Japan Geoscience Union Meeting 2022

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[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS26] Gas hydrates in environmental-resource sciences

Thu. May 26, 2022 3:30 PM - 5:00 PM 203 (International Conference Hall, Makuhari Messe)

convener:Hitoshi Tomaru(Department of Earth Sciences, Chiba University), convener:Akihiro Hachikubo(Kitami Institute of Technology), Shusaku Goto(Institute for Geo-Resources and Environment National Institute of Advanced Industrial Science and Technology), Chairperson:Shusaku Goto(Institute for Geo-Resources and Environment National Institute of Advanced Industrial Science and Technology), Akihiro Hachikubo(Kitami Institute of Technology)

4:00 PM - 4:15 PM

[MIS26-07] Marine CSEM survey and 3-D resistivity structure inversion at Mogami Trough, offshore Sakata, Yamagata Pref., Japan: investigation of the presence of shallow methane hydrate

*Shogo Komori1, Toshiyuki Yokota1, Shusaku Goto1 (1.National Institute of Advanced Industrial Science and Technology)

Keywords:methane hydrate, CSEM, HR3D, resistivity, anisotropy

We investigated the spatial distribution of shallow methane hydrate in mud-dominant sediment in and around a small knoll (called Sakata Knoll) at Mogami Trough in 2017, using the marine controlled source electromagnetic (CSEM) method. In the knoll, gaseous fluids under the seabed were suggested by sub-bottom profiling (SBP) surveys. Logging-while-drillings (LWD) suggested existences of massive methane hydrates at and around the top of the knoll. In the CSEM survey, we used the SUESI-Vulcan system owned by Scripps Institution of Oceanography. The equally spaced four receivers recorded time series data including three components of electric field (Ex, Ey, Ez), which are generated by the injected current of c.a. 200 Amps from the transmitter with the dipole length of 50 meters. The obtained data were transformed to frequency-domain electric field after the correction of the transmitter and receiver positions and normalization of the field by the dipole-moment of the current source. The processed data were used for three-dimensional imaging of the resistivity structure. In order to examine the robustness of the inverted models, several inversions were performed by controlling the inversion settings as follows: 1) number of the electric field component, 2) anisotropy of the resistivity of the sediments, and 3) initial condition of the resistivity. Note that the initial conditions of the resistivity were specified using the result from high resolution three-dimensional seismic survey conducted in 2019. We will report the overview of the CSEM survey and the inverted results.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).