Development of High-Temperature Seismometers for Near-Field Microearthquake Monitoring

Abstract

High-resolution monitoring of microearthquakes near enhanced geothermal system (EGS) reservoirs is essential for understanding rock-fluid interactions and reservoir evolution during and after stimulation and production. However, the extreme downhole conditions of EGS environments, characterized by high temperatures and pressures, pose significant challenges for conventional seismic and other geophysical sensors. To address this, we are developing a high-temperature, single-level, three-component seismometer based on a 4.5 Hz string-type geophone with a seven-conductor cable. The mechanical and electrical components have been redesigned to enhance durability under conditions up to 260 degree C and 40 MPa. In July 2025, we deployed the sensor at a depth of 2,132 m (176 degree C) in a vertical borehole at the Cape field, Utah, to continuously monitor reservoir activity and seismicity. The sensor has operated successfully since installation, detecting more than 100 times as many earthquakes as the nearby UU.FORK station at 282 m depth. Even compared with borehole distributed acoustic sensing (DAS) data, our instrument recorded approximately 3-5 times more events, demonstrating superior sensitivity and robustness in high-temperature environments.