Abstract The US Geological Survey (USGS) recently assessed the potential for undiscovered oil and gas resources of the East Barents Basins and Novaya Zemlya Basins and Admiralty Arch Provinces as part of the USGS Circum-Arctic Resource Appraisal. These two provinces are located NE of Scandinavia and the northwestern Russian Federation, on the Barents Sea Shelf between Novaya Zemlya to the east and the Barents Platform to the west. Three assessment units (AUs) were defined in the East Barents Basins for this study – Kolguyev Terrace Assessment Unit (AU), South Barents Basin and Ludlov Saddle AU, and North Barents Basin AU. A fourth, defined as Novaya Zemlya Basins and Admiralty Arch AU, is coincident with the Novaya Zemlya basins and Admiralty Arch Province. These AUs, all lying north of the Arctic Circle, were assessed for undiscovered, technically recoverable resources resulting in total estimated mean volumes of approximately 7.4 billion barrels of crude oil, 318 trillion cubic feet of natural gas and 1.4 billion barrels of natural gas liquids.

Abstract The Siberian Craton consists of crystalline rocks and superimposed Precambrian sedimentary rocks deposited in rift basins. Palaeozoic rocks, mainly carbonates, were deposited along the margins of the craton to form an outwardly younger concentric pattern that underlies an outward-thickening Mesozoic sedimentary section. The north and east margins of the Siberian Craton subsequently became foreland basins created by compressional deformation during collision with other tectonic plates. The Tunguska Basin developed as a Palaeozoic rift/sag basin over Proterozoic rifts. The geological provinces along the north and east margins of the Siberian Craton are immature with respect to exploration, so exploration-history analysis alone cannot be used for assessing undiscovered petroleum resources. Therefore, other areas from around the world having greater petroleum exploration maturity and similar geological characteristics, and which have been previously assessed, were used as analogues to aid in this assessment. The analogues included those of foreland basins and rift/sag basins that were later subjected to compression. The US Geological Survey estimated the mean undiscovered, technically recoverable conventional petroleum resources to be approximately 28 billion barrels of oil equivalent, including approximately 8 billion barrels of crude oil, 103 trillion cubic feet of natural gas and 3 billion barrels of natural gas liquids.

Abstract Geological features of NE Greenland suggest large petroleum potential, as well as high uncertainty and risk. The area was the prototype for development of methodology used in the US Geological Survey (USGS) Circum-Arctic Resource Appraisal (CARA), and was the first area evaluated. In collaboration with the Geological Survey of Denmark and Greenland (GEUS), eight ‘assessment units’ (AU) were defined, six of which were probabilistically assessed. The most prospective areas are offshore in the Danmarkshavn Basin. This study supersedes a previous USGS assessment, from which it differs in several important respects: oil estimates are reduced and natural gas estimates are increased to reflect revised understanding of offshore geology. Despite the reduced estimates, the CARA indicates that NE Greenland may be an important future petroleum province.

Abstract The Siberian craton consists of crystalline rocks and superimposed Precambrian sedimentary rocks deposited in rift basins. Palaeozoic rocks, mainly carbonates, were deposited along the margins of the craton to form an outwardly younger concentric pattern that underlies an outward-thickening Mesozoic sedimentary section. The north and east margins of the Siberian craton subsequently became foreland basins created by compressional deformation during collision with other tectonic plates. The Tunguska Basin developed as a Palaeozoic rift/sag basin over Proterozoic rifts. The geological provinces along the north and east margins of the Siberian craton are immature with respect to exploration, so exploration-history analysis alone cannot be used for assessing undiscovered petroleum resources. Therefore, other areas from around the world having greater petroleum exploration maturity and similar geological characteristics, and which have been previously assessed, were used as analogues to aid in this assessment. The analogues included those of foreland basins and rift/sag basins that were later subjected to compression. The US Geological Survey estimated the mean undiscovered, technically recoverable conventional petroleum resources to be c. 28 billion barrels of oil equivalent, including c. 8 billion barrels of crude oil, 103 trillion cubic feet of natural gas, and 3 billion barrels of natural gas liquids.

Abstract Reserve growth is the net increase in estimated recoverable resources of an oil or gas field or group of fields through time. This phenomenon is important in North Sea oil fields and is observed in all classes of reservoirs and in all country sectors. Oil fields with chalk reservoirs have exhibited particularly large increases in estimated recoverable reserves. Whereas chalk reservoirs contain only about 16% of recoverable North Sea oil, almost one third of the growth of reserves in existing fields has been in fields with chalk reservoirs. More than 60% of the currently reported recoverable oil (cumulative production plus remaining reserves) in chalk fields is attributed to reserve growth since 1985. In contrast, only about 34% of recoverable oil in all North Sea fields (chalk and clastic reservoirs) is from reserve growth. The large increase in estimated recoverable resources in the chalk reservoir fields of the North Sea results from both increases in estimated original oil in place and from improvements in recovery efficiency. Although the largest fields generally display the greatest volumetric additions to reserves, on a percentage basis reserves in small fields increase as much as reserves in larger fields. So far, growth of reserves in the chalk fields has been directly proportional to development effort, as indicated by numbers of wells drilled for delineation, development and improved recovery (including injector and observation wells). In spite of great improvements in understanding chalk reservoirs, estimates of original oil in place are still uncertain and overall recovery factors remain relatively low. Therefore, opportunity remains for further large additions to reserves in chalk reservoir fields. The experience of operators of the North Sea chalk fields indicates that large, complex accumulations with difficult reservoir engineering problems may present possibilities for additional oil recovery in such fields elsewhere.

Abstract The U.S. Geological Survey (USGS) recently assessed potential volumes of undiscovered technically recoverable conventional oil, natural gas, and natural gas liquids (NGL) of the world, exclusive of the United States (USGS, 2000). Using a geology based methodology, the USGS defined 149 total petroleum systems (TPS) and 246 assessment units (AU) in 128 oil and natural gas provinces worldwide, and quantitatively assessed undiscovered resources in each of the 246 AU. This assessment provides estimates of the quantities of conventional, technically recoverable oil, natural gas, and natural gas liquids, exclusive of the United States, that have the potential to be added to reserves in the next 30 yr (1995 to 2025). These amounts include estimates of undiscovered volumes and the estimated volume of reserve growth for discovered fields. The assessment results are shown in Table 1 , and are summarized as follows: a mean of 649 billion bbl of undiscovered conventional oil with a range of 344–1107 billion bbl of oil; a mean of 4669 tcf of conventional natural gas with a range of 2299–8174 tcf, and a mean of 207 billion bbl of natural gas liquids with a range of 95–378 billion bbl of NGL, exclusive of resources in the United States. Adding these assessment results to estimates of undiscovered oil and natural gas resources of the United States, the cumulative production, remaining reserves, and reserve growth of provinces throughout the world, a total world endowment of conventional oil resource, was estimated by the USGS to be about 3 trillion barrels

Abstract Fossil fuels will remain an important source of energy for much of this century under most energy projections, although their abundance and potential shortages are debated. Their distribution, quantities, and availability will thus continue to be of paramount importance for world economies. Policy decisions made in the U.S. and elsewhere depend on detailed knowledge of petroleum resources and their distribution in the world. Therefore, petroleum resources are periodically reassessed, not just because new data become available and better geologic models are developed, but also because many non-geologic factors such as technologic advances, accessibility to markets, and geographic or societal constraints determine which part of the crustal abundance of petroleum will be economic and acceptable throughout some foreseeable future. Detailed petroleum information was published in a recent world assessment of petroleum resources conducted by the U.S. Geological Survey (USGS) in their World Petroleum Assessment (WPA) 2000 (USGS, 2000). Two major components of world petroleum resources exclusive of the United States were assessed by the U.S. Geological Survey (USGS, 2000): undiscovered conventional resources and reserve (field) growth. This assessment provided estimates of the quantities of conventional technically recoverable oil, natural gas, and natural gas liquids (NGL), outside the United States, that have the potential to be added to reserves (Table 1). Many individuals and groups, such as the International Energy Agency (IEA 2000, 2001, 2002) and the Energy Information Administration of the Department of Energy (EIA, 2000, 2001a,b), Cavallo (2002), and Greene et al. (2003) use the USGS (2000) study as

Abstract Volumes (statistical mean estimates) of undiscovered conventional oil, natural gas, and NGL (exclusive of the U.S.) as assessed in USGS (2000) are: Â∈¢ 649 billion bbl of oil (Figure 9) Â∈¢ 4669 tcf of natural gas (778 billion BOE) (Figure 10) Â∈¢ 207 billion bbl of natural gas liquids (NGL) (Figure 11) Table 1 summarizes the estimates of the ranges of volumes of undiscovered conventional oil, natural gas, and NGL for the world both exclusive and inclusive of U.S. petroleum resources. Lognormal probability distributions for the three commodities, exclusive of the U.S., are shown in Figures 9, 10, and 11. These estimates demonstrate that a significant volume of undiscovered petroleum is yet to be found in the world. The estimates of undiscovered resources of individual assessment units were aggregated into TPS, provinces, regions, and finally the world. Perfect positive dependency among estimates was assumed at the AU, TPS, province, country, and region levels. In aggregating the eight region-level sets of estimates to the world level, a positive dependency of 0.5 was assumed. Dependencies assumed for aggregations are described in USGS (2000) by Charpentier et al. (2000).

Abstract Reserve growth refers to the increases, in estimated sizes of discovered fields, that can occur through time as oil and natural gas fields are developed and produced. In the U.S., which is one of the most intensely explored countries in the world, reserve growth is widely considered to be a major component of remaining oil and natural gas resources ( Arrington, 1960 ; Root and Mast, 1993 ; Attanasi and Root, 1994 ; Root et al., 1995 ; Schmoker and Attanasi, 1996, 1997; Attanas and Schmoker, 1997; Attanasi et al., 1999 ; Verma, 2000; Klett, 2003; Klett and Schmoker, 2003 ). A forecast of world potential reserve growth was therefore a necessary element of the World Petroleum Assessment 2000 (USGS, 2000). The forecast (Table 1) shows that the estimated potential additions to reserves from reserve growth are nearly as large as the estimated undiscovered resource volumes ( Schmoker and Klett, 2000 ). Unlike World Petroleum Assessment 2000 (USGS, 2000), allocations of the world reserve growth were made in this study for the eight regions of the world for liquid petroleum, oil and natural gas liquids, ( Figure 30 ), and natural gas ( Figure 31 ). Reserve growth refers to the increases, in estimated sizes of discovered fields, that can occur through time as oil and natural gas fields are developed and produced. In the U.S., which is one of the most intensely explored countries in the world, reserve growth is widely considered to be a major component of remaining oil and natural gas resources ( Arrington, 1960 ; Root and Mast, 1993 ;

Abstract Although there have been individual analyses of source rock intervals and some elements of the total petroleum system ( Klemme, 1986 ; Tissot et al., 1987; Klemme and Ulmishek, 1991 ; Perrodon, 1992 ; Magoon and Dow, 1994), the USGS (2000) study of world TPS provides many new geologic insights, petroleum volumes associated with the TPS, and a significant database for further studies. Some of these insights are discussed briefly for the elements of the TPS, and supporting data are shown in a series of Figures, maps, and Appendices. In this study a large body of geologic information was assembled and synthesized for the TPS of the world included in the assessment. Eight geologic parameters from the geologic summaries for each of the assessment units (AU) were recorded in a spreadsheet (Appendix 4) and for each TPS (an aggregation of AU into their TPS) in Appendix 5. The geologic parameters are (1) source rock age, (2) source rock character, (3) peak maturation age, (4) reservoir rock age, (5) reservoir rock deposi- tional environment, (6) reservoir rock lithology, (7) seal lithology, and (8) trap type. The data from the eight geologic parameters were examined in terms of frequency of occurrence in the world TPS and their correlation with petroleum resource volumes. Total petroleum resource volumes, in billion BOE, are further distinguished as (1) known (cumulative production plus remaining reserves, [data from Petroconsultants, 1996]); (2) undiscovered volumes (data from USGS, 2000); and (3) conventional endowment, which consists of the sum of known

Abstract To understand where the greatest potential for undiscovered resources lies, a summary of the estimated largest undiscovered fields from the USGS (2000) assessment is included here (Appendices 6, 7). Additionally, analyses of the depth, pressure, and temperature attributes of the world’s oil and natural gas fields provide insights into the world distribution of these parameters. Appendices 6, 7, 8, and 9 present information about possible locations of large, undiscovered fields in the world by assessment units (AU). Because of the extreme skewness of field-size distributions, much uncertainty exists as to the size of the largest undiscovered fields. The procedure used provides a distribution that shows the uncertainty for size of the largest undiscovered field for each AU ( Charpentier and Klett, 2000 ). Because of high uncertainty, the statistics in Appendices 6 through 9 should be viewed for their relative, rather than absolute, value. Appendix 6 presents a ranked list of AU by the estimated size of the largest undiscovered oil field. Appendix 7 shows a similar list for the largest undiscovered natural gas field. Appendix 8 shows the ranking of AU by number of expected oil fields with at least 1024 MMBO. Appendix 9 illustrates AU ranking by number of expected natural gas fields with at least 6144 bcf (1024 million BOE). All four of these appendices show that many of the largest fields remaining to be discovered are expected in Region 2, the Middle East and North Africa. East Greenland is also high on the oil ranking (Appendix 6)

Abstract Economics of onshore petroleum exploration and production are very different from offshore. In the assessment process, allocations of estimated undiscovered volumes were made to onshore and offshore locations (where applicable) in order to enhance the utility of the results for further economic analysis. Offshore areas were deemed those that required offshore infrastructure, in either fresh or salt water. Estimated volumes of onshore and offshore undiscovered oil by region (excluding the U.S.) are shown in Figure 96 ; of undiscovered natural gas, in Figure 97 ; and of NGL, in Figure 98 . Most of the onshore undiscovered resources are expected to be in Regions 1 (Former Soviet Union) and 2 (Middle East and North Africa). Figure 99 shows that, at the world level, approximately equal amounts of each of the three undiscovered commodities are expected to be onshore and offshore. Figure 100 shows that for Regions 3 through 8, about one-fourth of the undiscovered volume of each commodity is expected to be onshore and nearly three-quarters of the potential is offshore. The offshore potential of each assessment unit (AU), total petroleum system (TPS), and province and the water depths associated with the offshore portion for each AU, is documented in USGS (2000). Most offshore provinces extend to water depths of 6562 ft (2000 m) with the exception of areas where exploration has already begun in deeper water depths. For example, the water depth limits of the AU were extended to 13,123 ft (4000 m) in the Campos Basin

Abstract Therefore, the grown endowment of recoverable oil is estimated in the USGS (2000) at about 3 trillion bbl of oil ( Table 1 ; Figure 107 ). The grown natural gas endowment is estimated at about 2.6 trillion BOE ( Table 1 ; Figure 107 ). Oil reserves as of 12/2001 are 1.1 trillion bbl of oil; world consumption is about 0.028 trillion bbl of oil per year. Natural gas reserves are about 0.8 trillion BOE; world consumption is about 0.014 trillion BOE. Without any additional discoveries of oil, natural gas, or natural gas liquids, there are about 2 trillion BOE of proved petroleum reserves. Of the oil and natural gas grown endowment of about 5.6 trillion BOE, the world has consumed about 1 trillion BOE, or 17% leaving about 83% of the grown endowment to be found and/or utilized ( Figures 12 , 13 , 107 ; 1 trillion bbl of oil = 1000 billion bbl of oil, 1 trillion BOE = 1000 billion BOE). The potential additions to reserves from reserve growth are estimated to be nearly as large as the estimated undiscovered resource volumes. The additional remaining reserves and the estimates for reserve growth from these known fields imply that 76% of the world’s grown conventional oil endowment ( Figures 12 , 107 ) and 66.3% of the world’s conventional grown natural gas endowment have already been discovered in the areas assessed ( Figures 13 , 107 ). For these areas, 23.5% of the world’s total conventional grown oil endowment and 11.4%

Abstract The USGS World Petroleum Assessment 2000 (USGS, 2000) provides estimates of the quantities of conventional oil, natural gas, and natural gas liquids outside the United States that have the potential to be added to reserves in the next 30 years (1995 to 2025). Excluding the U.S., the mean estimated volumes of undiscovered resources are 649 billion bbl of oil, 4669 tcf, and 207 billion bbl of NGL. The estimated mean additions to reserves from discovered fields (reserve growth) are 612 billion bbl of oil, 3305 tcf, and 42 billion bbl of NGL. The potential additions to reserves from reserve growth are nearly as large as the estimated undiscovered resource volumes. These estimates imply that 75% of the world’s grown conventional oil endowment and 66% of the world’s grown conventional natural gas endowment have already been discovered in the areas assessed (exclusive of the U.S.). Additionally, for these areas, 20% of the world’s grown conventional oil endowment and 7% of the world’s grown conventional natural gas endowment had been produced by the end of 1995. By way of calibration, the 8 years since 1995 are less than one-third of the 30-yr forecast span (1995–2025) for the assessment. During this period, 18% of estimated oil resources and 27% of the estimated natural gas resources have been added to reserves from new field discoveries and reserve growth for the provinces assessed in USGS (2000). If the entire world is considered, exclusive of the U.S. and Canada, these percentages increase to 23% of

Abstract Presented in this publication are the results of a major study of the petroleum resources of the world as analyzed by total petroleum systems. The distribution and volumes of resources available in these systems are critically important for the future of the world's economies. Geologic insights gained from studying these 149 systems and their constituent assessment units in 128 provinces and 96 countries, exclusive of the United States, allow a new look at petroleum accumulations and the rocks that are intimately associated with them. The geographic distributions of oil and natural gas systems show significant differences. Lists of new areas of potential and new estimates of resources make this a must-have addition to the petroleum geologist's library.