Abstract: An Integrated Geochemical and Geological Approach for Determining Hydrocarbon Generation-Migration Patterns: Central Gulf Coast Basin

J. B. Echols, R. K. Zimmerman, D. A. Goddard

New geochemical, geological, and well-production data indicate a Mesozoic hydrocarbon source for many younger reservoirs in central Louisiana and southwest Mississippi. A Jurassic source has been determined for several oil and gas fields in northeast Louisiana.

The characteristic Wilcox and Sparta biomarker, bisnorhopane, identified in Austin Chalk oils from southwest Mississippi, links these Mesozoic and Tertiary oils. Cross-plots of ^dgr¹³C_AROM vs. ^dgr¹³C_SAT indicate a lower Cretaceous source for certain upper Cretaceous and Tertiary oils, while crossplots of pristane/nC₁₇ ratio vs. ^dgr¹³C_SAT crossplots indicate that Wilcox and Sparta oils are heavily biodegraded Mesozoic (lower Cretaceous) oils.

There is an absence of gas accumulations in central Louisiana and southwest Mississippi in Midway, Wilcox, and Sparta reservoirs updip from coeval gas-prone source rocks. This is an indication of a sealing regional fault system and/or stratigraphic migration barrier paralleling the Paleocene-Eocene shelf edge.

Vertical migration of hydrocarbons in northeast Louisiana, central Louisiana, and southwest Mississippi was accomplished primarily through fracture systems caused by wrench faulting; to the south and west, salt tectonics and related normal faulting played significant roles in the process. In onshore and offshore south Louisiana, normal faulting and salt-related tectonics created primary migration pathways.

Regional hydrocarbon generation-migration patterns differ conceptually from those illustrated in previous models employing long-range migration based primarily on geochemical considerations. This new interpretation integrates geochemical, geological, and production data especially useful in identifying new exploration plays in north and central Louisiana and in southwest Mississippi.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994