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The Canyonlands grabens in southeast Utah form an active extensional fault array covering 200 km2 southeast of the Colorado River. The fault array formed as a result of gravity gliding above a thick layer of salt. Growth of this fault array within the last 0.5 m.y. (possibly last 0.1 m.y.) has resulted in major changes in the stream drainages across the area through processes of stream capture and diversion. During growth of the fault array, relay ramps between overlapping fault segments form topographic lows along the graben margins. These commonly act as access points for captured streams to enter a graben system. As fault segments continue to propagate laterally, linkage leads to breaching of the relay ramp structures....
Three upper Pictured Cliffs Sandstone tongues in the northern part of the San Juan Basin record high-frequency transgressive episodes during the Late Cretaceous and are inferred to have been caused by eustatic sea level rise coincident with differential subsidence. Outcrop and subsurface studies show that each tongue is an amalgamated barrier strand-plain unit up to 100 ft (30 m) thick. Successive upper Pictured Cliffs tongues display an imbricate relation and are offset basinward, reflecting net shoreline progradation northeastward. Upper Pictured Cliffs barrier strand-plain sandstones underlie and bound thickest Fruitland coal seams on the seaward side. Controls on Fruitland coal-seam thickness and continuity...
Wavelengths of hummocky cross-stratified (HCS) beds (a common sedimentary feature of storm-dominated shorefaces) are documented for the first time using measurements in three- dimensional (3-D) ground-penetrating radar (GPR) data for a well-developed Upper Cretaceous lower-shoreface succession at Dry Wash in the Ferron Sandstone Member, Utah. The shallow-marine sequence consists of upward-thickening HCS sand beds alternating with interstorm deposits. The thickness variation of the storm beds indicates locally steadily growing storm intensity with at least four cycles. Weakly coarsening- upward (mud to very fine-grained sand) fair-weather back- ground deposits suggest a slow progradation of deposition with no significant...
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Alicia Groeger has a B.S. degree in geology (University of North Carolina Chapel Hill, 1995) and spent one year of undergraduate study at the Geosciences Institute of Göttingen University in Germany. She then received her M.S. degree in geology (University of Utah, 1997) with a concentration in structure and tectonics. Since then Alicia has been living in Peru, working in exploration geology and in sustainable development, cultivating responsible relationships between large mining companies, local peasant communities, and the Peruvian national park system.Since receiving his Ph.D. in geology (Columbia University, 1976), Ron Bruhn has worked as a professor of structure and tectonics at the University of Utah, where...
The Tertiary Green River petroleum system in the Uinta basin generated about 500 million bbl of recoverable, high pour-point, paraffinic crude oil from lacustrine source rocks. A prolific complex of marginal and open-lacustrine source rocks, dominated by carbonate oil shales containing up to 60 wt. % type I kerogen, occur within distinct stratigraphic units in the basin. Petroleum generation is interpreted to originate from source pods in the basal Green River Formation buried to depths greater than 3000 m along the steeply dipping northern margin of the basin. Producing fields in the Altamont-Bluebell trend have elevated pore-fluid pressures approaching 80% of lithostatic pressure and are completed in strata where...
Sandy braided-river deposits with high net-to-gross sand ratios are commonly attractive reservoirs, yet internal lithologic heterogeneities, particularly the presence of low-permeability mudstone deposits, significantly complicate the development of such units. Previous work has focused on measuring the scale and distribution of mudstone deposits in outcrop analogs; however, because of extreme differences in scale, discharge, sediment load, and geologic history, the results of these studies are difficult to apply with confidence to a wide range of sandy braided-river reservoirs. Based on work in modern braided rivers (Niobrara and North Loup rivers, Nebraska) and ancient braided-river deposits (Kayenta Formation,...
The Fruitland Formation of the San Juan basin is the largest producer of coalbed methane in the world. Production patterns vary from one well to another throughout the basin, reflecting factors such as coal thickness and fracture and cleat density. In this study, we integrated conventional P-wave three-dimensional (3-D) seismic and well data to investigate geological controls on production from a thick, continuous coal seam in the lower part of the Fruitland Formation. Our objective was to show the potential of using 3-D seismic data to predict coal thickness, as well as the distribution and orientation of subtle structures that may be associated with enhanced permeability zones. To do this, we first derived a seismic...
Walter B. Ayers Jr. is visiting professor in the Harold Vance Department of Petroleum Engineering and adjunct professor in the Department of Geology and Geophysics at Texas A&M University. His teaching and research interests include petroleum geology, integrated reservoir studies, clastic depositional systems, and unconventional hydrocarbon reservoirs. He holds B.S. and M.S. degrees in geology from West Virginia University and a Ph.D. in geology from the University of Texas at Austin. Coalbed gas has been produced commercially from the northern Appalachian basin since the 1930s and from the San Juan basin since the early 1950s. However, the magnitude and economic significance of coalbed gas resources were realized...
The geochemistry of formation fluids (water and hydrocarbon gases) in the Uinta Basin, Utah, is evaluated at the regional scale based on fluid sampling and compilation of past records. The deep formation water is dominated by Na-Cl type where halite dissolution has the greatest effects on water chemistry. Its distribution and composition is controlled by both the lithology of geological formations and regional hydrodynamics. The origin of the saline waters in the southeastern basin is interpreted to be a mix of ancient evaporatively concentrated seawater with meteoric water recharged in the geological past, which has experienced water-rock interactions. At the basin scale, three-dimensional mapping of the dissolved...
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This article presents a unique cross section of a 13.5-km (8.3-mi)-long by 150-m (492-ft)-thick stratigraphic interval containing braided stream and associated flood-plain deposits. The cross section is oriented approximately parallel to depositional strike. This cross section is a resource for geoscientists and engineers interested in the measurements of stratigraphic architectural elements, such as dimensions and continuity of facies tracts and facies associations, stratigraphic and geographic changes in sandstone/mudstone proportions (net to gross), and frequency and cause of vertical fluid communication between superposed reservoirs. In addition to presenting this rich data resource, observed and documented...
Keith W. Shanley is a consulting geologist with more than 22 years experience in exploration, development, and research. He has published numerous papers dealing with sequence stratigraphy and reservoir architecture and has served as editor of several publications. He received his B.A. degree in geology from Rice University and his M.Sc. degree and his Ph.D. in geology from the Colorado School of Mines. His current research interests include sequence stratigraphy and reservoir architecture, the integration of petrophysics, and risk analysis.Bob Cluff is a geologist with 28 years petroleum exploration and development experience. Bob's research interests include the integration of geology with petrophysics and the...
The Altamont oil field in the deep Uinta basin is known to have reservoir fluid pressures that approach lithostatic. One explanation for this high pore-fluid pressure is the generation of oil from kerogen in the Green River oil shale at depth. A three-dimensional simulation of flow in the basin was done to test this hypothesis. In the flow simulation, oil generation is included as a fluid source. The kinetics of oil generation from oil shale is a function of temperature. The temperature is controlled by (1) the depth of sediment burial and (2) the geothermal gradient. Using this conceptual model, the pressure buildup results from the trade-off between the rate of oil generation and the flow away from the source...
The upper Green River Formation at the Bluebell-Altamont Field, Utah (Figure 1) is a tight gas sand reservoir where economic production can be sustained only in regions of high natural fracturing. In 1994, a demonstration seismic project was conducted at the field to show how exploration for, and the characterization of, naturally fractured gas reservoirs can be more effective through the integrated use of seismic techniques. Study of field exposures, well logs, and regional stress indicators prior to the seismic survey indicated a high degree of preferential orientation to the dominant fracture trend at the field. The seismic survey consisted of two crossing, nine-component surface seismic lines and a nine-component...
Excellent three-dimensional exposures of the Upper Jurassic Salt Wash Sandstone Member of the Morrison Formation in the Henry Mountains area of southern Utah allow measurement of the thickness and width of fluvial sandstone and shale bodies from extensive photomosaics. The Salt Wash Sandstone Member is composed of fluvial channel fill, abandoned channel fill, and overbank/flood-plain strata that were deposited on a broad alluvial plain of low-sinuosity, sandy, braided streams flowing northeast. A hierarchy of sandstone and shale bodies in the Salt Wash Sandstone Member includes, in ascending order, trough cross-bedding, fining-upward units/mudstone intraclast conglomerates, single-story sandstone bodies/basal conglomerate,...
Geologic interpretations made during the current enhanced oil recovery project at Rangely field (Rio Blanco County, Colorado) have shown the relationships between alteration of reservoir mineralogy and texture, changes in produced water composition, and increased problems with oil production. The bottom-hole pH of Weber brine has decreased from approximately 7.5 to 4.5 since the initiation of CO[2] injection into the Pennsylvania-Permian Weber Sandstone in the central portion of the field. Much of the Weber is partially cemented with carbonate minerals, including ferroan calcite and ferroan dolomite, with authigenic clay minerals, predominately illite and mixed-layer smectite/illite, also present. These minerals...
Accurate assessment of downhole natural gamma-ray logs requires a reference database built up from well-exposed outcrops where the recognition and interpretation of lithofacies is unequivocal. Although only a few cases have been published for spectral gamma-ray logs, some of these show there is a strong correlation to depositional environment. We present detailed spectral gamma-ray data, within an interpretative framework of the sedimentology and petrography, for a mixed fluvial-eolian succession in the Cutler Group of southeastern Utah, United States. In this case, these data did not help identify depositional environment. Discrimination of eolian from fluvial deposits is not reliable because there is much overlap...
New seismic and gravity data across the hydrocarbon-producing Divide Creek and Wolf Creek anticlines in the southern Piceance basin reveal contrasting styles of deformation within two widely separated time frames. Seismic data indicate that prebasin Paleozoic deformation resulted in block faulting of the Precambrian crystalline basement rocks and overlying Cambrian through Middle Pennsylvanian strata. Movement along these block faults throughout much of Pennsylvanian time, during northeast-southwest crustal extension, likely influenced distribution of the Middle Pennsylvanian (Desmoinesian) evaporite-rich facies. Younger rocks, including the thick succession of Cenozoic basin strata, then buried the Paleozoic structures....
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Jonah field, located in the northwestern Green River basin, Wyoming, produces gas from overpressured fluvial channel sandstones of the Upper Cretaceous Lance Formation. Reservoirs exist in isolated and amalgamated channel facies 10-100 ft (3-30 m) thick and 150-4000 ft (45-1210 m) wide, deposited by meandering and braided streams. Compositional and paleocurrent studies indicate these streams flowed eastward and had their source area in highlands associated with the Wyoming-Idaho thrust belt to the west. Productive sandstones at Jonah have been divided into five pay intervals, only one of which (Jonah interval) displays continuity across most of the field. Porosities in clean, productive sandstones range from 8 to...
Cyclic fluvial, fan-delta, and lacustrine margin depositional systems dominate the lower part of the Chinle Formation, Canyonlands area, southeastern Utah. Detailed facies analysis of the Moss Back Member and related strata document two alternating fluvial-lacustrine sequences. (1) During high fluvial output, coarse-grained meander belts built fan-deltas into shallow lakes. (2) During low fluvial output, braided streams waned before reaching the lakes, and algal and evaporatic mud flats formed on broad lacustrine perimeters. The high fluvial output phase comprises three depositional systems. (1) The coarse-grained meander belt system consists of point-bar and channel deposits. Abundant carbonate grains were cannibalized...
Petrographic and geochemical studies of coal from the Almond Formation in the greater Green River basin demonstrate that the coal contains important volumes of stored liquid petroleum, as well as methane. Modeling indicates that at the basin center, most of the oil generated in the coal has been thermally cracked to gas, whereas at the basin flank the oil-to-gas reaction has barely proceeded. Several new concepts are presented about the mechanism of petroleum generation in coal based on (1) natural maturation trends gleaned from examination of Almond coal samples from different burial depths and (2) similar maturation trends observed in hydrous pyrolysis experiments using immature Almond coal samples. These new...
map background search result map search result map Architecture and stratigraphy of alluvial deposits, Morrison Formation (Upper Jurassic), Utah Structure and geomorphology of the Duchesne graben, Uinta basin, Utah, and its enhancement of a hydrocarbon reservoir Jonah Field, Sublette County, Wyoming; gas production from overpressured Upper Cretaceous Lance sandstones of the Green River basin Structure and geomorphology of the Duchesne graben, Uinta basin, Utah, and its enhancement of a hydrocarbon reservoir Architecture and stratigraphy of alluvial deposits, Morrison Formation (Upper Jurassic), Utah Jonah Field, Sublette County, Wyoming; gas production from overpressured Upper Cretaceous Lance sandstones of the Green River basin