Lithologic controls on reservoir quality and production trends in the Pettet Formation, Rusk County, east Texas

Abstract

The Early Cretaceous Pettet Formation of east Texas, United States, was deposited as part of the giant Comanche carbonate platform of the northern Gulf of Mexico. It is largely characterized by shallow-water platform interior carbonates, including skeletal-oolitic shoals and muddy green algae-rich lagoons. The Pettet is broken up into four subunits (Pettet A, B, C, and D), each of which represents a high-frequency sequence. Within the framework of these sequences, mapping of distribution and thickness of skeletal-oolitic shoal intervals uncovers progradational and retrogradational patterns at a larger scale. These shoal intervals are the main hydrocarbon targets in the Pettet play. Integration of mapped shoal intervals with historic well production data from Rusk County, Texas, reveals that there are three main controls on productivity: (1) reservoir facies type, (2) diagenetic alteration, and (3) regional structure. Shoal-complex mixed skeletal-oolitic grainstones are shown to have significantly better reservoir quality than shoal-complex ooid grainstones and off-shoal packstone facies. Although the Pettet B and C shoal intervals are both widespread throughout Rusk County, the Pettet B is dominated by mixed skeletal-oolitic grainstones, whereas the Pettet C is ooid dominated. The Pettet B is also less diagenetically altered, with fewer late-stage pore-occluding calcite cements than the Pettet C; consequently, it is considered to be a better reservoir interval. Production data corroborate these findings and additionally show the influence of structure on hydrocarbon accumulations. The integrated data highlight the continued potential of the Pettet, both in terms of new exploration and existing wells that may bypass potential Pettet reservoirs.