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Alexei V. Milkov1, Roger Sassen1
(1) Texas A&M University, College Station, TX

Abstract: Maximum depths of gas hydrate stability, Gulf of Mexico continental slope

Gas hydrate accumulations of the Gulf slope are structurally focused by salt and fault migration conduits from depth. Gas hydrate occurs as mounds and as vein-fillings in fracture porosity with free gas, deformed sediments, and authigenic carbonate. Our research focuses on modeling the thickness of the gas hydrate stability zone (GHSZ) to improve estimates of the total volume of gas hydrate, and to better understand gas hydrate as an exploration and exploitation hazard. Thickness of the GHSZ is a function of hydrocarbon gas availability and composition, water depth, bottom water temperature, pressure and thermal gradients in sediments, and pore water salinity. We used Sloan’s (1998) CSMHYD to estimate equilibrium conditions of bacterial methane gas hydrate (structure I) and thermogenic gas hydrate (structure II). Models are constrained by research submarine observations, piston cores, well logs, and seismic profiles. Study areas include oil and gas seeps with gas hydrate at Green Canyon 185 in 540 meters water depth, Mississippi Canyon 853 in 1060 meters water depth, and Atwater Valley 425 at 1930 meters water depth. The GHSZ of structure Ii gas hydrate increases in maximum thickness from 650 meters at Green Canyon 185 to 1150 meters at Atwater Valley 425. The total volume of gas hydrate in the Gulf slope is lower than previously estimated, but gas hydrate is concentrated rather than dispersed. Because gas hydrate accumulations occur near oil and gas fields, the Gulf slope is particularly prone to gas hydrate hazards.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana