Wolfcampian shelf-to-basin stratigraphic framework of the Central Basin Platform and Midland Basin, Andrews County, Texas

Date

2019-09-12

Authors

Draper, Cody Hale

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Abstract

Despite collection of extensive subsurface data, the icehouse climatic forcing and tectonic modification of the Wolfcampian Hueco carbonates have frustrated attempts to adequately link shelfal and time-equivalent basinal depositional patterns. This study attempts to create a stratigraphic framework for correlating eastern Central Basin Platform Hueco shelfal carbonates and Wolfcamp Shale basinal stratigraphy by generating core-based vertical facies successions, wireline log and seismic-derived stratal architecture and sedimentation patterns, and isopachs along a contemporaneous shelf-to-basin depositional profile. Where available, fusulinid biostratigraphic control from the Midland Farms field area, provided by Dr. Greg Wahlman, constrained correlations, as did basinal palynologic data collected by Fasken Oil and Ranch. A total of 1,569 ft of core was described from the Midland Farms Deep Unit132, 101, 135, and 74 wells, the Midland Farms Unit 37 and AX-5, the Midland Farms Operating 3, and the Fasken Fee AL-910 and BI-307 wells. Thirteen depositional facies are recognized, which are grouped into seven facies tracts. Two depositional sequences were interpreted on the basis of 1D core lithofacies stacking patterns and were linked to selected shelf-to-basin log sections and seismic stratigraphic relationships. Shelf-to-basin correlations were made using a volume of nearly 2000 well-logs and 500 sq mi of 3D seismic data. The two major composite sequences recognized are termed the Lower Hueco and the Upper Hueco. The transgressive systems tract (TST) of the Lower Hueco Sequence LW-1 is characterized by phylloid algal patch reefs and associated bioclastic-oolitic grainstones that transition around the maximum flooding surface to skeletal packstones. The highstand systems tract of LW-1 records a shallowing-upward succession of slope, outer platform, and shelf crest facies. The LW-1 tract is capped by paleosols overlying shelf crest facies. The shelfal LW-1 is correlative to interbedded sediment-gravity flows and organic-rich siliciclastic mudstones in the Midland Basin, which represent platform shedding in conjunction with hemipelagic sedimentation. Despite the significant exposure recorded at the top LW-1, the mid-Wolfcamp unconformity is not identified as a significant erosive surface in this study, as suggested in other studies. The correlative mid-Wolfcampian interval in the adjacent basin is a stacked gravity flow complex that might represent a period of shelfal erosion related to exposure and/or tectonism. The transgressive systems tract of the Upper Hueco sequence UW-1 shows aggradation over the upper LW-1. The transgressive facies tract deepens to skeletal wackestone and is overlain by a thicker shallowing upward highstand systems tract that culminates in a large accumulation of grain-dominated packstone to grainstone facies which show evidence of subaerial exposure at the top Wolfcamp sequence boundary. This Wolfcampian-Leonardian unconformity is expressed by uppermost Hueco grainstones overlain by Leonardian deepwater basinal mudstones and gravity flows. Contemporaneous basinal sedimentation is mostly organic-rich siliciclastic mudstone with scarce sediment-gravity flow deposits. This study contributes an integrated model for the shelf-to-basin stratigraphic architecture of the Wolfcampian Hueco Group on the Central Basin Platform and the equivalent Wolfcamp Shale of the adjacent Midland Basin. Identifying controls on basinal sedimentation is important because allochthonous carbonate debris flows in the western Midland Basin can act both as drilling hazards and as reservoirs. Understanding the connections between the Hueco Group shelfal carbonate facies and sequences to the adjacent basinal stratigraphy could greatly improve reservoir prediction and development in the adjacent Wolfcamp Shale play.

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