Wilcox Depositional Systems: Shelf, Slope, and Basin Floor

The onshore Wilcox has been an important petroleum province for the last 80 years, and has been penetrated by tens of thousands of wells. The emerging deep-water Wilcox trend, located more than 250 miles downdip from onshore production, has been penetrated by approximately 40 wells in the last 7 years.

The onshore Wilcox has historically been subdivided into lower, middle, and upper lithostratigraphic units. A high resolution sequence framework is required to move beyond lithostratigraphic correlations, and accurately correlate chronostratigraphically equivalent lithofacies associations from shallow to deep subsurface and regionally along strike. In outcrop the Wilcox is represented by marginal- to shallow-marine interbedded sandstone and shale plus locally abundant lignite. Onshore subsurface well control documents fluvial, deltaic, and open shelf to upper slope depositional systems in latest lowstand, transgressive, and highstand systems tracts. The next downdip Wilcox well penetrations are 250 miles farther in the basin, in Alaminos Canyon, Keathley Canyon, Walker Ridge, and Green Canyon protraction areas in the deepwater Gulf of Mexico trend.

A new deep-water chronostratigraphic framework is the key to accurately correlating the onshore Wilcox to the deep-water Wilcox trend. Five deepwater chronostratigraphic units are recognized. In ascending order, they are; Wilcox 4, Wilcox 3, Wilcox 2, Wilcox 1B, and Wilcox 1A. These units represent early lowstand turbidite deposits of single third-order sequences or groups of third-order sequences. Various examples of shallow water to deep-water depositional settings are presented to characterize Wilcox depositional styles across the basin and through time. Chronostratigraphic calibration also reveals that while equivalent volumes of sediment were deposited onshore during the late Paleocene and early Eocene, more than 90% of the deep-water Wilcox section was deposited during the late Paleocene.