--> ABSTRACT: Evaluation of Sub-Salt Hydrocarbon Potential Using Structural Restorations, by Barry C. McBride; #91020 (1995).

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Evaluation of Sub-Salt Hydrocarbon Potential Using Structural Restorations

Barry C. McBride

Assessing the evolving petroleum system of the deep Gulf of Mexico sub-salt play requires a means of quantifying allochthonous salt flow and associated structures through time. Sequential structural restorations of allochthonous salt provide an evolving framework for integrating both reservoir distribution and hydrocarbon migration pathways. An understanding of the structural evolution of salt and its influence on reservoir deposition and hydrocarbon migration pathways illuminates why some sub-salt regions have a much greater potential of containing hydrocarbons than supra-salt mini-basins or other sub-salt areas. Such an analysis can focus an exploration program and identity key areas for detailed prospect evaluation.

Eleven regional seismic profiles across the Green Canyon and Ewing Bank lease areas of offshore Louisiana have been depth converted and sequentially restored back to 55 Ma. The restorations illustrate the evolution of allochthonous salt and suggest that certain sub-salt regions should experience a significantly higher concentration of hydrocarbon flow, for longer times, than equivalent age strata within adjacent mini-basins. Precursor bowl-shaped salt bodies formed the current mini-basins through evacuation. These precursor salt bodies should have diverted the underlying hydrocarbon flow laterally and upward toward reservoirs beneath adjacent shallow salt tongues until salt welds formed within the mini-basins. Therefore, reservoirs beneath the shallow allochthonous salt bodies adjacent to mini-basins (such as at Mahogany) are more likely to receive and trap a larger quantity of hydrocarbons over time.

Because of the inherent three-dimensional structural complexity of salt flow and its influence on sediment deposition and deformation, three-dimensional structural restorations and structure maps are used to identity shallow sub-salt areas which experienced concentrated hydrocarbon flow in three-dimensions through time (four-dimensional analysis).

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995