SEGJ Technical Conference

Seismic Monitoring for the Super Critical Geothermal Energy Development at the Medipolis Geothermal Field, Kyushu

Abstract We conducted a second DAS seismic study in 2019. We deployed the optical-fiber system at a 1,545-m depth in a borehole. We conducted DAS-offset VSP at five locations and performed a frequency sweep of 10-75 Hz. To enhance the S/N we operated MiniVib 8 hours each day for five days. Stacking for 480 or 960 times considerably improved the arrival waveforms. Based on an analysis of DAS data, we constructed the 2D seismic profile. We estimated three major hydrothermal layers, at depths of 800-1,000 m, 1,300-1,600 m, and 3,600 m. The zone around 3,600 m suggests a high Vp/Vs value and the possible presence of a fluid layer.