5:15 PM - 7:15 PM
[STT42-P01] Seismic exploration around the Mori Geothermal Power Plant in Hokkaido using optical fibers by two geothermal boreholes
Keywords:Seismic exploration, DAS, geothermal structure, Geothermal reservoir
In 2021, we conducted geophysical exploration at Nigorikawa of Mori town, in Hokkaido, Japan by borehole optical fiber system in the geothermal borehole of the Mori Power Plant. We analyzed the seismic data acquired by distributed acoustic sensing (DAS) and surface geophones. The results were described in Kasahara et al., (2022). The Vp structure along the Esat-West line was determined. The Vp structure showed the caldera shape distribution similar to the previous geothermal model (e.g., Hanano et al.,2005). The seismic reflections were migrated using the Vp profile. The reflection image was done. Seismic reflections are distributed done to 3 km depth.
Because the Vp structure and reflection images were two-dimensional, we conducted the second seismic survey in the same geothermal filed as that in 2021. The main objectives are to know three-dimensional Vp and seismic reflection subsurface structure. In 2024, we used another borehole from the first study. The optical fiber was placed to 2,000 m depth. Twenty seismic sources, two DAS data in two boreholes and two surface geophone arrays were used for the analysis. The three-dimensional Vp structure was determined by the P first arrival readings. The synthetic seismograms of DAS and surface geophone waveforms were compared each other, and the Vp structure was modified. The Vp profiles along the production and injection boreholes were extracted from the Vp structure, and were confirmed to be reasonable fittings. Figure shows the two Vp depth profiles perpendicular each other. X-X’ profile shows the caldera structure, but the Y-Y’ section does not show such structure. Using reflection arrivals the three-dimensional migrated image was obtained.
This survey was supported by NEDO (JPNP21001). We express our thanks to Hokkaido Electric Co. Ltd., WELMA Co. Ltd., and Hanshin Consultants Co. Ltd.
Because the Vp structure and reflection images were two-dimensional, we conducted the second seismic survey in the same geothermal filed as that in 2021. The main objectives are to know three-dimensional Vp and seismic reflection subsurface structure. In 2024, we used another borehole from the first study. The optical fiber was placed to 2,000 m depth. Twenty seismic sources, two DAS data in two boreholes and two surface geophone arrays were used for the analysis. The three-dimensional Vp structure was determined by the P first arrival readings. The synthetic seismograms of DAS and surface geophone waveforms were compared each other, and the Vp structure was modified. The Vp profiles along the production and injection boreholes were extracted from the Vp structure, and were confirmed to be reasonable fittings. Figure shows the two Vp depth profiles perpendicular each other. X-X’ profile shows the caldera structure, but the Y-Y’ section does not show such structure. Using reflection arrivals the three-dimensional migrated image was obtained.
This survey was supported by NEDO (JPNP21001). We express our thanks to Hokkaido Electric Co. Ltd., WELMA Co. Ltd., and Hanshin Consultants Co. Ltd.