| Abstract |
Since 1989, in furthering the development of HDR technology, CRIEPI has conducted numerous experiments at their Ogachi test site in southern Akita Prefecture, Japan. At a depth of 1000m at this site, the reservoir rock is granodiorite at a temperature of 230?C. From 1989 to 1992, an injection well (OGC-1) was drilled to a depth of 1000m and then two vertical separated artificial reservoirs were created by hydraulic fracturing. Then, in 1993, a production well (OGC-2) was drilled through the two HDR reservoirs to a depth of 1100m. From 1993 to 1995, three water circulation tests were conducted between the injection and production wells. In the 1995 circulation test, hot water and vapor at a temperature of 165?C was produced from the HDR reservoirs at a recovery rate of 25%. During the past three years, individual flow testing of the upper and lower HDR reservoirs was conducted which showed that the production capacity of the upper reservoir was less than 1/20 that of the lower reservoir. Supporting reservoir diagnostic testing and analyses, to determine the fracture structures and flow paths within and around the two separate reservoirs, was also performed during this time. These included the observation and analysis of pressureinduced acoustic emissions (AE), the determination of the orientations and magnitudes of the in-situ stresses, and 3D numerical simulations of the reservoir flow. The results from this most recent series of flow tests and supporting AE analyses suggest that both the upper and lower reservoirs were formed by the pressure-opening of natural joints within the rock mass, and that the upper reservoir has a length of about 800 m and an orientation roughly 90o from the orientation of the 1000-m-long lower reservoir. |