STRUCTURAL CONSTRAINTS ON THE BURIAL OF JURASSIC AND CRETACEOUS PETROLEUM SOURCE ROCKS OF EAST TEXAS: INSIGHTS FROM INTERPRETATION AND RESTORATION OF REGIONAL 2D SEISMIC LINES

The U.S. Geological Survey has conducted assessments of the undiscovered technically recoverable oil and gas resources in Jurassic, Cretaceous, and Tertiary strata of the onshore coastal plain and State waters of the U.S. Gulf Coast. The assessment methodology includes a detailed examination of the geometric and kinematic evolution of structural traps. The histories of trap growth are then integrated into models that describe petroleum source rock burial and the subsequent expulsion of petroleum. For the Jurassic and Cretaceous portion of the assessments, a sparse regional set of 2D seismic lines covering parts of east Texas and southern Louisiana were interpreted. Based upon this seismic interpretation, a 2D structural restoration was built along key seismic lines to show the Jurassic to Holocene evolution of east Texas. The restoration extends from Texas State waters of Galveston County in the south to Delta County near the Texas-Oklahoma state line in the north. The restoration models the evolution of the region’s primary structural features, including the Talco and Mount Enterprise fault zones, the East Texas salt basin, the Sabine uplift, the Angelina-Caldwell flexure, and the Houston diapir province. The seismic interpretation and structural restoration document the genetic relationship between potential structural traps and movement of the Jurassic Louann Salt. Furthermore, it appears that unexplored structures that exhibit a wide variety of geometries may exist beneath the current drilling floor.

Thermal models that integrate burial histories and kinetics were also created for the region’s two primary petroleum source rocks, the Oxfordian Smackover Formation and the Cenomanian-Turonian Eagle Ford Shale. The thermal models suggest that, across east Texas, oil generation from the Smackover Formation and the Eagle Ford Shale began at depths of about 5,800 ft and 10,000 ft, respectively. Integrating these results with the structural model permits a general understanding of the timing and spatial extent of petroleum expulsion from these primary source rocks along the line of the structural restoration in east Texas. Additionally, it appears that the timing of formation of salt-related structural traps was favorable for petroleum charge.