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Estimation of spatial distribution and fluid fraction of a potential supercritical geothermal reservoir by magnetotelluric data: a case study from Yuzawa geothermal field, NE Japan
  • +11
  • Keiichi Ishizu,
  • Yasuo Ogawa,
  • Keishi Nunohara,
  • Noriyoshi Tsuchiya,
  • Masahiro Ichiki,
  • Hideaki Hase,
  • Wataru Kanda,
  • Shinya Sakanaka,
  • Yoshimori Honkura,
  • Yuta Hino,
  • Kaori Seki,
  • Kuo Hsuan Tseng,
  • Yusuke Yamaya,
  • Toru mogi
Keiichi Ishizu
Volcanic Fluid Research Center, Tokyo Institute of Technology

Corresponding Author:[email protected]

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Yasuo Ogawa
Volcanic Fluid Research Center, Tokyo Institute of Technology
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Keishi Nunohara
Graduate School of Environmental Studies, Tohoku University
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Noriyoshi Tsuchiya
Tohoku University
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Masahiro Ichiki
Tohoku University
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Hideaki Hase
Geothermal Energy Research & Development Co., Ltd.
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Wataru Kanda
Volcanic Fluid Research Center, Tokyo Institute of Technology
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Shinya Sakanaka
Unknown
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Yoshimori Honkura
Tokyo Institute of Technology, Volcanic Fluid Research Center
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Yuta Hino
Volcanic Fluid Research Center, Tokyo Institute of Technology
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Kaori Seki
Kokusai Kogyo Co., Ltd.
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Kuo Hsuan Tseng
Department of Earth and Planetary Sciences, Tokyo Institute of Technology
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Yusuke Yamaya
Fukushima Renewable Energy Institute, AIST
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Toru mogi
Volcanic Fluid Research Center, Tokyo Institute of Technology
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Abstract

Magmatic fluids within the crust may exist under supercritical conditions (e.g. >374°C and >22.1 MPa for pure water). Geothermal systems using such supercritical fluids have gained attention as unconventional geothermal resources because they can offer significantly more energy than conventional geothermal fluids with temperatures <350°C. Although an understanding of the spatial distribution and fluid fraction of supercritical geothermal reservoirs is necessary for their resource assessment, the spatial distribution and fluid fraction of supercritical geothermal reservoirs worldwide are poorly understood due to the limited number of geophysical observations. Here, the magnetotelluric (MT) method with electrical resistivity imaging was used in the Yuzawa geothermal field, northeastern Japan, to obtain information on the fluid fraction and spatial distribution of a supercritical geothermal reservoir. Our MT data revealed a potential supercritical geothermal reservoir (>400°C) with a horizontal dimension of 3 km (width) × 5 km (length) at a depth of 2.5–6 km. The estimated fluid fraction of the supercritical reservoir was 0.5–2% with a salinity of 5–10 wt%. The melt was imaged below a supercritical geothermal reservoir. Based on the resistivity model, we propose a mechanism for the evolution of a supercritical fluid reservoir, wherein upwelling supercritical fluids supplied from the melt are trapped under less permeable silica sealing. As a result, supercritical fluids accumulate under the silica sealing. This study is the first to present a detailed estimation of the spatial distribution and fluid fraction of a potential supercritical geothermal reservoir.
Feb 2022Published in Journal of Geophysical Research: Solid Earth volume 127 issue 2. 10.1029/2021JB022911