Controls on Hydrocarbon Distribution within a Sequence-Stratigraphic Framework: A Case Study from the Miocene of Offshore Louisiana

Tucker F. Hentz, Hongliu Zeng, Lesli J. Wood, Adrian C. Badescu, Claudia Rassi, and Cem O. Kilic1

ABSTRACT

A detailed sequence-stratigraphic analysis of most of the Miocene Series of offshore Louisiana tests the hypothesis that overall hydrocarbon distribution is better understood within a sequence-stratigraphic framework. The study focused on the 10,000-ft-thick regressive Miocene interval in the mature Starfak and Tiger Shoal fields, offshore Louisiana. High-resolution sequence-stratigraphic analysis shows that the Miocene comprises 10 third-order and 60 fourth-order sequences. A full range of systems tracts and depositional facies are encountered, and hydrocarbons have been produced from all fourth-order systems tracts. However, reserves are concentrated where fourth-order systems tracts stack to form third-order LST’s, which compose only ~30% of the succession. Within the fields, 92.6% of all gas and 98.0% of all oil has been produced from third-order LST’s. Although a strong structural-trapping component is present in the fields, the stratigraphic control on reservoir occurrence explains much of the resource-distribution patterns.

Third-order LST’s have optimal reservoir-quality, seal, and source juxtapositions. They are overlain by thick shales of third-order TST’s and early HST’s that create effective regional hydrocarbon seals. Component fourth-order LST’s are dominated by high-quality lowstand incised-valley and deltaic-wedge sandstone facies. They are typically the coarsest grained rocks in the succession and typically have porosity and permeability values higher than those of sandstones from other systems tracts. Commonly thick, stacked deltaic-wedge sandstones isolated within slope and basinal shales have ideal conditions for potential hydrocarbon migration and entrapment. This pattern of resource distribution keyed to third-order LST’s may serve as a guide for more regional resource development in Miocene strata of the northern Gulf of Mexico.

1Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713; e-mail: tucker.hentz@beg.utexas.edu; hongliu.zeng@beg.utexas.edu; lesli.wood@beg.utexas.edu; adrian.badescu@beg.utexas.edu; claudia.rassi@beg.utexas.edu; cem.kilic@beg.utexas.edu.