Experimental studies on the occurrence, formation, and dissociation of methane hydrates.

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For the first year of this project, experimental apparatus was designed, manufacutured and installed in the laboratory. Head investigator participated in ODP Led 164 cruise to recover natural gas hydrates from deep sea sediments in the area of Blake Ridge, Atlantic. Therefore, most of experimental and analytical data were obtained for the second year.1, Marine gas hydrates of blake Ridge were observed to occur in sediments between 200 and 450 meters below sealevel. The lower limit is easily explained interms of temperature and pressure of the sediments, but the upper limit is likely to be controled by drastic changes in mineralogy, lithology, and physical roperties at that depth.2, Oxygen isotopic fractionation between methane hydrates and ambient interstitial water was analyzed to be 3-4 permil. These values are similar to the fractionation between ice and water.3, CO_2 hydrates were synthesized in pure water with pH of 3.2-3.3, and in CH3CO2Na-CH3CO2H buffer solutions with pH of 3.1 and 5.2. Total concentration of acetic acid and acetate anion of the buffer solutions range between 0.2M AND 1M.The results imply that change of pH value has minimum influence on the equilibrium condition of CO_2 hydrate. The equilibrium condition are mainly controlled by the total concentration of acetic acid and acetate anion, and Na+ cation plays a minimum role. The total concentration also controls the induction time for the formation of CO_2 hydrate in the pH buffer solutions. The solubility change of CO_2 gas in solutions, which is possibly caused by the pH variation, is another factor controlling the induction time.