A Geologic-Based Evaluation of the Potential for Undiscovered Oil and Gas Accumulations in Paleogene Strata of the Gulf of Mexico Coastal Plain and State Waters

The U.S. Geological Survey (USGS) recently conducted an assessment of the technically recoverable undiscovered conventional oil and gas resources in Paleogene sediments underlying the U.S. Gulf of Mexico Coastal Plain and State waters. For purposes of the assessment, an Upper Jurassic-Cretaceous-Tertiary total petroleum system (TPS) was defined for the Gulf of Mexico basin. Paleogene strata were divided into the following stratigraphic study intervals: 1) Wilcox Group (including Midway Group and the basal Carrizo Sand of the Claiborne Group; Paleocene-Eocene); 2) Claiborne Group (Eocene); 3) Jackson and Vicksburg Groups (Eocene-Oligocene); and 4) Frio-Anahuac Formations (Oligocene). Based on a generalized structural and stratigraphic model, each assessed Paleogene stratigraphic interval was subdivided into an updip, stable shelf assessment unit (AU), a middip, expansion (extension) zone AU, and a downdip, slope and basin floor AU. A significant controlling factor for the location of the middip expansion zone AU is the location of underlying, stratigraphically older shelf margins. Using the geology-based assessment methodology, the USGS estimated mean a of 83.8 trillion cubic feet of undiscovered natural gas, a mean of 396 million barrels of undiscovered oil, and a mean of 3.1 billion barrels of undiscovered natural gas liquids in the assessed Paleogene strata. A significant portion of the undiscovered resources (53 % or 48.7 trillion cubic feet of gas) is estimated to occur in Paleogene slope and basin floor AUs. The Wilcox Slope and Basin Floor AU is estimated to hold about one third of the undiscovered hydrocarbon resources for the assessed intervals.