Contrasting geothermal and geopressured environments of the Western and Central deepwater Gulf of Mexico

Abstract:

I have compiled geopressure and geothermal gradients in the Central Gulf of Mexico (CGOM) protraction areas of Garden Banks, Green Canyon, Keathley Canyon, and Walker Ridge to gain a better understanding of overpressure distribution in the deepwater CGOM. Disequilibrium compaction is a minor component of the overall overpressure and is limited to the interval from the seafloor down to where the formation was ˃60°C, at which point temperature-based chemical reactions commenced sequentially with rising temperature. These reactions which produce more overpressure than disequilibrium compaction include hydrocarbon generation, smectite to illite transformation, sandstone diagenesis, and thermal gas production. This study includes the Western Gulf of Mexico (WGOM) protraction areas of East Breaks, Alaminos Canyon, Corpus Christi, and Port Isabel, where 227 wells were analyzed to verify the CGOM results. The result is that the WGOM is very different than the CGOM because the WGOM is geothermally warmer and considerably under-pressured. When measured and calculated temperature-pressure pair data points at varying depths along the boreholes were plotted for both regions separately, both the CGOM and WGOM exhibited a linear relationship. The linear regression R² for the CGOM plot =0.781 for 381 data points; and for the WGOM with 513 data points, R² = 0.718. The distribution of the data on each plot is very different. Due to the cooler geothermal gradients in the CGOM, most overpressure encountered was likely created in situ or proximal, whereas in the WGOM with much warmer geothermal gradients and noticeably diminished quantities of expected overpressure, I conclude that formations fractured at some point in geological time and excess pressure escaped.