International Conference on Gas Hydrates (ICGH) (6th : 2008)

FORMATION PROCESS OF STRUCTURE I AND II GAS HYDRATES DISCOVERED IN KUKUY, LAKE BAIKAL Hachikubo, Akihiro; Sakagami, Hirotoshi; Minami, Hirotsugu; Nunokawa, Yutaka; Yamashita, Satoshi; Takahashi, Nobuo; Shoji, Hitoshi; Kida, Masato; Krylov, Alexey; Khlystov, Oleg; Zemskaya, Tamara; Manakov, Andrey; Kalmychkov, Gennadiy; Poort, Jeffrey

Abstract

Structure I and II gas hydrates were observed in the same sediment cores of a mud volcano in the Kukuy Canyon, Lake Baikal. The sII gas hydrate contained about 13-15% of ethane, whereas the sI gas hydrate contained about 1-5% of ethane and placed beneath the sII gas hydrate. We measured isotopic composition of dissociation gas from both type gas hydrates and dissolved gas in pore water. We found that ethane δD of sI gas hydrate (from -196 to -211 ‰) was larger than that of sII (from -215 to -220 ‰), whereas methane δ13C, methane δD and ethane δD in both hydrate structures were almost the same. δ13C of methane and ethane in gas hydrate seemed several permil smaller than those in pore water. These results support the following idea that the current gas in pore water is not the source of these gas hydrates of both structures. Isotopic data also provide useful information how the “double structure” gas hydrates formed.

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