Geologic Assessment of Undiscovered Hydrocarbons in Lower to Upper Cretaceous Carbonate Rocks of the Fredericksburg and Washita Groups, U.S. Gulf Coast Region
Sharon Swanson, Kristin Dennen, Catherine Enomoto, Celeste Lohr, and Brett Valentine
As part of the assessment of undiscovered oil and gas resources in Jurassic and Cretaceous strata of the U.S. Gulf Coast in 2010, the U.S. Geological Survey (USGS) assessed carbonate rocks of the Fredericksburg and Washita groups and their equivalent units underlying onshore lands and State waters. One conventional assessment unit (AU) extending from south Texas to the Florida panhandle was defined: the Fredericksburg-Buda Carbonate Platform-Reef Gas and Oil AU. Assessed strata range in age from Early Cretaceous Albian to Late Cretaceous Cenomanian. The assessment was based on a geologic model that incorporated the Upper Jurassic-Cretaceous-Tertiary Composite Total Petroleum System of the Gulf of Mexico Basin. The following factors were evaluated to define the AU and estimate oil and gas resources: potential source rocks, hydrocarbon migration, reservoir porosity and permeability, traps and seals, structural features, depositional framework, and potential for water washing of hydrocarbons near outcrop areas. The production history of discovered reservoirs and well data within the AU were also examined to estimate the numbers and sizes of undiscovered oil and gas reservoirs within the AU. Based on the geologic model developed for the assessment, the downdip boundary of the AU was drawn as a line extending 10 miles downdip of the Lower Cretaceous shelf margin, to include potential reef-talus reservoirs. Updip boundaries of the AU were drawn based on the updip extent of AU carbonate rocks, the presence of basin margin fault zones, and the presence of producing wells within the assessed interval. Using USGS methodology, means of 40 million barrels of oil, 622 billion cubic feet of gas, and 14 million barrels of natural gas liquids were estimated for the AU.
AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013