Interpretation of the Gravity Changes Patterns Observed at the Takigami Geothermal Field, Oita Prefecture, Japan

Abstract

It is important to understand the geothermal reservoir behavior in order to produce geothermal fluid for a long time. Micro-gravity measurement is one of the suitable methods for geothermal reservoir monitoring. In the Takigami geothermal field, we have conducted repeat micro-gravity measurements using Scintrex CG-3 and CG-3M relative gravimeters since before 1996, when the Takigami geothermal power plant started power generation. We estimated the gravity change caused by shallow part fluid flow by using a computer code which calculates gravity change caused by precipitation. We divided the Takigami geothermal area into 3 areas and 5 stages from the pattern of the gravity change during 1996 and 2008. Based on these stages, we made a conceptual reservoir model of the Takigami geothermal field.