Gas hydrate and free gas accumulations in the Kumano forearc basin: Insights from seismic velocity analysis via automatic picking algorithm

Chanmaly Chhun, Arata Kioka, Jihui Jia, Takeshi Tsuji

Research output: Contribution to conferencePaperpeer-review

Abstract

To better define the accumulations of gas hydrates and free gases in the Kumano forearc basin which is located above accretionary prism in the Nankai margin off the Kii peninsula, Japan, we performed a high-resolution seismic velocity analysis to 3D seismic data using the method of conventional semblance spectra via automatic velocity picking algorithm. The results revealed that gas hydrate-bearing sediments above bottom-simulating reflector (BSR) and free gas-bearing sediments below BSR are characterized by P-wave velocities of 1900 - 2500 m/s, and 1000 - 1800 m/s, respectively. Gas hydrates are highly concentrated around the rim of the outer ridge where faults are densely developed, whereas free gas reservoirs are widely distributed below BSRs and are considerably high above ridge topography, which is considered as a structural trap for gas reservoirs. Then, the velocity model was converted into a gas hydrate and free gas saturation model using Archie's equations and rock physics models. The results indicated that saturation of gas hydrates and free gases ranges from 0 to 50% and 0-20% in the pore space, respectively. In addition, based on the velocity model of gas hydrates and free gas distribution, we suggested that gas hydrates concentrated due to the free gas influx which migrated upward through steeply dipping strata and faults or fractures cutting through the basin. Therefore, these factors generated by intensive tectonic movements in the plate subduction zone controlled the distribution and saturation pattern of gas hydrate and free gas formations.

Original languageEnglish
Publication statusPublished - Jan 1 2017
Event23rd Formation Evaluation Symposium of Japan 2017 - Chiba, Japan
Duration: Oct 11 2017Oct 12 2017

Other

Other23rd Formation Evaluation Symposium of Japan 2017
CountryJapan
CityChiba
Period10/11/1710/12/17

All Science Journal Classification (ASJC) codes

  • Geotechnical Engineering and Engineering Geology
  • Geology
  • Energy Engineering and Power Technology
  • Economic Geology
  • Geochemistry and Petrology

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