1887

Abstract

Summary

To explore unknown geothermal reservoirs, we carried out a geothermal seismic study using a distributed acoustic sensor (DAS) at the Ohnuma geothermal power plant ownd by Mitubishi Material Co. in September 2020. The Ohnuma geothermal power station, the third commercial geothermal power plant in Japan, was completed in 1974. We installed an optical fibre system for the DAS measurements, on the site. We deployed the optical fibre system down to a depth of 1973 m in the O- 13R borehole. To enhance the S/N, we stacked the DAS data for 480 times and correlated it with the source signature. By stacking for a long duration, we obtained excellent DAS records down to the bottom of the boreholes. Using 2D migration of observed and synthetic DAS seismic records, we recognised intense seismic reflections from 2.8–3.0 km depth, suggesting the possibility of geothermal reservoirs. The velocity decrease in this zone could be more than 1 km/s, possibly implying that the fracture zone is filled with fluid. The two field studies in the Medipolis and Ohnuma geothermal fields in Japan showed that the DAS-seismic method in the borehole can efficiently image seismically reflective zones, and the findings suggest high possibility of geothermal reservoirs.

Loading

Article metrics loading...

/content/papers/10.3997/2214-4609.202112540
2021-10-18
2025-12-14
Loading full text...

Full text loading...

References

  1. Hartog, A.
    [2017] “An Introduction to Distributed Optical Fibre Sensors”, 442pp, CRC press.
    [Google Scholar]
  2. Kasahara, J., Hasada, Y., and Yamaguchi, T.
    [2019a] Seismic imaging of supercritical geothermal reservoir using full-waveform inversion method, Proceedings, 44th Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA.
    [Google Scholar]
  3. Kasahara, J., Hasada, Y., Kuzume, H., Fujise, Y. and Yamaguchi, T.
    [2019b] Seismic feasibility study to identify supercritical geothermal reservoirs in a geothermal borehole using DTS and DAS, EAGE extended abstract, EAGE 2019 Annual meeting, London.
    [Google Scholar]
  4. Kasahara, J., Hasada, Y., Kuzume, H., Mikada, H., and Fujise, Y.
    [2020] The second seismic study at the geothermal field in southern Kyushu, Japan using an optical fiber system and surface geophones, 44th Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA.
    [Google Scholar]
  5. Kubota, Y.
    [1985] Conceptional model of the north Hachmantai-Yakeyama geothermal area, Journal of Geothermal Society of Japan, 7(3): 231–245.
    [Google Scholar]
  6. Kubota, Y., Hatakeyama, K., Banba, M., Kato, H.
    [1989] Chemical changes of Ohnuma geothermal fluid since operation and related reservoir management, Journal of JGEA (Japan Geothermal Energy Association), 26(1): 1–20.
    [Google Scholar]
  7. Yora, M., Watanabe, K., Ito, J., Wakita, K., Kubota, Y.
    [1977] On the geothermal system of the northern Hachimantai, Mining Geology, 27233–244.
    [Google Scholar]
/content/papers/10.3997/2214-4609.202112540
Loading
/content/papers/10.3997/2214-4609.202112540
Loading

Data & Media loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error