produced by conventional means. They reduce the porosity/permeability of the reservoir bodies, and can act as specific permeability barriers within the field inducing compartmentalisation, early water cut or interference with the water drive. As a result, the survey and prediction of bitumens in petroleum reservoirs is of prime importance for exploration and production. The direct detection of bitumen in the reservoir relies on several available methods. These methods are based on electric logs and sample analysis (geochemical extraction, Rock-Eval pyrolysis, petrophysical data base, microscopical examination, etc.). The pertinence of these methods depends on the type of bitumen and lithology. There is a wide spectrum of situations controlling the occurrence of bitumen in reservoirs; these include thermally immature oil, biodegradation, thermosulfate reduction (TSR), waterwashing, thermodynamic disequilibrium (P/T change, gas de-asphalting, gravitational segregation), in-reservoir thermal cracking and deposition along the migration avenues. Each of these phenomena will promote specific bitumen occurrences in terms of quality and distribution. Assessing the distribution of bitumen accumulation within a field requires extrapolation of well-based information to the reservoir scale. Such an exercise can be achieved using geostatistical techniques. The quality of the prediction will be a function of the constraints provided by the diagnosis of the specific type and origin of the bitumen occurrences.

Alain-Yves Huc joined IFP in 1981 and is currently head of Organic Geochemistry. Alain was educated at the University of Nancy, France, and received his PhD in Organic Geochemistry from the University of Strasbourg, France, in 1978. He spent a year and a half as a postdoctoral fellow at Woods Hole Oceanographic Institution, USA, and two years as a CNRS researcher at the Applied Geology Department of the University of Orleans, France. He is a member of the AAPG, EAOG, EAPG and ALAGO and has published more than 80 papers on geological and geochemical subjects.

Bernard Y. Carpentier is a Research Engineer at the IFP Geochemical Department since 1986 and is currently involved in reservoir geochemical studies. He graduated form the Pierre and Marie Curie University, Paris where he studied geology and j geophysics. Bernard spent four years as a Scientific Consultant with Gaz de France where he served in various fields: core description, log analysis, field and basin synthesis. He also spent one year with Triton France where he was in charge of the Villeperdue oil field. He has published more than 25papers on source rocks sedimentology, evaporitic basin modeling and tar mats.

European Association of Geoscientists & Engineers

EAGE 58th Conference and Technical Exhibition

3-7 June 1996

Amsterdam International Exhibition and Congress Centre

Environmentally-Induced Biofacies Events in the Arab-D Reservoir of Saudi Arabia

Hughes, Geraint Wyn

Saudi Aramco

Micropaleontological analysis of thin-sections of closely spaced core-plug samples from the Arab-D Formation of the Ain Dar, Shedgum and Uthmaniyah areas of the Ghawar Field, Saudi Arabia, has revealed an ordered vertical arrangement of microfaunal and microfloral events. These events monitor the response of the biofacies to the episodic changes in sea level during the Late Jurassic. A fine-scale biozonation has been attained, for which there is no known published equivalent in the region. Events are based on the semi-quantitative distribution (generic predominance facies) and biometric variations of the benthonic foraminiferal species Trocholina spp., Pfenderina salernitana, Mangashtia viennoti, Nautiloculina oolithica, Kurnubia palastiniensis, Pseudocyclammina/Everticyclammina spp., Lenticulina spp., polymorphinids and the calcareous algae Heteroporella jafferezzoi, Clypeina jurassica and stromatoporoids including Cladocoropsis mirabilis. Within local areas, and certainly between adjacent wells spaced at less than 10 kilometers, these biozones may be considered to be geologically isochronous events and therefore provide a unique tool to assist in correlating depositional layers. Where these depositional layers coincide with reservoir layers, the scheme provides a more definitive tool for correlation than that provided by wireline logs. The scheme needs careful use, however, as local modification is likely wherever progradation of facies is suspected, with the consequent result that the scheme is probably diachronous over the region, and may not be used to provide regional time-lines.

Geraint Wyn Hughes holds PhD, MSc and BSc degrees from the University College of Wales, Aberystwyth, and has been a Micropaleontologist/Stratigrapher with Saudi Aramco for the past 4 years. He has over 20 years experience in stratigraphy, of which 10 years were with the Solomon Islands Geological Survey, and 10 years of biostratigraphic consultancy of North Africa, the Middle East, Australasia, the Americas and the North Sea with Robertson Research in Singapore and the United Kingdom. He is a Fellow of the Cushman Foundation for Foraminiferal Research, and a member of the British Micropaleontological Society and the Dhahran Geological Society.

Geochemistry of Ain El Hummar-2 Crude Oils, Jordan

Hughes, William B.

ARCO International Oil and Gas Company, USA

Three medium gravity (23.3 to 31.1° API) and medium sulfur (2.14 to 2.65%) crude oils from the Ain El Hummar-2 well on the eastern shore of the Dead Sea, Jordan, were characterized by a variety of geochemical techniques. Despite residing in shallow reservoirs (327 to 427 meters), a full suite of normal alkanes and high n-alkane/isoprenoid ratios show the oils are not biodegraded. API gravities and sulfur contents correlate with the ratio of xylene to n-octane suggesting that water-washing, which would preferentially remove light aromatics, is responsible for the variations in gravity and sulfur content. The three oils are very similar in their carbon isotopic and biomarker compositions indicating they are from the same source and of the same thermal maturity.

Detailed GC and GC/MS analyses show the oils have low pristane/phytane, high dibenzothiophene/phenanthrene, high norhopane/hopane, high C35-homohopane/C34-homohopane and low diasterane/sterane ratios indicating generation from a carbonate source rock containing a sulfur-rich kerogen. Other oils, heavy oils and asphalts from the Dead Sea area are similar in these same biomaker characteristics to the Ain El Hummar-2 oils. Comparison of the Ain El Hummar-2 oils to oils from the Wadi Sirhan and Hamza areas using published data shows that oils from the three areas are from isotopically distinct source rocks. Age-specific biomarkers (ratio of dinosteranes to the sum of all A-ring methylated C30 steranes) indicates the oils were derived from a source of Triassic or younger age. The ratio of C28/C29 ß, ß steranes suggests the oils are derived from a Late Cretaceous source rock. Several saturated biomarker indicators indicate a thermal maturity of the source rock at the time of oil expulsion approximately equivalent to a vitrinite reflectance of 0.8%. The biomarker characteristics of the oils themselves as well as comparison with rock extract data from the literature indicates that the oils are derived from a marine marl/carbonate source, most likely the Late Cretaceous (Senonian) Ghareb Formation although the Turonian Wadi Essir Formation cannot be eliminated as a possible minor contributor.

William B. Hughes is Staff Geochemist with ARCO. He has 20 years of experience in geochemical research and the application of geochemistry to petroleum exploration of which 12 were with Phillips and 8 with ARCO. William has published a number of papers on geochemical subjects. He has a B.A. degree in Chemistry from Central Methodist College and a PhD in Chemistry from MIT.

Silurian “Hot” Shale Labyrinths in the Middle East and North Africa

Ibrahim, Muhammad W.

Target Exploration Consultants, UK

Paleo-environments and fairways of the Afro-Arabian Silurian “Hot” source rocks were interpreted by combining the frontier Silurian-Ordovician geology of northern Arabia with the mature Silurian-Ordovician play models of North Africa. Common lop-sided distribution of the early Silurian “Hot” Shales in the glacially scarred Cambro-Ordovician intracratonic basins invites paleo-environmental models other than the regional basin-wide euxinic event. Regional correlations of the Silurian Shale across the political borders in the Sirhan-Risha-Tabuk Basins of northern Arabia led to the recognition of more than one Silurian “Hot” source rock. This has been suspected to occur in the cratonic basins of North Africa but hitherto not published. Through this study new Silurian “Hot” source rock trends (including those of the basal Silurian “Hot” Shale) were defined in areas in the Middle East and North Africa.

Muhammad W. Ibrahim is currently Petroleum Geologist for Europe, Africa and the Middle East with Target. He previously worked for the Iraqi Geological Survey and Mineral Exploration, and as Assistant Professor and Head of Department of Petroleum Geology, King Abdul Aziz University, Consultant Geologist with Kuwait Institute for Scientific Research, Staff Geologist with Mobil Oil Libya, VEBA Oil, and Lasmo International. Muhammad received his BSc in Geology from the University of Baghdad (1969), and MSc (1972) and PhD (1978) in Petroleum Geology from Imperial College, London. He is an active member of the Iraqi Geological Society, AAPG, SEPM, SPE, PESGP and COGS. He is interested in the petroleum geology of the North Sea, Middle East, Africa and the Gulf Coast of the US.

Development of the Multi-Disk Type Downhole Seismic Source

Ishii, Yoshiro*

Japan National Oil Corporation, Bahrain

Nobusuke Shimada

Japan National Oil Corporation, Japan

Takeichiro Ohashi and Yasunori Syoji

OYO Corporation, Japan

The study of the multi-disk type downhole seismic source which is expected to be utilized for crosswell and reverse VSP survey began in 1992. From the experimental results, we have concluded that this seismic source is an effective non-explosive downhole seismic source. The principle of the mechanism is such that a hammer, accelerated by the force of a spring, collides with an anvil and causes a pressure pulse to propagate throughout the borehole fluid among the disks. We have been able to prove its advantages of simple operation, good reproducibility and small power requirements. Utilizing this concept, we have continued to improve its efficiency and practicability. We have constructed models with larger disk diameters and multi-stories of multi-disks. The expected increase in performance was proven by a recent field test. It has an excitation energy of more than 3,000 Joules and the generated seismic wave, propagating through a layer of limestone, can be clearly observed over a distance of more than 600 meters. Considering the attenuation and noise level, an offset distance of more than 1,000 meters could be achieved by the latest model.

Yoshiro Ishii is currently the Assistant General Manager of JNOC Middle East Representative Office in Bahrain. He received his BSc from Tokai University and joined JNOC in 1981. He had been working for new project evaluation and implementation of geophysical surveys around the world including Oman, Jordan and Myanmar. From 1992 to 1995 Yoshiro was Head of Reservoir Geophysics Group at the Technology Research Center (JNOC/TRC). His current responsibilities are not limited to technologies but include all matters concerning the Middle East.

Nobusuke Shimada (see Yoshioka et al., p. 212)

Takeichiro Ohashi is currently the Manager of the R&D Department of Instrument Division, OYO. He has 10 years experience in geotechnical and geophysical research and 9 developing instruments. Takeichiro is a member of many international associations and has published several papers on geophysical and geotechnical subjects. He received his BSc in Physics from Saitama University and a MSc in Applied Physics from the University of Electro Communications.

Yasunori Shoji is currently an Engineer in the R&D Department of Instrument Division with OYO. He has 5 years experience in the research of rock mechanics and 7 developing instruments for geotechnical surveys. He is a member of SEG Japan, the Mining and Materials Processing Institute of Japan and the Japanese Geotechnical Society. Yasunori holds BSc and MSc degrees in Mining from Tohoku University.

The Depositional and Tectonic Setting of the Early Silurian Hydrocarbon Source Rock Facies of Central Saudi Arabia

Jones, Peter J.*, Thomas E. Stump and Mohammed I. Al-Khan

Saudi Aramco

The Early Silurian Qalibah Formation consists of two members: the upper member is termed the Sharawrah and the lower is termed the Qusaiba. The latter member is the main hydrocarbon source rock facies for the known Paleozoic hydrocarbon accumulations in Central Saudi Arabia. The Qusaiba Member is composed mostly of claystone/shale with minor interbeds of coarse siltstone and sandstone. Depositionally, the Qusaiba Member is interpreted to represent the pro-delta, delta toe clays, while the Sharawrah Member was deposited as pro-delta sandstones of an immense delta system that dominated the Silurian-Carboniferous of Arabia. The Qusaiba Member in central and south Arabia accumulated in a trough that began subsiding during the Late Ordovician following the Taconic Uplift of central and southern Arabia. In this trough at least 3,000 meters of Late Ordovician through Early Devonian strata were accumulated. This trough probably resulted from rifting produced by the counter clockwise rotation of the Arabian Peninsula during the Late Paleozoic.

The Qusaiba Member organic-rich facies occurs at the base of the unit and has up to 8% total organic carbon content. The development of favorable source rock facies in the Qusaiba is observed along the peripheral edge and extending distally from the depositional thick associated with the lower Qusaiba unit. The basal Qusaiba organic facies was produced in normally oxygenated bottom water settings by elevated primary production in a sediment starved setting. The low level of bioturbation in the organic facies suggests that while the water column was normally oxygenated, the sediment below the sediment/water interface was anoxic. Geochemical data show that the organic-rich Qusaiba shale closely associated with the depositional thick, exhibits characteristics consistent with a more oxidized sediment column, while those deposited more distally are more dis-oxic to anoxic in their characteristics. Apparently the depositional thick was produced under conditions which either re-worked organic-rich sediments, thereby oxidizing them, or diluted the organic matter resulting in less preservation of organic matter.

Peter J. Jones is a Laboratory Scientist at the Laboratory Research and Development Center of Saudi Aramco. He received his BA degree in Earth Sciences from Dartmouth College and a MSc in Geology from the University of Oklahoma (1986). Before joining Saudi Aramco in 1991, Peter worked in exploration and production geology for Mustang Production, OKC (1982-1986) and Union Pacific, Ft. Worth (1986-1991). His current areas of interest include basin-wide thermal maturity modeling, hydrocarbon migration timing/path assessment, reservoir geochemistryand variations in fluid properties, and petrophysical log related issues.

Thomas E. Stump is a Geological Specialist with Saudi Aramco. Prior to joining Saudi Aramco in 1990, he worked with Unocal between 1980 and 1990 and with Amoco in the late 1970s. Tom obtained his BSc in 1972from San Diego State University and received his PhD from University of California Davis. He is particularly interested in the regional geology of Africa, the Middle East and Far East.

Mohammed I. Al-Khan is a Laboratory Scientist at the Laboratory Research and Development Center of Saudi Aramco. He received his BSc in Petroleum Geology from King Abdulaziz University in 1988. His current areas of interest include core study, SEM, and geochemical evaluation of source rocks, tars and oils.

A New Stratigraphic Model for the Khuff Formation in the Sub-surface of Central and Eastern Arabia: Implications for Reservoir Geology

Kamal, Rami A.* and Geraint W. Hughes

Saudi Aramco

The Khuff Formation carbonates and evaporites in the sub-surface of central and eastern Saudi Arabia are a series of cyclic shallow marine and tidal flat carbonate and evaporite deposits which accumulated aggradationally on a broad shelf in Late Permian time. Within the Khuff Formation, carbonates can develop three important natural-gas bearing reservoirs. A new stratigraphic model, rooted in sequence stratigraphy, has been created to be reservoir prediction friendly. Eustatic control was utilized in an attempt to better understand the cyclicity of the intra-carbonate units and the alternation of evaporites and carbonates. The presence or absence of evaporites, dolomites or carbonates is considered to be related to catch-up and keep-up carbonate depositional regimes, which are in direct response to different rates of sea level rise and fall. Over the years, the Khuff Formation has developed a reputation for being a difficult formation for reservoir prediction. Recent studies have shown, however, that this is not the case. Lithostratigraphic intervals that are prone to reservoir development can be recognized within predictable stratigraphic positions in the model, which in turn are discernible on wire-line log traces and in rock core. The lithostratigraphy of the Khuff Formation is also simplified and standardized, in order to provide a new practical and functional model for explorationists, reservoir geologists, and reservoir engineers. Micropaleontological analysis of selected rock cores has also revealed important information on vertical and lateral variations with strong implications to reservoir prediction. Micropaleontology has also enhanced the ability to identify second- and third-order depositional cycle breaks.

Rami A. Kamal has been a Reservoir Geologist with Saudi Aramco since 1984 and specializes in modeling carbonate reservoirs from Miocene to Permian. Prior to Saudi Aramco, Rami worked in the drilling industry in Saudi Arabia. He received his MSc in Geology from King Fahd University of Petroleum and Minerals in 1973, a MSc in Geology from Boston University in 1977, and he wil be completing his PhD in Geology from the University of London in 1996. Currently, Rami is the President of the Dhahran Geological Society, and he is also a member of the AAPG, Sigma Xi, SEPM, IAS and the NY ACAD Sci.

Geraint W. Hughes (see Hughes, p. 150) 154

Structural Development of Jebel Abd Al Aziz, Syria

Kent, W. Norman* and Robert G. Hickman

UNOCAL, USA

Jebel Abd Al Aziz, one of the most prominent topographic features in northeastern Syria, is a large surface anticline. Work done by UNOCAL, from 1988 to the present, outlines the following structural evolution of this structure. Prior to the development of the Abd Al Aziz structure, Senonian shelf carbonates prograded southward from Turkey into the Palmyride-Sinjar Trough which extended from west central to northeastern Syria. The shelf edge of the carbonate system was south of and subparallel to the Syrian border. In the Abd Al Aziz area, fine grained basinal mudstones were deposited on a thin, transgressive, rudistid, bioclastic unit. In Early Maastrichtian, an east-west trending graben developed at the present site of Jebel Abd al Aziz. Structural blocks within the graben were bounded by reactivated northwest and northeast striking faults. Seismic data indicate that the edges of the rift basin were deeply eroded. Channels cut into the sides of the basin along the trend of the older crosscutting regional faults, exposed Carboniferous and possibly older strata. Olistostromes formed along the basin bounding fault scarps and turbidite fans developed at the channel mouths. Paleocurrent direction data from the turbidite sand bodies corresponds well with the trends of the channels mapped on seismic data.

Maastrichtian age sediments are largely confined to the graben proper. Early Tertiary sediments filled a wider basin, but there is evidence that minor episodic inversion on some northeast and northwest trending faults occurred during the Eocene and early Miocene. However, the main inversion of the Abd Al Aziz structure occurred in the Late Pliocene and Pleistocene. Inversion produced a large faultpropagation fold above east-west trending faults near the northern margin of the graben. Smaller folds developed above other graben-bounding faults and the northeast and northwest striking faults within the graben underwent oblique slip during the deformation.

W. Norman Kent is a Senior Advising Geologist with UNOCAL Corporation in Sugar Land, Texas. Before returning to the United States in January, 1995, he was Chief Geologist for UNOCAL, Syria, Ltd. He has 20 years of experience as a petroleum exploration geologist. He is a member of the AAPG, The Geological Society, Geological Society of America, and Wyoming Geological Association. He has a BSc from the University of Arizona and a MSc from Northern Arizona University.

Robert G. Hickman is currently Coordinator of Structural Geology and Sequence Analysis with UNOCAL Corporation in Sugar Land, Texas. He has 21 years of experience with petroleum research and exploration. Robert is a member of the AAPG, American Geophysical Union, Geological Society of America and the International Association of Structural/Tectonic Geologists. He has a BSc from Stanford University and MSc and PhD degrees from the University of Wisconsin.

Seismic-While-Drilling in Kuwait: Results and Applications

Khaled, Osman S., Alaa M. Al-Ateeqi

Kuwait Oil Company

Andrew R. James and Richard J. Meehan*

Schlumberger Cambridge Research, UK

During early 1994, Kuwait Oil Company and Schlumberger completed an extensive study of the seismic-while-drilling (SWD) technique in the Raudhatain Field in north Kuwait. This unconventional technique promises to provide real time well seismic information without interrupting drilling and without deploying any downhole hardware. However, to date, this service has been very seldom used in the Middle East.

This paper begins with a discussion of the recent developments in the theory and mechanics of measurement of drill vibrations for Vertical Seismic Profiling (VSP) and time-depth correlation. Concepts of the SWD data acquisition and data processing sequence relating to two KOC wells will be developed and will lead to favorable comparisons with both wireline VSP and surface seismic methods. The conclusion will be that the SWD technique can work successfully in the Raudhatain Field.

The relative merits of the SWD technique will be presented in the context of the north Kuwait study and with reference to future developments.

Osman S. Khaled is Senior Geophysicist with Kuwait Oil Company. He has twenty years of geophysical and exploration experience including 13 years in KOC and 7 years with the Syrian Petroleum Company. Osman received his MSc in Geophysical Engineering from the Geophysical Prospecting Institute, Russia.

Alaa M. Al-Ateeqi received his BSc in Geology from Kuwait University in 1993 and joined KOC in September of the same year. Alaa worked as a Well Site Geologist for one year and joined the Geophysics Division as a Trainee Geophysicist.

Andrew R. James is the resident Country Manager for Schlumberger GeoQuest in Kuwait. He has seventeen years of oilfield experience starting as a Field Engineer with Schlumberger Wireline and moving to staff positions specializing in borehole geophysics and acoustic operations. Andrew joined GeoQuest in 1994. He has a BSc (Honors) in Physics from the University of Birmingham, UK and a Professional Degree in Geophysical Engineering from the Colorado School of Mines, USA.

Richard J. Meehan is a Research Scientist with Schlumberger Cambridge Research. He has been with Schlumberger for 10 years, during which time he has conducted research into the mechanical properties of shales, the interpretation of drilling vibrations and most recently, the development of the drill bit seismic technique. Richard received his BSc in Engineering from the University of Strathclyde and a MSc in Engineering from Cranfield University.

Semi-arid Distal Alluvial Fan Deposits of the Permian Unayzah Formation Along the Nuayyim Trend, Central Saudi Arabia

King, W. Allan

Saudi Aramco

Significant reserves of Arabian super-light oil, condensate and gas occur within the Permian Unayzah Formation of central Saudi Arabia. The Unayzah unconformity overlies Silurian sediments and infill this variable topographic surface with clastics ranging in thickness from 60 to 850 feet. Sediment was sourced from highlands to the north and west and transported to lowlands in the south and east.

Three stages of deposition are recognized. The basal Stage I is the infilling of a series of northwest-southeast oriented wadis with water-laid sands, gravels and mud deposited predominantly by gravity flows. The wadis were ultimately infilled as the highlands retreated and braided channels became dominant.

Stage II sharply overlies Stage I, and the central portion of the Nuayyim field is composed of fine grained lake-margin sediments that border thin playa lake deposits. These are replaced laterally in the south and north of the Nuayyim field plus Abu Markhah field by extensive stacked aeolian dune sands and interdune silty sands. The wind-laid interval can be up to 200 feet thick and consists of transverse-type dunes deposited by winds blowing towards the present-day east-northeast to east-southeast.

Stage III sediments were deposited under a wetter climatic regime. It began with fluvial channels and overbank sediments that reworked the upper portion of the Stage II sediments. This fluvial sequence is composed predominantly of overbank sheet sands and fine-grained floodplain deposits, including field wide paleosols and lacustrine deposits.

Reservoir quality within Stage I and the very-friable Stage II aeolian sediments is excellent (greater than 1 Darcy). The inter-dune, playa and lake-margin sediments are predominantly non-reservoirs. Stage III sediments only have good reservoir qualities within reworked Stage II sandstones and channel deposits.

W. Allan King is currently an Exploration Geologist with Saudi Aramco. He has 15 years of exploration and development experience, of which 7 years were with Home Oil Co. and four years with Novalta Resources, both of Calgary, Canada. He has been with Saudi Aramco since 1991. Allan has BSc and MSc degrees in Geology from the University of Guelph, Ontario, Canada.

Genetic Stratigraphy, Depositional Systems and Reservoir Performance of the Burgan Formation, Greater Burgan Field

Kirby, Robert H.

Chevron Overseas Petroleum Technology Co., Kuwait

and Jamal A. Al-Humoud*

Kuwait Oil Company, Kuwait

Sediments of the Middle Cretaceous Burgan Formation form the principal oil producing reservoir in Kuwait‘s Greater Burgan field. The Burgan sands, which were deposited in braided plain, deltaic and shallow marine environments, attain a thickness of approximately 1,150 feet in the field area. The Magwa, Ahmadi and Burgan domes make-up the Greater Burgan structural complex. These substructures exhibit an intricate pattern of faulting that, in many cases, acts to compartmentalize the reservoir.

A chronostratigraphic zonation was developed for the Burgan Formation to provide a comprehensive framework for correlating and mapping sedimentary strata. The strata components often have characteristic vertical stacking patterns, lateral continuity and bed geometry, and can be grouped into progradational, aggradational and retro-gradational units. Recognizing these cycles and their associated depositional systems has provided insight into fluid movement within the reservoir facies of the formation.

Open hole logs, pulsed neutron logs and production performance data were used to interpret water encroachment patterns in the reservoir, which often vary due to changes in reservoir continuity and production procedures. Several areas in the reservoir that exhibit vertical water rise or lateral water encroachment (i.e. “water fingering”) were identified, and the extent of the water movement can be shown to correspond to the stratigraphic architecture of the Burgan Formation.

Robert H. Kirby is a Reservoir Geologist with Chevron Overseas Petroleum Technology Company in Ahmadi, Kuwait. Over the past 19 years Bob has worked for A.P. Green Refractories Co., Trans Ocean Oil, Gulf Oil Corporation, Chevron Geosciences, Arabian Chevron (Saudi Aramco) and Chevron USA. He received a degree in Geology from Georgia Southwestern College and is affiliated with the AAPG and SPE.

Jamal A. Al-Humoud has been with Kuwait Oil Company since 1992. Jamal received a BSc in Geology from Kuwait University in 1990. He is affiliated with the AAPG.

Fluid Saturation Predictions in a “Transition Zone” Carbonate Reservoir, Abu Dhabi

Kirkham, Anthony*, Mohamed Bin Juma

Abu Dhabi Company for Offshore Oil Operations (ADCO)

Anthony F. Palmer, Alan H. Thomas, Tilden A.M. McKean, Michael J. Smith

BP, United Kingdom

Bryan N. Twombley

Independent, United Kingdom

The field is a low amplitude structure with a chalky Lower Cretaceous reservoir characterized by a large hydrocarbon transition zone. Porosity generally decreases with depth within the trap although porosity versus depth trends are skewed by tilting. Porosity and permeability mapping was therefore achieved using templates based on seismic amplitudes.

SCAL data were used to construct algorithms of Leverett J functions versus saturation for a variety of lithotypes mapped throughout the 3-D geological model of the field. The templated poroperms were then combined with capillary pressures to predict fluid saturations from these algorithms. The modeling of fluid distributions was therefore dependent upon heterogeneities imposed by the rock fabrics.

Calibrating the model-predicted saturations against log-derived saturations at the wells, involved regression techniques which were complicated by: notional structural tilting of the free water level, imbibition, hysteresis and permeability averaging procedures.

Filtered “stick displays” proved useful in assessing the quality of the calibrations and were invaluable tools for highlighting data anomalies. Laterally variable correction factors, based upon “bubble templates”, were applied to ensure perfect calibrations if desired.

Anthony Kirkham (see Al-Silwadi et al., p. 27)

Mohamed Bin Juma is Head of Reservoir Engineering in ADCO, Abu Dhabi. He has been working for ADCO for the past 15 years as Drilling Engineer, Production Engineer, Reservoir Engineer and has held several Reservoir Engineering Supervisory positions. He holds a BSc in Petroleum Engineering from the University of Tulsa (1981).

Anthony F. Palmer graduated from the University of Portsmouth in 1989 with a BEng (Hons) in Engineering Geology and Geotechnics. He then completed an MSc in Petroleum Engineering at Imperial College, University of London in 1990. Since joining BP Exploration in 1990 he has experience in open-hole log evaluation, special core analysis, production logging and well testing. He has worked on several large projects concerning Abu Dhabi Carbonate reservoirs for the last 3 years and he has also gained experience in physical evaluation from various North Sea fields.

Alan H. Thomas has worked for British Petroleum since 1978 and is currently employed as a Reservoir Engineer. He has been involved in many reservoir studies and for the past 6 years was mainly involved in the analysis of Middle East fields. Alan holds a BSc in Mechanical Engineering from the University of Bristol and a MSc in Fluid Mechanics and Thermodynamics from City University, London.

Tilden A.M. McKean graduated from Victoria University of Wellington, New Zealand in 1977 with a BSc in Geochemistry (Hon). He has 16 years wide-ranging experience in exploration and production. His past working experiences are Exploration Review/Operations Geologist (4 years), Petrophysicist (5 years), and Reservoir Engineer (7 years). He has reservoir engineering experience in simulation and recent sub-surface field development responsibility for Qatar Genral Petroleum Corporation (QGPC). As Reservoir Engineering Manager in BP‘s Abu Dhabi office, he manages BP studies for ADNOC and OPCO and is BP‘s member on ADCO/ADMA-OPCO RSSCs and TCMs.

Michael J. Smith received a BSc in Mathematics and Mathematical Methods from RMCS, UK. He joined BP in 1971 and is currently Exploitation Manager, Cusiana for BP Exploration Colombia. He has worked in numerous operational centers for BP including Alaska, North Sea and Abu Dhabi, UAE.

Bryan N. Twombley (see Al-Silwadi et al., p. 27)

Abqaiq Field 3-D Seismic Mapping of the Hanifa and Arab-D Reservoirs, Saudi Arabia

Lawrence, Paul*, Abdulkader M. Al-Afifi, Stephen T. Luthy and George A. Grover

Saudi Aramco

The Abqaiq 3-D seismic survey was acquired to map major fracture zones within the Hanifa reservoir and faults responsible for fluid communication between the Hanifa and Arab-D reservoirs. The Hanifa reservoir is a Type 2 fractured reservoir containing a stylolitic fracture system identified by high flow rates over thin stratigraphic intervals, large disparities between well test permeability (Kh) and core Kh, and observations of fractures in vertical/horizontal cores. Interpretation of borehole image data, cross dipole shear sonic logs, and observations from core suggest that Hanifa and Arab-D reservoir fluid communication is locally controlled by throughgoing faults and associated fractures.

The 3-D seismic data has confirmed the existence of numerous faults and fracture zones, some of which are responsible for fluid communication between the two reservoirs. Faults and fracture zones are most readily identified in the Arab-D due to a sharp acoustic impedance boundary at the top of the reservoir. Major faults were defined from reflector offsets while minor faults and fractures were defined from reflector amplitude, dip, and azimuth attributes. Faults and fracture zones form a regional pattern generally consistent with anticlinal-domal uplift of the structure during the Late Cretaceous. This pattern includes a radial system of faults and fractures mapped on the structural flanks and an axial parallel system on the structural crest. Well test analyses and reservoir simulation runs confirm the existence of a number of the 3-D seismically defined faults and fractures.

Paul Lawrence joined Saudi Aramco, in 1991 as a Geologist, where he has been interpreting 3-D seismic data for reservoir characterization. Prior to joining Saudi Aramco, Paul was employed as a Geophysicist with Marathon Petroleum in Tunisia, Terra Resources in Denver, and Atlantic Richfield Co. in Dallas and Denver. Paul received his BSc in Geology in 1976 from Kent State University and his MSc in Geology/Geophysics in 1978 from Wright State University.

Abdulkader M. Al-Afifi has been with Saudi Aramco since 1991 where he is presently working on 3-D seismic interpretation. He holds a PhD in Geology from the University of Michigan and is a member of the AAPG and SPE.

Stephen T. Luthy received a BA in Geology from the University of California, Santa Barbara, and a MSc from the University of Montana. After 3 years with the US Geological Survey, Steve worked for 4 years with Gulf Oil Corporation, followed by 10 years with Chevron Oil Company. Since 1991, he has been with Saudi Aramco, conducting studies of both the Arab-D and Hanifa reservoirs at Abqaiq Field.

George A. Grover (see Abu-Ali et al., p. 97)

A Case Study of Mapping Gas Cap in a Carbonate Reservoir, Using 3-D Seismic Data

Lee, Jia J., Constantine Tsingas*, and Paul Lawrence

Saudi Aramco

An integrated study has been conducted to map the mobilized gas cap in a carbonate producing field of the Arabian Peninsula, utilizing 3-D seismic data. Detection of reservoir fluids using any single attribute in this field has been found difficult due to tight rock matrix and small changes of Poisson‘s ratio. In this study, we attempted to delineate the boundary of a gas cap by examining attributes from zero-offset amplitude mapping, seismic modeling, AVO analysis, traveltime anomaly and structural mapping. Due to the high-velocity rock matrix, the oil/gas contact yields small AVO effects and amplitude signatures in the stacked 3-D seismic volume. Seismic signatures of the reservoir were found to have largely resulted from the combined effects of porosity and gas accumulation. However, detailed traveltime anomalies mapped through the field using isopach and isochron attributes were found useful for decoupling the contributions between these two components. In this paper, additional results from structurally mapping the depth-migrated seismic volume and other borehole data analyses will be shown to better constrain the lateral extension of the gas cap.

Jia J. Lee is currently a Geophysical Specialist with the Research and Development Division in the Geophysical Department of Saudi Aramco. He is involved with special seismic processing and integrated studies of exploration problems. Before joining Saudi Aramco in 1992, he was with ARCO for nine years engaged in seismic exploration and development on worldwide prospects. He received his MSc in Geophysics from Columbia University and a PhD from Penn State University. Jia is a member of the SEG.

Constantine Tsingas is currently a Research Geophysicist with the Research and Development Division in the Geophysical Department of Saudi Aramco. He has over 12 years of experience, 6 years of which were in the USA and Canada, and 6 in the Middle East. He has a BSc in Physics from the University of Athens, Greece, a MSc in Geophysics from McGill University, and PhD from the University of Alberta, Canada. He is a member of the SEG and EAEG.

Paul Lawrence (see Lawrence et al., p. 160)

Time to Depth Conversion: Relating Seismic Data to the Real Earth

Littman, Mark* and Alex Litvin

Paradigm Geophysical Ltd., UK

This paper discusses the possibility of using interpreted seismic arrivals along with interval velocities (derived from pre-stack seismic data) for time to depth conversion.

Within the oil and gas industry today the standard work flow for time to depth conversion involves vertical stretching of time migrated interpretation into depth using the available well velocity information. Pitfalls of such an approach will be discussed using a number of real examples spanning from simple low relief plays to complex subsalt plays. The reliability of interpreting within the time migrated domain will be compared with that of interpreting in depth, showing how lateral variations in interval velocity can create structures in time which do not exist in depth, as well as creating structures in depth which cannot be seen in time. The local velocity variations responsible for these structures may lie in between available well information and thus deciding whether structures seen in time actually exist in depth is the key to any drilling project. In such cases pre-stack seismic data can be used in conjunction with well data to derive velocities for time to depth conversion.

In structurally complex areas it is often difficult to interpret in the time migrated domain due to the assumptions made by the time migration process. It will be shown that in such areas depth migration must be used in order to understand subsurface structure.

The second part of this paper will look at the process of deriving interval velocity information from pre stack seismic data thus allowing interpolation between well points. The advantages and pitfalls of the direct use of these seismic velocities for time to depth conversion will be shown. The influence of anisotropy and shallow velocity variations on seismic interval velocity analysis and methods of handling these effects are discussed. In particular it will be demonstrated how a tomographic approach can be used to update and improve static models.

Mark Littman graduated from Royal Holloway College, London with an MSc in Geophysics. He worked as Interpretation Geophysicist at NOPEC, UK for two and a half years before joining Paradigm Geophysical where he has worked in the following roles: Support Geophysicist, Service Manager and presently as Pre-sales Support Manager.

Alex Litvin graduated from Moscow State University, Russia with a degree in Geophysics. His PhD thesis dealt with the modeling and interpretation of refraction seismics. Alex has more than 15 years experience in data processing, interpretation and software development.

Effect of Fault Planes on Breakout and Drilling Induced Fracture Generation in Boreholes

Liu, Xingzhou, Saeed Rafie, Eliseo Rodriguez

Western Atlas Logging Services, USA

and Joerg E. Mattner*

Atlas Geoscience Services, Bahrain

The in-situ stress field of a reservoir has a major impact on hydrocarbon production. Detailed knowledge of the in-situ stress field can aid, for example, the effective placement of infill wells. In practice only regional in-situ stress data is taken into consideration without including the effect of local anomalies. These local in-situ stress anomalies are known to be caused by structural features such as faults, and can be detected by the rotation of the breakout trend and the attitude change of drilling induced fractures along wellbores. This paper discusses the use of finite element analysis (FEA) to calculate near wellbore stress in conjunction with regional stress anomalies. Results from the FEA are compared with analytical solutions from simple models developed for earthquake mechanism studies. The study evaluates the effects of rock elastic properties, such as Young‘s modulus and Poisson‘s ratio, elastic anisotropy, bedding and fault attitude, borehole deviation, far-field stresses and boundary conditions along the fault. The results are used to estimate the in-situ stress field, the rock mechanical strength and their associated uncertainties. The accuracy of the modeling is tested against field data from the Middle East.

Xingzhou Liu is a Research Scientist with Western Atlas Logging Services in Houston. His current project assignments include modeling of in-situ stress and rock mechanical properties in the borehole environment from well logs and core data. From 1987 to 1994, he worked for China‘s aerospace industry and Amoco Production Research. He has a BSc in Physics, a MSc in Geostatistics and a PhD in Geophysics from Stanford University.

Saeed Rafie is a Staff Engineer at the Mechanical Engineering Department of Western Atlas Logging Services in Houston. He is responsible for failure and stress analysis, finite element analysis and its applications in engineering projects. Saeed received his PhD in Engineering Mechanics from Pennsylvania State University, USA.

Eliseo Rodriguez is the Manager of the Interpretation and Geosciences Group of Western Atlas Logging Services in Houston. Over the last 2 decades, he has held various engineering and managerial positions in the logging industry and oil companies. Eliseo received his MSc in Electro-mechanical Engineering from San Juan University in Argentina.

Joerg E. Mattner is currently the Chief Geologist and Manager of Western Atlas Geoscience Services in Bahrain. He has 12 years experience in large scale structural and sedimentological mapping projects e.g. in the Arctic regions of North America, and the geological interpretation of wellbore data for reservoir characterization. Since 1991 he has been working with Western Atlas Logging Services in the Middle East. Joerg holds a PhD from Clausthal University, Germany.

Precambrian-Cambrian Basin Evolution and Source Rock Development in South Oman

Loosveld, Ramon J.H., Andy Bell* and Peter J.R. Nederlof

Petroleum Development Oman

The formations of the Huqf Supergroup in Oman represent the oldest sedimentary rocks in Arabia. They contain an alternation of clastic and carbonate sequences with source rock intervals of varying quality. The richness and distribution of these source rocks has been controlled to a large degree by the tectonic framework of the Huqf basins.

Initial rifting of the Arabian craton resulted in the deposition of the lower Huqf in the northeast-southwest trending grabens. These basal sediments were deposited under glacial conditions and the sea level rise resulting from final deglaciation led to discontinuous source rock deposition.

The absence of volcanics and coarse-grained clastics in the middle Huqf is indicative of tectonic quiescence during the subsequent thermal relaxation/subsidence period. A series of carbonate platforms were deposited, generally with a low average organic carbon content. The source rocks of the middle Huqf are laterally extensive and thicker than the lower Huqf source rocks.

Renewed rifting in the upper Huqf resulted in the formation of salt basins parallel to the pre-existing lower Huqf grabens. These rifts filled with thick evaporite and source rock sequences. The source rocks are of exceptional quality and thickness, reflecting deposition in a stable euxinic environment. As salt deposition ceased, east-west shortening of the Huqf sequence in the southwestern part of south Oman occurred. Uplift associated with this deformation may have provided clastics for the lower Haima. The Angudan Unconformity marks the end of this tectonic event.

Ramon J.H. Loosveld (see Loosveld et al., p. 51)

Andy Bell (see Loosveld et al., p. 51)

Peter J.R. Nederlof is Team Leader, Regional Studies in Petroleum Development Oman. Before joining PDO in 1992, he was employed as a Petroleum Geochemist by Shell Canada in Calgary and Shell Research in The Netherlands. Peter‘s main interests lay in the fields of reservoir geochemistry and hydrocarbon habitat studies. Peter obtained his MSc and PhD in Chemistry in 1973 and 1978, respectively, from the University of Amsterdam. He did a Post Doctorate at Stanford University in 1979. Peter is an active member of the AAPG and the American Chemical Society and has been a member of the board of the European Association of Organic Geochemists since 1991. Peter is a member of the Editorial Advisory Board of GeoArabia.

An Overview of Recent Hydrocarbon Exploration Activities, Achievements and Future Challenges in Abu Dhabi, U.A.E.

Loutfi, Galal

Abu Dhabi National Oil Company (ADNOC)

The first discoveries in Abu Dhabi, up to the early 1970s, focused on the giant structures with their large hydrocarbon potential. A total of 25 fields, onshore and offshore Abu Dhabi, were discovered which included the supergiants of Bab, Bu Hasa, Asab on land and Zakum and Umm Shaif offshore. The emphasis thereafter was on developing this large hydrocarbon potential.

By the mid-seventies, and following the establishment of ADNOC which acquired 60% of the assets of the major oil concessionaires in the country, in addition to concession areas, which were relinquished by ex-concessionaires, covering about 30% of the total area of Abu Dhabi, reactivation of the exploration efforts were adopted and implemented. The challenge was that available criteria indicated that the remaining potential oil and gas accumulations were in relatively small, shallow-relief and subtle traps. This was a different task altogether, and far removed from the early exploration days in Abu Dhabi.

It was a prerequisite to optimize the exploration effort by adopting and implementing modern and advanced techniques in seismic data acquisition and processing (high resolution 2-D and 3-D), drilling, mud logging and gas detection, electric logging, integrated geologic analyses and modeling. Besides the intensive use of computer software applications, all had made it possible to discover, to date, additional 45 new oil and gas fields, ranging in size between giants and small discoveries. In addition to disclosing new oil and gas reservoirs within the old fields, all had added considerable amount of reserves to the State.

In addition to advances in surface seismic, there were also advancements in borehole data acquisition that played a critical role in the search for hydrocarbon. These advances include: (1) imaging, that provided a 3-D aspect to borehole logging; (2) high vertical resolution, that provided better definition of thinner reservoir layers (in order of 1 foot); and (3) downhole sampling and testing that improved reservoir evaluation and obtaining fast estimate of hydrocarbon potential.

Geologic and geophysical review and studies of the huge technical data acquired during the last 45 years, had enabled explorationists in Abu Dhabi to well recognize diversified problems which are currently being tackled with the hope to achieve better assessment of the hydrocarbon potential of the remaining unexplored areas in the country.

In this paper, the latest play concepts and modern exploration techniques adopted during the last 20 years to help define new hydrocarbon accumulations, in addition to problems tackled with examples for each, are briefly presented and discussed.

Additionally, an overview of the challenges and potential technical problems to be encountered in the future are made. The level of expertise and the range of modern wealth of data to achieve our goals and fulfill this task are also analyzed and discussed.

Galal Loutfi is Superintendent of Exploration Geology with the Abu Dhabi National Oil Company (ADNOC) since 1975. He received his BSc in Geology and Chemistry in 1959 from Cairo University and MSc in Petroleum Geology in 1965 from Ain Shams University, Egypt. He has also received an additional MSc in 1971 on Carbonate Sedimentology in Kuwait. Galal has over 36 years experience as a Petroleum Geologist with oil companies in the Middle East (Egypt, Syria, Kuwait, Kuwait-Saudi Arabia Neutral Zone and the United Arab Emirates) mainly in evaluation of hydrocarbon potential and play concepts of frontier/under-explored areas, planning, directing and monitoring exploration programs. He is an active member of the AAPG, SEE and EGS.

Predicting Reservoir Quality Using Integrated Geological and Statistical Models: Examples from Carbonate and Siliciclastic Reservoirs

Love, Karen M.*

Exxon Production Research Company, USA

Christian J. Strohmenger, Konrad Rockenbauch

Beb Erdgas und Erdöl GmbH, Germany and

Alex Woronow

University of Houston, USA

A unique method for predicting the three-dimensional distribution of reservoir attributes has been developed that integrates geological and statistical models. The integrated method, applicable to carbonate and siliciclastic reservoirs, has been successfully applied to the prediction of the distribution of dolomite, calcitized dolomite, porosity, and permeability in a carbonate reservoir and to the distribution of halite cement in a siliciclastic reservoir.

The Permian Zechstein 2 Carbonate of northern Germany provides an example where the methodology has been successfully applied. In this reservoir, mineralogy serves as a strong control on reservoir quality because dolomites are generally porous whereas calcitized dolomites (dedolomites) are generally non-porous. First, multivariate linear regression models were used to help develop a geologic model explaining the calcitization of the dolomite and the resulting calcite distribution. This model suggested that paleo-faults controlled the distribution of calcite. Although the geologic model elucidated the cause-and-effect relationship regarding the mineralogy distribution, it was ineffectual in predicting the distribution of mineralogy because the distribution of paleo-faults was unknown. For this reason, location variables (latitude, longitude, and depth) were used as proxies for the unattainable paleo-fault information. Linear regression modeling using the location variables along with facies and general structural style provided the best predictions of mineralogy. In addition to predicting mineralogy, models were generated to directly predict porosity and permeability. Because the spatial distributions of porosity and permeability are typically complex, a nonparametric predictive technique (neural network) was implemented, producing more reliable models than linear regression. These predictive models were used to generate maps, cross-sections, and three-dimensional representations of mineralogy, porosity, and permeability throughout the reservoir.

Karen M. Love has been a Geologist with Exxon Production Research Company in Houston, Texas for four years. She has worked in carbonate and siliciclastic reservoir quality, and has published papers on a variety of topics, including carbonate diagenesis, reservoir quality prediction and statistics. She holds a BSc in Geology from the University of Oklahoma, and a MSc and PhD in Geology from the University of Houston.

Christian J. Strohmenger joined BEB Erdgas und Erdoel GmbH in 1990 and is currently working as a team Geologist/Seismic Interpreter in the gas exploration and development department. From 1989 to 1990 he worked as a Research Assistant in carbonate sedimentology and sequence stratigraphy at the University of Geneva, Switzerland. He holds a diploma in Geology from the University of Giessen, and a PhD in Mineralogy/Sedimentology from the University of Heidelberg, Germany.

Konrad Rockenbauch is Geological Technical Expert with BEB Erdgas and Erdoel GmbH in Hannover, Germany. He has 3 years of university research practice and 11 years of petroleum and exploration industry experience. With BEB, he was involved in the development of oil and sour gas fields and in research application projects. Konrad has published several papers on structural and reservoir quality subjects. He holds a MSc and PhD from the University of Stuttgart, Germany.

Alex Woronow is an Associate Professor of Geology at the University of Houston. He has more than 20 years of experience in computer, statistical, and artificial-intelligence applications to the geosciences and holds membership in both geological and statistical societies. Alex has more than 50 publications in international journals and has more than 70 published abstracts. His degrees are an AB in Astronomy from the University of California, a MSc in Geology from the University of Houston, and a PhD in Geology from Harvard University.

Seismic Modeling of Shallow Gas Anomalies in the Yibal Field, Oman

MacDonald, Calum

Petroleum Development Oman (PDO)

The 1993 Yibal field 3-D survey showed a brightening of shallow reflection events within the Umm Er Radhuma (UER) limestone sequence and at the interfaces with the overlying Rus (dolomite and anhydrite) and underlying Fiqa shale formations. Amplitude maps show the large amplitudes to be concentrated in the highly faulted crestal zone and the effect may indicate that gas has leaked along faults from the Natih A Formation and filled the UER Formation. Where the UER has been filled with gas it poses a significant drilling risk and it may cause premature casing corosion in existing wells.

A modeling study was initiated to evaluate the effect of gas on reflection amplitudes at UER levels. Gassmann replacement indicates that the velocity in the UER Formation is very sensitive to gas saturation. Even 1% gas saturation causes a velocity decrease of up to 500 meters per second (m/s). At 10% gas saturation the velocity has decreased by as much as 900 m/s from the initial value (a 20% decrease). Such large velocity reductions give rise to significant pull down effects - more than 30 milliseconds at 10% gas saturation. In the most porous sections, the density at 100% gas saturation is 0.2 gram per cubic centimeter lower than at 0% saturation. When combined with the velocity change, the resulting impedance variations show that gas in the UER will give 50% to 100% increases in reflection amplitude. Where amplitude anomalies correlate with pull downs we have a strong indication of regions where gas has leaked up into the UER.

Calum MacDonald received a BSc in Geophysics from Edinburgh University and a MSc and PhD in Geophysics from the University of California, Los Angeles. After several years at the Geophysical Institute, University of Karlsruhe, he joined Shell Research in 1989 and worked at the E&P Lab in The Netherlands. Since 1993 Calum has been working with PDO‘s Quantitative Interpretation Group.

An Innovative Technique Resolves Apparent Anomalies in Detection of Gas Zones Based on Density-Neutron Logs

Mallick, Ravi K.*, Biswajit Choudhury

Oil India Limited, India

and Pradeep Vishunavat

Schlumberger-Geoquest, India

Cross-over effect on Density-Neutron logs has been one of the most accepted techniques in the oil industry for identification of gas-bearing sands. However, two contrary situations have been encountered where the inference on the presence of gas based on Density-Neutron cross-over can be misleading. Many formations which do not exhibit significant or any Density-Neutron cross-over subsequently produced gas on testing while many other formations which exhibit appreciable Density-Neutron cross-over have been proved to be oil-bearing.

This paper discusses the reasons for these anomalies and concludes that quicklook interpretation of gas from cross-over effect on Density-Neutron log on a compatible scale is restricted to clean sandstone formations. It further concludes that when the percentage of silt in the reservoirs approaches a certain upper limit no cross-over may be seen against gas-bearing sands on the Density-Neutron log. An equation has been developed to correct the magnitude of Density-Neutron cross-over for the presence of silt before inferring the presence of gas. On the other hand, false gas effects can be seen on the Density-Neutron log if the reservoir matrix density is considerably lower than the clean sand matrix density. In these cases, the matrix density needs to be determined from integration of cross-plots and laboratory measurements and a modified compatible scale needs to be fixed on the Density-Neutron log for locating gas zones. This paper illustrates these points by means of field case examples from wells of two newly discovered oil fields in Upper Assam, India.

Ravi K. Mallick is a Superintending Geologist with Oil India Limited based at its field head quarters, Assam, India. In his 14-year career with the company, he has held various positions in the fields of petroleum exploration and development. Ravi‘s fields of specialization include formation evaluation and application of well log data to various aspects of petroleum geological studies. He obtained his MSc in Applied Geology from the Indian Institute of Technology, Kharagpur. Ravi is author of a number of international publications, and is a member of the Society of Professional Well Log Analysts and the International MWD Society.

Biswajit Choudhury is a Superintending Reservoir Engineer with Oil India Limited. He obtained his BSc and MSc degrees in Petroleum Engineering from the Indian School of Mines, Dhanbad, India. Biswajit has been associated with Oil India Limited since 1984 and has worked in diverse areas of reservoir engineering including reservoir simulation, well testing, open and cased hole log interpretation and development of gas fields.

Pradeep Vishunavat received his MSc in Applied Geology from Roorkee University, India in 1988. He joined Schlumberger Asia Services in 1989 and is currently working as a Log Analyst in Bombay. Pradeep is a member of the Society of Professional Well Log Analysts.

Reservoir Filling is Controlled by Petroleum Expulsion - What Controls Petroleum Expulsion?

Mann, Ulrich

Institute for Petroleum and Organic Geochemistry, Germany

The rate of reservoir filling is controlled by the velocity of the advancing petroleum front during secondary migration. This velocity is controlled by the oil saturation of the carrier rock; hence, reservoir filling is largely controlled by source rock release rates.

However, there are several petroleum expulsion mechanisms, and the pathways and efficiencies of individual mechanisms vary from case history to case history due to the variable abundance of macropores and fractures in source rocks as well as different mechanisms for the build-up of a pressure gradient.

In order to collect information about petroleum expulsion that is as complete as possible, the investigation of primary petroleum migration requires a correct integration of all information. The volume of information and its relative importance will vary from case to case, but four specific tasks will always represent key elements for the quantification of petroleum expulsion: (1) identification of migration pathways by applying the principles of sedimentary petrography; (2) evaluation of transport-related properties of rocks from migration pathways by petrophysical measurements; (3) determination of expulsion stage, of expulsion process, and of expulsion efficiency by organic-geochemical analyses; and (4) reconstruction of migration processes within the geologic framework by numerical modeling.

Ulrich Mann has more than 15 years experience as Coordinator of Petroleum Geochemistry Analytical Services at the Research Center, Jülich, Germany. He is author of about 100 petroleum geochemistry reports for oil companies world wide, and he has published more than 40 papers on sedimentological, petrophysical and organic-geochemical subjects. Ulrich gained his PhD as a Sedimentologist from the University of Heidelberg, Germany. He is an AAPG certified Geologist, a member of the ACS, ALAGO, EAPG, SEPM, member of Executive Board of the GV, and a lecturer at the University of Erlangen-Nürnberg, Germany. His current research interest is a multi-disciplinary approach to petroleum migration.

Forecasting Undefined Prospectivity in Oman

McCoss, Angus M.

Petroleum Development Oman

Two parallel approaches are used to constrain the undefined potential of the exploration portfolio of Petroleum Development Oman. One is statistical and the other is geological.

The statistical approach is based on the observation that prospects, like faults, often have fractal or self similar geometries, which when sorted have power law distributions. Using this technique, a population of prospect volumes is sorted by size and a power law fit is made through the largest, and extrapolated into the smaller volumes. This conservatively assumes that the largest volumes have been identified, and that the undefined portion of the play lies in smaller prospects, below the current exploration resolution (a function of seismic and well spacing, and the current status of geological intuition).

The geological approach is the more traditional. It utilizes the knowledge and skills of teams of geologists and seismic interpreters, through interviews, to arrive at estimates of the undefined potential. Various type-prospects are identified in a given play, and a discussion develops as to how many more of them there could be in a given domain. Although a less objective and less auditable method, it utilizes very many more dimensions of reasoning than the cold statistical approach.

However, the true power of the two approaches comes when they are combined and reconciled. A balanced population of geo-statistically risked volumes can then be assigned to the undefined portion of a given play.

Angus M. McCoss is currently a Senior Geologist with Petroleum Development Oman based in Muscat. He has nine years of exploration industry experience and has been employed in Shell‘s central office and research laboratory in The Hague, and with Shell China Ltd. in Beijing before assuming his responsibilities in Oman. He has published several papers on structural geology and has a BSc in Geology from the University of Dundee and a PhD, sponsored by BP, in Structural Geology from the Queen‘s University of Belfast.

The History and Geology of the Safah Oil Field, Sultanate of Oman

McGann, Gerard J.*, Michael N. Cleveland and Hsiu Kuo chen

Occidental of Oman, Oman

The Safah field is the most northerly onshore oil field in Oman and was discovered in 1983. Located on the Lekhwair Arch, the field is dip closed to the west and east, with northern dip closure into the foreland basin. Critical updip trapping to the south is stratigraphic, with reservoir degradation from shelf carbonates to deeper water shales and marls.

Production is from the Lower Cretaceous Shu'aiba Formation, a predominantly shelfal carbonate with isolated areas of rudist biohermal accumulations. Reservoir quality is generally poor to moderate, with average permeability of five millidarcies. Vertical seal is the overlying Nahr Umr shale. A gas cap is present in the eastern part of the field, with at least two separate gas-oil contacts.

The significant stratigraphic component of the trap disguised the real size of the accumulation for a number of years. The first three wells were drilled on an apparent structural closure, and only when the hydrocarbon column was greater than the mapped closure was a stratigraphic component recognized. The small size of the field dictated the installation of “second hand”, short-term production facilities for a number of years. With increased drilling, the true size of the field became apparent, and daily production has increased every year since discovery, with average production in 1994 of 33,000 barrels of oil per day. The history of this change of perception is discussed with full field statistics. Initial oil in place is about 750 million barrels with cumulative oil production of about 70 million barrels.

The changes in development philosophy of the field are discussed with particular emphasis on the gas re-injection program, and horizontal open hole completions. Some aspects of geophysics and production geology are discussed.

Gerard J. McGann is currently Exploration Manager with Occidental in Muscat. He has 25 years of petroleum and exploration experience and has worked in more than 10 countries, from Japan to Pakistan. He is a member of many international societies including AAPG, SPE and SPWLA, where he is past President of three chapters and on the editorial board. He has a BSc (Honors) from the University of Western Australia.

Michael N. Cleveland and Hsiu Kuo Chen

(see Cleveland et al., p. 125)

Correlation and Connectivity of Carbonate Reservoirs Based on Strontium Isotopes: A Case Study of the Sidi El Kilani Chalk Field, Tunisia

Mearns, Euan W.*

Isotopic Analytical Services Ltd., Scotland

Mark G. Bramwell

KUFPEC, Kuwait

and John J. McBride

IAS Ltd., Scotland

Oil is produced primarily from open fracture porosity in Upper Cretaceous chalk in the Sidi El Kilani oil field. One of the challenges in developing this field has been understanding the distribution of open fractures within the structure. Strontium isotope analysis (87Sr/86Sr) is one of several techniques that has been applied to this problem.

Strontium stratigraphy analyses of primary, unaltered matrix chalk has allowed chrono-stratigraphic dating of the reservoir with a resolution of ± 1 million years. This has facilitated correlation of the reservoir, allowed estimates to be made of depositional rates and has indicated where section is missing due to faulting.

Isotopic analyses (87Sr/86Sr, δ18O, δ13C) of fracture-fill authigenic carbonate cements has confirmed the presence of at least two generations of cemented fractures. An early generation of calcite cement may have formed by redistribution of CaCO3 from the chalk at relatively low temperatures in the region of 35 to 55°centigrade (C). A later generation of dolomite and barite cements have Sr-O-C isotope composition consistent with their precipitation from fluids circulating at the time of hydrocarbon charge at temperatures close to current reservoir conditions of 70 to 75°C.

Strontium isotope analyses of residual salts extracted from core provide information on the formation water chemistry and on reservoir connectivity at the time of oil filling. These data have been used to clarify both vertical and lateral connectivity in the Sidi El Kilani field. A link between dolomite/barite cementation and waters circulating in the reservoir at the time of hydrocarbon charge has also been confirmed. Prediction of the distribution of dolomite cemented fractures has thus helped guide the development strategy of the field.

Euan W. Mearns is the founder and Managing Director of Isotopic Analytical Services Ltd. (IAS) in Aberdeen. He received a BSc in Geology in 1979 and a PhD in Isotope Geochemistry in 1984 from the University of Aberdeen. Following 6 years at the University of Oslo, and 2 years at IFE, Norway, he returned to Scotland in 1991 to establish IAS. Euan is a member of The Geological Society and Petroleum Exploration Society of Great Britain.

Mark G. Bramwell is currently Senior Geologist with the Kuwait Foreign Petroleum Exploration Company (KUFPEC) in Kuwait. He has 10 years development and exploration experience of which 5 were with Shell (UK) in London and Aberdeen, and 2 as an independent consultant. He received his BSc (Honors) and PhD in Geology from Queen‘s University, Belfast. Mark is a member of several professional societies.

John J. McBride is Senior Isotope Geochemist with IAS Ltd., Aberdeen working on the applications of isotope techniques to reservoir correlation, connectivity, stratigraphy and diagenesis. He received his BSc in Geology from Edinburgh University in 1985 and a PhD in Diagenesis from Aberdeen University in 1992. Prior to joining IAS in 1992, he worked on reservoir diagenesis with SPT and the Geochem Group.

The Upper Cretaceous Sedimentary Environments and Oil Leads of Central Saharan Atlas and the Hodna

Merabet, Souhir*, Hamza Tourqui and Fadhila Braik

Sonatrach Exploration, Algeria

The study area (which includes two distinct geomorphological groups: the Hodna Basin and the central Saharan Atlas) is located in the northern part of Algeria. It is bounded northward by the Tell Range and the Saharan Platform in the south.

The Cenomanian is constituted, in the central Saharan Atlas, by an anhydritic facies in the south which is related to the lagoonal environment, and a marly-calcareous facies related to the supratidal to intertidal conditions. It is represented northward in the Hodna Basin by benthic foraminifers limestones which correspond to the subtidal domain, and bio constructions and finally with Globigerines marls of the open marine area.

The same sedimentary process has been repeated during the Turonian and Senonian therefore with a more extensive supratidal to lagoonal domain in the Saharan Atlas. A paleogeographical evolution is displayed with euxinic deposits in the south and an open marine in the north.

Considering the facies distribution, the main reservoir objectives are the Upper Albian-Vraconian, the Upper Cenomanian and the Middle to Upper Turonian. The main caprocks are represented by marls of Cenomanian age and Campanian shales. The zone of interest for oil exploration is located in the Hodna (the region of Sidi-Aissa) and the south east area (Barika district).

Souhir Merabet is a graduate of Algiers University. She is an Engineer Sedimentologist and has been working for Sonatrach Exploration since 1991.

Hamza Tourqui graduated from Algiers University. He has 14 years exploration experience and is currently a Senior Research Geologist on sedimentary basins.

Fadhila Braik graduated from Algiers University. She has 12 years exploration experience. She is currently a Senior Research Geologist on sedimentary basins.

Outcropping Strata Equivalent to Arab-D Reservoir, Wadi Nisah, Saudi Arabia

Meyer, Franz O.*, Rex C. Price, Ibrahim A. Al-Ghamdi, Ibrahim M. Al-Goba, Saleh M. Al-Raimi and John C. Cole

Saudi Aramco

Two short outcropping sections in Wadi Nisah of central Saudi Arabia expose sedimentary successions of the Jubaila and Arab formations which are stratigraphic equivalents to the Arab-D reservoir rocks of Ghawar field. Additionally, these carbonate exposures consist of lithofacies and stacking patterns similar to the succession found in Arab-D reservoir strata. Outcropping sections are punctuated by disconformities that subdivide the stratigraphic succession into three depositional cycle types: (1) stromatoporoid, (2) skeletal bank, and (3) thinning upward and laminated mud. Depositional cycle types can be repetitive and define five successive sedimentary episodes within the outcrop.

The lateral distribution of lithofacies within these cycles show that capping stromatoporoid grainstones form organic buildups that locally exhibit thickness increases of more than 50 percent of the cycle thickness over a horizontal distance of 500 meters. Conversely, the capping five foot-thick skeletal grainstone of the skeletal bank cycle forms a continuous sheet exceeding 2 kilometers in width. Other carbonate sand units that are thinly bedded exhibit pronounced lateral discontinuity over distances of less than a hundred meters.

Results of the outcropping stratigraphic analysis enable visualization of lateral and vertical stratigraphic relationships and potential fluid-flow pathways. This study demonstrates that outcropping cycles and their lithofacies components have several important implications for ongoing subsurface reservoir characterization and modeling of the Arab-D. Firstly, cycle definition forms envelopes for the interwell distribution of lithofacies. Secondly, the lithofacies define geometries for the interwell distribution of petrophysical characteristics. Thirdly, the understanding of lateral relationships of these carbonates aid in reservoir simulation modeling.

Franz O. Meyer is currently a Staff Geologist with Saudi Aramco. He has 17 years experience in exploration and production of carbonate reservoirs. His experience includes a 13 years with Shell, USA, during which he spent the last 7 teaching applied carbonate geology. As a member of numerous professional societies, Franz published on a diverse range of topics that include stratigraphy petrography paleontology, and reef ecology. He has a BSc in Geology from SUNY College at New Paltz, and holds MSc and PhD degrees in Paleontology from the University of Michigan.

Rex C. Price is currently a Staff Geologist on loan from Chevron to Saudi Aramco. He has university teaching experience and has spent the last 14 years in the oil industry. Rex has worked in research, exploration, production, and geophysics. As a member of numerous professional societies, he has published on stratigraphic, paleontologic and petrographic topics. He has BSc and MSc degrees in Geology from the University of Alabama, and holds a PhD in Geology from the University of Iowa.

Ibrahim A. Al-Ghamdi is an Exploration Geologist working with the Exploration Organization in Saudi Aramco since 1985. He has worked in area exploration, reservoir geology and wellsite, and in special projects including reservoir modeling with Exxon in 1989. Most of his work concentrated on carbonates of the Jurassic and the Cretaceous of Saudi Arabia. Ibrahim is interested in carbonates, sequence stratigraphy, artificial intelligence, geostatistics and field geology.

Ibrahim M. Al-Goba is a graduate of Petroleum Geology from King Abdul Aziz University in 1988. He worked with Southern Area Reservoir Geology for 1 year, and with the wellsite unit for 2 years. Since 1991, he has been working on the Ain Dar Field.

Saleh M. Al-Raimi is a Carbonate Sedimentologist with Southern Area Reservoir Geology since 1992. He joined Saudi Aramco in 1980 and since then has worked in wellsite, hydrology, exploration and reservoir geology. Saleh obtained his BSc in 1980 from King Abdul-Aziz University. Saleh is a member of the AAPG, SPE and Dhahran Geological Society. His interests are reservoir characterization, modeling and computer geology.

A Multi-disciplinary Approach to Evaluate the Continuity of Complex Carbonate Reservoirs: Example from Onshore Abu Dhabi

Mohammed, Awad A.*, Salah E. El-Shazly, and Neil Young

Abu Dhabi Company for Onshore Oil Operations (ADCO)

The “S” field produces oil from multiple Lower Cretaceous reservoirs separated by dense limestone intervals. The field anticline structure is dissected by many short sub-vertical normal faults and subordinate wrench faults. The multi-stacked reservoirs show a great deal of heterogeneity in reservoir quality and facies thickness which affects vertical and lateral continuity.

Strontium isotopes ratios of residual salts analyses indicate appreciable differences between the southern and the central parts of the field with a slight increase towards the north. Vertically, the consistent profile that increases slightly with depth attests to the gradual filling of the reservoir with hydrocarbons without any significant interruptions. Similarly, the long-range gas chromatography (Carbon 34+) and the pressure data analyses indicate vertical continuity in the reservoirs but with sharp lateral discontinuity in the southern part of the field. A gradual change in the various characteristics toward the north indicates the presence of a semi-barrier due to deterioration in the reservoir quality and the incurred capillary pressure differentials. Initially, the classical analysis of the fault displacements/juxtapositions does not support the sealing nature indicated by other techniques. However, log and stress analyses indicate the seal effectiveness of at least one fault zone in the south, and confirm the results indicated by the pressure data, strontium isotopes and the molecular composition of the hydrocarbons.

Awad A. Mohammed is a Staff Geologist with Abu Dhabi Company for Onshore Oil Operations (ADCO). Prior to joining ADCO in 1991, Mohammed was with UAE University and with the Chevron companies from 1979 to 1989. He has a BSc (Honors) in Geology from Sudan and received his MSc and DIC in Petroleum Geology from Imperial College, London in 1983. Mohammed is a former Assistant Secretary of the Society of Explorationists in the Emirates (SEE) and is a member of the AAPG.

Salah E. El-Shazly and Neil Young (see El-Shazly et al., p. 135)

True 3-D Post-Stack Amplitude Inversion for Improving Reservoir Characterization

Mougenot, Denis and Claude A. Vuillermoz*

Compagnie Générale de Géophysique, France

To meet the requirement for more efficient reservoir characterization, a new true 3-D seismic amplitude inversion program has been implemented.

The program uses a sophisticated algorithm (global optimization) to fit an impedance model to the migrated zero-phase 3-D seismic data. The result is an impedance volume consisting of spatially coherent layers as opposed to seismic reflections corresponding to the boundaries between layers. The depth, thickness and impedance variations for each layer can easily be output and mapped, and using well information, can be linked to changes in the lithological properties. In this way, the geologist can use 3-D seismic data to build an accurate model, not only of the structure, but also of the stratigraphy of the reservoir.

This 3-D inversion program uses a multi-channel process which is better able to cope with the noise that is present on most seismic data than existing single-channel 1-D algorithms. Comparison of the two methods, on a 3-D block, shows that the 3-D approach gives improved vertical resolution, layer visualization, and spatial coherency. With respect to multi-channel 2-D algorithms, this program provides a complete spatial coherency in both the in-line and cross-line directions which is not obtainable with the 2-D approach.

Denis Mougenot is currently Head of the Seismic Imaging Department with Compagnie Générale de Géophysique, France. He has 22 years of seismic processing and interpretation experience, 16 years of which were as Marine Geologist with the University of Paris and 6 years as Reservoir Geophysicist with CGG. Denis is a member of the AAPG and the French Geological Society and has published many papers in several international publications on the geodynamics of the continental margin and reservoir studies. He is a graduate of Ecole Normale Supérieure and has a PhD from the University of Paris.

Claude A. Vuillermoz (see Vuillermoz et al., p. 207)

Sequence Stratigraphic Controls on Porosity/Permeability Relationships in Thamama Group Reservoir Zone C (Kharaib Formation, Barremian, Cretaceous), Abu Dhabi

Mueller, III, Harry W.

Abu Dhabi Company for Onshore Oil Operations (ADCO)

In the Thamama Zone C reservoir in one of ADCO‘s major fields, the relationship between porosity and permeability is strongly controlled by sequence stratigraphic position. Description of 450 feet of core from five wells through Thamama Reservoir Zone C (upper Kharaib Formation, Barremian, Cretaceous) led to the delineation of five texture-based parasequences within the reservoir; four in the Highstand System Tract below the top C sequence boundary and one in the Transgressive System Tract above. Comparison of descriptions with porosity and permeability distribution demonstrates that there is no apparent relationship between porosity and depositional facies, sequence stratigraphic position or depth below the top of the zone. However, a plot of permeability versus depth below the top of the zone shows strong correlation between higher permeability intervals and the upper parts of the parasequences. When the porosity and permeability data are cross-plotted for the upper and lower parts of each parasequence, the data cluster much more tightly around trend lines than they do when plotted by other breakdowns. The only deviations from this distribution occur in those rare instances where the rock type is different in one well from that in the other wells over the field. Note that, given the lack of porosity expression of the parasequences, correlation of the parasequences into uncored wells will be imprecise. However, the thickness can be predicted based on neighboring wells, so the permeability footage, and therefore the ability to simulate flow in the reservoir, should be essentially correct even if the detailed correlation is imprecise.

Harry W. Mueller, III is currently a Senior Reservoir Geologist with Abu Dhabi Company for Onshore Oil Operations (ADCO). Since receiving his PhD in Geology from the University of Texas, he has spent 20 years in the oil industry, mostly at Exxon Production Research Company, where he has been involved in service work and training in the application of carbonate sedimentology and sequence stratigraphy to exploration and production problems. Harry is a member of the AAPG, SEPM, SPWLA, SPE, SEE and HGS.

Improving Wara Sand Reservoir Mapping with Seismic Data

Mukhtar, A. Nabi

The Bahrain National Oil Company

The Ac pay zone is the sandstone facies of the Wara Formation of the Wasia Group (Middle Cretaceous). In the Bahrain field the Wara varies from 60 to 100 feet in thickness and the sand interval from 0 to a maximum of 60 feet. The Ac sandstone is one of the main Bahrain oil reservoirs but unlike others, its distribution is very erratic. The risk to locate new Ac reservoirs has always been high. Most of the good Ac sand was found by drilling for other objectives. In view of the erratic and random distribution of Ac sand in the field area where close well control exists, it was concluded by previous work on the Ac sand that any attempt to predict the occurence of this sand in an undeveloped area would be very risky. An attempt was made to use the available 2-D seismic data to improve the Ac sand mapping and possibly to delineate new areas for further testing. Since the seismic data covers Bahrain field and the areas outside the well control, integration of these data should give some light to the areal distribution of the Ac sand. The onshore 2-D seismic survey was carried out during 1983-1984. The conventional processed seismic data is not to the standards usually required for stratigraphic or reservoir analysis. However, by close integration of well data and seismic attributes, a new Ac map was prepared enhancing its distribution in the field area and predicting prospective areas for further testing outside the field limit.

A. Nabi Mukhtar has been with The Bahrain National Oil Company (Banoco) since 1986 as Senior Geophysicist. He received his BSc in Geological Engineering/Petroleum from the University of Texas at Austin. He has worked for the past 10 years mainlyin exploration and development geophysics. He is professionally interested in structural geology and reservoir characterization using seismic information.

Drilling the Flanks of Fields, Satellite Structures and Complicated Horizontal Wells with Advanced Geosteering Technology and Extended Reach Wells

Murphy, Eugene*, Hussein S. El-Sayed Schlumberger Anadrill, UAE

and Roy D. Nurmi Schlumberger, UAE

Drilling has rapidly evolved to where there are now a variety of horizontal well types including some long and/or complicated well trajectories. Gulf of Suez fault block reservoirs, which are now being probed with both hook and horizontal wells, will soon have 'extended reach' wells as are being used in the North Sea and Gulf of Mexico. Horizontal wells allow the probing of the areas between reservoir wells and are being used to also assess newly discovered structures. 'Extended reach' wells provide the chance to effectively reach, evaluate and test the flanks of reservoirs, marginal compartments and pinchouts and even satellite structures too far for standard deviated well drilling. Drilling the edges and satellite structures around producing fields has shown that structure and isochron maps and general reservoir characterization are poorly controlled at the edges of the seismic and well data. This greater uncertainty at the edge requires the use of advanced geosteering system with which to steer and maintain a trajectory which has just become available. The abundance of faulting in Cretaceous reservoirs and also the erosional irregularities of unconformities both cause difficulty in keeping a horizontal well within the reservoir. Fortunately, measurements of the formation at the bit, together with computer modeling allow one to take proper corrective action if unexpected changes are encountered. In addition, azimuthal formation resistivity measurements allow definition of structure and, thus, permit changes of the trajectory in response to structural changes.

Eugene Murphy is Sales and Marketing Manager for Anadrill in the Middle East and India. He began his career in seismic and later well log acquisition. Eugene joined Anadrill in 1984 working in mud logging, directional drilling MWD and LWD in the North Sea, South America and Nigeria before coming to Dubai.

Hussein S. El-Sayed received his BSc in Mechanical Engineering from Ain Shams University, Cairo. He joined Schlumberger Technical Services in 1982 as Field Engineer. His field assignments took him to Oman, Pakistan, India and Kuwait. In 1989, he became the Field Service Manager for Wireline Operations in Islamabad. In 1990, he joined the newly formed Logging While Drilling Group to become the LWD Operation Coordinator for the Middle East. In 1993, he became Anadrill Marketing Manager for the Gulf Area. Hussein is Manager for Anadrill Operations in the UAE since 1995.

Roy D. Nurmi (see Nurmi, p. 178-179)

Integrated Methods for Geochemical Prospecting of Oil and Gas Fields

Muslimov, Renat Kh., Rasim N. Diyashev*, Rimma P. Gottikh and Irina A. Larochkina*

Tat NIPIneft Institute, Russia

Regional studies in the Republic of Tartarstan (Russia) have shown that hydrocarbon accumulations are formed mainly through vertical migration of oil and gas. A clear relationship exists between the tectonic structure of crystalline basement and the presence of hydrocarbon accumulations in the overlying sedimentary column. The vertically migrating fluids will eventually reach the surface, where they can be detected by physical and chemical methods such as aero-gamma spectrometry, magnetometry, hydrocarbon and radon measurements. Maps of uranium, thorium, potassium and their derivatives enable the study of sub-surface fluid movements. Zones of increased conductivity are apparent from mapping methane, radon and radio element concentrations. The integration of these chemical anomalies with geological data allows the location of oil and gas accumulations.

Exploration drilling has proved the efficiency of these techniques and allowed the optimization and integration of methods. The applications of the studies will be discussed.

Renat Kh. Muslimov is currently the Deputy General Director, Chief Geologist of JSC Tatneft. He has been involved in oil propecting works, field geology, improvement of oil fields development processes with this company for more than 35 years. He is an honorary member of the Houston Geological Society, member of the Scientific Council of RAS Nuclear Physics Affiliation, elected corresponding member of Academy of Natural Sciences in the Russian Federation, member of the academy of Mining Sciences, and a member of the Academy of Sciences in the Repubic of Tatarstan. Renat has published more than 290 papers and 79 inventions (one of which has been patented abroad).

Rasim N. Diyashev is the Deputy Director of Geology and Development of oil and gas fields with TatNIPIneft Petroleum Institute. He has 34 years of petroleum exploration and production experience. He was a visiting professor of Moscow and Ufa Petroleum Institutes. Rasim is a member of the SPE and the AAPG and has published more than 150 papers on well tests, oil reservoir management, heavy crude and bitumen production. He received his Doctoral of Science in 1983 from the Russian Academy of Natural Science.

Rimma P. Gottikh is the main scientific worker of the All Russian Scientific Research Institute of geological, geophysical and geochemical systems. She has more than 30 years of experience in petroleum geochemistry and nuclear physics, and has published more than 150 papers on geology, geochemistry and geophysics. Rimma is a Doctor of Science (1977).

Irina A. Larochkina is currently Head of the Exploration Geology Department at TatNIPIneft Petroleum Institute. She has 23 years of oil and gas fields exploration experience. Irina has published more than 50 papers on the exploration of oil and gas fields.

Shabwa - Lithostratigraphy and Structural Evolution

Nani, Abdul Sattar O., MOMR, Yemen

The Shabwa area of Yemen encompasses the south-eastern part of the rather narrow northwest-southeast trending Marib-Shabwa Graben. This formed part of an extensive rift system developed across much of Yemen and northern Somalia during the late Jurassic. Bounded by two major normal faults, the graben has a complex block faulted floor rising up from two marginal sub-basins towards a central axial basement high. The entire area is blanketed by Cretaceous clastics, 300 to 1,500 meters thick within the graben itself and thinning onto the flanking rift shoulders to the north and south with shallow and sometimes outcropping basement.

Abdul Sattar O. Nani received his MSc (Honors) and PhD (Honors) in Exploration from Baku University in 1978 and 1985, respectively. He completed his PhD Equivalency from the University of Karachi in 1986. He has worked for the Ministry of Oil and Mineral Resources, Yemen since 1978. Abdul Sattar has published a number of scientific articles.

High Resolution Mapping of Carbonate Porosity Using Seismic Lithology Inversion

Neff, Dennis B., Scott A. Runnestrand and David W. Burge*

Phillips Petroleum Company, USA

Enhanced mapping of carbonate porosity distribution has been accomplished by using a new method of seismic lithology inversion. This method has been applied to reservoirs worldwide for high resolution structural mapping, horizontal well and in-fill well placement, in-place reserve estimation, 3-D lithology estimation for reservoir simulation, and prediction of downdip field limits.

The poster will illustrate Phillip‘s proprietary Incremental Pay Thickness and Non-Unique Inversion (IPT/NUI) process as applied to several carbonate porosity mapping projects. Field examples will be used to illustrate how the methodology improved drilling success and initial well performance.

The IPT/NUI inversion scheme differs from other techniques in that thousands of synthetic seismic traces are generated using petrophysical logs (porosity, water saturation, shale volume), geologic models, and other apriori information. Comparison of these model traces to the seismic traces during the NUI inversion process creates maps for predefined geologic layers and produces three-dimensional pseudo log volumes, which are used for trend mapping, as input for reservoir simulation, and for volumetric calculations.

This method has been successfully used for horizontal well placement in North Sea Cretaceous carbonate reservoirs, resulting in initial production rates of over 11,000 barrels of oil per day. New drilling locations in a Permian carbonate field have also been defined with this method. A reservoir characterization of a 15 year old field benefited from the petrophysical maps with reduced simulator model preparation time and improved production history matching.

Dennis B. Neff is a graduate of Emporia State University in Kansas, with BSc and MSc degrees in Physical Science and Mathematics. He has worked for Phillips Petroleum Company since 1977 doing seismic processing, seismic stratgraphic interpretation and applied research. Dennis holds patents for seismic processing, lithology inversion, and direct hydrocarbon mapping schemes. He is a member of the SEG, AAPG, and is an SPE distinguished lecturer.

Scott A. Runnestrand is a graduate of Colorado School of Mines with a BSc in Geophysical Engineering. He has worked for Phillips Petroleum Company since 1979 doing seismic processing, interpretation and applied research in signal processing and lithologic inversion.

David W. Burge is currently a Staff Geophysicist with Phillips Petroleum Company, Bartlesville, Oklahoma. He has 7 years experience in 2-D and 3-D seismic data processing, and in seismic lithology inversion. He has a BSc degree in geophysics from the University of Oklahoma and a MSc degree in Geophysics from the University of Houston. He is a member of the SEG, AAPG, and AGU.

Geological Characterization and Modeling of Middle East Carbonate Reservoirs Through Multidisciplinary Integration, Advanced Technology and New Techniques

Nurmi, Roy D.

Schlumberger, UAE

Geological reservoir analyses continue to improve with advances in technology, integration, multidisciplinary efforts and geostatistical insights. Particularly important are new reservoir insights coming from the integration of geological data, well logs, and well testing from horizontal well data. Geologically guided pressure sampling and pressure-transient testing is quantifying the connectivity and production potential of a variety of heterogeneous pore systems and, thus, helping to define by-passed oil and also the multiple origins of early water production. Leached sub-aerially exposed surface and biostromal zones often act as conduits for lateral water flow, whereas open faults allow water flow both vertically and along their strike. Such high permeability zones can be used to enhance production if they do not extend to the oil/water or gas/oil contacts.

Careful integration of multi-disciplinary data is critical to bringing together measurements and data of different disciplines, especially with a variety of scales - Scanning Electron Microscope (SEM) to seismic - technologies. Pores and heterogeneities too large to be defined by core and/or borehole imagery alone, are present in Arab and Mishrif biostromes and Tertiary coral/algal reef facies. These are best defined by the integration of geoscience and logging data with fluid and/or pressure data. Although microporosity is generally examined in very small samples with a SEM, the continuous vertical distribution of microporosity and its variation around the wellbore is being mapped by integrating of high resolution Neutron Magnetic Resonance (NMR) well logging measurements and electrical borehole imagery. These recent investigations show micropores can be important in the evaluation of high permeability Jurassic grainstones in addition to the well known pervasive microporosity in Tertiary reservoirs of Egypt and India and also Cretaceous (Thamama) reservoir zones of Arabia.

Roy D. Nurmi is Chief Geologist for Schlumberger‘s Middle East Organization based in Dubai. He formerly headed the Geological Reservoir Characterization Group in Tokyo and earlier was the Leader of the Production Geological Research Effort in the USA starting in 1975. Roy started his industry career in 1968 with Texaco in exploration and reservoir development in Texas and New Mexico. Roy received his PhD in 1975 in Geology from Rensselaer Polytechnic Institute, New York. He is a member of the SPE and Northern Emirates SPE Chapter, where he is currently serving on the Horizontal Well Mini Forum Committee as well as a SPE Regional Distinguished Lecturer for the Middle East. He is also a member of the AAPG, SEG and SEE and an Associate Editor for both the AAPG Bulletin and the Log Analyst magazine of the Society of Professional Well Log Analysts.

Basin Hydrologic, Chemical and Mechanical Modeling for Integrated Water, Mineral and Petroleum Resource Assessment

Ortoleva, Peter J.

Indiana University, USA

A unique three-dimensional model that accounts for the hydrology, mineral, aqueous and organic reactions and stress, thermal and sedimentological history is presented. Application of the model to assess the resources of a sedimentary basin are discussed.

The compositional state and producibility of deep-lying aquifers is strongly affected by the mineralogy and hydrologic properties of the constituting formations. These are affected by the long time mechanical, thermal and sedimentological history of the basin. In turn, the distribution of minerals and petroleum are affected by the motion of the aqueous fluids. In short, in basins the mineral, petroleum and water resource assessments and exploitation can most effectively be carried out by a fully integrated modeling approach.

Such a model (named CIRF.B) has been developed by us. Stresses and rock deformation, fracturing and compaction due to tectonic history and chemical processes are accounted for via an incremental stress rheology and simulator. Fluid migration is described via Darcy‘s law with permeability that reflects changes in mineral deposition and fluid density and viscosity that changes with composition and temperature. Aqueous fluid composition is calculated in a way that rigorously accounts for aqueous phase and mineral reactions and exchanges with non-aqueous phases. Multi-phase fluid migration is accounted for via a model incorporating the effects of capillarity and relative permeability and differences in fluid densities and viscosity. All the underlying reaction, transport and mechanical equations are solved consistently in that any one process can affect all the others.

Peter J. Ortoleva has worked since 1970 on reaction-transport phenomena. Since 1978 this work has emphasized the coupling of mechanics, reaction and transport in geological media. He has developed a number of coupled mechanochemical and reaction-transport codes that are presently used in his and other academic research organizations and in the petroleum and environmental industries. Peter is a Professor of Chemistry and Geological Sciences, and has been the Director of the Laboratory for Computational Geochemistry at Indiana University since 1988. He received his PhD in Applied Physics from Cornell University in 1970 and was post-doctoral Research Associate in Physical Chemistry at MIT between 1969 and 1975. Peter is a member of the AAPG. He has published 142 papers, 2 books and 3 edited volumes.

A Strategy for Near-Surface Model Construction and Subsurface Structural Discrimination

Pecholcs, Peter I.* and Costas G. Macrides

Saudi Aramco

In Saudi Arabia, a wide range of near-surface seismic velocities caused by sand dunes, karst topography, buried channels, etc. overlay deeper structures of higher velocities. A reliable estimation of long and medium wavelength static components of the near-surface velocity-depth model is crucial for accurate mapping of these time structures which in some cases can have closures as small as 10 to 20 milliseconds (ms).

One of the difficulties in testing the reliability of time structures in stacked sections lies in separating the effects of the near-surface irregularities from structural changes in the deeper part of the section. We propose a strategy for the estimation and verification of the velocity-depth models by using both midpoint and depthpoint oriented estimation techniques. First we construct an initial multi-layer near-surface model and compute static corrections using uphole measurements, shallow refraction/reflection arrival times and optimum offset refraction stacks with geologic constraints. An initial interpretation of deeper reflection events is made from the resulting brute stack. This initial interpretation and near-surface model are used in a depthpoint oriented interval velocity estimation scheme operating from the surface to build a deeper velocity-depth macro model in a top-down approach. Pre-stack depth migration and forward modeling with iterative ray tracing are used to verify and update the near-surface and subsurface velocity-depth models. A real data example is shown to illustrate how this strategy of integrating geologic and geophysical data with midpoint and depthpoint oriented schemes can improve the interpreter‘s ability to reliably map subsurface structures.

Peter I. Pecholcs received a BSc in Geology from StonyBrook University in 1980 and a MSc in Geophysics from Columbia University in 1982. His career has included positions with Sohio Petroleum Geophysical R&D, University of Hawaii, and United States Geological Survey. He has been a Research Geophysicist with the Geophysical Research & Development Division of Saudi Aramco since 1992. His current interests are near-surface modeling and inversion.

Costas G. Macrides received a BSc in Physics from the University of Athens in 1980, a MSc in Geophysics in 1983, and a PhD also in Geophysics in 1987 from the University of Alberta. He has been an Assistant Professor in Geophysics at the University of Manitoba and a Senior Research Geophysicist with Seis-Pro and Consultants in Calgary. He joined the Geophysical Research and Development Division of Saudi Aramco in 1993. His interests include seismic tomography, refraction statics, AVO and multi-component seismology in oil exploration. He is a member of SEG.

Chemostratigraphy of Carbonate-Evaporite Successions from the Arabian Gulf

Peebles, Ross G.*

Halliburton Energy Services, USA

John J. McBride Isotopic Analytical Services, UK

and Muriel Shaner Consultant, USA

Stratigraphic correlation and age dating of the carbonate-evaporite successions of the Upper Jurassic of the Arabian Gulf have been problematic due to a paucity of stratigraphically significant fossils. As a result, much of the high-resolution stratigraphy (reservoir zonation) of these successions is based strictly on wireline log signatures. There exists a need for a chronostratigraphic methodology that is independent of biostratigraphy and applicable to both carbonates (limestone and dolomite) and evaporites. Chemostratigraphy uses the results of isotopic and elemental analyses to characterize a stratigraphic succession and can provide high resolution reservoir zonation, correlation and dating. We have developed chemostratigraphic frameworks for the Upper Jurassic Arab formations (A-C) and the Miocene Gachsaran Formation. Samples from these carbonate-evaporite successions were analyzed for carbon, oxygen, sulfur, and strontium isotope ratios as well as for trace element composition. Sample material included limestones, dolostones, and evaporites (anhydrite and gypsum) representing a full suite of arid coastal depositional and diagenetic facies. Modern sediments and waters from the Abu Dhabi coastal zone were also analyzed for comparison and correlation with the ancient material.

In addition to correlation and dating, our chemostratigraphic frameworks aided in the identification of sequence and parasequence boundaries, condensed sections, and in the location of paleo-watertable horizons that influenced diagenesis.

Ross G. Peebles is Senior Geoscientist with Halliburton Energy Services. He is currently on leave of absence from Halliburton ‘s Reservoir Description Group working with the Abu Dhabi Marine Operating Company as a Consultant Geologist. Ross previously worked with Halliburton Reservoir Description Services in Abu Dhabi from 1991 to 1993. He received his BSc in Geological Oceanography from the Florida Institute of Technology in 1985 and a MSc in Geoscience from the University of Texas at Dallas. Ross is currently investigating the deposition and diagenesis of carbonate-evaporite successions within a sequence stratigraphic framework as part of PhD research at the University of Durham, UK.

John J. McBride (see Mearns et al., p. 170)

Muriel Shaner has been an independent consultant since 1993. Prior to this, she worked with Halliburton Reservoir Description Services in Abu Dhabi (1991-1993). She has also worked for the American Petroleum Institute, ARCO Oil and Gas, and Standard Oil. Muriel received a BSc in Geoscience from the University of Texas at Dallas in 1987.

Muriel is interested in the deposition and diagenesis of modern arid coastal systems and in strontium isotope stratigraphy. Exploration Difficulty, Undiscovered Reserves, and the Middle East

Pierce, Walter H.* and Victor H. Vega

Amoco, USA

The result of this paper is a graphical display that aids undiscovered reserve estimation. This paper presents a new methodology for analysis of undiscovered reserves in the Middle East. We concentrate on ways of extrapolating historical discovered reserves to estimate Historical Undiscovered Reserves (HUR). We propose that Total Undiscovered Reserves (TUR) be divided into three components: (a) HUR, (b) Analogue Undiscovered Reserves (AUR), and (c) Unexplored Undiscovered Reserves (UUR). We subdivide the basin or area of interest into fractions that can best be estimated by one or more of these components. We emphasize that the HUR results improve estimates of AUR and UUR. Understanding Middle East hindrance exploration difficulty is critical to total undiscovered reserve estimates.

The methodology uses extrapolation of cumulative discovered reserves against a parameter we call hindrance exploration difficulty. We divide exploration difficulty into scarcity exploration difficulty and hindrance exploration difficulty. We create a parameter that attempts to quantify the change in hindrance exploration difficulty by using the ratio through time of exploration well sequence at maximum oil discovered in million barrels per exploration well to exploration well sequence. This parameter ranges from One, hindrance exploration difficulty at the beginning of exploration, and Zero, hindrance exploration difficulty at an imaginary point when everything is understood about the Basin. The difference between the cumulative discovered reserves and the extrapolated cumulative reserves at Zero hindrance exploration difficulty is HUR.

Graphs and maps show the variation of historical undiscovered reserves, and hindrance exploration difficulty of the Middle East.

Walter H. Pierce is currently Associate Geologist with Amoco‘s Strategic Regional Studies Group. He has 14 years of international exploration experience with Amoco and 8 years of University teaching experience. His current exploration interests include the Middle East, exploration statistics, and hydrocarbon systems. He has a BA from DePauw University and MSc and PhD degrees from The Colorado School of Mines.

Victor H. Vega is currently a Petroleum Geophysicist with Amoco Exploration and Production Company. He has been with Amoco since 1993. During the last 2 years, Victor has been working in the Strategic Regional Studies group doing analysis of the Hydrocarbon Systems for several basins in the Central Asia and Middle East areas. He received his BSc from the Universidad Nacional de Colombia in 1989 and his MSc from the University of South Carolina in 1993.

Three-Dimensional Analysis of Direct Hydrocarbon Indicators

Poelen, Hugo J.,

Shell Expro, UK (formerly Shell Research BV)

Richard M. Dalley and Ronald C. Hoogenboom*

Shell Research BV, The Netherlands

In the late 1970s data from three-dimensional (3-D) seismic surveys were interpreted using paper sections. In the late 1980s computer-aided trace interpretation systems (TISs) helped make interpretation easier. With the recent advent of 3-D visualization hardware and software, seismic data and interpretation results can now be displayed and analyzed interactively in true 3-D perspective. To fully explore the added value of 3-D visualization technology in 3-D seismic interpretation, 3-D volume description techniques have been developed and implemented in the 3-D visualization environment to capture, manipulate, store and visualize selected (sub) volumes in 3-D. Prior to the analysis, the entire 3-D seismic survey is pre-processed to enhance the detectability of seismic events associated with the presence of hydrocarbons. Reservoir geometries can then be extracted directly from the processed 3-D data set, for use in reservoir geological modeling and reservoir engineering studies. After calibration with well data and time-to-depth conversion, first estimates of gross rock volume for individual bodies can be obtained. Field examples have proven the added value of these new techniques to the interpretation and analysis of 3-D seismic data sets.

Hugo J. Poelen graduated from the State University of Utrecht, The Netherlands, in 1973 with a MSc in Mathematics and Physics, with a specialization in Applied Geophysics and Numerical Analysis. Since 1974 he has served the Shell Group in Oman (PDO), The Netherlands (NAM), Denmark (Maersk) and The Netherlands (Shell Research). His current posting is as a Senior Seismic Interpreter in Shell Expro, Aberdeen. He has a special interest in using new technologies in multi-disciplinary subsurface interpretations teams.

Richard M. Dailey graduated from St. Andrews University, Scotland in 1967 with a degree in Physics and Mathematics. He joined Seismograph Service Ltd. and served in Mozambique and in Oman as Party Chief during the period of transition from analogue to digital recording equipment. In 1977 he joined Shell, first as a Seismic Interpreter, later as Head of In-house Processing in NAM, Shell‘s operating company in The Netherlands. Since 1984 he has been involved with the use and development of workstations for the interpretation of 3 D data sets. Richard is a member of the SEG and the EAEG and in 1989 received (with co-authors) the Hagedoorn Award from the EAEG for his work on Dip and Azimuth Displays of seismic horizons.

Ronald C. Hoogenboom joined Shell in 1978 after obtaining a MSc in Applied Physics from the University of Technology in Delft, The Netherlands. He worked in seismic acquisition and reservoir characterization research until 1985 when he was transferred to Sarawak, Malaysia. During his assignment to Sarawak Shell he worked as an Exploration/Production Seismic Interpreter, and as Head Seismic Acquisition, Geophysical Studies and Support. In 1991 he returned to Shell Research as Head Prospect/Field Interpretation Research. Ronald is a member of the SEG and AAPG.

Degradation of Reservoir Quality by Clay Content, Unayzah Formation, Central Saudi Arabia

Polkowski, George R.

Saudi Aramco

Reservoirs in central Saudi Arabia are important new sources of light sulfur-free crude oil. Development work on these wells has shown the adverse effect of clay minerals on their productivity or injectivity. The clay minerals may be affected during drilling of the well, during completion, during production, and/or injection. Kaolinite, chlorite, illite, and ordered and random mixed layer illite/smectite are commonly occuring clay minerals within the Unayzah reservoir rock. As little as 2% clay causes permeability to be drastically reduced. Clays cause problems due to the swelling of smectite caused by injection water or drilling fluids of low salinity; clay mineral migration and subsequent pore blockage; precipitation of gelatinous pore-blocking iron hydroxides caused by the dissolution of chlorite by acid; high water saturations; and disaggregation of the formation into its component sand grains if the weak clay cements are disturbed. It is therefore important to characterize the clay minerals present in the Unayzah Formation in order to lessen the likelihood of formation damage and to maximize production. The distribution of the clay minerals within different fields, a new method to determine the pore volume they affect with their associated absorbed water, and non-damaging fluids will be discussed.

George R. Polkowski is currently a Senior Laboratory Scientist in the Laboratory R&D Center, Saudi Aramco, Dhahran, Saudi Arabia. He has 30 years of geological and 15 years of petroleum industry experience. This includes 7 years with Saudi Aramco and 8 with Western Company of North America ‘s R&D Center in Fort Worth, Texas. He is a member of the AAPG and GSA and has published many papers concerned with geology and the petroleum industry. He has a BSc (1966) in Geology from Purdue University and a MSc (1967) from Stanford University.

Generation of Carbon Dioxide/Methane Accumulations During Metagenesis

Polutranko, Alexander J.

Ukrainian State Geological Research Institute, Ukraine

During metagenesis, formation waters generally have low salinities and low densities (below 1,000 kg/m3). The amount of gas dissolved in the water reaches a maximum, with methane being generated from organic-rich formations and carbon dioxide from the decomposition of carbonate rocks.

Carbon dioxide will form a separate phase as soon as the gas saturation of the formation water is reached. When the density of gas mixtures with the carbon dioxide predominance is equal to that of water, gas will not flow to the surface but instead remain in the pore space. This is caused by the fact that the density of CO2 at a temperature of 238 °C and a pressure of 70 MPa is 1,400 kg/m3 (T.P. Shuze, 1981). In this case, the CO2 will move in a downward direction displacing the water. When the carbon dioxide content in gas mixtures is low, its separation will take place only under extreme pressure conditions. The generation of methane will decrease the density of the gas mixtures. The depth of formation of CO2/CH4 accumulations will thus depend on the density of the water, the gas composition and the thermobaric conditions. In 1967, V.I. Nikolin et al. established the swelling of sandstones from the Donbas coal beds at methane saturation. When methane migrates from the deep accumulations, it might fill traps at shallower levels in the sedimentary column.

Alexander J. Polutranko is Senior Scientist with the Ukraine State Geological Research Institute, where he has been working since 1975, after graduating from Ivano-Frankivsk Oil and Gas Institute, Ukraine.Alexander holds a PhD in Geology. He is the author and co-author of more than 30 publications devoted to thermobaric oil and gas fields conditions and geochemistry of the Ukrainian sedimentary basins. He is a member of the AAPG.

TEEMS: Texaco Energy and Environmental Multispectral Imaging Spectrometer

Prelat, Alfredo E.

Texaco Inc., USA

A Hyperspectral Airborne Imaging Spectrometer has been contracted by Texaco. The system is designated by the acronym TEEMS (Texaco Energy and Environmental Multispectral Imaging Spectrometer). The system, which will become operational in the first quarter of 1996, will have the unique capability of acquiring information with an optical imaging spectrometer and synthetic aperture radar simultaneously from the same platform. Data acquisition with geo-referencing and co-registering of UV, VIS, NIR, SWIR, TIR and SAR channels will be achieved in one flight path.

The imaging spectrometer system will have a state-of-the-art optical scanner and multiple spectrometers to cover UV, VIS, NIR, SWIR and TIR. Spectrometers are designed to meet the application requirements of Texaco. All spectrometer band centers, band widths and S/N are selected by Texaco for specific applications. The spectral data will be fully calibrated. The system control uses a state-of-the-art on-board real-time workstation. Real-time data monitoring and geo-referencing are standard. The imaging spectrometer is mounted on a fully stabilized platform. The recording system is flexible and expandable.

The Synthetic Aperture Radar is built as an independent system connected via communication links to the imaging spectrometer controller workstation. The radar system still have an on-board real-time quick look capability for real-time reconnaissance for oil spill monitoring. For exploration and other applications, the data are recorded and processed later on a ground processing computer.

Alfredo E. Prelat, Texaco Honorary Fellow and Senior Scientist at Texaco Inc., holds MSc and PhD degrees in Geology from Stanford University. His doctoral dissertation on oil exploration decision-making systems focused on designing methods to estimate oil discovery probabilities. Alfredo spent two years in Norway as a Research Fellow for the Royal Norwegian Scientific and Industrial Research Academy and six years at Stanford University. He worked as a Technical Advisor for the United Nations in Asia and South America. He also worked for Bechtel and Unocal Corporation. Alfredo joined Texaco in December 1989. He has set up a remote sensing laboratory primarily designed to define prospecting areas and environmental assessment for various exploration groups in the company.

3-D Interval Velocity Inversion: A Case History from the Middle East

Richardson, Timothy M., Alfonso Gonzalez and Darko Tufekcic*

Western Geophysical, USA

Lateral velocity variations in the overburden distort seismically derived stacking velocities, introducing uncertainty when converting seismic data to depth. This two-part study shows a method to remove distortions so that a more certain depth image can be obtained. This is particularly important in many oil producing provinces of the Middle East, where complex depositional environments associated with strong facies changes between evaporites, calcareous and argillaceous lithologies, and their alterations produce lateral velocity variations. This complex overburden raises considerable doubt when conventional depth interpretation of deeper subtle structures is attempted. In the first part of this work, we use synthetic 3-D seismic data to illustrate the impact of lateral velocity variations in seismic stacking velocities. The effect depends on the size and depth of lateral velocity variations, the depth of the measurements, and survey design properties such as azimuth, offset, and fold distribution. In the second part, we introduce a 3-D interval velocity inversion method to estimate a geologically meaningful interval velocity field. Experience so far with synthetic and field data has shown that resolution of our method depends on the quality of the interpreted stacking velocity field and its sampling. Our results show that definition of geological structures in the transitional zone at the shelf margin is significantly improved with this technique, when compared with the conventional approach using Dix‘s equation. In addition, we are able to identify a new prospective play in the target zones previously masked by the effect of a shallow low velocity overburden.

Timothy M. Richardson received his BSc in Geology in 1986 from the University of New Mexico and his MSc in Geophysics in 1989 from the New Mexico Institute of Mining and Technology. He joined Western Geophysical in 1989, where he is currently in the Research and Development Group. He has conducted research in the areas of velocity analysis, multiple attenuation, and signal processing. He is a member of the SEG.

Alfonso Gonzales received a BSc in Oceanography from the University of Baja California in Mexico (1977), MSc (1979) and PhD (1982) degrees in Geophysics from Stanford University, and an MBA (1988) from the University of Houston. While at Stanford, he was a member of the Stanford Exploration Project where he did research in wave equation velocity estimation. Between 1982 and 1988, Alfonso worked in research and development for Geosource Inc. In 1988, he joined the staff of Western Atlas International as Senior Research Geophysicist where he has been responsible for research in 3-D seismic data processing, in particular 3-D velocity estimation. He has been granted two patents. Alfonso was an instructor of the 3-D Seismic Exploration SEG course and is a member of the SEG, EAEG, IEEE, and SEG of Houston.

Darko Tufekcic (see Carvill and Tufekcic, p. 124)

The Production and Interpretation of Time Slice Velocity Maps

Rivett, Arnold M.*, James A. Richard, Hashim M. Al-Nahwi and Adil A. Al-Khelaiwi

Saudi Aramco

Velocity maps were generated from stacking velocity data. The intent was to produce velocity data volumes which could serve as the starting point for processing of 3-D data.

Once the velocity volume was prepared, the analysis planes were mapped. These were seen to be velocities on time slices which could be spatially filtered and used for stacking 3-D data. It was seen that the unfiltered maps contained useful information about seismic data which were used in making these maps.

One example shows that two lines in a survey may not be optimumly stacked. A second example shows an area where three surveys had been combined. The boundaries between surveys illustrate that the stacking velocities were quite different for the three areas. A third example is an area where we wished to prospect for deeper targets. The velocity maps show good consistency to 1.40 seconds. At times greater than 1.40 seconds the maps begin to break up. This indicates that the earlier processing concentrated on shallow targets. To make these lines useful for deeper targets the seismic data must be reprocessed to improve velocities used to stack deeper events. Time slice velocity mapping can be done routinely from a data base. Interpretation of maps produced can indicate areas where seismic could be reprocessed for new exploration objectives. This can produce new results from old data and reduce the effort needed in large areas by defining problems which need to be solved.

Arnold M. Rivett received a BSc in Geophysics and Physics from the University of British Colombia in 1968. He has been employed by a variety of petroleum producing companies and has worked in Canada, USA, Iran and Libya before coming to Saudi Aramco in 1991. Arnold‘s primary interest is seismic interpretation and he is currently the Supervisor of the Depthing/Mapping unit of the Geophysical Technology Division of Saudi Aramco. He is a member of the SEG and the DGS.

James A. Richard, Hashim M. Al-Nahwi, and Adil A. Al-Khelaiwi (see Al-Nahwi et al., p. 108-109)

Sedimentology, Biostratigraphy, and Diagenetic History of Shu'aiba Formation (Lower Cretaceous) Wadis Muaydin, Bani Kharus and Kamah, Oman Mountains

Russell, Steven D.*, Richard F. Hulstrand, Harry W. Mueller, III

ADCO, UAE

Colin P. North and Gordon M. Walkden

University of Aberdeen, UK

The Lower Cretaceous Shu'aiba Formation of Wadis Muaydin, Bani Kharus and Kamah was measured to resolve small-scale vertical heterogeneity in lithofacies and biostratigraphic assemblages. The thickness of comparable depositional packages is considerably less than in the adjacent sub-surface areas, primarily as a result of intense stylolitization produced by Hawasina nappe overburden. Ongoing research suggests that the shallow-water shelf and shelf-margin sediments of the Shu'aiba Formation in all three wadis were deposited during a second-order sea-level late highstand with associated third-order systems tracts. Thick, typical inner-shelf algal platform lithofacies (Bacinella sp. and Lithocodium sp.) characterize the lower Shu'aiba Formation. Differentiation of the shelf and shelf-margin during mid-upper Shu'aiba deposition is evidenced by rudistid biostromes, rudistid debris deposits, and associated back-biostrome lagoonal shoals. Lithofacies of the fore-biostrome environment and intrashelf basin are not evident. Lower Cretaceous carbonates are disconformably overlain by thin, restricted transgressive sediments of the basal Nahr Umr Formation which is characterized by highly argillaceous, Orbitolina-rich wackestones and packstones. There is no clear evidence of subaerial exposure in the upper Shu'aiba Formation. The establishment of a litho-biofacies architecture allows interpretation of established reservoir units and depositional environments from producing fields. The cement sequence stratigraphy of large syntaxial overgrowths of echinoderms was interpreted using cathodoluminescence petrography. Four distinct phases of syntaxial cement development reflect precipitation within an evolving diagenetic environment from shallow meteoric/phreatic to deep burial phreatic with pressure solution.

Steven D. Russell is currently a Senior Geologist with ADCO. After receiving his BSc in Geology from North Carolina State University and MSc in Geology from Duke University, he spent over 16 years as a Geologist in various exploration and producing assignments with Mobil Oil Corporation and as a Geophysicist at Amoco Production Company. He is currently preparing his PhD at the University of Aberdeen in Carbonate Sedimentology. Steven is a member of the AAPG, SEPM, SEE and SPE.

Richard F. Hulstrand is a Reservoir Geologist with ADCO. Prior to rejoining ADCO in 1990, he worked with Mobil in Nigeria, Iran, USA Mid Continent and the Gulf of Mexico. He received his BSc and MSc in Geology from the University of Michigan. His 18 years of Middle East experience have covered field, regional, exploration and development aspects. Richard‘s interests include combining outcrop and sub-surface information, regional mapping and rigsite operations.

Harry W. Mueller, III (see Mueller, p. 175)

Colin P. North is a Lecturer in Petroleum Geology at Aberdeen University. After 8 years with BP, where his last assignment was Senior Geologist on coal reserves assessments, he had a year as Research Fellow jointly with Shell Research Lab and Delft University, then joined Aberdeen University in 1989. Colin researches and publishes on two complimentary themes: methods of sub-surface geological prediction and modeling, and arid-region continental sedimentology. He is a Chartered Geologist and holds a BSc in Geology from London University and a PhD from Bristol University. Colin is also a member of the AAPG, SPE, and several other international professional societies.

Gordon M. Walkden is currently the Head of the Department of Geology and Petroleum Geology at the University of Aberdeen, Scotland. After receiving a degree from Quintin School in 1970 in London, he obtained his PhD from Manchester University in Carbonate Sedimentology in 1970. He was appointed Lecturer in the Department of Geology and Petroleum Geology and Senior Lecturer in 1988, and became Department Head in 1993. He has extensive field experience and supervision in research in Britain, Europe, North America and the Middle East. Gordon is the author of numerous scientific publications on carbonate stratigraphy, diagenesis, geochemistry, cathodoluminescence, vertebrate paleontology and speleothem deposits.

Target Characterization by Seismic Attribute Analysis: A Case History from a Central Arabian Field

Russell, Timothy S.* and Robert B. Lathon

Saudi Aramco

3-D seismic attributes were used to investigate the apparent reservoir heterogeneity and depositional complexity associated with a central Arabian field and recommend drilling locations. This field has an unambiguous structural closure; however, two factors, rapidly changing lithology and sparse well control, put a critical dependence on the seismic data. Seismic attribute analysis is an extremely sensitive job that requires careful data preparation and detailed analysis of the seismic information. By integrating the geophysical, geological and engineering information, four well locations were selected. The results were accurate well prognoses, increased reserves and validation of a method of interpretation.

Timothy S. Russell is currently a Geophysical Descriptor working on reservoir characterization for Saudi Aramco. He has 12 years of broad based industry experience of which 2 years were with Woods Geophysical in Mt.Pleasant, Michigan, 5 years with Petro Star Energy, Michigan, 2 years with GeoQuest Systems in Houston, Texas and the last three years with Saudi Aramco. He has a BSc in Geology with a Geophysics option from Michigan State University. Timothy is also an Armed Service veteran.

Robert B. Lathon graduated in 1969 from the University of California with a BSc in Geophysics. He worked as an Interpreter for Gulf Oil ‘s West Coast/Alaska Division from 1969 to 1974. He then worked as an Exploration and Production Seismologist for Sarawak Shell from 1974 to 1979 and as Consultant in Houston from 1979 to 1987. Robert is currently a Geophysical Consultant with Saudi Aramco working on geophysical reservoir description.

The Impact of Sequence Mapping and Detailed Depth Conversion on Field Development, an Example from Block 4, Shabwa Basin, Yemen

Sahota, Gurdip*, Keith D. Gerdes, Leslie S. Peterkin,

Nimir Energy Services Limited, UK

and Tony F. Corrigan,

Corrigan Associates, UK

The stratigraphy and tectonic evolution of Block 4, Yemen is complex. The basin architecture has evolved through multi-phase rifting and salt tectonics. Drilled stratigraphy contains clastic, evaporatic and carbonate sediments that reflect depositional environments ranging from deep marine to continental. Several fields and, as yet, undrilled plays exist within this complex setting. An evaluation of the hydrocarbon potential in Block 4 requires a suite of depth maps that accurately tie drilled sequence stratigraphic horizons to seismic data. Eighty development and exploration wells and approximately kilometers of seismic data were available for this study. Wireline log data were used to establish a sequence stratigraphic framework for Block 4. Well imaged seismic data allowed qualitative sequence correlation between wells. The critical well to seismic ties, however, could not be achieved using standard well calibration techniques as many wells had limited sonic coverage and none had checkshot information. Velocity information for depth converting time maps was derived from a cross-plot study of sonic logs. Limitations imposed on seismic wavelet information are discussed. Velocity fields estimation and depth conversion methodology in the absence of quantitative well to seismic ties are discussed fully. Salt tectonics in Block 4 cause further complications for depth mapping of sub-salt targets. The impact of blockwide depth maps on the understanding of producing and non-producing accumulations identified in Block 4 is discussed in detail.

Gurdip Sahota is a Senior Geophysicist with Nimir Energy Services Limited. He has 11 years experience in petroleum exploration and development. Prior to this position, he worked for British Petroleum for 9 years in several site offices and head office. He has BSc and PhD degrees in Geophysics from Newcastle University, UK and Swansea University, Wales. Gurdip is a member of the PESGB and RAS.

Keith D. Gerdes (see Gerdes et al., p. 140) (cont. p. 188)

Leslie S. Peterkin is Petroleum Engineering Manager with Nimir Energy Services Limited. Prior to joining Nimir in 1994, he worked for 11 years with Shell International in various operating companies outside of the UK as a Reservoir Engineer and Petroleum Economist. This was followed by 3 years working for Sun International as Reservoir Engineer Advisor. He received a First Class BSc in Physics from St. Andrews University in 1975 and followed this with a PhD in 1979.

Tony F. Corrigan is a Reservoir Geologist with 20 years experience in the oil industry. After university, he joined the Shell Research Laboratory in The Hague, and this was followed by a period with the UK Department of Energy. For the last 13 years he has consulted, initially with Intercomp and IPEC, and with his own company, Corrigan Associates for the last 8 years. Tony has a BSc from Imperial College, London University and a PhD from the University of Calgary. He is a member of the PESGB, SPE, and SPWLA.

The Precambrian Basement: An Additional Reservoir in the Rifted Basins, North Africa

Salah, Mohamed G.* and Abdulrahman S. Al Sharhan

Desert and Marine Research Center, UAE

The instruction from the exploration manager to stop drilling and abandon the well as the bit hit the Precambrian basement, no longer applies. The fractured and altered Precambrian basement rocks are the most prolific reservoirs in the southern Gulf of Suez and the northern Red Sea rifts where hydrocarbons are produced from 7 fields, with porosity and permeability values up to 13% and 300 millidarcy, respectively. This work provides a comprehensive study on the reservoir characteristics of the Precambrian basement in these rift basins, including composition, nature and genesis of pore spaces, fracture pattern analysis and factors controlling production. The surface and sub-surface Precambrian basement rocks are related to the final stage of the tectonic-magmatic cycle of the Arabo-Nubian Shield, and composed of quartz-diorite, andesite porphyry, syenogranite and alkali granites dissected by dykes, fractures and joints. Three main directions of fractures, northwest-southeast, northeast-southwest and east northeast-west southwest have been detected in the study area. The porosity and production rate of this reservoir, as well as the oil-water contact movement, depends mainly on the age, intensity and direction of the fractures, the diagenetic processes and the dip and direction of the dykes and brecciated zones. The alteration processes reach their maximum intensity in the top-most section known as the basement cover, where the solution and leaching led to the enlargement of the fractures and vertical communications. The underlying fracture zone has been affected by differential alteration processes, creating zones of high and low vertical porosity and permeability. Thus the reservoir potential of the Precambrian basement has been greatly underestimated.

Mohamed G. Salah received a MSc in 1989 and a PhD in 1995 in Petroleum Geology and Basin Analysis from Cairo University, Egypt. He joined BP Petroleum Development in 1984 and moved to Norsk Hydro in 1990. He has also worked with Gulf Canada Resources Ltd., Egypt as Senior Geologist in 1990. Mohamed is currently Research Associate with the Desert and Marine Environment Research Center, UAE University. He has presented and pubhshed numerous papers. His research interests includepetroleum geology, basin modeling and computer applications in geology.

Abdulrahman S. Al Sharhan received his MSc (1983) and PhD (1985) in Geology from the University of South Carolina. He is currently Dean of the Faculty of Science at United Arab Emirates University. His current research interests include Holocene Coastal Sabkha of the UAE, and geology and hydrocarbon habitat in the Arabian Gulf and adjacent areas. He is currently working on his first book with A.E.M.Narinentitled “Petroleum Geology of the Middle East” to be published in 1996 by Elsevier. Professor Al Sharhan is a member of the Editorial Advisory Board of GeoArabia.

3-D Seismic Survey in Ashrafi Area, Gulf of Suez Egypt: A Case History of Challenging the Seismic Acquisition in a Hostile Environment

Sakr, Mohammed E.

and Samir Sanad,

Agiba Petroleum Company, Egypt

Ashrafi field produces oil from four reservoirs, trapped in compartments formed by a complex pattern of two intersecting sets of faults. This pattern is mantled by thick evaporites of Middle Miocene age which form salt plugs with steep walls in some areas, causing severe deterioration of data quality. Some wells were drilled during exploration and field development were dry due to very poor 2-D seismic. Feasibility studies concluded that a 3-D seismic approach is the only solution to field mapping problems. Acquiring the 3-D data in Ashrafi area was not an easy task. The area represents one of the most difficult environments for seismic data acquisition. Abrupt change in water depth, dense reefs (sometimes exposed forming large shallow lagoons or deep narrow channels) and strong currents, made it very difficult for conventional marine seismic surveys. An attempt to acquire Ocean Bottom Cable data over the area, in 1993, failed due to operational problems related to those environmental conditions. The survey was executed utilizing two modes for acquisition appropriate to the area: (1) deep water multivessel multistreamer, operation in accessible areas in water depth more than 20 meters (covering 100 square kilometers), and (2) Ocean Bottom Cable in reefal areas, less than 20 meters, which are not suitable for streamer towing operations (covering 35 square kilometers). The survey was successfully concluded in 77 days, over 95% of the proposed areas and covering about 135 square kilometers.

Mohammed E. Sakr is currently Chief Geophysicist with Agiba Petroleum Company, Egypt. He received his BSc (1970), MSc (1981) and PhD (1985) degrees from Cairo University. Prior to joining Agiba Petmleum, Mohammed worked for Suez Oil Company as Head of the Geophysics Department and then at EGPC as Exploration Operations Sector Manager. He is an active member of EPEX and EGS.

Samir I. Sanad is currently the Exploration General Manager and member of the board of Agiba Petroleum Co., Egypt since 1992. He received his BSc in Geology and Physics in 1966 from Ain Shams University. Prior to joining Agiba in February 1985 as Chief Geophysicist he worked for General Petroleum Co. until 1983 as Senior Geophysicist and for Mediterranian Oil and Gas from 1983 to 1985.

Geological Analysis of Early Water Production in Oil Reservoirs and Horizontal Wells in the Middle East, Egypt and India

Sapru, Ajay K.*, Schlumberger, Oman,

Elliott W. Wiltse, Schlumberger, Saudi Arabia and

Eric Standen, Schlumberger, France

Water coning in producing horizons is an important reason for drilling horizontal wells. However, early water production from horizontal wells is now recognized to be a surprisingly common phenomenon even in fields where water production was not anticipated. Analysis of many of these horizontal wells suggests that open, permeable faults are commonly the actual cause of early water and/or gas production. Often there are more of these faults present than had been originally mapped. Horizontal wells and 3-D seismic are revealing both high-angle normal and strike-slip faults which had not been mapped or penetrated by previously drilled vertical wells. Geological characterization of the fracture/fault systems in horizontal wells is critical to the completion design to prevent early water or unwanted gas production. Generally open faults must be isolated before they are allowed to flow water or gas into either in the oil zone or in the horizontal wellbore itself. This characterization must be included into an integrated, multidisciplinary effort to test the points of water and unwanted gas entry. This multidisciplinary integration approach of geology, petrophysics and pressure test analysis of these zones might be called “geotesting”.

Ajay K. Sapru is a Division Geologist for the Oman and Pakistan Division with Schlumberger Overseas, based in Muscat. Ajay has been involved in various geological studies and his experience with Schlumberger includes geological application development. Ajay worked in India and Jakarta before moving to Muscat in April 1993. He is a member of the AAPG, SPE and a life member of the Geological Society of India (GSI). He holds MSc and PhD degrees from the University of Jammu, India.

Elliott W. Wiltse has been with Schlumberger since 1985 and is currentlya Division Geologist with the company Prior to joining Schlum-berger, Elliott worked with Pennzoil (1980-1985) and AMOCO Inter national (1978-1980). He obtained a BA and MSc from the University of Oklahoma in 1969 and 1978, respectively. Elliott is aafiliated with the AAPG and the SPE and is interested in structural geology.

Eric J.W. Standen graduated from UBC in 1971 with a BASc in Geological Engineering. He worked for several years in mineral exploration before joining Schlumberger in 1975. His career took him from Field Engineer through Sales and Applications Development in Canada, after which, in 1989, he moved to Cairo as a Division Geologist with Schlumberger‘s East Mediterranean Division. In 1993 he was transferred to Unit Geologist‘s position for Europe-Africa, based in Paris and presently is Log Analyst for the Platform Express group in S.R.P.C. Engineering. Eric has written numerous papers on a wide range of well logging subjects and is a member of the GAC and APEGGA.

Optimizing Horizontal Well Steering and Analysis

Scott, Gill*, Rob Crossley, Paul R. Marshall, Thomas H.A. Slater and Dennis R. Clowser

Robertson Research, UK

In order to maximize the economic benefits of horizontal wells it is critical that well placement is optimized. The high resolution now achievable in geometrical steering in 3-D space is highlighted. The difficulties of seismic depth conversion and sub seismic resolution for predicting geology, even with the best 3-D seismic surveys, are illustrated. It is therefore clear that geological steering, not geometrical steering, is the key to economic success in these wells.

The practicalities and limitations of geological steering by mechanical “bouncing” techniques are discussed. The theory, practicalities and uncertainties with logging-while-drilling tools (gamma and resistivity) are examined for geological steering. It is concluded that some form of cuttings analysis is critical for reducing interpretational uncertainty.

The circumstances in which conventional cuttings analysis can be used successfully in geological steering are shown to be limited, and the case made that specialist cuttings analysis is necessary in many scenarios. The type of specialist analysis, biostratigraphic or reservoir geological, is determined by the geology, and stress is placed on the need for adequate planning studies in advance of horizontal drilling.

The practicalities of specialist ditch cuttings analysis at well site are explained, and performance to date illustrated with results from the Middle East area, including successive world record horizontal wells. The particular problems of geological analysis of wireline logs, image logs and core from horizontal wells are examined. We stress that the enormous successes achieved are the results of team efforts involving not only Robertson Research specialists, but also dialogue between the drillers, loggers and client company geologists.

Gill Scott joined Robertson Research in 1982 and is currently a Senior Reservoir Geologist. She received a BSc in 1979 and a PhD in Carbonate Sedimentology in 1985 from the University of Southampton, UK. She is a member of AAPG. Her particular professional interests are Middle East Mesozoic carbonate sedimentology and reservoir geology and their applications to exploration, appraisal, field development and reservoir simulation.

Rob Crossley joined Robertson Research in 1986 and is currently the Manager of Reservoir Geology and Sedimentology. He has a BSc from Reading in 1972 and a PhD from the University of Lancaster in 1976. Before joining Robertson Research, for 9 years Rob undertook rift valley research while lecturing for the University of Malawi. He is a member of the International Association of Sedimentologists. His current interests are assisting the development of digital core description software and the evaluation of reservoir uncertainty.

Paul R. Marshall joined Robertson Research in 1979 and is currently Senior Stratigrapher. Prior to joining Robertson Research, he worked with the Oil Service Company of Iran (OSCO) between 1977 and 1979 as a Senior Micropaleontologist. He obtained a BSc from the University of Newcastle-upon-Tyne in 1971, a MSc from University College, London in 1972 and a PhD in 1976. He is a member of the British Micropaleontological Society and Paleontological Association. He is particularly interested in Foraminiferal Ecology and Paleoecology.

Thomas H.A. Slater joined Robertson Research in 1980 after obtaining a BSc from the University of Liverpool. He is currently Senior Reservoir Geologist, specializing in Middle East sedimentology. His particular interests are problems associated with production from low permeability reservoirs.

Dennis R. Clowser is currently a Senior Stratigrapher and has been working with Robertson Research since 1970. He received his BSc from the University College of Wales in 1970. Dennis is a member of the Geological Society and the AAPG. His areas of professional interests include Mesozoic and Tertiary stratigraphy worldwide and wellsite biostratigraphy.

Stratigraphy and Sedimentology of the Storm and Tide-Dominated Shallow Marine Siliciclastic Members of the Qasim Formation, Qasim Region, Saudi Arabia

Senalp, Muhittin and Abdulaziz A. Al-Duaiji*

Saudi Aramco

Detailed measured stratigraphic and sedimentologic sections from the Qasim Region indicated that the Ordovician Qasim Formation was deposited as two distinctly different progradational coarsening upward shallow marine sequences.

The Hanadir and Kahfah members which are middle Ordovician in age form the lower progradational sequence. The Hanadir Member overlies the Saq Formation. It is entirely composed of greenish-gray, laminated, fissile shale, and occasional silt laminae which were deposited in an offshore marine environment. The overlying Kahfah Member is composed of alternations of greenish-gray shale and sandstone. The sand/shale ratio, grain size, and bed thickness of the sandstones increase upward. Five parasequences were identified. They are composed of offshore shales and followed by hummocky cross-bedded strongly storm-dominated lower shoreface sandstones. Each parasequence ranges in thickness from 3.70 to 7.45 m and is separated from the other by a flooding surface. The uppermost part of the Kahfah Member has one complete parasequence consisting of offshore, lower shoreface, upper shoreface and foreshore facies. Eastward the shales gradually pinch out, sandstone beds become thicker and the entire unit changes into Tigillite burrowed foreshore sandstone facies.

The Ra'an and Quwarah members (Upper Ordovician) together form the upper progradational sequence. The Ra'an Member is a dark gray, homogeneous fissile shale with occasional siltstone laminae. Its upper contact is transitional. The Quwarah Member is composed of sandstone with minor amount of shale. Tidal bundles, reactivation surfaces, bidirectional cross-bedding, and double mud layers are very common in the sandstones. Flaser, lenticular, and wavy bedding were observed in the shaly parts. They were deposited in a tide dominated shallow marine environment.

The Qasim Formation is cut sharply by the Sarah Formation which is middle Ashgillian in age and was deposited as braided stream and braided-delta changing into storm-dominated shelf facies eastward. The rapid facies variation of these formations indicate clearly the importance of finding paleoshorelines for hydrocarbon exploration.

Muhittin Senalp is a Geological Consultant with Saudi Aramco in the Research and Development Division. He has worked on the geologic modeling of the Khafji reservoir, Unayzah and basal Khuff Sandstones. Prior to joining Saudi Aramco, Muhittin was employed as Chief Geologist at the Mineral Research and Exploration Institute of Turkey until 1981. He obtained his BSc in Geology in 1965 from the University of Istanbul, a MSc in 1970 and PhD in 1974 from the Imperial College of Science and Technology in London. He is a member of the AAPG, SPE and the Dhahran Geological Society. Muhittin has a professional interest in reservoir characterization, sequence stratigraphy and clastic depositional environments.

Abdulaziz A. Al-Duaiji joined Saudi Aramco in 1984 as a Wellsite Geologist. In 1985 he became Northern Area Exploration Geologist and since 1992 has been Research and Development Geologist. He received his BSc in Geology from the University of Petroleum and Minerals in 1984 and a MSc in Geology from Texas A & M University in 1991. The regional geology of central Saudi Arabia and its environment of deposition is an area of particular interest to Abdulaziz.

Stratigraphy and Age of the Glacial Deposits in Qasim Region, Central Arabia

Senalp, Muhittin and Abdulaziz Al-Laboun*

Saudi Aramco

The stratigraphy and depositional environments of the Sarah and Zarqa formations have created significant confusion and controversy among geologists since they were first introduced. The two formations are generally used together and have been interpreted as Late Ordovician-Early Silurian glacial deposits.

Detailed stratigraphic and sedimentologic sections were measured from the Qasim, between the towns of Unayzah and Tabuk to understand the type of glaciation and its effect on deposition during Late Ordovician time. The Sarah Formation of Williams and others (1986) cuts deeply into the Saq and Qasim formations indicating a substantial drop in sea-level and formation of an incised-valley system. It is filled with sandstone and conglomerate of a braided stream facies. Therefore the conglomerates are fluvial lag deposits rather than tillite. Towards the east, this fluvial system has deposited a braid-delta. During our studies, no evidence of glaciation was found in the Sarah Formation which is overlain by the offshore marine shales of the Qusaiba Member of the Qaliba Formation.

The Zarqa Formation of Vaslet and others (1989) creates a real problem. Our field work at Jal Az Zarqa indicated that this section conformably overlies the tigillite burrowed, hummocky cross-bedded sandstone facies of the Kahfah Member. It is composed of olive-green shale, siltstone, and very fine-grained, wave rippled sandstone forming a coarsening upward sequence due to shoreline progradation. This sequence is identical to the Ra'an Member of the Qasim Formation. Large, faceted, striated and polished granite boulders and other basement-derived materials (dropstones) of distant provenance occur in the shales. There are slumpings around the boulders indicating their impact on the sea-bottom. In addition to basement-derived boulders (glaciomarine drift), till, polished glacial pavements and large-scale striations strongly support that marine glaciation occurred during the Ra'an and Quwara deposition which is Middle-Upper Caradocian time.

Muhittin Senalp (see Senalp and Al-Duaiji, p. 192)

Abdulaziz Al-Laboun is a Geological Specialist with Saudi Aramco in the Research and Develepment Division. He obtained his BSc in Geology/Chemistry from Riyadh University, Saudi Arabia in 1973, and MSc in Petroleum Geology from University of Tulsa, USA. He obtained his PhD from King Abdulaziz University, Saudi Arabia. Abdulaziz is interested in held geology. He is a member of many geological and scientific societies and also a member of the board of Saudi Society for Earth Sciences. He has published many papers on the Geology of Arabia mainly on Paleozoic. He also published Part I of Lexicon of Arabia: Lexicon of the Paleozoic and Lower Mesozoic of Arabia.

Advances in Integrated 3-D Stochastic Reservoir Modeling

Shanor, Gordy G.*, Lars E. Kjellesvik and Reider B. Bratvold

Geomatic AS

Application of geostatistical analysis and stochastic modeling techniques within accurate 3-D stratigraphic framework models is now recognized as a powerful approach to the characterization of known reservoir heterogeneity, spanning all scales of description, from special core analysis to flow simulation grid scales. Integration of multi-source data into the building of multiple, equiprobable stochastic reservoir models enable interdisciplinary teams to simulate quantifiable, detailed heterogeneous models of depositional facies (channels, deltas, porosity facies, etc.) and their corresponding petrophysical distributions as direct input to the flow simulator via the upscaling process. Based on ranking procedures applied to both the detailed and upscaled stochastic realizations, key reservoir management risk analysis can be performed more objectively and intelligently, with significant potential savings. This paperpresents a number of new, sophisticated techniques developed for the characterization of very complex, heterogeneous geological models of clastic and mixed carbonate/siliciclastic reservoirs worldwide as input to full field flow simulation studies. The paper includes detailed examples of 3-D framework modeling, statistical analysis functionalities, stochastic structural modeling, object-based, grid-based and combined stochastic facies simulations of clastic, mixed, and transitional depositional environments, stochastic simulations of the corresponding petrophysical properties, ranking of static and dynamic realizations, and upscaling to flow simulation grids.

Gordy G. Shanor is Advisor, Geology, for Geomatic AS, based in Stavanger, Norway. Gordy has 20 years of international exploration and reservoir geoscience experience. He worked for eight years with major oil companies in the USA, Europe and Southeast Asia, followed by 10 years in Asia and the Middle East with Schlumberger where he specialized in the development of borehole interpretation techniques and their applications to integrated field studies. Prior to joining ODIN (now Geomatic) in 1994, he headed up the geology for Schlumberger‘s Reservoir Characterization team established in Dubai for major stochastic reservoir simulation studies of giant fields in the Middle East. Gordyholds a BSc in Geology from the University of Oklahoma, and is a member of the AAPG, SPE and numerous international geological societies.

Lars E. Kjellesvik holds a MSc in statistics, with diploma work on geostatistics at the Norwegian Institute of Technology (1993). Lars has been employed with Geomatic AS as Geostatistician since completing his degree. He has been involved with several case studies utilizing geostatistical techniques and stochastic modeling, provides theoretical geostatistics courses and Geomatic‘s STORM software user courses and has been involved in the development of new modeling techniques within STORM.

Reider B. Bratvold is the Director of Research and Development with Geomatic AS. He was instrumental in the establishment of ODIN (now Geomatic) and in the specification of STORM software and ODIN‘s other products. From 1983 through 1987 Reider worked with Statoil and Rogaland Research. In 1989, he joined IBM‘s European Petroleum Application Center and was responsible for reservoir related activities at the center. Reider holds an undergraduate degree from Rogaland University, a MSc in Petroleum Engineering from the University of Tulsa, MSc in Mathematics and a PhD in Petroleum Engineering from Standord University.

Tórtola Fluvial System; A Modern Analogue for the Upper Gharif of the Sultanate of Oman

Silva, Fernando P.T.* and António Costa Silva

Partex, Portugal

Allard W. Martinius and Koenraad J. Weber

T.U. Delft, The Netherlands

The Early Permian Gharif Formation is the most important siliciclastic oil reservoir in the hydrocarbon province of Oman. The fluvial sediments were deposited in a broad alluvial plain, by rivers shed from peripheral highs to the East, at the end of Gondwana glaciation (Westphalian-Sakmarian) and the initiation of rifting that led to the development of Tethys Ocean. The Gharif Formation is usually sub-divided into three units. The Lower Gharif consists of a basal unit of cross-bedded quartz sandstones that locally contain crinoid debris and brachiopods. The Middle Gharif consists of quartz feldspar-rich, cross-stratified sandstone with trough-shaped sets inter-bedded in red-brown shales and siltstones of fluvial origin. The Upper Gharif shows more abundant cross-stratified channel sandstones inter-bedded with varicoloured shales deposited in an alluvial environment. Each of the sandy intervals probably represent deposition during “wet” pluvial periods, intercalated within the overall semi-arid environment. Exploitation of this formation is particularly challenging given the rapid lateral variation of facies imprinted by the sedimentological environment of deposition. Present knowledge of the Gharif Formation comes mainly from cores and log data, and only a minor part is derived from small outcrops in the basin margin. This is clearly insufficient to describe reservoir internal architecture and characteristics of discrete sandstone bodies in order to perform reservoir modeling with a reasonable degree of confidence. Thus, there is an urgent need to obtain both qualitative and numerical information from equivalent modern analogues. This paper presents a detailed comparison between the Omani Upper Gharif member and the distal deposits of the Tertiary Tórtola fluvial system of the Loranca Basin in the central Iberian Peninsula. The outcrops of this system have also a labyrinthine reservoir architecture, characterized by a poor lateral and vertical interconnectedness and low net-gross ratio.

Fernando P.T. Silva graduated in Geology from Lisbon University in 1990. Since then he has been working with PARTEX-CPS as a Reservoir Geologist in several projects in the Middle East and Africa. Parallel to this activity, he also participated in a number of research and development projects related with the application of fractal geometry to the characterization and modeling of naturally fractured reservoirs. Fernando is currently a member of the Portuguese Geologists Association.

António Costa Silva obtained his MSc in Petroleum Engineering in 1984 from Imperial College and a PhD in 1993, from the Technical University of Lisbon with a work on mathematical modeling of oil reservoirs. He joined PARTEX-CPS in 1984 and has conducted reservoir studies for several fields in the Middle East and Africa. António also developed a number of research and development projects related to the application of mathematical models for improving the estimation of reservoir properties. He is a member of the Imperial College of Science and Technology, Portuguese Order of Engineers and SPE. He has published about 20 papers on reservoir characterization and modeling.

Allard W. Martinius received his MSc in Geology from the University of Utrecht. In 1995, he obtained a PhD in Geology from the University of Technology at Delft, The Netherlands. His PhD research focused on the sedimentology characterization of labyrinthine fluvial sediments as a tool for reservoir modeling. He has published papers on topics related to reservoir characterization, fluvial and shallow-marine sedimentology and paleoecology of marine macro invertebrates.

Koenraad J. Weber graduated in 1960 from Delft University of Technology with a MSc in Mining and Petroleum Engineering. He retired in 1993 as Senior Consultant Reservoir Geology from Shell Inter-national Petroleum Maatschappij having worked 33 years in Shell research operations in many countries. Since 1985 Koenraad was Professor in Production Geology at the Delft University of Technology and in 1993 he was nominated Associate Professor at the Ecole National Supérieure du Pétrole et des Moteurs. He was a distinguished lecturer for the SPE in 1980 and the AAPG in 1993 and in the same year he received the Distinguished Achievement Award from the AAPG. He is an Honorary Member of the Nigerian Association of Petroleum Explorationists and has published some 40 papers on reservoir characterization topics.

The Middle Jurassic-Early Cretaceous Geological Evolution of the Republic of Yemen

Simmons, Michael D.

University of Aberdeen, UK (previously British Petroleum)

The upsurge in hydrocarbon exploration activity in Yemen, coupled with renewed academic study of outcrops, has led to much new stratigraphic data being made available. Of particular interest is the hydrocarbon bearing Middle Jurassic - Early Cretaceous succession of southern Yemen and the equivalent succession of northern Yemen. Biostratigraphy has proved to be an invaluable tool for correlating these sediments and developing a chronostratigraphic framework on which a sequence stratigraphy model can be developed. It also assists in refining the complicated lithostratigraphy which exists in this region.

In this paper a biostratigraphically controlled correlation is presented extending from the Sana'a region in the north-west of the Republic to Ras Sharwayn in the south-east. This incorporates data from outcrops and wells. A number of sequences are recognized, each representing a distinct phase in the evolution of the basin. The biostratigraphic criteria used to recognize and define each sequence will be discussed. It is concluded that use of the proposed sequence nomenclature permits a clearer understanding of basin evolution than does the current complex lithostratigraphy.

Michael D. Simmons is Senior Lecturer in Petroleum Geoscience at the University of Aberdeen. From 1985 to early 1996 he worked for BP Exploration. He has a BSc and PhD from Plymouth Polytechnic. He is interested in applied biostratigraphy and the geology of the Tethyan region.

Geo-Steering of Horizontal Wells in Thin Oil Bearing Formations in Block 5, Offshore Qatar

Sonderskov, Carsten* and Morten W. Jeppesen

Maersk Oil Qatar AS, Qatar

Maersk Oil Qatar AS operates the Al-Shaheen field in Block 5 offshore Qatar. In the past the field has been penetrated by several vertical wells because it is situated above the North Field, the giant gas field in the Arabian Gulf. However, until recently the thin Cretaceous reservoirs were considered non commercial. Maersk Oil commenced an appraisal program of the oil bearing reservoirs in 1992 and since then drilled 7 horizontal wells in the Kharaib B, Shu'aiba and Nahr Umr formations. The Kharaib B wells have been drilled as very long (up to 13,000 feet) horizontal sections in a limestone reservoir which does not exceed 30 feet in thickness. The Nahr Umr wells have been drilled as 6,000 to 7,000 foot sections in an unconsolidated sandstone reservoir which is only 10 to 15 feet thick. Recently, a well was drilled in the Shu'aiba with 16,410 foot (more than 5 kilometers) long horizontal section within a 30 foot thick limestone reservoir. These achievements have only been possible due to geo-steering of the wells using 3-D seismic, biostratigraphy, Logging While Drilling and rigorous show description. Examples are shown from the horizontal wells drilled in the Kharaib B and Shu'aiba limestones and in the Nahr Umr sand.

Carsten Sonderskov is currently Chief Geologist with Maersk Oil Qatar AS, Qatar. He received a MSc in Geology from the University of Copenhagen. Prior to joining Maersk Oil Qatar AS in 1994, Carsten worked with the Geological Survey of Denmark, The Danish Energy Agency and Maersk Olie og Gas AS in Denmark. Carsten is a member of the SPE and DGF.

Morten W. Jeppesen joined Maersk Olie og Gas AS in Denmark as a Geologist in 1991. In 1994 he transferred to Maersk Oil Qatar AS where he has been working as a well-site Geologist and Petrophysicist. He received a MSc in Geology from the University of Copenhagen in 1991. Morten is a member of the AAPG and SPE and is particularly interested in production and development geology.

Stratigraphic Interpretation of Magnetotelluric Data in Central Saudi Arabia

Stewart, Ian C.F.*, Thomas C. Connally, Saudi Aramco and Jeffrey H. Copley

Arnold Orange Associates, USA

(See paper by Stewart et al., p. 52-63)

Measurement of Formation Resistivity Through a Metal Casing

Strack, Kurt M.*, Otto Fanini, Hans-Martin Maurer, Bentsion S. Singer and Lev A. Tabarovsky

Western Atlas Logging Services, USA

Over the last 60 years, numerous attempts have been made to measure the earth formation resistivity behind a steel casing. The knowledge of the formation resisitivity is important because it is one of the prime indicators of water saturation. The scope of applications for the Through Casing Resistivity (TCR) technology includes controlling water floods, monitoring producing zones, and searching for hydrocarbons by-passed in open-hole logging operations. This has inspired a number of authors to investigate opportunities and limitations of the TCR measurement. In this presentation, we discuss the results of the feasibility study carried out by Western Atlas Logging Services. The study was co-funded by the Gas Research Institute. Results of a field test of the prototype tool developed by ParaMagnetic Logging Inc. confirmed the theory. Our numerical feasibility study addressed a wide range of issues important for the development of the tool. This included evaluation of the signal levels, operating frequency, vertical resolution, etc. Distortions due to the presence of the cement sheath around the casing, proximity to the casing bottom, and casing imperfections were addressed as well. The field test confirmed the conclusions of the feasibility study. The TCR logs were found in good correlation with the open-hole resistivity measurements made more than a decade ago.

Kurt M. Strack is currently Research Manager with Western Atlas Logging Services. He received his MSc in Geophysics from Colorado School of Mines in 1981 and PhD in Geophysics from the University of Cologne, Germany. Kurt worked for Group Seven Inc., Denver as Geophysicist from 1981 to 1982, Assistant Professor at the University of Cologne from 1983 to 1992 and President of Harbour Dom Consulting from 1989 to 1992.

Otto Fanini is currently Project Manager with Western Atlas Logging Services. He received his MSc in electrical Engineering from Texas A&M University in 1982. Otto worked for Texas Instruments as Design Engineer from 1982 to 1986, in telecommunications from 1986 to 1990, and in instrumentation electronics area from 1990 to 1992.

Hans-Martin Maurer is currently Scientist with Western Atlas Logging Services. He received his MSc in Physics in 1986 and his PhD in Geophysics in 1993 from the University of Braunschweig, Germany. Hans-Martin had a research stipend at Uppsala University, Sweden in 1994.

Bentsion S. Singer is currently with Macquarie University, Australia. Bentsion received his MSc in Physics from Moscow State University and his PhD in Physics and Mathematics from the USSR Academy of Sciences. He was Senior Scientist with Western Atlas Services from 1993 to 1995.

Lev A. Tabarovsky is a Scientist in a senior position with Western Atlas Logging Services. He has a MSc in Nuclear Physics from Novosibirsk University, a PhD in Geophysics and a Doctoral Degree in Technical Applications from the Russian Academy of Sciences. From 1968 to 1989 Lev was working in different positions for the Institute of Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences.

Stratigraphy and Facies Definition of the Lower Cretaceous Minagish Oolite, Umm-Gudair Field, West Kuwait

Sungur, Dogan

Kuwait Oil Company, Kuwait

The Umm-Gudair Field produced oil from the middle “Oolitic” member of the Lower Cretaceous Minagish Formation. This bioclastic limestone reservoir has produced over 310 million barrels of oil since the discovery of Umm-Gudair in 1954.

The Minagish reservoir was deposited in shallow subtidal to supratidal conditions resulting from deposition on gently sloping carbonate banks. Sonic log correlations identified fifty consistent stratigraphic layers with differing porosities. Minor oscillations in sea level are indicated by numerous abrupt vertical changes of facies. Lateral facies variations also occurred within these layers. Descriptions of selected cores determined 13 major lithofacies. Grainstone and packstones dominate some layers, while wackestones are characteristics of the less permeable layers.

Facies interpretations and mapping provide evidence that the stratigraphic layers can be combined into seven distinctive genetic groups. Each group has a characteristic assemblage of facies, reservoir properties and well productivities. Productive reservoir intervals are dominantly grain-supported, high-energy limestones. They are of field-wide extent, vertically stacked and separated from each other by relatively low permeability and less productive wackestones.

This geological model will assist reservoir simulation, as well as improve primary recovery and analysis of water performance. Selective perforation of the more productive zone will optimize primary recovery and water flood design by assuring continuity of fluid flow between injection and production wells.

Dogan Sungur is a Senior Geologist at Kuwait Oil Company. He has 21 years of petroleum and exploration experience including 2 years in Kuwait Oil Company, 7 years in AGOCO, Libya, 5 years in Norcen Oil, Calgary, Canada, 2 years in Husky Oil Operation Ltd., Calgary and 5 years in the Turkish Petroleum Corporation, Ankara, Turkey. He has BSc and MSc degrees in Geology from Hacettepe University of Ankara, Turkey.

Delineation of Organic Richness and Thermal History of Thamama Group in Eastern Abu Dhabi: A Modeling Approach

Taher, Ahmed A.

Abu Dhabi National Oil Company (ADNOC)

The source rock potential of the Thamama Group in eastern Abu Dhabi was assessed by a new efficient technique which uses wireline logs. This technique models the areal extent of organic richness and thermal maturity of source rocks. The Thamama Group has rich petroleum resources and possibly multiple source rock layers associated with various depositional setting. The source rock screening proved the presence of an excellent source through good to moderate source layers within Thamama basinal facies.

The scarcity of vitrinites in the predominantly carbonate environment of the Thamama Group has forced researchers to use thermal history modeling to delineate mature kitchens. The modeling resulted from reconstruction of maturity and temperature histories based on Lopatin‘s Algorithm and Arrheneous Equation. The modeling indicated that the Thamama mature kitchens are mainly located in the central part of the study area adjacent to the foredeep basin. Migration from these kitchens is mainly lateral westwards updip toward the main Thamama producing fields in east Abu Dhabi.

The modeling results are compared with available observation and analytical data to serve as a basis for modeling calibration and gave confidence in the applicability of these methods in areas where rock samples are very limited or even not available.

Ahmed A. Taher is a Geologist with the Abu Dhabi National Oil Company (ADNOC) since 1982 and has worked as an Explorationist for the ADNOC Concession areas. He received his BSc in Geology from UAE University. He is a member of the Society of Explorationists in the Emirates (SEE). Ahmed is particularly interested in the statistical modeling of source rocks and its maturation regime.

Modifying Near-surface Velocities Using Pre-Stack Reflection Tomography

Teemull, Franklin A.

Saudi Aramco

There are some areas where fast velocity material outcrops, and little near-surface velocity information is available. In these environments, the near-surface velocities which focus the stacked sections from some seismic datum may be incorrect. Under certain conditions, it is possible to isolate the velocity components which can distort low relief depth imaging. Offset dependent reflection traveltimes are used in a 2-D generalized linear inversion modeling procedure to capture and update the near-surface velocities. A typical example of the problem and a demonstration of one methodology to resolve nearsurface effects is discussed in this paper.

Franklin A. Teemull is a Geophysicist with Saudi Aramco. He has been with the company for 15 years. Previously, he worked as a consultant for Monenco, Alberta, Canada. He has a BSc in Mathematics and Physics from the University of the West Indies, St. Augustine and a MSc in Geophysics from McGill University, Canada.

E & P Optimization for Salt-Associated Reservoirs Using a 3-D Stress, Hydrology and Diagenesis Salt Tectonics Simulator

Tounsi, Faical*, Julie Boyd, Changxin Qin, Miles Maxwell, Khaireddine Sakrani and Peter J. Ortoleva

Indiana University, USA

Diapirism and other salt tectonics are involved in many aspects of salt-associated reservoirs. We have developed a fully three-dimensional simulator for these phenomena to predict the evolution in time of salt layers into swells, massifs, diapirs, overhangs and other salt formation morphological features that make the exploration of salt-associated reserves difficult. Our simulator can also be used to predict the velocity of salt motion given its present topography (as determined from 3-D seismic or other data). In this way one may optimize exploration strategies and also plan well and pipeline placement to avoid damage from salt motion by avoiding areas of huge salt flow velocity. The quantitative predictive capability of our simulator arises from the fact that it fully integrates all relevant processes in three spatial dimensional simulations. Processes accounted for are rock and salt deformation by an incremental stress (poroelastic, viscous, pressure solution, fracturing) model, pore fluid flow, grain and pore fluid diagenetic reactions, energy balance (to calculate the temperature) and sediment and (possible) underlying fault motion. Input to the simulator is seismic and well data gathered during usual E & P activities. The output is the evolution over geological or engineering timescale of the spatial distribution of rock and salt deformation, fluid pressure and composition, temperature, diagenetic mineralization and, in particular, reservoir location, extent and characteristics. Our simulator naturally integrates seismic and well data with data on rheology, chemical kinetics and thermodynamics to optimize E & P strategies. Our model and E & P optimization is calibrated and tested using examples from the US Gulf Coast.

Faical Tounsi is a post-doctoral fellow at the Laboratory for Computational Geochemistry, Indiana University. He has seven years experience in modeling geophysical systems and 2 years in basin modeling. Faical received his MSc and PhD degrees from the University of Michigan, Ann Arbor.

Julie Boyd received her BSc in Geology (1993) from Texas A&M University and MSc in Geology from Indiana University (1995). Her MSc thesis focused on metamorphic petrology. She also worked on pressure solution - mediated compaction at the Laboratory for Computational Geochemistry. Currently she‘s working as a Geologist at Philips Petroleum Co., dealing with offshore prospects in the US Gulf of Mexico.

Changxin Qin received a BSc in Geology from Northwestern University in China (1982), and a MSc in Economic Geology from China University of Geoscience. He did research on mineral deposits, fractal characterization of geological phenomena and geological systems. Changxin is presently working on a PhD thesis at Indiana University.

Miles Maxwell received his BSc in Chemistry from Spring Hill College in Alabama (1987). He is currently working toward his PhD in Physical Chemistry at Indiana University. His current research interests are non-linear phenomena in geology and overpressuring mechanisms and episodic fluid release in sedimentary basins.

Khaireddine Sakrani received his BSc in Civil Engineering (1988), University of Annaba, Algeria, MSc in Geotechnical Engineering (1991), University of Montreal. He is currently working on his PhD in Geochemistry at Indiana University. Khaireddine‘s main interest is rock mechanics and basin stress analysis.

Peter J. Ortoleva (see Ortoleva, p. 179)

An Integrated Methodology Based on 3-D Seismic Amplitude Inversion in Support of Reservoir Characterization

Triebwasser, Harold L.*, Jung J. Kim, Charles H. Wagner III, Gary C. Robinson, Ming-Ren Hong and James P. Tung

Saudi Aramco

In this paper, we detail a modeling methodology using seismic amplitudes inverted to acoustic impedance calibrated with log, core, and lab data, and geologic, geophysical and engineering interpretations. Results from this methodology are shown for studies in a clastic and carbonate environment using geostatistics to produce porosity models. This is a multi-disciplinary approach for impacting reservoir characterization efforts at the early delineation or field production stage based on the following four-step approach: (a) petrophysical study to establish a relationship between seismic/geophysical attributes and some reservoir rock property; (b) build an initial acoustic impedance model in time referenced to the depth model from sonic and density logs evaluated to be petrophysically reasonable and areally consistent; (c) extract relevant geophysical attributes; and (d) relate geophysical attributes to reservoir properties. The methodology allows for alternative tools to be brought to bear depending on the particular geologic scenario involved.

Harold L. Triebwasser is currently a Geophysicist working as a modeler in the Geophysical Technology Division of Saudi Aramco. He has 21 years of exploration experience of which 13 were with Teledyne Exploration as a Seismic Crew Geophysicist, Party Chief, Land Field Supervisor, and Land and Marine Data Processor. Harold has a BSc in Physics and Mathematics.

Jung J. Kim is currently a Research Geophysicist with Saudi Aramco. He has 14 years of petroleum and exploration experience beginning with Petro-Canada Resources, Texaco Canada Resources and Esso Resources Canada. He has been with Saudi Aramco since 1991 where he is principally involved with interactive applications programming and reservoir geophysics. Jung has a BSc in Geology from Seoul National University and a PhD in Geophysics from Texas University, USA.

Charles H. Wagner III is currently a Senior Petroleum Engineering Systems Analyst with Saudi Aramco. Prior to joining Saudi Aramco in 1992, he spent 12 years (8 on loan to Saudi Aramco) with Chevron as a Mining Technician, Well Log Analyst, and Programming Analyst. He has a BA in Geology from the University of Tennessee at Knoxville.

Gary C. Robinson is currently Team Leader of the Borehole/Marine Modeling and Inversion Team in the Geophysical Technology Division of Saudi Aramco. He has 17 years of experience in the petroleum industry with Mobil, CGG and Elf Aquitaine. Gary is a member of the SEG, EAPG, AAPG, and the SPE. He has a BSc in Geology from Stanford University and a MSc in Geophysics from the University of Houston.

Ming-Ren Hong is a Geophysicist working on 3-D modeling and reservoir characterization using seismic inversion in Saudi Aramco. Before joining Saudi Aramco, Ming-Ren worked for Arco Oil and Gas Company in the Exploration and Petroleum Research Center from 1984 to 1991. He graduated from the University of Texas with a PhD in Geophysics in 1982.

James P. Tung is currently a Geophysicist working as a Modeler in the Geophysical Technology Division of Saudi Aramco. He has 22 years of exploration experience of which 17 were with Shell Oil Company as a Seismic Crew Geophysicist, Party Chief, and Seismic Interpreter. James has BSc and MSc degrees in Geology and a PhD in Geophysics from the University of Southern California.

Prediction of Reflectors Below Drill Bit by Seismic While Drilling: Application for Carbonate Rocks at South West Andrews Oil Field

Tsuru, Tetsuro*, Takeshi Kozawa

Japan National Oil Corporation and

Philip F. Johnston

Unocal Corporation, California

Seismic While Drilling (SWD) is a real-time technique to estimate sub-surface structures while drilling and uses seismic waves generated by a working drill bit as a seismic source. Since each source and receiver location in SWD is the opposite configuration of VSP, SWD is considered a reverse VSP technique. Generally, this technique is used in normal sedimentary basins in Southeast Asia. However, it is rarely applied to high velocity carbonates because of the presence of dominant conical waves that radiate from the drillstring into the earth. In the SWD experiment at the South West Andrews oil field in USA, the conical waves were attentuated by stacking multi-channel data. As a result, some reflectors below the bit were identified and the effectiveness of SWD in carbonate rocks was demonstrated.

Tetsuro Tsuru received a B.E. degree (1981) and a M.E. (1983) in Earth Resources Engineering from Kyoto University. Since 1992 he has been a Research Associate with the Technology Research Center of Japan National Oil Corporation in Chiba, Japan, working on reservoir characterization projects. From 1984 to 1991 he worked on exploration projects in China, Myanmar and Akita in Japan. Tetsuro is a member of the SEG and SEG Japan.

Takeshi Kozawa received a B.Eng. (1987) and a M.Eng. degrees from from Kyoto University both in Earth Resources Engineering. He joined Japan Petroleum Exploration Co. Ltd. in 1989 and worked for Japex Geoscience Institute from 1989 to 1992. He has been working with Technology Research Center of Japan National Oil Corporatio (JNOC) since 1992. His area of professional interest is borehole geophysics and seismic data processing. Takeshi is a member of SEG, SEG Japan and the Japanese Association for Petroleum Technology.

Philip F. Johnston received a BSc from Occidental College (1977) and a MSc from Colorade School of Mines (1979), both in Geophysics. He has been a Research Associate with Unocal in Brea, California since 1989, working on reservoir characterization projects. He also worked on exploration and development projects in the Santa Maria, Sacramento and San Joaquin basins. Philip is a member of the SEG, SEP and AGU.

Description and Characterization of a Fractured Carbonate Reservoir: Southeast Turkey

Ulu, Murat*, Alaattin Sayili and Haki Naz

Turkish Petroleum Corp., Turkey

In Güney Karakus field, located in the northeast of Adiyaman town, southeast Turkey, the main reservoir rocks are Upper Cretaceous carbonates. This study focuses on a 45 meter thick, Campanian shallow to deep marine, organic-rich, carbonate reservoir. The carbonate is analyzed in terms of sedimentary facies, diagenetic characteristics, reservoir facies and petrophysical properties and interpreted via statistical techniques in ten wells. Fracture evaluation has been done by detailed core and well log analysis.

As a result of the study, three units: two reservoir units and one non-reservoir unit were differentiated. The main reservoir unit, forming the lower portion of the studied section, is characterized by bioclastic, partially dolomitic limestones with matrix, intra intergranular, vuggy, stylolitic and fissure-type porosities ranging between 2 to 8%. Permeability values of this unit range between 0.05 to 0.7 millidarcy (mD). This unit is described as a fractured diagenetic reservoir and is observed in 9 wells, 3 of which are already producing from this unit. The second one overlying the main unit is characterized by cherty, dolomitic limestones with matrix, stylolitic and fracture type porosities ranging between 2 to 4%. Matrix permeabilites of this unit range between 0.04 to 0.05 mD and interval permeability values are expected to be higher due to fractures in areas close to faults. This unit is described as a fractured, low porosity, potential reservoir and is observed in 2 wells that have not been tested yet. Above these two reservoirs, a non-reservoir unit, serving as a cap rock with extremely low porosity and permeability values is differentiated and extends all over the field.

Murat Ulu is currently a Geologist with the Turkish Petroleum Corporation, Turkey. He has 3 years of petroleum exploration and research industry experience and is specialized in reservoir geology, well logs and geostatistics. Murat received his BSc from Middle East Technical University, Turkey. He is a member of the Turkish Association of Petroleum Geologists and has published papers on carbonate reservoirs.

Alaattin Sayili is currently a Staff Geologist with the Turkish Petroleum Corporation. He has 10 years experience in carbonate petrology and oil exploration with Turkish Petroleum. Alaattin holds a BSc in Geology from the Technical University of Istanbul and a MSc from the University of Colorado at Boulder, USA. Alaattin is a member of the Turkish Association of Petroleum Geologists and has published several papers on sedimentology and diagenesis of carbonates and sandstones.

Haki Naz is Senior Staff Geologist currently working in the Research Center of the Turkish Petroleum Corporation, Ankara. He has 12 years experience in the petroleum and research industry. Haki received his MSc in Geological Science from the University of Tusla, USA. He is a member of the AAPG, Chamber of Geological Engineers of Türkiye and Turkish Association of Petroleum Geolgists. He has published several papers on geological subjects especially on deep-marine clastics and shallow-marine carbonates.

High Resolution Sequence Stratigraphy of the Natih Formation (Cenomanian/Turonian) in Oman: Distribution of Source Rocks and Reservoir Facies

Frans S.P. Van Buchem* (IFP), Philippe Razin (BRGM), Peter W. Homewood (Elf Aquitaine), Jean M. Philip (Université de Provence), Gregor P. Eberli (University of Miami), Jean-Pierre Platel (BRGM), Jack Roger (Elf Aquitaine), Rémi Eschard, Guy M.J. Desaubliaux (IFP), Thierry Boisseau, Jean-Pierre Leduc, Richard Labourdette and Solange Cantaloube (Elf Aquitaine)

(See paper by van Buchem et al., p.65-91)

Sidi El Kilani Field, Tunisia: Fracture Prediction Through Detailed 3-D Seismic Attribute Studies

Van Derck, Richard W.*

Kuwait Foreign Petroleum Exploration Co., Kuwait

Cameron W. Davis and Chris Tyson

Landmark Graphics, UK

The Sidi El Kilani field is located onshore Tunisia in the southern area of the North Kairouan Permit. The discovery well, SLK-1, was drilled in 1989 and tested oil at 3,360 barrels of oil per day from fractured chalky limestones of the Upper Cretaceous Abiod Formation. A further four wells were drilled on the structure in the next three years with a 50% success rate. All wells encountered Abiod Formation with significant fracturation, but only two of the four wells encountered open fractures capable of flowing oil. Although fractures have been generated episodically since the Maastrichian, only those fractures which developed coincident with oil migration have remained open and capable of oil production. The problem was to identify areas of open fractures. During 1993-1994, a 3-D seismic survey was acquired and studies were undertaken to determine both the mechanisms and the distribution of open fracturation. Maps were made of “probability of open fracturation” based upon empirical observations and correlations between (a) seismic attributes, particularly reflection amplitude, reflection coherence and acoustic impedance, (b) formation imaging log results for open and closed fractures, and (c) structural models for field development. SLK-6 was drilled and successfully encountered more open fractures than had previous wells.

In 1995, additional studies were undertaken to refine and quantify the magnitude and distribution of open fracturation across the field using Landmark‘s Reservoir Attribute Visualization and Extrapolation (RAVE) package. This allowed multi-dimensional cross-plotting of seismic and well attributes to be identified and statistically significant reservoir relationships to be mapped interactively on the 3-D seismic workstation.

The combination of 3-D data visualization, parameter analysis and geostatistics has been effective in highlighting fracture “sweet-spots” for future drilling. The use of 3-D seismic attributes and modern analytical software allows the interpreter to search for the subtle relationships between seismic variations and significant reservoir information which may be the key to successful field development.

Richard W. Van Derck is currently Chief Geophysicist and Far East Exploration Coordinator with Kuwait Foreign Petroleum Exploration Company (KUFPEC), Kuwait. He has 26 years of diverse international experience in petroleum exploration and development, having worked 9 years for Gulf Oil Corporation in various research and operations positions, 2 years with UNOCAL in Ventura, California followed by 12 years as an independent consultant specializing in seismic interpretation, direct hydrocarbon detection, project management and prospect generation. He has a BSc from Utah University and is a member of SEG.

Cameron W. Davis is currently employed by Landmark Graphics EAME as a Sales Geophysicist. Cameron started in the oil and gas exploration industry as Marine Gravity Geophysicist before becoming a Field Geophysicist for Western Geophysical based in the Middle East providing contract services to Saudi Aramco. During the past four years Cameron has been working for Advance Geophysical which merged with Landmark Graphics. Cameron graduated with a BSc (Honors) in Geophysics with Geology from Liverpool University.

Chris Tyson is currently employed as a Technical Consultant with Landmark Graphics EAME. In the 16 years Chris has been working in the oil and gas exploration industry, he spent 14 years with Seismograph Services Ltd. working in Peru, Libya, Oman and Norway. Chris has a very broad understanding of the seismic exploration business having worked under contract for companies such as Shell, BP, Elf Aquitaine and a number of small independents. Chris graduated with a BSc (Honors) in Geophysics at Southampton University.

Investigation of Hydrocarbon Productivity Variations in Ilam Reservoir of the Sirri Fields

Vasseghi, Behrooz

National Iranian Offshore Oil Company, Iran (previously)

Through ten years of exploration in the Sirri region of the Gulf, the Ilam horizon (Santonian-Campanian) of the Upper Cretaceous was found to be oil-bearing in shallow marine chalky limestone of Sirri A, C, D, E and North Fateh (Nosrat) fields. Whereas production is from only one well in Sirri A, recognition of this anomaly is vital to explorers in the Gulf. The reasons for this phenomenon which depends on lithostratigraphic positions, salt diapirism, lateral migration of the structure paleotops, differential erosions, will be demonstrated in this paper.

3-D Symmetric Sampling in Land Data Acquisition

Vermeer, Gijs J.O.

Shell Research BV, The Netherlands

In the course of time numerous different geometries have been devised for acquisition of 3-D seismic data. Many of these geometries can be classified as either patch or line geometries. Patch geometries use shots or receivers in an areal arrangement, whereas line geometries deploy shots and receivers along separate acquisition lines. The various geometries can be subdivided into single-fold 3-D subsets. The spatial continuity provided by these subsets can be exploited optimally, if the subsets are properly sampled, and if their extent is maximized. These requirements lead to an extension of the 2-D symmetric sampling criteria to 3-D. The 2-D symmetric sampling criteria are based on the properties of the seismic wavefield in the common-shot gather, combined with the reciprocity principle. For 3-D symmetric sampling, the 2-D criteria - equal shot and receiver intervals, and equal shot and receiver patterns - apply similarly, but have to be extended with additional criteria dependent on the type of line geometry. The additional criterion for the orthogonal geometry is to acquire as many shots in the common-receiver gathers as receivers in the common-shot gathers. 3-D symmetric sampling provides a starting point for the design of 3-D acquisition geometries. It strips the design of nominal 3-D surveys from its apparent complexity. Pre-stack seismic processing, such as dual-domain fk-filtering, benefits from the better spatial continuity offered by 3-D symmetric sampling.

Gijs J.O. Vermeer received his MSc in Applied Mathematics from the Technology University of Delft in 1965. After military service he joined Shell, where he worked in seismic processing and seismic inter pretation, both in research and operations. Since 1991 he has been in research working on seismic data acquisition techniques. Gijs is the author of “Seismic Wavefield Sampling” published by SEG in its Geophysical Reference Series. His main interest is the interrelationship between seismic data acquisition and seismic data processing. He is a member of the EAEG, SEG and CSEG.

Behrooz Vasseghi has 28 years of experience with the oil industry of the Iranian Government. He is currently completing his PhD in Geology with the University of Tehran, Iran.

Preserved Amplitudes in 3-D Seismic Acquisition and Processing for Stratigraphic Interpretation

Vuillermoz, Claude A.*, Denis Mougenot

Compagnie Générale de Géophysique, France and

Philippe Lamant

Compagnie Générale de Géophysique, Bahrain

For 3-D land surveys using cross-spread acquisition, the azimuth and offset distribution have significant variations from one bin to the next. This heterogeneity will have an undesired effect on final amplitudes. It is therefore mandatory to study the trace distribution derived from a near optimum set of 3-D grids suggested by geological and economic criteria. The effect of the geometry may be tested as a whole or in a bin-to-bin mode. For near regular types of acquisition, it is possible to define an elementary generating pattern, representative of the whole 3-D grid: the smaller this generating pattern, the less heterogeneous the geometrical distribution of the traces. Taking into account the real offset distribution, it is then advantageous to use well sampled 2-D data to simulate a 3-D stack section to observe the effect of the acquisition irregularities at the target level. During acquisition, variable attenuation in the weathering zone and coupling changes of the source and receivers may impact the amount of energy recorded. The relative amplitudes are no longer representative of the sub-surface reflectivity. A 3-D PAM processing sequence is designed to correct these surface related variations: (1) an amplitude decomposition in source and receiver modes compensates for surface effects; (2) a surface consistent deconvolution compensates for differential attenuation in the frequency domain. After final processing, the seismic depicts the true reflectivity to be used for a meaningful stratigraphic interpretation.

Claude A. Vuillermoz is currently the Chief Geophysicist Corporate Technical Advisor with CGG. He has spent over 30 years with CGG. Claude was Party Chief in Europe, Indonesia, Africa, Canada, and a member of technical management. Claude holds a Doctorate in Geology from the University of Grenoble, a degree in Engineering from ENSPM, and a MSc from the Universlty of Lyon. He has contiibuted to numerous publications and is a member of the SEG, EAEG, AAPG DGS and HGS.

Denis Mougenot (see Mougenot et al., p. 175)

Philippe Lamant is currently Manager of the CGG Processing Center, Bahrain. He has spent his entire 15-years career with CGG. His experience includes operations in Europe, China and Turkey, in acquisition and processing. Philippe holds an Engineering degree from the Geology School of Nancy, France.

Distribution of Porosity and Permeability in a Complex Carbonate Reservoir: Application of Permeability Prediction Techniques at Southwest Andrews Oil Field, Permian Basin, West Texas

Walden, Skip F.*

Unocal Corporation, USA

and Yoshiro Ishii

Japan National Oil Corporation, Bahrain

Comprehensive wireline logging suites were acquired in 3 wells at Southwest Andrews oil field in the Permian Basin of West Texas. Each well penetrated approximately 335 meters (1,100 feet) of Permian age Wolfcamp Formation and Pennsylvanian age Cisco, Canyon, and Strawn formations. This predominantly limestone interval has a complicated porosity and permeability distribution, with approximately 10% of the total section being producible reservoir (porosity is greater than 4%; permeability is greater than 1 millidarcy). For a given porosity, permeability values can range over 3 orders of magnitude. Estimating the porosity and permeability distribution from wireline logs is critical to the successful development of this reservoir. Each of these wells has a complete core through the reservoir section, allowing wireline logging results to be compared to known porosity and permeability distributions. Seven wireline logging techniques were evaluated: (1) Porosity-Permeability Regression, (2) Multivariate Histogram, (3) Flow Zone Indicator, (4) Principal Component Regression, (5) NML Logging, (6) Acoustic Stoneley Wave Attenuation, and (7) Neural Network. Permeability estimates from the Multivariate Histogram and the Neural Network techniques have the closest match to the core measurements.

Skip F. Walden is a Geophysicist in the Reservoir Technologies Group of Unocal. His responsibilities include specialized log analysis, borehole geophysics, and 3-D reservoir models. Skip has worked for Unocal 14 years in the areas of seismic attribute analysis, fracture and porosity prediction using seismic shear waves, and permeability prediction from wireline logs. He has a BSc in Earth Science from the University of California, Fullerton, with minors in Math and Physics.

Yoshiro Ishii (see Ishii et al., p. 151)

Recent Developments in 3-D Seismic Acquisition Techniques in Oman

Wams, Jan* and Justus Rozemond

Petroleum Development Oman

Acquisition of 3-D seismic surveys in Oman commenced in 1984 (Suwaihat). The results were disappointing, probably due to the acquisition technique and low fold. Continuous acquisition of 3-D surveys was not started until 1987, with a total of some 20,000 square kilometers recorded to date. Improvements have been made over the years in small steps. The maximum offset increased from 1,600 to (standard) 4,400 meters, the fold from 16 to (standard) 60, a much improved stack operator due to the double zig-zag technique and most recently the introduction of shifted double zig-zag for better ground roll suppression. In early 1994 a study was carried out to try and further improve data quality and efficiency. The approach to find alternatives to the current acquisition techniques was two fold: (1) try to find improvements to the double zig-zag technique which satisfy the above constraints; and (2) try to find different acquisition geometries which give better and/or cheaper data. A number of possible improvements, both geophysically and economically, on the current double zig-zag were identified and evaluated on cost. Of the alternative acquisition geometries a number of possibilities were identified which were either attractive in cost or could provide higher resolution. A number of these proposals have been the subject of PDO‘s yearly Eid tests.

Jan Wams graduated in 1975 from the University of Delft in Medical Acoustics. He was drafted into the Dutch Army in early 1976 where he researched laser- and night-vision equipment. Jan joined Shell in 1978 and shortly after was transferred to the UK to take up a position in sesmic data processing, followed by postings in Thailand and Brunei as a Seismic Interpreter. Jan was transferred back to Holland in 1988 to head the Land Acquisition group, followed by a posting to Yemen as Chief Geophysicist. After a further year in Holland as an advisor on acquisition matters, he joined PDO in 1993 to head the geophysical operations department.

Justus Rozemond graduated in 1988 from the University of Utrecht in Geophysics. He completed his education in Hydrocarbon Exploration at the IFP (1990). In the same year Justus joined Shell Internationale Research Maatschappij. He worked on seismic acquisition in the Shell EP Research Laboratory in Holland until 1994, after which he was posted to Oman, where he now works as an Operations Geophysicist for Petroleum Development Oman.

Rift Basin Sequence Stratigraphy: Some Examples from the Gulf of Suez

Wescott, William A.* and William N. Krebs

Amoco Production Company, USA John C. Dolson

Salah A. Karamat

GUPCO, Egypt Dag Nummedal

Louisiana State University, USA

Unconformity-bounded sequences within the Miocene strata of the Suez Rift reflect a complex interplay between tectonism and sea level fluctuations. Analyses of Miocene outcrops along the Sinai margin of the Gulf of Suez have provided some new insights into the sequence stratigraphy of this basin. The Miocene strata can be subdivided into seven major sequences separated by biostratigraphically defined time breaks. These lacunae represent depositional sequence boundaries, transgressive surfaces, and condensed sections. Formation of these basin-wide time breaks was related to major tectonic events in the evolutionary history of the basin from rift initiation through rift climax, and post-rift stages. These events include regional sag and fault initiation, fault linkage, footwall uplift, and thermal subsidence.

Superimposed on this complex structural evolution were Miocene sea level fluctuations of a magnitude of several tens of meters to a hundred meters. The Sinai outcrops expose the four oldest Miocene biostratigraphic sequences. In general, they represent the following depositional history: within the overall transgressive Nukhul Formation, the lower order events are recorded as local erosional surfaces, flooding surfaces, and ravinements. The Mheiherrat Formation was deposited during a relative high stand followed by low stand deposition of the Asl Formation. Another high stand resulted in the progradational Ras Budran Formation.

William A. Wescott received his undergraduate degree from Franklin and Marshall College in 1972. After serving in the U.S.Army he received a MSc from Southern Illinois University-Carbondale in 1976 and a PhD from Colorado State University in 1979. He joined Amoco Production Company in Houston in 1979 where he has worked on a variety of domestic and international assignments. His present assignment is with Amoco‘s Egypt Exploration Team.

William N. Krebs has a BSc in Geology from the University of California in Los Angeles and a PhD from the University of California in Davis. He joined Amoco Production Company in Denver, Colorado in 1978 where he worked as a micropaleontologist/stratigrapher in domestic exploration. Since 1987, he has worked for Amoco in Houston, Texas in a similar capacity for international exploration. His specialty is siliceous microfossils, and he is particularly interested in fossil continental diatoms and applications of graphic correlation to exploration.

John C. Dolson received his undergraduate degree from Colorado College and has a MSc in Geology from Colorado State University. He joined Amoco in 1980 and has worked on a variety of domestic and international exploration projects in Denver and Houston. John is presently an Exploration Geologist with the Gulf of Suez Petroleum Company in Cairo, Egypt.

Salah A. Karamat received his BSc in 1975 and MSc in 1987 in Geology from Cairo University. In 1995 he completed the requirements for a PhD in Geology from the same institution. He has been employed as an Exploration Geologist with the Gulf of Suez Petroleum Corporation in Cairo, Egypt since 1977.

Dag Nummendal was born in Norway and educated at the Universities of Oslo and Illinois.Since 1978, he has been a Professor of Geology at Louisiana State University, Baton Rouge, where he specializes in rift basin tectonics and sedimentation, sequence stratigraphy, and shallow marine and lacustrine depositional systems. His current rift basin research focuses on the Paleogene rifts of Eastern China and the Miocene of the Gulf of Suez.

Resolution of Water Influx Patterns Through Application of Multi-disciplinary 3-D Reservoir Modeling

Wigley, Paula L.*, David Masson, Jerry C.W. Hadwin* and Richard W.A. Keech

Petroleum Development Oman (PDO)

The Sayyala field is located in Oman, some 530 kilometers southwest of Muscat. The oil accumulation lies in the fluvial sediments of the Permian Upper Gharif Formation, at a depth of around 1,200 meters. The penultimate primary grid location was drilled as a horizontal well in 1993 and produced only water when tested, despite continued oil production from nearby vertical wells. A field review and multi-disciplinary 3-D reservoir modeling project was therefore started in late 1993, primarily to resolve the incoming water pattern and to assess the possibility of locating bypassed oil through infill drilling.

A number of 3-D geological realizations were built using a probabilistic modeling package and subsequently 3-D reservoir property models were constructed based on revised petrophysical parameters for each of the modeled facies. The resultant geological and property models led to a re-evaluation of oil in place distribution in the field. A number of reservoir simulations were carried out using the 3-D geological and property models as input. A “simulation prover” will be drilled in 1996 in order to test the integrity of the models and the applicability of probabilistic modeling for location of remaining reserves in complex fluviatile reservoirs. A plan for further field activity will be compiled based on the results of the 3-D modeling, simulation study and the test well.

Paula L. Wigley is a Production Geologist with Petroleum Development Oman. She has 12 years of operational and research experience with Shell, located in Turkey and Holland prior to moving to Oman. She is a member of the AAPG and holds a BSc in Geology from Exeter University.

David Masson is a Senior Reservoir Engineer with Petroleum Development Oman. He has 16 years of production and exploration experience with Shell, variously located in The Netherlands, Malaysia and Denmark prior to moving to Oman. He is a member of the SPE and holds a MEng degree in Petroleum Engineering from Heriot-Watt University.

Jerry C.W. Hadwin is a Reservoir Engineer with Petroleum Development Oman. He has 12 years of production and exploration experience with Shell, located in Aberdeen and North Holland prior to moving to Oman. He is a member of the SPE and holds a MEng degree in Petroleum Engineering from Heriot-Watt University.

Richard W.A. Keech is a Senior Petrophysicist with Petroleum Development Oman. He has 15 years of production and exploration experience with Shell, located in Oman, United Kingdom and The Netherlands, prior to returning to Oman. He is a member of the SPE and holds a BSc in Geology/Geophysics from the University of Durham.

Separation of In Plane Multiples from Out of Plane Primaries Using 3-D Pre-stack Time Migration

Williams, Richard G.* and Nicholas J. Cooper

Digicon Geophysical Limited, UK

In a V(z) medium where velocity increases with depth, out of plane primaries can easily be confused with in plane multiples on CDP gathers. Depending on the velocity gradient and their dip, out of plane primaries may be either over corrected, flat or under corrected after NMO with the RMS velocity of the medium. This anomalous behavior makes them very hard to identify and interpret on velocity analyses. Application of constant velocity DMO removes the dip component of the stacking velocity in the shot-receiver direction and, in general, leaves the out of plane primary under corrected at all in-line dips. Thus, its behavior on a velocity analysis is very similar to that of a multiple. Application of 3-D pre stack (zero-offset) time migration after DMO collapses the out of plane energy to its true location. The confusing out of plane energy is removed from CDP gathers for velocity analysis, thus allowing clearer identification and separation of primaries and multiples. This separation of primaries and multiples has been analyzed on 3-D synthetic data. It has been applied successfully to real data from a 3-D marine survey in an area where low relief carbonates generate strong multiples.

Richard G. Williams received his PhD from Southampton University in 1979. He has worked for Digicon since 1981 as a Research Geophysicist. From 1985 to 1987 he was Research Manager for Digicon‘s Far East Division and is currently Research and Marketing Manager for Europe, Africa and Middle East division of Digicon.

Nicholas J. Cooper received a BSc (Honors) in Geophysics from Leicester University in 1981. Since then he has worked in seismic data processing in a number of locations worldwide, most recently as Technical Supervisor in Digicon‘s Jakarta processing center. He is currently a member of Digicon‘s UK-based Research Group.

Data Management: The Key Enabler For IT In Exploration and Production

Wilson, Hamish

Paras, UK

Computer applications and database software have advanced considerably over these last few years. A complete range of tools is available to help the explorer be more effective. But the industry is still having problems making use of computer technology. The root of the problem is data management. Current industry practices are geared to dealing with hard copy and paper data. We have not designed the systems to cope with digital data. This paper explores the problems and presents some approaches to implementing solutions.

The implementation of computer technology occurred at a time of significant cost reduction in the industry. The increasing use of digital data is part of the reason to reduce the staffing in hard copy data management. There is still a great need to provide and manage the digital data used and generated by interpretation software. These facilities have not been provided for. Hence most companies are wasting significant parts of their investments in IT as the interpretation systems are not being used due to lack of data.

A data management infrastructure is needed to deliver data and manage interpreted data. This must involve the following: (1) the definition of user responsibility for digital data; (2) the definition of roles and responsibilities for data management services; and (3) the provision of technology to allow project and interpretive data to be captured and retrieved. A service supplier and user relationship should be established between exploration users and their data management support staff. In doing the analysis for setting up this relationship, it may be appropriate to consider outsourcing data management. It is a non-core activity and the company may not have the skills in-house to provide an effective service in the changing environment. Data management is a fundamental requirement to enable the effective use of a company‘s softwareapplication suite. Without the mechanisms to deliver data to workstations and manage the resultant interpretations, a company is wasting the investment in computer technology.

Hamish Wilson is Director of Paras Limited, a consultancy founded in 1994 which specializes in strategic technology management. Hamish worked for 10 years with BP in exploration and production geology and corporate database development. In 1989 following an MBA from IMD in Switzerland, he became a consultant in the field of information management.

Through-Tubing Well Seismic: A Mast Campaign Across an Offshore Producing Field

Yamaguchi, Kaoru, Arabian Oil Company, Saudi Arabia

and Bernard G. Frignet*, Schlumberger Middle East, Saudi Arabia

3-D seismic is gaining popularity in the Gulf region for fault delineation and the goal of improving ultimate recovery of mature reservoirs. Valuable integration of the 3-D with other reservoir data requires well seismic data (VSP‘s or Check Shots) to establish a good tie at key wells. When little well seismic data is available, it is possible to acquire VSP‘s in newly drilled and worked-over wells. This paper demonstrates the feasibility of another strategy, by recording well seismic Through-Tubing.

Well seismic Through-Tubing had been proven feasible in the Gulf region on a single well basis. In this paper we describe a VSP-through tubing campaign with an objective to survey two neighboring mature fields totaling more than 200 wells. Following a close cooperation between reservoir engineers and geophysicists, 9 candidate key wells were selected on the basis of: (1) spatial distribution; (2) previous well data availability; and (3) completion type. At the planning stage and excluding night work for safety, it was estimated that 3 days would be required per well (1 day to rig-up mast, 1 day to acquire seismic data, 1 day to rigdown). Local experience indicated that a single airgun would be a convenient surface source. A slim hole monocable single axis geophone sonde was selected as the downhole seismic tool. The zero-offset VSP configuration, with 80 foot level spacing from bottom-hole to surface was adopted. A supply boat was dedicated for the duration of the campaign. The actual operation was completed in 24 days, 3 days earlier than planned. An average of 90% of the VSP levels were found suitable for first break detection, which provided accurate time-depth curves at all 9 wells. Geophone coupling quality isdependent on the Tubing-Casing contact, and tube wave is present at all 9 wells, but overall 80% of the levels were selected by VSP processing. In 5 wells where sonic had been logged, synthetic seismograms were generated and confirmed the validity of VSP reflections. The data is now integrated in a 3-D velocity model.

Kaoru Yamaguchi is currently Geophysicist with Arabian Oil Company, Saudi Arabia. He received his BSc and MSc degrees in Geophysics from Hokkaido University, Japan. Kaoru started his career with AOC in 1988, and held various assignments in the Far East before coming to the Middle East in 1994. He is a member of the SEG, EAEG and SEG Japan.

Bernard G. Frignet is Interpretation-Development Geophysicist with Schlumberger Wireline and Testing in Al-Khobar, Saudi Arabia. He graduated from Ecole des Mines de Paris in 1975 and has a degree in Geophysics from IFP. He started his career with Bureau de Recherches Geologiques et Minieres in Orleans, France and joined Schlumberger in 1982. Bernard has held various assignments in North Africa and the Far East before coming to the Middle East in 1990. Bernard is a member of the SPE and SEG and has published several papers in the field of VSP and sonic interpretation.

Application of Neural Networks and Geostatistical Approach for Reservoir Characterization

Yoshioka, Katsuhei*, Nobusuke Shimada

Technology Research Center of Japan National Oil Corporation, Japan and Yoshiro Ishii

Middle East Representative Office of Japan National Oil Corporation, Bahrain

Geostatistics is recognized as the most powerful tool for reservoir characterization, integrating geological, geophysical and reservoir engineering data. In general, the information derived from well data is precise but sparsely located for reservoir characterization. In such cases, seismic data are useful because they are uniformly distributed. However, it is a disadvantage of seismic data that its relationships to reservoir properties are still not clear because of its limitation of frequency band width, low S/N ratio, and ambiguous physical relationships to reservoir properties. Thus, the relationships vary with region and with depth.

In order to deal with such an ambiguous relation, geostatistical techniques, such as cokriging and co-simulation, can integrate well data and seismic data in order to estimate the spatial distribution of reservoir properties. Especially, the co-simulation technique reproduces the equi-probable multi-realizations of the distribution.

This paper introduces the case study of reservoir characterization in an actual oil field. More than 20 attributes were extracted from 3-D seismic data. Since each of these attributes has only weak correlation to reservoir parameters, the approach of neural networks was considered for application in order to obtain a strong relationship between seismic attributes and reservoir parameters from the well log data. After which, we estimated the spatial distributions and their uncertainties using geostatistical methods.

We also discuss validation and problems of the approach, which is the combination of neural networks and geostatistics, using blind tests by hiding some well data.

Katsuhei Yoshioka has 4 years of exploration experience of which one year was with JAPEX Geoscience Institute Ltd. and 3 years with Japan Petroleum Exploration Co. Ltd. He has been working at the Technology Research Center of Japan National Oil Corporation since 1993. Katsuhei has a BSc in Geophysics and a MSc in Seismology from Kyoto University.

Nobusuke Shimada received his BSc (1983) and MSc (1985) in Geophysics from Tohoku University, Japan. Since joining Japan National Oil Company in 1985, he has been working in project evaluations and geophysical surveys for Japanese and overseas projects. Nobusuke is currently an Assistant Director of Geophysical Laboratory in Technical Research Center of JNOC. His current interests are reservoir geophysics and reservoir characterization.

Yoshiro Ishii (see Ishii et al., p. 151)

Identifying Hidden Reserves Through Visualization Technology Application

Zeitlin, Michael J.

Texaco Exploration and Production, USA

Most oil fields have reserves which are “hidden” from the well drilled to produce them. These untapped compartments could yield upwards of 50% additional reserves throughout an oil field‘s commercial life. 3-D seismic and 3-D visualization technology can help identify these additional zones by providing data at a much finer scale than was possible using 2-D technology.

Conventional approaches to seismic data analysis involved seismic line by seismic line examination of structural detail. Using 3-D seismic volumes, such 2-D examination of data is very time consuming and difficult. Data examined in cross section often misses subtle oil containing compartments. 3-D volume rendering, however, allows for very quick examination of all the data collected. Pattern recognition programs help the eye see compartments in 3-D data. Using 3-D visualization techniques, these patterns can be revealed and related to the geologic model necessary for efficient production. 3-D seismic analysis normally taking 6 weeks to complete is routinely done in less than a few days and with higher accuracy.

Michael J. Zeitlin has been a Portfolio Manager at Texaco since 1994 in Integrated Reservoir Information and Visualization Technology. He has held previous leadership positions with Texaco since 1980 in expert systems design, computer aided exploration and hydrogeology. Over the past 6 years, Michael has been the driving force behind Texaco‘s effort to acquire, develop and deploy visualization technology throughout Texaco‘s business units. He led the effort to develop the first commercial installation of a global standards database tied to visualization and reservoir characterization. He has received Texaco‘s Outstanding Contributor Award in 1993 and again in 1995 and has received other Texaco awards for bottom-line contribution. Before joining Texaco, Michael received a BSc and MSc degrees in Earth Science and Marine Science from the State University of New York at StonyBrook. He is an active member of the AAPG and the Institute of Electrical Engineers' Computer Society.

Silurian-sourced Oils from the Arabian Plate

Zumberge, John E.* and Folke C. Johansson

Geo Mark Research, Inc., USA

Crude oils from the Arabian Plate generated from Silurian source rocks were identified using stable carbon isotope composition and distributions of sterane and terpane biomarkers. Principal component and cluster analyses aided in distinguishing oils sourced from Silurian shales versus various Mesozoic carbonate-sourced oils and crudes from Eocene marine shales. Silurian-sourced oils from Saudi Arabia (reservoired mostly in Permian clastics) are isotopically light (-30 to -31‰; C15+ saturate hydrocarbon fractions) while Upper Jurassic carbonate oils are 2 to 3‰ more positive. Eastern Turkey Silurian oils (reservoired in Turonian carbonates) are about 0.5‰ more positive than Saudi Arabian Silurian oils. Although Silurian oils contain low concentrations of biomarkers due to age and thermal maturity, their marine shale origin is demonstrated by high rearranged to regular sterane ratios, tricyclic terpane distributions typical of marine shales, and relatively high diahopane to hopane ratios. Turkish Silurian-sourced oils are less thermally mature than the Saudi oils as illustrated by both absolute biomarker concentrations and maturity-sensitive terpane ratios. Permian-reservoired condensates from Bahrain appear to have been derived from very mature Silurian sources based primarily on carbon isotope composition since biomarkers have been thermally degraded. Some oils from west central Oman and eastern Jordan also were generated from Silurian shales. A few Saudi Arabian fields such as Abu-Jifan, Qirdi, and Ghawar contain both Silurian oils in deeper reservoirs and Jurassic carbonate oils in shallower reservoirs. It is likely that Sharar and Faridah fields contain oils of mixed Silurian shale and Upper Jurassic carbonate origin in Middle Jurassic reservoirs. Other Upper Jurassic fields may contain a small percentage of Silurian oil. Some eastern Turkey fields also contain oils of mixed Cretaceous carbonates and Silurian shale origin.

John E. Zumberge received his BSc in Chemistry from the University of Michigan and his PhD in Geosciences from the University of Arizona in 1976. He was a Research Associate in the Laboratory of Organic Geochemistry at the University of Arizona from 1976 to 1979. From 1979 to 1985 he was employed by Cities Service/Occidental Oil Company where he served as Research Geochemist, Manager of Geochemical Research, and Manager of Geological Research. In 1986 he joined Ruska Laboratories in Houston as Vice President and General Manager. He was Director of Geochemistry for Core Laboratories until 1991 when he co-founded GeoMark Research, a company specializing in regional crude oil studies.

Folke C. Johansson received a BSc, MSc and PhD in Geology from the University of Wisconsin - Madison. After several years with Texaco working in the US Gulf Coast he transferred to Aramco where he spent 17 years in various exploration positions including Chief Geologist and Manager of Geology. In 1982 he formed Arabian Gulf Exploration Consultants, Inc. (AGECON) and has since been involved in numerous studies and exploration activities covering the entire Arabian Plate.

1.
TOTAL operator, in association with KUFPEC, UNOCAL and COMPLEX.
2.
TOTAL then HUNT operator, in association with YCIOM (Yemen Company for Investment in Oil and Minerals), EXXON, KUFPEC and TECHNOEXPORT.