Gas Hydrate System Modeling in the Eastern Nankai Trough, Japan

Fujii, Tetsuya; Ukita, Toshiyasu; Komatsu, Yuhei; Oikawa, Nobutaka; Wygrala, Bjorn P.; Fuchs, Thomas; Rotke, Wolf; Aung, Than Tin

Gas hydrates are pressure/temperature controlled accumulations of mostly methane which occur in sediments at relatively shallow depths. They have not yet been proven commercially, but recent progress in developing appropriate exploration/production methods has provided encouraging results. JOGMEC is conducting long-term feasibility studies to assess the available gas hydrate resources and offshore production methods in the Eastern Nankai Trough, Japan.

More than 10 gas hydrate concentrated zones have been delineated by 2-D/3-D seismic interpretation and petrophysical analysis of multiwell drilling surveys in this area. However, the accumulation mechanisms and gas hydrate systems in this area are not yet well understood. In order to understand gas hydrate accumulations and their spatial distribution and controls by complex geological/geochemical processes and factors, a gas hydrate petroleum systems modeling study had been conducted advanced 2-D/3-D petroleum systems modeling simulators with gas hydrate modeling capabilities.

The study area is 70km from the coast in water depths of 800+m. The first study based on 2-D type-sections was conducted using models based on 11 key geologic horizons with ages measured by oxygen isotope measurements from foraminiferal shells and volcanic ash of core samples. Pressure and temperature distributions were modeled as they are the basic factors which control the Gas Hydrate Stability Zone (GHSZ). High-resolution seismic facies analysis and interpretations were also used to define facies distributions in the 2-D and 3-D models. In the second phase, 3-D petroleum systems modeling is used to determine not only the extent of the GHSZ through geologic time, but also to directly simulate the generation of methane from biogenic sources and the formation of gas hydrates in the available pore space in the GHSZ as well as the resulting effects of the gas hydrates on the physical properties of the sediments. Recent developments in 3-D technology such as high resolution local grid refinements and time steps, provide significant benefits such as improved resolution and accuracy of generation and formation of gas hydrate.

The methodology can then be applied to frontier areas in Japan and will enable predictions of gas hydrate resources to be based on better understanding of the controlling factors and with greater confidence, even in areas with sparse data.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013