A trial of the delineation of gas hydrate-bearing sediments using multi seismic attributes analysis offshore Tokai Japan

MITI Research well Nankai Trough was drilled at the offshore Tokai Japan in 1999/2000 and the occurrence of gas hydrate was confirmed by borehole measurments or core. It gave us so big impact to the view of Japanese future energy resources and other scientific interests. METI, Ministory of Economy, Trade and Industry of JAPAN, started "The Research for Methane Hydrate Resources in Japan" from fall of 2001. Bottom Simulating Reflectors (BSRs) were widely found on the marine seismic data acquired offshore Japan, especially in the shelf-slope near the Nankai Trough. If we will explore and exploit the gas hydrate, we have to get the information of hydrate-bearing sediments, such as their saturation, porosity or thickness. BSRs indicate the existance of gas hydrates accurately, they, however, do not estimate reservoir parameters. In order to estimate the amount of gas hydrates accurately, we have to get the more detailed reservoir parameters. We computed the multi-seismic attributes and after that, we tried to delineate hydrate-bearing sediments. Firstly, we get some seismic attibutes sections which show such as the P-reflectivity(P), Gradient(G), Products(P*G), Poisson's ratio change sections from pre-stack(AVO) analysis and the P-wave interval velocity section and P-wave impedance sction.