Reservoir Monitoring Using Hybrid Micro-Gravity Measurements in the Takigami Geothermal Field, Central Kyushu, Japan

Abstract

Repeated gravity measurements have been applied at the Takigami geothermal power plant in central Kyushu, Japan. We applied a multivariate regression model and removed the effects of shallow groundwater level change in order to extract the gravity change associated with the production and reinjection of geothermal fluids. We used Scintrex CG-3 and CG-3M gravimeters to measure precise gravity change. We detected gravity changes caused by the production and reinjection. However, we cannot assess the gravity change at the reference station, because we only used the relative gravimeter. Hence we introduced the A10 absolute gravimeter (Micro-g LaCoste, Inc) for not only the assessment of the gravity changes at the reference station, but also the detection of the gravity change caused by the underground fluid flow changes.