This paper describes the replacement of the Onikobe geothermal power station located in Miyagi prefecture in Japan. The Onikobe geothermal power station, 15 MW single flash plant, began operation in 1975 as the 4th geothermal power plant in Japan. The power station was shut down in 2017 after 42 years of operation due to aging of the facilities and power output decline due to abandonment of production wells those were damaged by steam explosion incident in 2010. The power station area is restricted to a relatively small area due to steep surface topography and a national park regulation. Moreover, different kinds of fluid, i.e. neutral and strong acidic brine, co-exist within a small space in the Onikobe reservoir. During 42 years exploitation of the former plant, we have experienced many operational difficulties which arise from the reservoir characteristics involving a rapid production decline in early stage of exploitation, silica scaling from neutral brine in surface facility and reinjection wells, corrosion problem of flow lines and well casing due to acidic brine, smectite scaling within a wellbore due to mixing of different kinds of fluid from different feed zones and cold water migration to production wells from reinjection wells. The new plant was designed based on the experiences of the 42 years operation. New production wells were completed using production casing of anti-corrosion material, and neutral and acidic brine are treated separately by different flow lines from production wells to injection wells to avoid severe scaling problem that could be occurred by mixing each other. The replacement work took place from 2019 to 2023, including drilling of 5 new production wells and 5 new reinjection wells. The temperature profiles of new production wells showed temperature decline in deeper part, which reveals a cold sweep process in the fractured reservoir by reinjected water during long term production and reinjection. Although the well production enthalpy were lower than expected, required steam flow rate was successfully obtained. The new Onikobe power station, 14.9 MW single flash system, began operation in April 2023 as scheduled.

Press the Back button in your browser, or search again.

Copyright 2024, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.