Lessons Learned from the Ogachi and Hijiori HDR/EGS Projects, Japan

Abstract

The Ogachi and Hijiori Hot Dry Rock (HDR) or Enhanced/Engineered Geothermal Systems (EGS) projects were conducted not in pure hot dry rock but in rock with many natural joints. Therefore, multiple reservoir and multiple well systems were planned to make water recovery higher during water circulation operations. Two reservoirs were created at different depths in the both projects. The results of the Hijiori project showed that water recovery during water circulation was improved by number of production wells. The water recovery in the water circulation system with one injection well and three production wells was more than 70%. These created reservoir characters and water flow in the reservoirs were strongly depended on geological conditions. In the Ogachi project it was very difficult to determine production well trajectory, because hydraulically created two fractures progressed completely different directions. However, after many hydraulic stimulation operations, water circulations were conducted through both the reservoirs. In the Hijiori project unbalanced water flow in the two reservoirs resulted in scaling problems during water circulation. However, a long-term flow test was conducted by controlled water circulation. No induced earthquake problem was occurred in both the HDR projects. In this paper, the Ogachi and Hijiori projects were reviewed and summarized lessons learned from these projects.