"New Insights on Gas Hydrate Reservoirs in the Gulf of Mexico from Pressure Coring"
Stephen C. Phillips, PhD
University of Texas Institute for Geophysics
Gas hydrates are ice-like solids stable in continental margin sediments that potentially represent a large energy resource. Pressure coring technology has allowed for the collection and characterization of sediments while maintaining the high pressures required for hydrate stability. We recovered the first pressurized cores from a coarse-grained hydrate reservoir in the Gulf of Mexico (Green Canyon 955; 410 to 447 m below seafloor; 2032 m water depth). Quantitative depressurization of these cores demonstrates a high methane hydrate concentration up to 93% of the pore space. There is a strong lithologic control of hydrate saturation at this site with interbedded high and low hydrate saturation lithofacies. Sandy silt beds at this site are characterized by consistently high hydrate saturation (79 to 93%). Intervals with lower bulk hydrate saturation (2 to 30%) are composed of thin, high-saturation beds diluted by clay-rich intervals containing little to no disseminated hydrate, as shown by high-resolution X-ray computed tomography and P-wave velocity scans. Gases recovered during these hydrates are composed of 99.99% methane and isotopic analyses suggest the methane is of a microbial origin. Based on the in-situ salinity near seawater concentration, we estimate that the hydrate formed either slowly or as a rapid event tens of thousands of years ago. Ongoing permeability, geomechanical, microbiological, and geochemical analyses will further increase our understanding of hydrate formation processes and reservoir properties.