OS2B-1:MODELING GAS HYDRATE PETROLEUM SYSTEMS OF THE PLEISTOCENE TURBIDITIC SEDIMENTARY SEQUENCES OF DAINI ATSUMI AREA, EASTERN NANKAI TROUGH, JAPAN

    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 MH R&D Division has been conducting long-term feasibility studies to assess the available gas hydrate resources and offshore production methods in the eastern Nankai Trough. More than 10 gas hydrate concentrated zones have been delineated by 2D/3D seismic interpretation and petrophysical analysis of multiwell drilling surveys in the eastern Nankai Trough. Diani Atsumi area with the Pleistocene turbiditic sedimentary sequences is one of prominent gas hydrate concentrated zones which has been selected for the first offshore production test site.

    We performed 2D and 3D gas hydrate petroleum systems modeling of Daini Atsumi Area to understand the accumulation mechanisms and their spatial distribution related to the geological/geochemical processes using advanced 2D/3D petroleum systems modeling simulators with gas hydrate modeling capabilities. Model area is 70 km from the coast in water depths of 800+m and occupied with 11 turbiditic sedimentary sequences of the Pleistocene Ogasa Group. Geologic ages are obtained from the oxygen isotope measurements of foraminiferal shells and volcanic ash of core samples. High-resolution seismic facies analysis and interpretations were also used to define facies distributions in the models. 2D models are built and ran simulation to confirm the parameters to be used in 3D modeling.

    Global sea level changes are taken into account in application of paleowater depth of the deposited sedimentary sequences. Pressure and temperature distributions were modeled as they are the basic factors which control the Gas Hydrate Stability Zone (GHSZ). We have applied measured thermal conductivity and heat capacity of AT1-MC well. Furthermore distributed temperature sensor (DTS) data at well AT1-MC was used for heat flow calibration. Simulated temperature using calibrated heat flow shows good match with DTS temperature at well AT1-MC. Preliminary 3D modeling results suggested that the direction of sediment supply (i.e. distribution of sandy sediments) and formation dip direction can be important controlling factor of gas hydrate accumulation. We will investigate more on simulation results in terms of the generation of methane from biogenic sources and accumulated gas hydrates volume 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. Those investigated results will be presented in the conference.