Ryo Matsumoto¹, Yoshikazu Takedomi², and Hironori Wasada³

¹Dept of Earth and Planetary Science, Univ of Tokyo
²Petroleum and Natural Gas Division, METI
³Technical Department, JNOC

ABSTRACT: Exploration of Marine Gas Hydrates in Nankai Trough, Offshore Central Japan

Nankai Trough, extending ~900 km SW-NE offshore southwest Japan, is one of the most prospective areas for marine gas hydrate and possible shallow gas deposits. This area is characterized by extensive distribution of high amplitude BSRs (e.g., Krason, 1992), approximating 32,000km². MITI (or METI: Ministry of Economy, Trade and Industry from Jan.2001) launched R&D project to explore marine gas hydrate in 1995, and JNOC (Japan National Oil Corporation) -JAPEX (Japan Petroleum Exploration) drilled exploration-stratigraphic wells in the eastern Nankai Trough ~50 km off Omaezaki, central Japan, in late 1999 – early 2000. The drilling successfully penetrated BSR at about 270 meters below sea floor and identified massive gas hydrates accumulation. LWD deployments prior to and after the main hole drillings have revealed prominent resistivity anomaly zones ~5 to 60 meters above BSR. Core-temperatures measured on board soon after core retrieval have also demonstrated strong anomalies to indicate that extensive dissociation of gas hydrates occurred during core recovery.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado