POSSIBLE STRUCTURAL CONTROLS ON SANDSTONE DISTRIBUTION AND HYDROCARBON PRODUCTION, UPPER JURASSIC–LOWER CRETACEOUS COTTON VALLEY GROUP, U.S. GULF COAST REGION

The Upper Jurassic–Lower Cretaceous Cotton Valley Group is present in the subsurface in an arcuate belt from southern Texas to the Florida panhandle. The U.S. Geological Survey (USGS) assessed undiscovered oil and gas resources in sandstone of the Cotton Valley Group onshore and for State waters of the U.S. Gulf Coast.

Resource assessments by the USGS are geology based and use the total petroleum system concept. Characterization of the geohistory of known and potential hydrocarbon accumulations permitted definition of four assessment units (AUs). The Cotton Valley Hypothetical Updip Oil AU includes areas between the updip limit of the Cotton Valley Group and a regional fault system. The Peripheral Fault System Oil and Gas AU brackets the Mexia-Talco, State Line, Pickens-Gilbertown, and other fault zones, which were crucial in trapping oil generated from source rock intervals within the underlying Smackover Formation. Hydrocarbons in the Downdip Oil and Gas AU are associated with salt structures in the East Texas, North Louisiana and Mississippi salt basins. The Tight Sandstone Gas AU contains gas-charged sandstone with lower porosity and permeability and required use of a different assessment methodology for continuous accumulations.

In addition to the assessment of the hydrocarbon resources, potential structural controls on depositional facies were curiously apparent; for example, development of paralic facies was typically associated with the regional fault system. It is an interesting challenge, however, to discern whether or not the regional structural history affected the distribution of certain types of sandstone and (or) the broad production trends used to characterize the distribution of these undiscovered resources.