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AAPG Bulletin

AAPG Bulletin, Preliminary version published online Ahead of Print 15 September 2022.

DOI:10.1306/08182221123

Difference in overpressure environments for the western and central deepwater Gulf of Mexico

Sharon Cornelius1 and Peter A. Emmet2

1 Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, 77204
2 Brazos Valley GeoServices, Inc., 19831 Cypress Church Rd., Cypress, TX 77433

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 geopressure distribution within the deepwater CGOM. Disequilibrium compaction is a major component of the overall GOM overpressure (Yu and Hilterman, 2014; Lahann, 2017); but is more easily discernible in the interval from the seafloor down to where formation temperatures are ˃65°C, at which point temperature-based chemical reactions commenced sequentially with rising temperature. These reactions, which usually produce greater quantitative overpressure than disequilibrium compaction, include hydrocarbon generation, smectite to illite transformation, and sandstone diagenesis. This study has incorporated the western Gulf of Mexico (WGOM) protraction areas of East Breaks, Alaminos Canyon, Corpus Christi, and Port Isabel, where 249 wells were analyzed to verify the CGOM results. The result is that the WGOM is geothermally warmer and considerably underpressured compared to the CGOM. 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 was likely created in situ or proximal to its source. In the WGOM, the formations fractured at some point and geopressure escaped. Compressional velocities versus density crossplots were created for four wells, each well representative of a different protraction area, to indicate the source of local overpressure.

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