| dc.description.abstract | Lithologic, petrologic, and geochemical analyses were performed on the Wolfcamp Formation (operational benches A and B), with a focus on a 400-ft-thick core recovered from wildcat well Strain 2V (API 42-335-53586) in northwestern Mitchell County, Texas. The core along with thin sections, mineralogical, and petrophysical data was made available by Devon Energy. Observations were supplemented with structural contour and isopach maps of the Wolfcamp A and B tops. The goals of the study were to (1) characterize the lithofacies in the Wolfcamp Formation, (2) interpret the environments and depositional conditions and processes that influenced deposition of the Wolfcamp Formation, and (3) assess the hydrocarbon-source rock potential and unconventional hydrocarbon-reservoir rock potential of Wolfcamp Formation lithofacies.
Seven lithofacies are recognized in the Lower Permian section of the Strain core based on primarily on sedimentary features and mineralogy determined by x-ray diffraction. The facies are complexly interbedded and include (1) sandstones, (2) siltstones, (3) siliceous mudstones (4) calcareous siltstones, (5) calcareous mudstones, (6) calcarenites, and (7) bioclast-lithoclast wackestone-floatstones. These lithofacies were deposited by a combination of sediment gravity flow and pelagic processes. Sediment gravity flows recorded in the Strain core are turbidity currents, hyperpycnal flows, debris flows, and transitional flows. The transitional flows, while thin-bedded and limited to the uppermost core intervals, record transitions of gravity flows from carbonate-dominated turbulent flows to mud-rich cohesive laminar flows. The vertical distribution of lithofacies was used to divide the Strain core into seven distinct lithofacies associations, each representing a distinct depositional environment and sea-level condition. The lithofacies associations, in ascending order, are: 1) interbedded sandstone and siltstone lithofacies association (LA-A), 2) mudstone with calcarenite, and bioclast-lithoclast wackestone-floatstone lithofacies association (LA-B), 3) calcarenites, bioclast-lithoclast wackestones-floatstone, and mudstone lithofacies association (LA-C), 4) calcarenite and calcareous siltstone with interbedded calcareous mudstone lithofacies association (LA-D), 5) siliceous mudstone lithofacies association (LA-E), 6) massive calcarenite and rare mudstone lithofacies association (LA-F), and 7) mudstone, thin calcarenite and bioclast-lithoclast wackestones-floatstone lithofacies association (LA-G).
Organic geochemical data from Rock-eval analyses indicate that the Wolfcamp Formation contains sufficient quantities of mature, mixed Type II and Type III organic matter to serve as a good to excellent hydrocarbon-source rock in the Mitchell County area. Industry-provided petrophysical and XRD data suggests clay-rich and siliceous facies are the highest quality hydrocarbon-source rocks and unconventional hydrocarbon-reservoir rocks, with carbonate facies being negatively associated with organic richness and reservoir quality.
Geochemical analyses of the Wolfcamp Formation lithofacies were performed using 14 geochemical proxies for sedimentation, redox state, and paleo-productivity. Results suggest the development of anoxic conditions during sea-level transgressions and highstands. | en_US |
