Sequence-Stratigraphic and Seismic Conceptualization of the Miocene Succession, Starfak and Tiger Shoal Fields, Offshore Louisiana: Implications for Gas-Resource Development in Mature Fields of the Federal OCS

Tucker F. Hentz

ABSTRACT

The Bureau’s Offshore SGR project is a 4-year study funded by the U.S. Department of Energy to investigate new techniques for defining the geologic context of hydrocarbons in an area of mature Miocene gas fields in the northern Gulf of Mexico. Ultimate objectives of the project are to identify additional gas resources and predict regional trends in Miocene hydrocarbon accumulation.

The study is focused on the 10,000-ft-thick regressive Miocene interval in mature Starfak and Tiger Shoal fields, offshore Louisiana. Paramount among the project tasks is construction of a high-resolution (fourth-order, reservoir-scale) sequence-stratigraphic framework to form the chronostratigraphic and genetic context within which all other primary and ancillary efforts of the project can be completed. This framework allows correlation of key genetic surfaces within and between fields, and it enables extrapolation of these surfaces within the 352-mi² area of 3-D seismic coverage. The study interval comprises 10 third-order and 60 fourth-order sequences that represent ~16.5 m.y. Paleontologic data indicate that third-order cycle tops coincide with those of published, basinwide, coastal-onlap curves. Areal patterns from isochore and net-sand maps, amplitude stratal slices, and log-facies analysis indicate that the succession represents basin-floor (bottom-lower Miocene) to proximal-shelf (top-upper Miocene) depositional settings.

Sixty-two reservoirs, representing the full range of systems tracts, occur in the two fields. However, reserves are highly concentrated where fourth-order systems tracts stack to form third-order lowstand systems tracts (LST), which compose only ~30% of the succession. This pattern of resource distribution keyed to third-order LST’s may guide regional resource development in Miocene strata of the northern Gulf of Mexico.

Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924; e-mail: tucker.hentz@beg.utexas.edu.