Wilcox Group, Gulf Coast, Gulf of Mexico

General Setting

The Wilcox Group is a lower Eocene sandstone/shale sequence that runs nearly parallel to the Texas Gulf Coast, overlying the Carrizo Sandstone, and thickening abruptly downdip of the Stuart City shelf margin with growth faults controlling structure and thickness contours. Sandstone trends thicken up to 80 miles wide in the Upper and Middle Texas Gulf Coast. Net sand reaches 2,000 feet in the north. More than 100 miles from the outcrop, the Wilcox Group is 10,000 feet below sea level. The subsurface is well known from several investigations into geothermal potential (Bebout et al., 1982). The Upper and Lower Wilcox have similar variations in porosity and permeability with deltaic and inter-deltaic depositional environments as a major contributor to variations in porosity and permeability (Grubbs, 1953) which would need to be parsed to reduce flow baffles during carbon dioxide injection. Hydrocarbon traps, which should be considered for carbon dioxide, in the Wilcox are a combination of structural and stratigraphic. Traps are formed by growth faults, faulted rollover anticlines, salt diapirs, and fluvial and deltaic sandstone pinch outs (Warwick, 2017).

References

Bebout, D.G., Weise, B.R., Gregory, A.R., Edwards, M.B. 1982. Wilcox sandstone reservoirs in the deep subsurface along the Texas Gulf Coast: their potential for production of geopressured geothermal energy. Bureau of Economic Geology: Report of Investigations No. 117.

Grubbs, E.L. 1953. Variations in porosity and permeability in the Wilcox Group of the Texas Upper Gulf Coast. Gulf Coast Association of Geological Societies Transactions, Vol. 3, pages 54-70.

Warwick, P.D. 2017. Geologic assessment of undiscovered conventional oil and gas resources in the lower Paleogene Midway and Wilcox Groups, and the Carrizo Sand of the Claiborne Group, of the northern Gulf Coast region: U.S. Geological Survey Open-File Report 2017–1111, 67 p., doi: 10.3133/ofr20171111.

Prepared by Emily Moskal, 2020.