[S-VC35] Hydrothermal systems of volcanoes

[SVC35-01] Geothermal exploration using distributed acoustic sensing (DAS) in two boreholes of the Kijiyama geothermal field, Japan

*Junzo Kasahara^1,2, Yoko Hasada^1,3, Masaru Suzuki⁴, Tomohiro Takahashi⁴, Hisashi Tatsunokuchi¹, Yoshihiro Fujise⁵ (1.ENAA, 2.Shizuoka University, 3.Daiwa Exploration and Engineering, 4.TOUSEC, 5.WELMA)

Keywords:Kijiyama geothermal field, DAS, geothermal structure, seismic reflection structure

We conducted two geophysical surveys in Kijiyama geothermal field using optical fibers in geothermal wells in 2022 and 2024. We obtained temperature-depth profiles using DTS (Distributed Temperature Sensor) and seismic records by DAS (Distributed Acoustic Sensor) and surface seismic seismometers for twenty-four seismic excitations surrounding the wellhead. The temperature was 294.03ºC at 2,058 m depth in the EW borehole. Combining two borehole DAS and surface seismometer records in 2022 and 2024, we obtained a 3D Vp structure. The synthetic waveforms of DAS and surface seismic records satisfy the first P arrivals of the seismic dataset. The Vp depth profiles along the six boreholes were extracted from 3D Vp volume, and the present Vp is well fitted to the borehole geology. On the southern side of the Kijiyama field, the higher Vp layer, 4.5 km/s, reaches 500 m depth. In the northern area, Vp = 3.5 km/s exists at a depth of 1 km.
This survey was supported by NEDO (JPNP21001). We express our thanks to TOUSEC Co. Ltd., JGI Inc., WELMA Co. Ltd., and Hanshin Consultants Co. Ltd.