Abstract

Previous results from the central Gulf of Mexico (CGOM) protraction areas of Garden Banks, Green Canyon, Keathley Canyon, and Walker Ridge included calculation of both geopressure and geothermal gradients from 150 wells and produced a new understanding of the overpressure distribution within the deepwater CGOM. Disequilibrium compaction is a major component of the overall GOM overpressure; but it is more easily discernible in the interval from the seafloor down to where formation temperatures were <65°C, at which point temperature-based chemical reactions commenced sequentially with rising temperature. These reactions, which generally produce more quantitative overpressure than disequilibrium compaction, include hydrocarbon generation, smectite to illite transformation, and sandstone diagenesis. Recent work has included the western Gulf of Mexico (WGOM) protraction areas of Port Isabel, Corpus Christi, East Breaks, and Alaminos Canyon, where 249 wells were similarly analyzed to verify the CGOM results. The result of this work indicates that the WGOM is very different from the CGOM in that it is geothermally warmer and considerably underpressured. Measured and calculated temperature-pressure pair data points at varying depths within the boreholes were plotted separately for both regions. The distribution of the data on each plot is regionally unique. In the CGOM, most overpressure encountered was likely created in situ or proximal. In the WGOM, due to increased geothermal heat, the implication is that formations fractured at some point in geological time and overpressure escaped. Therefore, in the WGOM, the majority of the overpressure observed today likely is either a diminished remnant pressure or geologically recent disequilibrium compaction pressure. Compressional velocities versus density crossplots were created for four wells, each well in a different protraction area to indicate the source of local overpressure.