Investigating fault control on reservoir accumulation and spatial distribution using 3D seismic data and well logging data: A Case study from the Lower Oligocene Vicksburg Formation, Brooks County, Texas
Turner, Ryan Lewis
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In southern Brooks County, Texas, the Lower Oligocene Vicksburg Formation (LOVF, Rupelian stage, approximately 33.9-27.82 million years ago), is being influenced by the Vicksburg Fault Zone (VFZ). The VFZ is characterized by listric-normal faults that have formed highly faulted rollover anticlines that are sought-after structural traps for hydrocarbon exploration. This research explored how secondary synthetic (dipping East), antithetic (dipping West), and coast-perpendicular faults are affecting the accumulation and spatial distribution of hydrocarbons within the La Rucias Field. Results indicate that synthetic, antithetic, and coast-perpendicular faults affecting the V-102, V-17, and V-19 horizons provide conduits for hydrocarbon migration. Antithetic faults and coast-perpendicular faults within the rollover anticline are terminating beneath the overlying shale seal layer between the V-16 and V-17, creating natural gas accumulation. While synthetic faults affect the overlying seal layer migrating gas out of the V-102, V-17, and V-19. Bidirectional faulting linking antithetic and perpendicular to the coast faults are acting as additional pathways for enhanced hydrocarbon accumulation. Spatial distribution of hydrocarbons within the La Rucias Field varies with the horizon being targeted. Productive V-102 reservoirs are located on the western flank of the rollover anticline, the V-17 and V-19 reservoirs are located on structural highs where antithetic faults are not affecting the overlying shale seal layer, and the most productive V-17 and V-19 reservoirs are being affected by bidirectional faulting terminating beneath the shale seal layer allowing accumulation and spatial distribution within the rollover anticline. Investigating the control of these fault systems enhances our understanding on subsurface fluid migrations and accumulations (oil, gas, groundwater, and contaminants) in the expanded Vicksburg productivity trends.