Cooling Effect and Fluid Flow Behavior Due to Reinjected Hot Water in the Hatchobaru Geothermal Field, Japan

Abstract

In the Hatchobaru geothermal field, the power output had declined due to a cooling effect from 110 to 90 within the first two years after commencement of commercial operation of the second power unit Unit). In order to clarify this cooling mechanism, tracer tests and numerical simulations were conducted. The simulation results show that 21% of reinjected hot water returned to the production area, and the temperature of production area dropped subsequently by within the first two years. Furthermore, results of case studies suggest that a distance of more than 500 m between production area and reinjection area are necessary to mitigate the cooling effect. Therefore, the locations of most reinjection wells were changed so that they were at least m away from the production area. As a result, the declining trend of power output was actually reduced.