Browsing by Subject "Wolfcampian"
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Item Lithofacies and chemostratigraphy of the upper Wolfcampian in the southeastern Delaware Basin, Pecos County, Texas(2018-05-07) Moede, Ian Hall; Kerans, C. (Charles), 1954-During the deposition of Wolfcampian sediments, the southern portion of the Delaware Basin was subject to active tectonism and an evolving basin configuration which led to a complex depositional environment. Intense interest exists in the petroleum geology of this region for hydrocarbon exploration. An increase in the understanding of the petrophysical properties, lithofacies and depositional processes are beneficial to their exploitation. Subsurface basinal Wolfcamp lithofacies were described from three cores in the Gomez gas field and analyzed for elemental abundance, bulk mineralogy and total organic carbon. Seven lithofacies were observed in the study area cores. Oligomictic limestone paraconglomerate, crinoid-fusulinid packstone, silty crinoid wackestone/packstone, structureless to laminated fine sandstone, bioturbated siliceous siltstone, argillaceous siliceous silty mudstone, laminated argillaceous siliceous silty mudstone and bioclastic argillaceous siliceous silty mudstone were identified and described. Two distinct lithostratigraphic features were defined by wireline log correlation; an upper carbonate debris flow unit and lower siliciclastic sandstone channel and lobe unit. An eight-mile long by nine-mile wide (at a minimum), 260-foot thick carbonate debris flow unit was interpreted as successive debris flows, concentrated density flows and hyperconcentrated density flows with argillaceous siliceous silty mudstone deposition separating the two units. The five-mile-long by three-mile-wide (at a minimum), 270-foot thick lower siliciclastic sandstone channel and lobe unit was interpreted as a sandy turbidite-filled channel with fine-grained to muddy interchannel configuration. Both of these units thickened towards the Coyanosa structure which was likely a local control of sediment transport. These units were vertically separated by hundreds of feet of high-gamma ray mudrock. Only four of 145 total organic carbon measurements were greater than two percent, which is commonly cited as the minimum organic carbon enrichment necessary for unconventional mudrock hydrocarbon generation and is lower than similar Wolfcampian mudrock successions in other areas of the Delaware Basin. Poor TOC preservation was likely to be at least partially caused by terrigenous quartz sediment dilution as well as microscopic and megascopic bioturbation.Item Lithofacies, diagenesis, and reservoir quality of the unconventional Wolfcampian succession in the Southeast Midland Basin, West Texas(2017-09-18) Zhang, Hualing; Janson, Xavier; Fu, QilongThe Lower Permian Wolfcampian basinal succession in the Midland Basin has become an important unconventional reservoir. Reservoir characterization of Wolfcampian strata is challenging because of the complex arrangement of lithofacies. This study combined petrographic and scanning electron microscope (SEM) cube observations from cores, and thin sections, as well as X-ray fluorescence (XRF) data, X-ray diffraction (XRD) data, and total organic carbon (TOC) data in order to provide an integrated characterization of the Wolfcamp succession. Lithofacies investigations were made using six cores (totally 667 ft total) from Glasscock, Sterling, and Irion Counties in Texas. Seven lithofacies were defined based on petrographic observations: (1) sandy siltstone, (2) argillaceous mudstone, (3) very fine to fine sandstone, (4) massive to weakly laminated calcareous mudstone, (5) laminated calcareous mudstone, (6) mud-dominated bioclastic packstone/rudstone, and (7) grain-dominated bioclastic packstone-grainstone/rudstone. Mudrocks were deposited mostly through hemipelagic settling and diluted turbidity flow. Depositional processes for sandstone, siltstone, and carbonate lithofacies include turbidity flows, debris flows, and hyperconcentrated density flows. These sediments are interpreted to be deposited in a deep-water, dysoxic to anoxic slope to basinal setting. High-frequency cyclicity is observed in meter scale as a relative carbonate-rich lithofacies overlain by a relative siliclastic-rich lithofaices. The Wolfcamp succession reveals a complex diagenetic history in sandstone and carbonate facies, including compaction, calcite, silica, and siderite cementation, and dissolution. The combined effects of compaction and cementation result in relatively low porosity. However, dissolution and siderite grain-coating in the sandstones create/save pore spaces for hydrocarbon storage. Measured core-plug porosity and permeability (por–perm) in sandstone successions suggest moderate porosity up to 11.6%. Based on por–perm results, siderite-coated sandstone is considered to be of the highest reservoir potential. The Wolfcamp has fair to good organically rich mudrocks, with an average TOC of 1.4%. TOC is facies-dependent with the highest value in the argillaceous mudstone lithofacies. The enrichment of organic matter increases with increasing primary productivity by showing positive relation with Ni, Cu, and P element. Organic enrichment also increases with bottom water anoxia by showing a positive relation with Mo and U elements. TOC enrichment is also affected by sediment influx during early Wolfcampian.Item Wolfcampian carbonate platform sequence stratigraphy of the southwestern Delaware Basin : Wylie Mountains, Van Horn, TX(2018-09-14) Canada, Taylor Wayne; Kerans, Charles, 1954-The Wolfcamp unconventional play in the Permian Basin is currently one of the most active drilling targets in North America. Despite its economic importance, the Early Permian Wolfcampian interval in the Delaware Basin lacks a detailed understanding of the linkage between carbonate platform sedimentation and basinal deposits. Previous studies on Wolfcampian platform carbonates in the Permian Basin and Orogrande Basin from outcrop and subsurface work have interpreted variable sequence frameworks, which suggests antecedent topography, local to regional tectonic activity, and/or other localized depositional controls likely have significant influence on sequence architecture. This study presents a stratigraphic framework from the Hueco Formation in the Wylie Mountains near Van Horn, Texas that records middle to late Wolfcampian deposition in the southwestern Delaware Basin. These inner ramp carbonate strata correlate with outer ramp to basinal deposits to the northwest in the Sierra Diablo Mountains on the western shelf of the Delaware Basin. This combined data set allows for the recognition of both eustatic and tectonic controls on carbonate platform sequence architecture during the Wolfcampian. Eleven partial measured stratigraphic sections totaling 1450 m were used to generate a 300 m composite section for the Hueco Formation exposed in the Wylie Mountains, which records middle to late Wolfcampian carbonate sedimentation overlying the early to middle Wolfcampian Powwow Formation siliciclastics. Nine depositional facies are recognized from field observations and petrographic analysis. These facies are grouped into four depositional facies tracts, including outer ramp, low energy inner ramp, high energy inner ramp, and tidal flat facies tracts. Three sequences were interpreted based on 1D and 3D facies and cycle stacking pattern analysis, including two middle Wolfcampian sequences and one late Wolfcampian sequence. The late Wolfcampian sequence backsteps relative to the middle Wolfcampian sequences, consistent with observations of Hueco Formation sequence architectures in outcrop around the Diablo Platform and in the subsurface. The top of the Hueco Formation in the Wylie Mountains is bounded by an unconformity caused by a relative sea level of fall of at least 40-45 m at the end of the Wolfcampian which was succeeded by an influx of siliciclastics in the early Leonardian. Additionally, extensive brecciation and deformation have been documented in the lower two sequences. This deformation is interpreted to be related to dissolution of interbedded evaporites associated with tidal flat deposition in the upper portion of the lowermost sequence. Structural data suggests that late Wolfcampian tectonism may also have influenced deformation in this stratigraphic interval. The primary contribution of this study is improved resolution of Wolfcampian platform sequence stratigraphy and relative sea level change in the southwestern Delaware Basin. Identifying periods of sea level lowstand in the platform record is important because these periods are often associated with siliciclastic bypass of the shelf and increased sedimentation to the basin. Due to the generally low porosity and permeability of the basinal Wolfcamp Formation, these bypass events are critical for the development of coarse grained or siliciclastic sand rich units that can serve as highly productive Wolfcamp oil and gas reservoirs. The end-Wolfcampian sea level fall and associated conglomeratic unit documented in this study at the top of the Hueco Formation suggests a period of siliciclastic bypass in the earliest Leonardian in the southwestern Delaware Basin.