Abstract
The Middle Eocene Claiborne Group was assessed using established U.S. Geological
Survey (USGS) assessment methodology for undiscovered conventional hydrocarbon resources as
part of the 2007 USGS assessment of Paleogene-Neogene strata of the United States part of the
Gulf of Mexico Basin including onshore and State waters. The assessed area is within the Upper
Jurassic-Cretaceous-Tertiary Composite total petroleum system, which was defined as part of the
assessment. Source rocks for Claiborne oil accumulations are interpreted to be organic-rich
downdip shaley facies of the Wilcox Group and the Sparta Sand of the Claiborne Group; gas
accumulations may have originated from multiple sources including the Jurassic Smackover and
Haynesville Formations and Bossier Shale, the Cretaceous Eagle Ford and Pearsall(?) Formations,
and the Paleogene Wilcox Group and Sparta Sand. Hydrocarbon generation in the basin started
prior to deposition of Claiborne sediments and is ongoing at present. Emplacement of hydrocarbons
into Claiborne reservoirs has occurred primarily via vertical migration along fault systems; long-range
lateral migration also may have occurred in some locations. Primary reservoir sands in the
Claiborne Group include, from oldest to youngest, the Queen City Sand, Cook Mountain
Formation, Sparta Sand, Yegua Formation, and the laterally equivalent Cockfield Formation.
Hydrocarbon traps dominantly are rollover anticlines associated with growth faults; salt structures
and stratigraphic traps also are important. Sealing lithologies probably are shaley facies within the
Claiborne and in the overlying Jackson Group.
A geologic model, supported by spatial analysis of petroleum geology data including
discovered reservoir depths, thicknesses, temperatures, porosities, permeabilities, and pressures,
was used to divide the Claiborne Group into seven assessment units (AU) with distinctive structural
and depositional settings. The AUs include (1) Lower Claiborne Stable Shelf Gas and Oil
(50470120), (2) Lower Claiborne Expanded Fault Zone Gas (50470121), (3) Lower Claiborne
Slope and Basin Floor Gas (50470122), (4) Lower Claiborne Cane River (50470123), (5) Upper
Claiborne Stable Shelf Gas and Oil (50470124), (6) Upper Claiborne Expanded Fault Zone Gas
(50470125), and (7) Upper Claiborne Slope and Basin Floor Gas (50470126). Total estimated
mean undiscovered conventional hydrocarbon resources in the seven assessment units combined
are 52 million barrels of oil, 19.145 trillion cubic feet of natural gas, and 1.205 billion barrels of
natural gas liquids.
A recurring theme that emerged from the evaluation of the seven Claiborne AUs is that the
great bulk of undiscovered hydrocarbon resources comprise non-associated gas and condensate
contained in deep (mostly >12,000 feet), overpressured, structurally complex outer shelf or slope
and basin floor reservoirs. The continuing development of these downdip objectives is expected to
be the primary focus of exploration activity for the onshore Middle Eocene Gulf Coast in the
coming decades.
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First posted October 24, 2012
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