Organic Geochemical Analysis of Oils from Coastal Plain Along Gulf of Mexico

James H. Landrum, Chris Sutton

Samples of 150 oils from Gulf Coast Jurassic to Tertiary reservoirs were geochemically characterized. Multivariate statistical analyses were used to assess the similarities and differences among the oils.

Four oil groups have been tentatively identified. Group I includes oils from Jurassic and Cretaceous reservoirs associated with the Smackover trend. These oils were generated by carbonate-rich source rocks deposited under highly reducing marine conditions. Differences among these oils reflect regional variations in the organic source facies and maturity of the oils.

Group II is composed of Cretaceous oils of southwestern Mississippi. These oils were generated by clastic, clay-rich rocks deposited in a paralic/deltaic environment.

Group III includes the Tertiary oils of southwestern Mississippi and southern Louisiana. Source rocks that generated these oils were deposited in a rapidly subsiding, marginal-marine environment.

Group IV is composed of oils from the Austin Chalk. These oils were generated by open-marine, carbonate source rocks with varying amounts of terrigenous organic matter.

The distribution and characteristics of each oil group should be useful in identifying the source rock for each hydrocarbon accumulation. These oil-source rock relationships can be used to postulate hydrocarbon migration pathways and to grade untested structural/stratigraphic traps along the Gulf of Mexico with regard to hydrocarbon accumulations.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.