AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
USGS Assessment of Undiscovered Oil and Gas Resources for the Lower Cretaceous Sligo (Pettet) Limestone, James Limestone, and Hogg Sand Formations, U.S. Gulf of Mexico Coastal Plain and State Waters
(1) U.S. Geological Survey, Reston, VA.
The Lower Cretaceous Sligo (Pettet) Limestone, James Limestone, and Hogg Sand formations were studied as part of an assessment of the technically recoverable, undiscovered conventional oil and natural gas resources underlying the U.S. Gulf of Mexico Coastal Plain and State waters. Assessments of accumulations within these formations were based on the geologic elements of a combined Upper-Jurassic-Cretaceous-Tertiary composite total petroleum system (TPS). Parameters examined in the Sligo (Pettet) Limestone, James Limestone, and Hogg Sand formations included characterization of hydrocarbon source rocks (maturation, hydrocarbon generation, and migration pathways), reservoir rocks, and traps (formation, timing, and seals). All assessments were conducted using USGS methodology (on-line at http://energy.cr.usgs.gov/oilgas/noga/methodology.html).
A single assessment unit, defined as the Sligo-James Carbonate Platform Gas, was delineated for discovered and undiscovered hydrocarbon accumulations in the Sligo (Pettet) Limestone, James Limestone, and Hogg Sand formations based on known geologic structural, stratigraphic, and depositional parameters. The Sligo-James Carbonate Platform Gas assessment unit is composed of reservoirs deposited within carbonate barrier platform (back-island reef and reef) environments. The updip limit of the assessment unit is based on the extent of the combined Upper Jurassic-Cretaceous-Tertiary TPS and transitional facies changes in the James Limestone, from a marginal marine carbonate-dominated environment to fluvial derived terrestrial clastics. The basinward downdip limit of the assessment unit is defined by the Lower Cretaceous shelf edge. The western boundary of the assessment unit is defined by the U.S.-Mexico international border and the eastern boundary is the limit of State waters in Louisiana and Mississippi.
Beginning in the late 1990’s, seismic and borehole data indicated that fore-reef debris flows in the Sligo reef trend may serve as potential targets for reservoir accumulations. The fore-reef debris flow deposits in the Sligo reef trend are anticipated to be the predominant target for future exploration of undiscovered gas accumulations within the assessment unit.