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Insights into deep, onshore Gulf of Mexico Wilcox sandstone pore networks and reservoir quality through the integration of petrographic, porosity and permeability, and mercury injection capillary pressure analyses
Calcite cement in Permian deep-water sandstones, Delaware Basin, west Texas: Origin, distribution, and effect on reservoir properties
Play analysis and leading-edge oil-reservoir development methods in the Permian basin: Increased recovery through advanced technologies
ABSTRACT Astudy of a tide-influenced deltaic sandstone investigated geologic variations that affect hydrocarbon production in analogous reservoirs. The Cretaceous-aged Frewens Allomember was deposited by a delta prograding into a narrow shoreline embayment between an older, wave-dominated delta lobe to the south and a basin-floor ridge created by subtle structural uplift to the north. The Frewens Allomember is exposed in outcrops of the Frontier Formation in central Wyoming (United States). It comprises two 5-km-wide by 20-km-long upward-coarsening sandstone bodies. Each body contains basinward-dipping internal beds. Heterolithic beds capped by extensive shale drapes record episodic tidal deposition in the lower portions of the sandstone bodies, whereas sandier cross-stratified beds in the upper parts of bodies record stronger and more uniformly ebb-directed currents. During diagenesis, calcite concretions formed preferentially at the top of the upper sandstone body as water circulated down from overlying shales. Diagrams of bedding, facies, calcite concretions, and bed-draping shales were compiled from high-resolution photomosaics and field observations. Sedimentologic logs, field permeameter measurements, and thin-section observations describe petrophysical properties of facies in the delta lobes. Variograms quantify the spatial correlation of permeability in lithofacies. The lengths of bed-draping shales were estimated from outcrop data using a termination frequency model. The spatial distribution of concretions was modeled with indicator geostatistics. Flow models integrated bedding geometry, lithofacies, and petrophysical properties in an appropriate structure for reservoir simulation. These models were used to analyze sensitivity of reservoir behavior to different geologic features and to investigate methods for modeling and upscaling interwell-scale heterogeneity. Intrafacies variability of permeability has negligible effects at the sandstone-body scale but significant effects at the bed scale. Shale lengths increase toward the lateral margins and toward the base of the sandstone bodies. Inclined shales reduce upscaled permeability, recovery efficiency, and breakthrough time. Calcite concretions decrease upscaled permeability. An upscaling method based on flow simulation and response-surface models accurately and efficiently represents the effects of geologic heterogeneity and flow rate on a coarse simulation grid.
Abstract Sandstones of the Upper Permian Bell Canyon Formation were deposited by turbidity currents in a basin-floor setting. The sandstones were deposited in a channel-levee system that terminated in broad lobes; overbank splays filled topographically low inter-channel areas. Diagenesis and reservoir quality of the sandstones were examined in cores from East Ford field, which is undergoing a CO 2 flood. Porosity and permeability are controlled by calcite cement, mainly concentrated in layers ranging from 5 to 40 cm in thickness. In a new infill well, initial production was of a high gas volume that contained a high concentration of CO 2 from the interval beneath several low-permeability, calcite-cemented layers. The CO 2 was most likely from an injector well and was trapped below the calcite layers. Geophysical log correlations support the interpretation that some calcite layers are laterally continuous over a distance of at least 300 m, causing vertical compartmentalization in the reservoir.
Reservoir characterization of a Permian deep-water sandstone, East Ford field, Delaware basin, Texas
Calcite Cement Distribution and Its Effect on Fluid Flow in a Deltaic Sandstone, Frontier Formation, Wyoming
Outcrop Analysis of a Sand-Rich, Basin-Floor Turbidite System, Permian Bell Canyon Formation, West Texas
Abstract Outcrops of the Bell Canyon Formation, Delaware Mountain Group, in Culberson County, Texas, were studied to better understand the sandstone depositional processes and determine the dimensions and arrangement of sandstone bodies. The depositional model developed from outcrop can be used to guide reservoir characterization of Delaware sandstone fields. The Bell Canyon Formation is a deep-water siliciclastic unit that accumulated in the Delaware Basin, located in West Texas and southeast New Mexico, during the Late Permian. The Bell Canyon is a sand-rich system that displays a net-to gross of about 70 percent. Grain size is limited to fine sand and coarse silt, and clay-size material is almost entirely lacking. Stratigraphic relationships indicate that the outcrop sandstones were deposited in a toe-of-slope or basin-floor setting by a system of leveed channels having attached lobes and overbank splays that filled topographically low interchannel areas. Channels are largely filled with massive and cross-stratified sandstones. They are as much as 15 m thick and 100 to 300 m wide. The channels are arranged in a radial pattern that bifurcates and expands down dip. The channels are flanked on both sides by wedges composed of thinly bedded sandstones and siltstones that are interpreted as levees. The levees thin away from the channel, decreasing in thickness from 8 to 1 m over the distance of 1 km. The levees are onlapped by massive sandstones interpreted as interchannel lobes or splays. The lobes, as much as 8 m thick and 10 km wide, display a broad tabular to irregular geometry. Individual channel-levee and lobe complexes appear to stack in a compensatory fashion and are separated by laterally continuous, meter-thick laminated siltstones. The laminated siltstones are interpreted to have been deposited by the settling of marine organic matter and airborne silt during periods when coarser particles were prevented from entering the basin. The paleogeographic setting, absence of mass-movement features, and high preservation of facies indicate that the outcrop sandstones were deposited in a basin-floor setting.
Abstract Reservoirs in deep-water sandstones of the Delaware Mountain Group in West Texas and New Mexico have low primary recovery efficiency (<14 percent). Reservoir characterization of a representative Delaware Mountain Group field was performed to identify geologic constraints on producibility. The Ramsey sandstone of the Bell Canyon Formation was investigated in the Ford Geraldine unit, Culberson and Reeves Counties, Texas. Outcrops of the Bell Canyon Formation in Culberson County, Texas, were studied to better interpret the depositional processes that formed the reservoirs at the Ford Geraldine unit and to determine the dimensions of reservoir sandstone bodies. On the basis of core descriptions, subsurface mapping, and the depositional model developed from outcrop, the 0-to 60-ft-thick (0- to 18-m) Ramsey sandstone interval in the Ford Geraldine unit was interpreted to consist of sheetlike turbidite lobe deposits overlain and incised by channel and levee deposits. Because of the narrow range of grain sizes in Ramsey sandstones and the absence of detrital clay, log patterns are generally not diagnostic of facies. Comparison of sedimentary structures viewed in core to facies identified in outcrop was key to interpreting the reservoir facies. Lobe deposits consist of massive and convoluted sandstones that have load and dewatering structures, suggesting that the sandstones were deposited rapidly from high-density turbidity currents. Channel facies, which are approximately 1,200 ft (370 m) wide and 15 to 35 ft (5 to 10 m) thick, overlie and locally incise the lobe deposits. They consist of massive and crossbedded sandstones interpreted to have been deposited from high-density turbidity currents. Channel margins, characterized by rippled and convoluted sandstones interbedded with siltstones, are interpreted as channel levees formed by overbanking of low-density turbidity currents. The levees are onlapped by massive sandstones interpreted as interchannel lobes or splays. Ramsey sandstones are bounded by laterally continuous, organic-rich siltstones deposited by settling from suspension. Siltstone beds and extensively calcite cemented sandstones are the most important causes of reservoir complexity and reduced sweep efficiency.
Comparison of outcrop and subsurface sandstone permeability distribution, Lower Cretaceous Fall River Formation, South Dakota and Wyoming
Abstract Secondary ion mass spectrometry (SIMS) was used to obtain microanalyses of oxygen isotope ratios on diagenetic quartz cements from the Travis Peak Formation, Texas Gulf Coast. These measurements on 15to 20-nm-diameter spots were made on standard polished thin sections, and the analyses allow new constraints on paleofluid isotopic compositions. Microanalyses of detrital quartz (13.7 ± 4.6%»; n = 76) compare well with conventional analyses on bulk samples (15.3 ± 3.4%o, n = 33), indicating good calibration of the microanalytical technique. The range of detrital quartz δ 18 O was 4 to 20%o, with larger detrital grains having lower values (~ 12%o) typical of a plutonic source and smaller grains (16 to 23%o) typical of a metamorphic source. Errors in individual analyses are 1.3—1.8%o (lcr). Bulk analyses of authigenic quartz in whole rock samples indicated an average oxygen isotopic ratio of 19 ± 3.3%o SMOW (n = 33). SIMS results ranged from 22%o to 35%o, with an average of 26 ± 3.5%o (n = 34). The isotopic results can be interpreted in terms of the geologic burial history, suggesting that sediments are buried and uplifted through waters that are isotopically stratified, becoming ,s O-enriched with depth. Under these constraints, authigenic quartz with 8 ,8 0 values >29%o must have precipitated from 2%o meteoric water at temperatures £50°C. Most δ 18 O values range from 25-29%o, implying that precipitation volumes peaked between 60-90°C, from waters with a positive δ 18 O value. Fewer quartz cements with 8 ,s O values <25%o were found, suggesting that quartz precipitation declined at temperatures >90°C. The burial history curve shows that the formation reached this temperature at —60 Ma. Quartz precipitation might have declined due to hydrocarbon infiltration, transition metals inhibiting quartz precipitation or occlusion of pores causing diminished fluid flow. The mass transfer of silica required to precipitate the observed abundance of quartz cement at temperatures between 60-90°C can be explained if Travis Peak paleofluids were actively converting. In this flow regime, the heterogeneity in 8 ,s O values of quartz cements would result from temperature variations during precipitation from a paleofluid having a δ 18 O value of approximately + 2%o. This fluid might represent a mixture of meteoric water (— 2%c) and deep-seated basinal fluids (+ 5%o). Hot fluids introduced along fracture zones associated with uplift of the Sabine Arch (—100 Ma), might have dispersed into the permeable Travis Peak sandstone and precipitated quartz upon cooling.
Timing of compaction and quartz cementation from integrated petrographic and burial-history analyses, Lower Cretaceous Fall River Formation, Wyoming and South Dakota
Depositional Controls on Reservoir Properties in a Braid-Delta Sandstone, Tirrawarra Oil Field, South Australia
Abstract Early precipitation of siderite cement in Sonora Canyon sandstones (Wolfcampian) in the Val Verde Basin, southwest Texas strongly influenced later diagenesis and reservoir quality in these low-permeability gas reservoirs. Sandstones of the Sonora Canyon interval were deposited in water depths of 100 to 500 m in coalesced submarine fans basinward (southwest) of the northwest-trending shelf margin. Sonora Canyon sandstones are composed of hundreds of feet of fanlobe turbidites and local channel-fill facies deposited on the continental slope and basin floor. Sonora Canyon sandstones are fine-grained sublitharenites and litharenites (average composition Q 77 F 9 R 19 ). Grain-rimming siderite rhombs 1 to 2 μm long were the earliest major cement to precipitate, in volumes ranging from 0 to 38%. Siderite is concentrateti in bedding-parallel layers 8 to 10 cm thick or in irregular patches 3 to 8 cm in diameter. Isotopic composition of the siderite falls in a narrow range, 5 I3 C averaging 2.4‰ (PDB) and 5 15 O averaging 31.1 ‰ (SMOW). The isotopic data indicate that siderite cement formed in a methanogenic geochemical environment at a burial depth of about 300 to 600 m (27°C) from sea-water-derived pore fluids (δ 18 O = 0‰). Bacterial reduction of iron accompanying anaerobic bacterial methanogenesis increased the Fe +2 in the pore fluids and, in the absence of sulfide, siderite precipitated. Subspherical nan-nobacterial bodies (0.05 to 0.15 μm) are revealed by etching siderite in warm HCl. These bodies are locally abundant, ranging to 100 per μm 2 of siderite crystal surface; other parts of the crystals contain virmally no bodies. The bacteria presumably helped trigger siderite precipitation. Abundant early siderite inhibited later porosity loss by compaclion and quartz cementation; siderite-rich sandstones (containing a 10% siderite) average 33% minuscement porosity and 6% quartz cement. Siderite-poor sandstones (<10%), are extensively cemented by quartz (average = 11%) and are much more compacted (16% minus-cement porosity). Siderite-rich sandstones retain higher porosity (7.9%) and permeability (0.042 md) than do siderite-poor sandstones (average porosity = 6.4%, geometric mean permeability = 0.006 md). Best matrix reservoir quality in Sonora Canyon sandstones occurs in siderite-cemented zones.
Influence of provenance and burial history on diagenesis of Lower Cretaceous Frontier Formation sandstones, Green River basin, Wyoming
Evolution of Porosity and Permeability in the Lower Cretaceous Travis Peak Formation, East Texas
History of quartz cementation in the Lower Cretaceous Travis Peak Formation, East Texas
Cementation and burial history of a low-permeability quartzarenite, Lower Cretaceous Travis Peak Formation, East Texas
Southern Midcontinent region
Abstract The Southern Midcontinent is a complex region characterized by great thicknesses of sediments preserved in a series of major depositional and structural basins separated by orogenic uplifts created mainly during Pennsylvanian time (Plate 5-A).Sedimentary rocks of every geologic system from Precambrian through the Quaternary are preserved within the region, and their diverse lithologies include limestones, dolomites, sandstones, shales, conglomerates, red beds, and evaporites. The strata are a mixture of marine and nonmarine deposits, and generally (except for the red bed-evaporite sequences), they are richly fossiliferous and are well suited to biostratigraphic correlation and interpretation of depositional environments. Dominant lithologies in most basins of the region are, in ascending order, as follows: a thin transgressive sandstone of Late Cambrian age that covered the basement-rock complex of intrusives, extrusives, and metasediments; overlain by a thick sequence of Late Cambrian through Late Mississippian (Meramecian) carbonates, with minor amounts of sandstone and shale; followed by a thick sequence of terrigenous clastics, with some carbonates, deposited from Late Mississippian (Chesterian) through Early Permian (Wolfcampian) time; then a thick series of red beds and evaporites were deposited during the remainder of the Permian; overlain, in the west only, by Triassic and Jurassic terrestrial red beds; then Cretaceous marine deposits in the south and west; and finally a mantle of Tertiary alluvial-fan, aeolian, and lacustrine sediments in the west. Owing to the great thickness of strata in most basins of the region, and the many surface and subsurface stratigraphie studies that have been conducted, a plethora of