INTERPRETATION OF GAS HYDRATE PROSPECT IN THE MIYAZAKI-OKI FOREARC BASIN, JAPAN

JOGMEC, as a member of Research Consortium for Methane Hydrate Resources in Japan (MH21), has been conducting resources assessment of Gas hydrate (GH) offshore Japan. This study presents interpretation of GH prospect in Miyazaki Oki area using four factors, high velocity, high amplitude, porous sedimentary formation and bottom simulating reflector (BSR), reported in previous studies by the JOGMEC resource exploration team. Presence of 3D migration seismic and velocity date makes this study feasible.

Study area comprises lower Miocene to Pleistocene, deep to shallow marine sedimentary successions of Hyuganada group and Miyazaki Group overlain the basement Shimanto Group. The BSR were interpreted in Pliocene Hyuganada group and Pleistocene Miyazaki Group. Based on previous studies, we assumed that velocity value of GH prospects are higher than surroundings. Using this velocity filter, better interpretation of GH prospects were achieved. Not only representing high velocity values, GH prospects were also closely associated with high amplitude anomalies and channel distribution depicted from seismic facies analysis. In this study area, several folds and faults were also observed. We have included presence of anticline structure in evaluating interpreted GH prospects. Usually hydrocarbon are trapped in anticline structure as it has upward migration tendency due to its physical nature. So we have conducted 2D petroleum system modeling to confirm the GH accumulation process in and around those anticlinal structures.

As above, even the area has not been drilled, the extraction of GH prospects can be made by our four factors interpretation method integrating with petroleum system modeling approach. And we hope these results will provide useful information in making decision of the future drilling program.