Gas hydrate stability in the Gulf of Mexico: Significance to resource estimation, geohazards, and global change.

摘要

Models of gas hydrate stability for the northern Gulf of Mexico continental slope address basic problems of gas hydrate geology. The maximum thickness of the gas hydrate stability zone (GHSZ) at key gas hydrate study sites is estimated, and a generalized GHSZ profile across part of the central Gulf of Mexico slope is constructed. The thickness of the GHSZ increases with increasing water depth and may reach >1 km at deepest gas hydrate sites.; Resource estimation is based on assessment of the volume of the GHSZ and concentration in sediments. The total estimate of gas hydrate resource in the Gulf of Mexico (10–14 × 1012 m3) is two orders of magnitude less than previously estimated. However, structurally-controlled accumulations of gas hydrate on the rims of salt withdrawal basins could be economic in the future. Bacterial gas hydrates in salt withdrawal basins are unlikely to represent a significant energy resource because they are disseminated.; The modeled minimum water depths at which gas hydrates crystallize at present in the Gulf of Mexico is 330–615 m, depending on the source gas composition. Bottom water temperature variations from seasonal changes and warm Loop Current eddies could affect seafloor gas hydrate stability only in the upper 1–2 m of sediments. A thin but extensive hydrate geohazard zone is hypothesized on the upper Gulf slope in 440–720 m water depth. Petroleum exploitation may be impacted in this zone by sediment deformation from repetitive cycles of gas hydrate formation and dissociation.; It has been suggested that release of methane from sudden decomposition of gas hydrates could cause geologically rapid global change. The potential effect of a 100 meter sea level drop on gas hydrate stability across the slope is not significant. Larger volumes of methane and other greenhouse gases could be released in response to an increase in seafloor water temperature of 4°C. However, several processes keep the released gas in sediments. More complicated models are needed to estimate the amount of hydrate-released gas that escapes to the ocean and participates in global change.