MINERALS MANAGEMENT SERVICE ASSESSMENT AND STUDIES OF GAS HYDRATES IN THE GULF OF MEXICO

Jesse L. Hunt, Jr.
Minerals Management Service, New Orleans, LA

Use of 3D-seismic surface amplitude mapping has proved to be a rapid and reasonably accurate method of identifying seafloor areas affected by fluid and gas expulsion. Minerals Management Service (MMS) to date has mapped the seafloor reflector on 138 contiguous and overlapping 3-D seismic surveys covering approximately 90% of the Louisiana slope and 80% of the Texas slope. Efforts to differentiate the seismic amplitude response of seep-related features such as gas hydrates, authigenic carbonates, and chemo-synthetic communities have been undertaken using existing core data, limited direct seafloor observations using manned submersibles, and other bottom samples and images. Further identification of seafloor hydrates from 3-D seismic amplitude data has been attempted on a limited basis using seismic wave-form analysis.

The decision has been made by MMS to include gas hydrates in the next resource assessment for the Outer Continental Shelf. An effort is currently underway using seismic amplitude data, existing core holes, shallow well logs, temperature data, gas composition distribution, and sediment thickness over salt to delineate and estimate the areas on the slope of the Gulf of Mexico which are likely to contain gas hydrates, and those areas where they are unlikely to occur. Four occurrence types will be evaluated: vein-filled muds adjacent to vent areas, pore-filling of sands which occur completely within the gas hydrate stability zone, pore-filling of sands which straddle the gas hydrates stability zone with free gas trapped below, and gas hydrates contained in cap rock. Economic models are being developed for the final evaluations.