Abstract In order to improve predictions of coastal morphological response to sea-level rise and sustainably manage dredged sediment there is an urgent need to develop a field methodology that can measure accurately transport pathways of the <63 µm sediment fraction in coastal and estuarine environments. Techniques such as sediment trend analysis and sediment tracing using fluorescent sands are well established for the silt and sand fraction but are unsuitable for clay sediments due to their cohesive nature. Geochemically labelled clays have been used as fine sediment tracers in freshwater environments with some success, although little is known about their chemical or physical behaviour once released in saline environments. A number of pure clays and natural estuarine sediments were labelled with La following agitation in a 0.01 M solution of La Cl 3 . In order to examine the retention of La on the clay mineral surface the labelled sediment was washed sequentially four times using both de-ionised water and artificial seawater. A labelled bentonite retained 43000 µg g −1 La and this was only reduced to 36000 µg g −1 La after washing in seawater. This suggests that retention of La is good even in saline conditions and concentrations of La are high enough to enable detection after considerable signal dilution. Sorption of La is dependent predominantly upon the cation exchange capacity of the sediment.

Abstract Inductively coupled plasma analytical techniques are widely used in forensic geochemistry because they can provide concentration data for a wide range of major and trace elements relatively rapidly and at reasonable cost. A pilot study was undertaken to identify the relative importance of uncertainty resulting from instrumental measurement sources and that due to the procedures used to prepare the samples initially. Three soils with a range of major and trace element concentrations were collected to permit an evaluation of uncertainty. A reference sample of demonstrated homogeneity was also prepared and analysed. Samples were prepared in replicate (five preparations) of each, and assessment made of uncertainty in the instrumental measurement alone and for replicated preparations of the same material. Small sample sizes (0.05g) were used to mimic the situation common in forensic investigation. Results show that, while instrumental variability may be an important factor during measurement, between-sample variation has a dominant effect on uncertainty in the final result. It is clear that, without replicated measurement and preparation, the uncertainty of the measured data is unknown. Thus, critical samples, on which a case might depend, must be analysed in a way that defines clearly that uncertainty.

Abstract A supersequence-scale stratigraphic framework is developed for the super-giant Tengiz field of western Kazakhstan through the integrated interpretation of seismic, core, log, and biostratigraphic data. Tengiz produces oilfrom an isolated carbonate platform (areal extent of 580 km 2 ) of Devonian and Carboniferous age. An initial broad Late Devonian platform exhibits vertical growth and was followed by punctuated backsteps during theEarly Carboniferous (Tournaisian and Viséan). The uppermost lower Carboniferous (Serpukhovian) is characterized by several kilometers of platform progradation seaward of the late Viséan platform break. The basal upper Carboniferous (Bashkirian) platform succession was aggradational. Drowning in theearly Bashkirian haltedcarbonate platform growth. Paleotopographic relief on the top of the Bashkirian platformto the basin floor approaches 1,500 meters within several kilometers lateral distance. The stratigraphic architecture defined in this study is used to subdivide the reservoir. The reservoir is also partitioned on the basis of geographic position along a platform-to-basin profile. Time-slice mapping of synchronous depositional facies provides the basis for predicting reservoir distribution and continuity. On the platform, hydrocarbons are produced from Upper Viséan, Serpukhovian, and Bashkirian reservoirs in grainstone and mud-lean packstone lithofacies of the shallow platform and in packstone lithofacies of the deeper platform. Multiple pore types are recognized in Tengiz, but matrix permeability is controlled mainly by intergranular porosity. In-place, upper-slope microbial boundstone and transported lower-slope boundstone debris forms thick and areally extensive mappable reservoirs (Upper Viséan and Serpukhovian) that have distinctive seismic facies and production characteristics. Fractures contribute to non-matrix permeability in these boundstones.

Abstract In this part we will examine in general terras how carbonate cycles are generated on carbonate platforms, types of carbonate cycles developed, stacking patterns, margin geometries, degree of disconformity development, and briefly overview any characteristic diagenetic effects. In order to do this, a brief review of controls on carbonate deposition, platform types, and sequence stratigraphy is given. This is followed by discussions of cycle development in greenhouse, transitional and icehouse worlds with brief examination of examples. I would like to emphasize that our understanding of climatic forcing of the cyclic stratigraphic record is still simplistic, and any of the models presented are tentative, and certainly will be modified and refined in the future. Part 2 (by Charlie Kerans) will examine cycles and one- and two-dimensional stacking patterns, high resolution stratigraphy, and reservoir geometry on Late Permian platforms in the Permian Basin of West Texas, using examples and exercises from Guadalupe Mt. outcrops, and outcrop and core data from a major Permian reservoir. The Late Permian examples typically reflect relatively low amplitude sea level fluctuations, following collapse of the Permo-Carboniferous ice-sheets. Part 3 (by Jim Weber, Rick Sarg and Frank Wright) will examine reservoirs formed in an ice-house world during the major Carboniferous glaciation of Gondwana, using the Middle Pennsylvanian carbonates of the Giant Aneth oil field, Paradox Basin, Utah. Again, outcrop and subsurface data are used to develop a regional sequence stratigraphic framework, and the controls on facies development and reservoir quality of these stratified reservoirs examined.

Abstract The central goal of this contribution is to development new methods for describing and modeling carbonate reservoirs. This pair of exercises focuses on establishing a high-resolution sequence framework for shallow-water platform-top carbonate reservoir strata and, for these specific examples, mixed-carbonate-clastic successions. The scale of particular interest is that of several thousand feet laterally and several hundred feet vertically, a scale useful in reservoir description and modeling. Specific topics for this discussion will be the development of a sequence stratigraphic framework that integrates observations from core, wireline logs, and outcrop analogs. This approach is similar to that applied by Van Wagoner et al (1988, 1990) for siliciclastic reservoirs. It downplays the emphasis on stratal geometry, the dominant player in seismically oriented sequence stratigraphy, putting it on par with other sequence stratigraphic tools, including cycle hierarchy, cycle stacking (both thickness and symmetry), facies proportions, and facies tract offset.

Abstract A sequence stratigraphic framework has been established for the Middle Pennsylvanian (Desmoinesian) section in southeastern Utah using: 1) surface exposures at Honaker Trail, Raplee Anticline, and Eight Foot Rapids located 25 to 40 miles (40-64 km) west of the Aneth field, 2) core and well logs in SE Utah, S W Colorado, NW New Mexico, and NE Arizona, and 3) regional seismic. Bounding discontinuities (sequence boundaries and maximum flooding surfaces) have been correlated over several thousand square miles in the Four Corners region. Systems tracts of 3rd-order composite sequences (0.5-5.0 m.y.) are comprised of 4th-order sequences (0.1-0.5 m.y.) and 5th-order depositional cycles or parasequences (0.01-0.1 m.y.). Nineteen discrete and mappable high-frequency depositional cycles are recognized within three fourth-order depositional sequences of the Desert Creek and lower Ismay section (Middle Desmoinesian) at the McElmo Creek Unit of the Aneth field, southeastern Utah. These simple sequences stack into parts of two third-order sequence sets. Facies analysis of 12,000 feet (3,660 m) of core was tied into the chronostratigraphic framework to constrain correlation of high-frequency depositional cycles (parasequences). Facies mapping within parasequences permitted 1) prediction of porous and permeable facies and 2) characterization of variability in reservoir pore systems. Syndepositional dolomitization and dissolution in peritidal facies, at shoal crests of parasequences and at sequence boundaries caused modification of reservoir character. Since discovery of the Aneth field (1956), 370 million barrels of oil (∼ 1.3 billion barrels original oil in place) have been produced from Middle Pennsylvanian carbonates of the Ismay and Desert Creek intervals. Stratified reservoirs occur within lowstand, transgressive, and highstand systems tracts. Siltstone, dolostone, and evaporites form lowstand wedges that were deposited 150 feet below the crest of the Aneth carbonate platform. Porous dolomudstone and dolowackestone are productive where they onlap and pinch out against the Aneth carbonate platform and are isolated from reservoirs on the platform. Within transgressive systems tracts, lagoonal/tidal flat dolomudstone/wackestone compose parasequences and display intercrystalline and solution-enhanced secondary porosity. Core analysis and production/performance data indicate that significant fluid pathways are developed in dolomudstone deposited on the carbonate platform on paleodepositional highs. In the lower Desert Creek, initial parasequences of the highstand systems tract represent a time of mound building and platform development as a result of coalescing biologic communities of phylloid algae. Interparticle and shelter porosity dominate. Subsequent parasequences within the lower Desert Creek highstand systems tract are composed of skeletal and nonskeletal wackestone to grainstone. Porosity is developed on paleodepositional highs at the top of parasequences where shoal water facies have preserved primary pore systems that are secondarily enhanced by leaching of less stable carbonate minerals by meteoric water. Reservoirs dominated by primary pore systems provide the best long term production and account for the majority of oil produced in McElmo Creek. In the upper Desert Creek highstand systems tract, ooid/peloid grainstones aggrade and prograde to fill available depositional space. Hydrocarbons are produced on the platform and along the platform to basin margin from carbonate sand sheets and allochthonous debris aprons. Grainstone debris aprons may also be deposited during early lowstand conditions of the lower Ismay sequence. On the platform meteoric diagenesis resulted in the formation of oomoldic porosity in ooid grainstone deposits beneath the upper Desert Creek sequence boundary. Within moldic pore systems storage capacity is favorable, but permeability is low, generally less than 1 md. Facies composed dominantly of moldic porosity in the absence of significant primary porosity are poor reservoirs.

ABSTRACT Rock petrophysical data and production/performance (i.e., engineering) data from the McElmo Creek Unit of the Giant Aneth Field, southeastern Utah, were integrated into a reservoir architecture or stratigraphic layer model that is based on high-resolution sequence stratigraphy. The layer model describes the architecture of high-frequency depositional cyclicity. Nineteen layers (i.e., parasequences or depositional cycles) are described within the Middle Pennsylvanian Desert Creek and lower Ismay section at McElmo Creek. Time-slice mapping of these synchronous layers, and of the facies contained within the layers, provides the basis for predicting the distribution and continuity of reservoirs. Geologic maps and cross sections were constructed to illustrate facies distribution and predict reservoir quality and continuity. Facies and layering data, coupled with core analysis data and engineering performance analysis, contribute to the understanding of fluid pathways. Several examples are selected that relate reservoir performance to changes in facies. At the field scale, porous and permeable facies stack to form a thick and areally extensive reservoir. Reservoir performance is related to the position of shallow-water facies along a platform-to-basin transect. High-resolution sequence stratigraphy provides architectural detail that permits mapping of successive stages of platform development. Field performance is improved in areas where injection and production wells are completed in platform algal buildup facies. Facies heterogeneity and reservoir eompartmentalization occur within a synchronous, genetically related cycle of deposition. Production/performance anomalies are observed at the interwell scale in laterally discrete reservoirs. Geologic maps show the distribution of facies and are used to predict the occurrence of reservoir quality rock. Engineering maps are compared with geologic maps to identify wells or areas of the field that require remedial action. Areas of improved reservoir performance are tied to diagenetic processes that crosscut depositional fabric. Basinally restricted fluids are interpreted to have flowed through porous and permeable rock along localized areas of the northern or windward margin of the carbonate platform, causing pervasive dolomitization. Cumulative oil production in these areas is much higher than for other areas of the field. A reservoir characterization study of the McElmo Creek Unit was conducted by technologists with Mobil Exploration and Producing U.S., Inc. A synergistic approach led to an improved geologic model, but, more importantly, aspects of this study have been used to increase reserves, increase production, and decrease production costs on a $/barrel basis.

ABSTRACT Building an accurate geologic model of a reservoir from well data is a challenge. Subsurface geologic data exhibit considerable variability, and interpretations are dependent on well data that are widely spaced. Outcrop analogs provide an additional source of data. Outcrops are used by geoscientists to gain a better understanding of subsurface geology, particularly reservoir architecture. Reservoir engineers would do well to follow the geoscience lead and use outcrop depiction to investigate how reservoir architecture might influence fluid flow. Rock exposures at Eight Foot Rapids exhibit an excellent Aneth Field reservoir analog, in all its detail. This locality is used to construct a model suitable for investigating, in cross section, the interwell behavior of a waterflood of the Aneth Field algal buildup reservoir. The work is particularly useful for demonstrating the impact of heterogeneity on unsteady state waterflood performance. Results illustrate the consequences of alternative well-to-well correlations.

Abstract This short course is in three parts. Part 1 examines in general terms how carbonate cycles are generated on carbonate platforms, types of carbonate cycles developed, stacking patterns, margin geometries, degree of disconformity development, and briefly overview any characteristic diagenetic effects. Part 2 examines cycles and one- and two-dimensional stacking patterns, high resolution stratigraphy, and reservoir geometry on Later Permian platforms in the Permian Basin of West Texas. Part 3 examines reservoirs formed in an ice-house world during the major Carboniferous glaciation of Gondwana, using the Middle Pennsylvanian carbonates of the Giant Aneth oil field, Paradox Basin, Utah.