Sequence Stratigraphic Controls on Reservoir Compartmentalization, Hydrocarbon Distribution and Optimization of Field Development Process: Vicksburg Trend, South Texas, U.S.A.

Victor D. Rahmanian, Martin L. Thering, and Patrick B. Ely

We have utilized integrated core facies, well log and 3-D Seismic Sequence stratigraphy and production history of the Vicksburg Formation to understand and delineate reservoir distribution, optimize field development and guide field management processes. In South Texas area, as much as 4000 feet of the Oligocene Vicksburg strata are preserved as rollover anticlines and their associated antithetic and synthetic faults. This stratal configuration resuited from syndepositional movement of the expanded Vicksburg strata along a composite decollement surface on top of the underlying Eocene Jackson shale. The highly compartmentalized and complex Vicksburg reservoirs were developed in a high-accommodation depositional setting controlled by a complex interaction between eustatic f uctuations and syndepositional listric normal fault movement The Vicksburg Formation is marked by a distinctive hierarchy of sequence stacking and an orderly and predictive pattern of lateral sequence distribution. It can be characterized as a super sequence composed of a lower aggradational lowstand, middle retrogradational transgressive, and upper progradational highstand composite sequence sets. The sequence sets are, in turn, composed of numerous high-frequency sequences. The high-frequency sequences range from 50-100 feet in thickness and are dominated by sandy lowstand and mud-prone transgressive systems tract parasequences of deltaic and shoreface to offshore origin, respectively. Lateral patterns of reservoir facies, geometry, quality and distribution are profoundly controlled by the structural positions of strata within the rollover sedimentary wedges and/or proximity to syndepositional faults. Reservoir facies are thicker, sandier and of better quality in a down flank or proximal direction.

During development of late lowstand to transgressive composite sequence sets the older Vicksburg depocenters were retrogradationally displaced in landward direction across the top of the underlying Jackson Shale. This displacement resuited in generation of progressively younger decollement surfaces and associated rollover sedimentary wedges which merged in landward direction with older segments to define the basal Vicksburg composite decollement surface. In time, these processes resulted in landward repetition of the reservoir facies and architecture observed in the older rollover sedimentary wedges.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California