Overview of the MITI Nankai Trough Wells: A Milestone in the Evaluation of Methane Hydrate Resources |
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Authors: | Yoshihiro Tsuji Hisashi Ishida Masaru Nakamizu Ryo Matsumoto Satoshi Shimizu |
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Affiliation: | Technology Research Center, Japan National Oil Corporation (Presently Japan Oil, Gas and Metals National Corporation), 1–2-2 Hamada, Mihama-ku, Chiba 261–0025, Japan [e-mail: ];Department of Earth and Planetary Science, University of Tokyo, 7–3-1 Hongo, Bunkyo-ku, Tokyo 113–0033, Japan;Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry, 1–3-1 Kasumigaseki, Chiyoda-ku, Tokyo 100–8931, Japan |
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Abstract: | Abstract. Bottom-simulating reflectors suggestive of the presence of methane hydrates are widely distributed below the ocean floor around Japan. In late 1999, drilling of the MITI Nankai Trough wells was conducted to explore this potential methane hydrate resource and a Tertiary conventional structure. The wells are located in the Northwest Pacific Ocean off Central Japan at a water depth of 945 m. A total of six wells were drilled, including the main well, two pilot wells, and three post survey wells at intervals of 10–100 m. All wells except the first confirmed the occurrence of hydrates based on logging-while-drilling, wire-line logging and/or coring using a pressure and temperature coring system in addition to conventional methods. Based on the various well profiles, four methane hydrate-bearing sand-rich intervals in turbidite fan deposits were recognized. Methane hydrates fill the pore spaces in these deposits, reaching saturation of up to 80 % in some layers. The methane hydrate-bearing turbiditic sand layers are less than 1 m thick, with a total thickness of 12–14 m. The bottom depth of high hydrate concentration correlates well with the depth of the bottom-simulating reflector. Based on these exploration results, the Japanese government inaugurated a 16-year methane hydrate exploitation program in 2001. |
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Keywords: | methane hydrate BSR Nankai Trough drilling turbidite resource LWD PTCS |
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