Potential Pressure Compartments Sub-Salt in the Gulf of Mexico and Beneath Massive Debris Flows in the Gulf of Cadiz

Abstract

Pressure compartments may be defined as those volumes within the earth’s subsurface that are characterized by specific temperature/pressure ranges for the contained fluid. These compartments are the result of lithology, ability to contain/expel fluids, and the stresses from local tectonics. Until now, pressure compartments have been described for those zones well explored by seismic and well data. Potential compartments are suggested for zones that are under initial geophysical reconnaissance. These zones are volumes beneath the sub-salt play of the deep- water Gulf of Mexico and in the lower slope/continental rise of the Gulf of Cadiz.

Three known pressure compartments include normal- and geo-pressured units above the Louann Salt and a "gumbo zone" beneath the salt in the Gulf of Mexico. Additionally, a shear couple may be established as the migrating salt wedge overrides stationary basement. Stresses may be compressive above the proposed shear zone and extensional below it, resulting in a right-lateral motion. Tectonic stresses coupled with a slight upward coarsening of sediments from basement may result in the development at least two separate pressure compartments, above and below the potential shear zone.

Mass wasting, from blocks to turbidites, has occurred along the Atlantic-facing Iberian and Moroccan continental margins over a downdip distance up to 300 km. Salt and clays within the migrating blocks and stacked thrusts have served as lubricants. The juxtaposition of varying lithologies could provide boundaries for complex compartments. The potential compartments discussed are located 5 to 12 km sub-surface. Local tectonics becomes an integral component in compartment development.