Hydrates are found in shallow, near-seafloor sediments in most deep-water environments. The source of the hydrocarbon gases that form these hydrates can be biogenic or thermogenic in origin. In prolific hydrocarbon basins such as the Gulf of Mexico, thermogenic gases can make a significant contribution to deepwater hydrate systems, particularly when there are vertical permeability pathways for deep gases to migrate upward to the seafloor where pressure and temperature conditions are optimal for hydrate stability.

Scientists at the Bureau of Economic Geology have developed unique methods for studying deepwater hydrates across the Gulf of Mexico. In these studies, fourcomponent ocean-bottom-cable (4C OBC) seismic data are used to produce highresolution P-P and P-SV images of nearseafloor geology. The energy source used to generate the 4C OBC data is a standard air-gun array towed at a depth of a few meters. Although this system generates an illuminating wavefield with frequencies of less than 200 hertz, geological detail as small as one meter can be imaged using proper data-processing procedures.

This discussion will explain how hydrates are embedded in nearseafloor sediment, illustrate the nature of the hydrate targets that are to be imaged, show how high-resolution target imaging is achieved, describe how P-wave and S-wave seismic attributes are used to estimate hydrate concentration, and compare seismic estimates of hydrate concentration with estimates calculated from resistivity logs at calibration wells.

Chunks of gas hydrates recovered from the sea floor in the Gulf of Mexico in 2002.Photograph source: United States Geological Survey.

End_of_Record - Last_Page 29---------------