Many active volcanoes are located along the Japanese islands. Japan has abundant geothermal resources, which represent promising renewable energy sources. However, we still cannot fully harness these resources. Geothermal fluid power generation consumes large amounts of geothermal steam generated from production wells. Then, cold water can be inserted into the strata through injection wells. Poor reservoir management may cause a temperature drop in the reservoir or a halt in power generation. Therefore, to predict the distribution of the temperature change in the geothermal reservoir and to systematically maintain the geothermal source, appropriate simulation research is necessary. In this study, we investigated the flow of geothermal fluid and simulated the steady state of the geothermal reservoir using the standard geothermal reservoir simulator TOUGH2. Using the steady state model, the temperature change due to the vapor production and water reinjection process was estimated to simulate the operation of geothermal power plants. It was found that the temperature dropped in a short period when the heat supply was small. To conduct sustainable power generation, over 1000 kg/s of hot water supply was necessary. It was also found that the region where the temperature dropped downstream of the reinjection well was more than 400 m.

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