A 3D Model of the Yamagawa Geothermal System: Insights into Reservoir Structure and Future Field Management

Abstract

The Yamagawa geothermal power station has been operating since 1995 with an output capacity of 30 MW. It is located at the southernmost part of the Satsuma Peninsula on Kyushu Island, in the southwest of Japan. The exploration activity (including geological survey, gravity survey, and exploratory well drilling and testing) was carried out from 1962 to 1988. Through the various surveys and analysis in the exploration stage, and through the subsequent drilling, geologically complex structures and the presence of a high temperature reservoir have been better defined.
In this paper, all of the subsurface information acquired has been used to build a 3D geological model. This model shows the major structural trends and also shows the impacts of key formations within the reservoir. Natural state temperature data has been used to create a temperature model, which has shed light on the importance of major geological structure as they relate to fluid flow. The resistivity survey result also gives us information regarding the indication of geothermal fluid flow path. The combined 3D model will be a tool used to contribute to the evaluation and management of the geothermal reservoir at the Yamagawa geothermal power station.