Hijiori was one of the hottest Hot Dry Rock reservoir in the world whose 
fracture system was reasonably restricted by natural fractures and faults 
associated with the formation of the caldera structure. Japanese HDR project in 
Hijiori was started in 1984 by NEDO and five companies (GERD, Mitsui Mining, 
JAPEX and CRIEPI) with a funding of Japanese government. The project finished 
its long life (18years) research activity in 2002 with the 550-day successful 
circulation test showing the feasibility to generate electricity by using the binary 
system. The project established the basis for essential technologies and 
cleared up issues for future development of EGS system. Fracture 
characterization was achieved by integrating core analysis, logging, 
microseismic monitoring, tracer test and geochemical monitoring. Successive or 
periodic applications of these measurements enabled an evaluation of the 
reservoir dynamics. Fracture network modeling based on the knowledge of the 
fracture system was sufficient to develop a circulation strategy. We believe the 
outcomes of the Hijiori HDR project will be utilized by successive EGS projects 
and will become valuable data to initiate a new project.

Campus SIAF, SP del Monte Volterrano
Localita' Il Cipresso
Volterra, Italy