Print this pageThe Impact of Allochthonous Salt on Petroleum Systems of Northern Green Canyon and Ewing Bank Areas, Northern Gulf of Mexico
McBRIDE, BARRY C., PAUL WEIMER, MARK G. ROWAN
The northern Green Canyon/Ewing Bank region, northern Gulf of Mexico basin, contains the Oxfordian-Neogene (.), Albian-Neogene (.),Turonian-Neogene (.), and Eocene-Neogene (?) petroleum systems. The systems encompass 25 fields/discoveries in the study area and include two subsalt discoveries. Essential elements of the systems include: source shales of Oxfordian, Albian, Turonian, and Eocene age; Neogene siliciclastic turbidite reservoirs; allochthonous salt; and overburden strata ranging in age from Jurassic to Quaternary.
The petroleum systems of the area are significantly impacted by the evolution of allochthonous salt. The high thermal conductivity of salt retards the thermal maturation of subsalt source rocks and causes late generation. Most traps were formed during the Plio-Pleistocene, and the generation-migration- accumulation of petroleum ranges from Early Miocene to the Present The critical moment of peak oil generation for each source varies spatially and temporally as a function of the overlying allochthonous salt evolution.
The impermeability of salt prevents vertical petroleum migration and causes migration pathways to be deflected laterally up the dip of base salt. Where salt welds form, petroleum migration is unimpeded and continues/resumes in a vertical manner. By integrating predictions of potential source rocks, structural restorations, thermal maturation modeling, regional salt maps, and petroleum systems logic, petroleum migration pathways and zones of concentration can be determined. All 25 fields/discoveries within the study area are associated with predicted zones of paleo-subsalt petroleum concentration. Present-day salt geometries do not delineate many of these zones because of salt weld formation during the Pleistocene. The technique enables geoscientists to focus their exploration efforts toward areas with a greater probability of success.