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Wolfcampian Shelf-to-Basin Stratigraphic Framework of the Central Basin Platform and Midland Basin, Andrews County, Texas

Abstract

Lower Permian (Wolfcampian) strata are important reservoirs and exploration targets on the Central Basin Platform, along its eastern slope, and in the adjacent Midland Basin. Controls on deepwater allochthonous carbonate reservoir facies development and stacking can be better understood through analyses of shelf-to-basin stratigraphic frameworks which identify the timing and mechanisms of sediment bypass and accumulation across the depositional profile. This study aims to provide context for the deepwater elements within the basinal Wolfcamp B and C by examining contemporaneous stratal architecture and sedimentation patterns along the shelf to basin depositional profile using 3D seismic, well-logs, and core lithofacies data with fusulinid biostratigraphic constraints from North Cowden, Midland Farms, and Mabee fields. Cores from Midland Farms Deep field show the Hueco Fm. includes up to 116 ft of Lower Hueco strata dominated by phylloid algal-calcisponge-Tubiphytes reefal buildup complexes with crinoid-dominated flank packstone beds. The mid-Wolfcamp unconformity (Upper-Lower Hueco Boundary) is marked by a gamma ray spike expressed in core as a subaerial exposure surface overlain by a green grey clay-rich mudrock. Well-log suites suggest this unconformity is correlative throughout Southeast Andrews County. The Upper Hueco includes up to 172 ft of upward shallowing successions of skeletal-fusulinid packstones, peloidal packstones, and ooid grainstones intercalated with carbonaceous shales, interpreted as representing deposition during an overall transgression. Lower Hueco strata generally have more consistent and lower gamma ray values than the Upper Hueco, consistent with the fewer clay-rich mudrocks and shales in the Lower Hueco. The Wolfcampian-Leonardian unconformity represents the early Leonardian transgression and the backstep of Leonardian deepwater carbonaceous to siliciclastic shales and debris flows over the Upper Hueco. Seismic data illustrates the evolution of the depositional profile from the subtle Pennsylvanian-Wolfcampian contact, to the distally steepened Wolfcampian profile, to the better-defined Leonardian downlap onto the Hueco. Reconstructing the Wolfcampian platform-to-basin stratigraphic architecture assists in predicting the timing and style of deposition on the slope and basin and improves the ability to predict sweet spots for hydrocarbon exploration in the deeper water facies.