ALBERT

Description: Fluviolacustrine strata host significant hydrocarbon volumes in basins characterized by syndepositional growth of passive salt diapirs. An understanding of salt-sediment interaction is critical to the prediction of reservoir distribution and architecture in these strata. Large-scale stratal geometries and thickness changes resulting from salt movement are commonly apparent on seismic data, but to date, there are few predictive models for facies architecture at subseismic, reservoir scale. This article uses a high-quality outcrop data set of fluviolacustrine strata in an exhumed salt basin (Upper Triassic Chinle Formation, Paradox Basin, Utah) as an analog for improved understanding of subsurface data sets of similar structural and sedimentological setting. Salt-sediment interaction in the Chinle Formation is expressed by localized lateral variations in stratigraphic thickness, angular stratal relationships, and changes in facies architecture. Based on these criteria, there is evidence for salt-sediment interaction across a series of syndepositional salt structures, including anticlines above buried salt pillows, salt walls exposed at surface, and salt-withdrawal minibasins. Stratigraphy and facies architecture across these structures reflect the following controls: regional subsidence, localized differential accommodation space, and localized paleogeomorphology. Both localized controls were driven by syndepositional salt movement, which exhibited subtle spatial and temporal variations during the deposition of the Chinle Formation. The outcrop data set is used to develop generic predictive models of facies distributions and architectures resulting from different conditions of regional tectonic subsidence and/or fluvial energy. Analysis of stratigraphic expansion across syndepositional passive diapirs suggests that the outcrop-derived models are applicable to many subsurface data sets. Wendy Matthews is currently a sedimentologist with the Exploration and Production Technology Group at BP, where her work involves sedimentary geology research and global technical consulting. She received her B.Sc. and M.Sc. degrees from the University of Sheffield and the University of Aberdeen, respectively. The research for this article was conducted as part of her Ph.D. at Imperial College London. Gary Hampson is senior lecturer in sedimentary geology at Imperial College London. He earned his B.A. degree in natural sciences from the University of Cambridge (1991) and his Ph.D. in sedimentology and sequence stratigraphy from the University of Liverpool (1995). His research interests lie in the understanding of siliciclastic depositional systems and their preserved stratigraphy and in applying this knowledge to reservoir characterization. Bruce Trudgill received a B.Sc. degree from the University of Wales, Aberystwyth, and a Ph.D. in structural geology from Imperial College London. He is currently an associate professor in the Department of Geology and Geological Engineering at the Colorado School of Mines. His current interests are in the growth of fault arrays, salt tectonics, and structural controls on depositional systems. John Underhill holds a B.Sc. degree in geology from Bristol University and a Ph.D. from the University of Wales. He worked for Shell International before moving to Edinburgh University in 1989, where he holds the Chair of Stratigraphy. John has twice been awarded the European Association of Petroleum Geoscientists Distinguished Lecturer Award, has won the AAPG Matson Award, and has also been an AAPG Distinguished Lecturer. John's current primary research focus is on understanding the function of salt in the tectonic development and evolution of sedimentary basins.

Description: Conventional reservoir modeling approaches are developed to account for uncertainty associated with sparse subsurface data but are not equipped for detailed reconstruction of high-resolution geologic data sets. We present a surface-based modeling procedure that enables explicit representation of heterogeneity across a hierarchy of length scales. Numerous surfaces are used to construct complex facies-body geometries and distributions prior to generating a grid, allowing sampled and conceptual data to be fully incorporated within field-scale models. Our approach is driven by the improved efficiency that surfaces introduce to reservoir modeling through their geologically intuitive design, rapid construction, and ease of manipulation. Cornerpoint gridding of the architecture defined by the surfaces reduces the number of cells required to represent complex geometries, thus preserving geologic detail and rendering upscaling unnecessary for fluid-flow simulations. The application of surface-based modeling is demonstrated by reconstructing the detailed three-dimensional facies architecture of a wave-dominated shoreface-shelf parasequence from a rich outcrop data set. The studied outcrop data set describes reservoir architecture in a generic analog for many shallow-marine reservoirs. The process of model construction has demonstrated the function of (1) shoreface-shelf clinoforms, (2) paleogeographic changes in shoreline orientation, and (3) storm-event-bed amalgamation in controlling facies architecture. These subtle geometric features cannot be accurately represented using conventional stochastic reservoir modeling algorithms, which results in poor estimation of facies proportions and associated hydrocarbon volumes in place. In contrast, the surface-based modeling approach honors all data and captures subtle geometric facies relationships, thus allowing detailed and robust reservoir characterization. Richard Sech is a research scientist at ExxonMobil Upstream Research Company, Houston. He holds a B.S. degree in exploration geology from Cardiff University, an M.S. degree in reservoir evaluation and management from Heriot-Watt University, and a Ph.D. in petroleum engineering from Imperial College, London. His research interests are in reservoir modeling and quantifying the influence of geologic heterogeneity on fluid flow behavior. Matthew Jackson is a senior lecturer in reservoir engineering in the Department of Earth Science and Engineering, Imperial College, London. He holds a B.S. degree in physics from Imperial College and a Ph.D. in geological fluid mechanics from the University of Liverpool. His research interests include simulation of multiphase flow through porous media, representation of geologic heterogeneity in simulation models, and downhole monitoring and control in instrumented wells. Gary Hampson is a senior lecturer in sedimentary geology in the Department of Earth Science and Engineering, Imperial College, London. He holds a B.A. degree in natural sciences from the University of Cambridge and a Ph.D. in sedimentology and sequence stratigraphy from the University of Liverpool. His research interests lie in the understanding of siliciclastic depositional systems and their preserved stratigraphy, and in applying this knowledge to reservoir characterization.

Description: Net transgressive sandstones form a significant component of many shallow-marine reservoirs, but their shale-poor character commonly masks complex facies architecture and stratigraphy associated with significant permeability variations that impact reservoir drainage patterns and ultimate recovery. In this article, the controls on net transgressive sandstone reservoir architecture are investigated through a detailed analysis of the Cretaceous Hosta Tongue of the Point Lookout Sandstone (informally termed Hosta sandstone in this article) outcrop in New Mexico. Mapping of facies architecture within a series of adjacent canyons has enabled a quantitative three-dimensional reconstruction of key stratigraphic surfaces and sand body distributions from an updip pinch-out to a downdip pinch-out of the net transgressive sandstone complex. The Hosta sandstone contains a complex arrangement of wave- and tide-dominated facies associations arranged in an overall transgressive pattern. Tidal channel-fill sandstones, tidal sheet-form sandstones, and heterolithic tidal-flat and lagoonal deposits comprise the stratigraphy in the updip part of the system. These deposits pass abruptly downdip into wave-dominated shoreface sandstones. The facies composition indicates that the Hosta sandstone represents a wave-dominated barrier shoreline and a tide-dominated back-barrier lagoon. Facies associations are partitioned both vertically and laterally by a hierarchy of transgressive erosion (ravinement) surfaces cut by wave and tidal processes. Reconstructing the geomorphology and spatial organization of these surfaces is critical to understanding sand body distribution and facies architecture at high-resolution (intrareservoir) scale. The exceptional quality of the Hosta Sandstone outcrops has enabled (1) improved understanding of patterns and controls of facies architecture in net transgressive sandstone reservoirs, (2) construction of predictive templates of facies architecture in interwell volumes, and (3) quantification of geobody dimensions and spatial distribution patterns. In combination, these data provide appropriate qualitative and quantitative conditioning for reservoir models. Peter Sixsmith is currently working as a stratigrapher with Chevron. He earned a B.Sc. degree in geology and physical geography (1996) and a Ph.D. in sedimentology and sequence stratigraphy (2000), both from the University of Liverpool. The research for this article was conducted as part of a postdoctoral research at Imperial College London. Gary Hampson is a senior lecturer in sedimentary geology at Imperial College London. He earned his B.A. degree in natural sciences from the University of Cambridge (1991) and his Ph.D. in sedimentology and sequence stratigraphy from the University of Liverpool (1995). His research interests lie in the understanding of siliciclastic depositional systems and their preserved stratigraphy, and in applying this knowledge to reservoir characterization. Sanjeev Gupta is a reader in sedimentology at Imperial College London. He graduated from Oxford University in 1987, where he also conducted his doctoral research (1995). His research interests include controls on sedimentation and stratigraphy in foreland and extensional basins, and field and modeling studies of shore-zone depositional systems. Howard Johnson is the Shell Professor of Petroleum Geology at Imperial College London. He holds a B.Sc. degree in geology from the University of Liverpool and a D.Phil. in clastic sedimentology from the University of Oxford. His main research interests are in clastic sedimentology, sequence stratigraphy, and reservoir characterization. John Fofana earned his B.Sc. degree in geology from Birkbeck College, University of London (2002), and undertook an M.Sc. degree in petroleum geoscience at Imperial College London in 2003–2004.

Description: Wave-dominated, shoreface-shelf parasequences are commonly modeled as simple layer-cake reservoirs, yet analysis of modern and ancient analogs demonstrates that these intervals contain a more complex physical stratigraphy. We investigate the impact of depositional and diagenetic heterogeneity associated with gently dipping clinoform surfaces on fluid flow and recovery during water flooding, using a three-dimensional model reconstructed from a well-exposed outcrop analog. We demonstrate that the volume of oil in place is affected by variations in facies thickness associated with interfingering along clinoforms, whereas waterflood sweep efficiency is affected by barriers to flow along clinoform surfaces, such as calcite-cemented layers, mudstones, and siltstones. Sweep efficiency is low when water flooding is down depositional dip because oil is bypassed at the toe of each clinothem as water flows preferentially through high-quality sandstone facies in the upper part of the parasequence. Sweep efficiency is higher when water flooding is up depositional dip because the gravity-driven, downward flow of water sweeps poorer-quality sandstone facies in the lower part of the parasequence. In both cases, injectors may offer limited pressure support to producers. Water flooding along depositional strike yields good pressure support but poor sweep because the gravity-driven flow of water into the lower part of the parasequence is significantly reduced. This yields highly variable fluid saturations but a uniform pressure gradient, which is consistent with pressure and fluid saturation data from the mature Rannoch Formation reservoir, Brent field, United Kingdom North Sea. Simple layer-cake models fail to capture the range of flow behaviors described above and overpredict recovery by up to 20% as a result. Matthew Jackson is a senior lecturer in reservoir engineering in the Department of Earth Science and Engineering, Imperial College, London. He holds a B.S. degree in physics from Imperial College and a Ph.D. in geological fluid mechanics from the University of Liverpool. His research interests include simulation of multiphase flow through porous media, representation of geologic heterogeneity in simulation models, and downhole monitoring and control in instrumented wells. Gary Hampson is a senior lecturer in sedimentary geology in the Department of Earth Science and Engineering, Imperial College, London. He holds a B.A. degree in natural sciences from the University of Cambridge and a Ph.D. in sedimentology and sequence stratigraphy from the University of Liverpool. His research interests lie in the understanding of siliciclastic depositional systems and their preserved stratigraphy, and in applying this knowledge to reservoir characterization. Richard Sech is a research scientist at ExxonMobil Upstream Research Company, Houston. He holds a B.S. degree in exploration geology from Cardiff University, an M.S. degree in reservoir evaluation and management from Heriot-Watt University, and a Ph.D. in petroleum engineering from Imperial College, London. His research interests are in reservoir modeling and quantifying the influence of geologic heterogeneity on fluid flow behavior.