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Abstract

This report presents a review of the U.S. Geological Survey (USGS) 2007 assessment of the undiscovered oil and gas resources in Paleogene strata underlying the U.S. Gulf of Mexico Coastal Plain and state waters. Geochemical, geologic, geophysical, thermal maturation, burial history, and paleontologic studies have been combined with regional cross sections and data from previous USGS petroleum assessments have helped to define the major petroleum systems and assessment units. Accumulations of both conventional oil and gas and continuous coal-bed gas within these petroleum systems have been digitally mapped and evaluated, and undiscovered resources have been assessed following USGS methodology.

The primary source intervals for oil and gas in Paleogene (and Cenozoic) reservoirs are coal and shale rich in organic matter within the Wilcox Group (Paleocene-Eocene) and Sparta Formation of the Claiborne Group (Eocene); in addition, Cretaceous and Jurassic source rocks probably have contributed substantial petroleum to Paleogene (and Cenozoic) reservoirs.

For the purposes of the assessment, Paleogene strata have divided into the following four stratigraphic study intervals: (1) Wilcox Group (including the 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) the Frio-Anahuac Formations (Oligocene). Recent discoveries of coal-bed gas in Paleocene strata confirm a new petroleum system that was not recognized in previous USGS assessments. In total, 26 conventional Paleogene assessment units are defined. In addition, four Cretaceous-Paleogene continuous (coal-bed gas) assessment units are included in this report. Initial results of the assessment will be released as USGS Fact Sheets (not available at the time of this writing).

Comprehensive reports for each assessment unit are planned to be released via the internet and distributed on CD-ROMs within the next year.

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