In the Ogachi HDR project, two reservoirs were created by hydraulic fracturing operations at different depths of 700 and 1,000 m from a 1,000 m deep injection well. Location and size of the reservoirs have been evaluated by induced micro-earthquakes hypocenter distribution. The reservoirs were estimated to progress in different directions. It was difficult to penetrate these reservoirs by a production well. Therefore the production well did not penetrate the best flow paths in the reservoirs and the water recovery rate of produced water to injected water was so small. Hydraulic stimulation operations in the both injection and production wells were conducted to enlarge water flow paths between the wells and to improve the recovery rate. Comparing the tracer test results before and after the stimulation operations, short paths between the injection and the production wells were estimated to occur. From the micro-earthquakes observation results the short path was created from the bottom of the injection well to the bottom of the production well. This short path in the production well was confirmed by the temperature logging results. Sand plug was set in the bottom of the injection well to conduct individual flow tests between the two wells through the two reservoirs. The tracer test results before and after the individual flow tests showed that the short paths were partially plugged. These results show that the flow paths in the HDR reservoir are very sensitive to hydraulic operations.

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