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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions Vol. 58 (2008), Pages 305-325

Hydrocarbon Generating Potential: Jurassic Cotton Valley – Bossier Group, North Louisiana Salt Basin

Donald A. Goddard1, Ernest A. Mancini2, Marty Horn3, and Suhas C. Talukdar4

1Center For Energy Studies, Louisiana State University, 1081 Energy, Coast and Environment Bldg., Nicholson Extension, Baton Rouge, Louisiana 70803

2Department of Geological Sciences, University of Alabama, 202 Bevill St., Tuscaloosa, Alabama 35487

3Louisiana Geological Survey, Louisiana State University, 2101 Energy, Coast and Environment Bldg., Nicholson Extension, Baton Rouge, Louisiana 70803

4Baseline Resolution, Inc., 143 Vision Park Blvd., Shenandoah, Texas 77384


Geological/geochemical evaluation of Upper Jurassic Cotton Valley – Bossier core samples from the North Louisiana Salt Basin (NLSB) indicates that fine-grained rocks associated with these units are thermally mature and represent petroleum source rock that generated and expelled mostly gas and some oil. These findings are based on source rock characterization of samples from wells within the NLSB, Vernon Field, Jackson Parish, using total organic carbon (TOC), Rock-Eval pyrolysis, and visual kerogen data.

The data indicate that these rocks at their present maturity level have low to moderate TOC contents and Type III kerogen. Original kerogen types in the immature stage, as assessed by kerogen petrography, were mainly gas-prone Type III and some oil-and gas-prone Type II/III. The principal macerals are partly oxidized, unstructured amorphous organic matter (liptinite) and vitrinite in varying proportions. Amorphous material was derived from degraded marine algal and humic matter (higher plant material). Visual kerogen data support the predominantly gas-prone nature of the source rocks. Vitrinite reflectance (Ro) values (0.94% to 2.62%) and thermal alteration indices (TAI)

(2.8 to 3.7) suggest that these source rocks entered the late oil window to main gas maturity window and thus have generated mostly gas with some oil. Thin section petrography of geochemically analyzed intervals documents the following rock types: muddy fine-grained sandstone, laminated fine-grained sandstone, sandy mudstone, and silty mudstone. These combined analytical results indicate that abundant woody organic material of continental origin was deposited in offshore areas in association with fine siliciclastic sediments in a marine prodelta environment during Jurassic time. The thickness and widespread deposition of predominantly gas-prone rocks within the NLSB and their high thermal maturity led to sourcing of mainly gas with some oil in overlying Jurassic and Cretaceous reservoirs, particularly in the Bossier and Cotton Valley.

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