Progress of the EGS Project for Water Injection in the Superheated Region at Okuaizu Geothermal Field in Japan

Abstract

An R&D project funded by Japan Oil, Gas and Metals National Corporation (JOGMEC) on the development of a technology for geothermal reservoir evaluation and control is underway. The purpose of the project is to develop a technical manual for geothermal power plants in Japan through a verification test and numerical simulation quantifying the effect of artificial water recharge　(EGS : Enhanced Geothermal Systems) on a geothermal reservoir and/or hot spring aquifer. This project is set in Okuaizu geothermal field in Fukushima prefecture with an installed capacity of 65MW which was started in 1995. Utilization factor of the power plant has reduced to 27.7% in 2014 mainly because of depletion of steam, acidification and declines of productivity and injectivity. To solve the problem a recharge well was drilled in the superheated region in 2014 and injection started in June 2015. Although thermal breakthrough was observed at Well-8 near the recharge well after about 4 months of recharge, a steam flowrate increase by about 5t/h at Well-8 was observed before the interference occurred. Steam rates at Wells 5 and 6 seem to have stabilized as a result of the recharge. The interference can be assumed by injection at shallow depths by the flow behind the casing. In this paper, the project results obtained so far and a future plan will be reported in detail.