STRATIGRAPHIC AND STRUCTURAL CONTROLS ON THE DEVELOPMENT OF PALEOGENE PETROLEUM SYSTEM ELEMENTS IN THE ONSHORE AND STATE WATERS OF THE TEXAS GULF COAST

To support the USGS assessment of technically recoverable undiscovered hydrocarbons in the downdip Tertiary of the onshore and State waters of the Gulf of Mexico Basin, an updated geologic model was developed to account, in part, for complex structural geology in the deep Paleogene of the Texas Gulf Coast. Interpretations of newly licensed regional 2-D seismic lines, legacy geophysical well logs, and associated biostratigraphic data have led to an improved understanding of prevailing structural styles in this frontier hydrocarbon exploration area.

Stratigraphic markers were interpreted for the top Cretaceous, top Upper Paleocene-Lower Eocene Wilcox Group, top Middle Eocene Claiborne Group (Cockfield Formation), near base Upper Eocene Moodys Branch Formation (Jackson Group), and top Oligocene using regional seismic reflectors correlated with a regional well log framework. The interpretations led to an updated geologic model for the downdip Tertiary petroleum system elements including the transition from stable shelf to expanded fault zone to slope depositional environments, and associated structural and stratigraphic elements such as growth faults and shale detachments, evacuated salt welds and salt-cored ridges, intra-slope basins and ponded turbidite fill, slumps, and channel-levee systems.

Representative depths interpreted for the top Cretaceous (base Paleogene) range from about 5,000 ft. on the paleo-shelf to over 20,000 ft. on the paleo-slope, whereas interpreted depths for the top Oligocene (top Paleogene) range from a few hundred feet on the paleo-shelf to over 10,000 ft. on the paleo-slope. Stratigraphic boundaries steepen considerably across the expanded fault zone, but resume to a more gradual regional dip in the paleo-slope. Variably scaled faulting may create migration pathways from deep source rocks and set up traps for hydrocarbons. However, faulting may increase the potential for hydrocarbon leakage and increasing burial depth may degrade reservoir quality. Thick deposits of sandy sediment in the Paleogene of the onshore and State waters of the Texas Gulf Coast indicate abundant fluvial-deltaic supply from Rocky Mountain sources along the ancient Rio Grande and Houston-Brazos Rivers input axes.