GAS HYDRATE FORMATION IN THE DEEP-SEA - IN-SITU EXPERIMENTS WITH CONTROLLED-RELEASE OF METHANE, NATURAL-GAS, AND CARBON-DIOXIDE

We have utilized a remotely operated vehicle (ROV) to initiate a progr am of research into gas hydrate formation in the deep sea by controlle d release of hydrocarbon gases and liquid CO2 into natural sea water a nd marine sediments. Our objectives were to investigate the formation rates and growth patterns of gas hydrates in natural systems and to as sess the geochemical stability of the reaction products over time. The novel experimental procedures used the carrying capacity, imaging cap ability, and control mechanisms of the ROV to transport gas cylinders to depth and to open valves selectively under desired P-T conditions t o release the gas either into contained natural sea water or into sedi ments. In experiments in Monterey Bay, California, at 910 m depth and 3.9 degrees C water temperature we find hydrate formation to be nearly instantaneous for a variety of gases. In sediments the pattern of hyd rate formation is dependent on the pore size, with flooding of the por e spaces in a coarse sand yielding a hydrate cemented mass, and gas ch anneling in a fine-grained mud creating a veined hydrate structure. In experiments with liquid CO2 the released globules appeared to form a hydrate skin as they slowly rose in the apparatus. An initial attempt to leave the experimental material on the sea floor for an extended pe riod was partially successful; we observed an apparent complete dissol ution of the liquid CO2 mass, and an apparent consolidation of the CH4 hydrate, over a period of about 85 days.