Development of a Fractured Geothermal Reservoir Simulator in terms of Mechanical and Chemical Water/Rock Interactions.

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Hot Dry Rock (HDR)/Hot Wet Rock (HWR) geothermal energy extraction systems, which attract a great deal of attention as one of new technologies to obtain energy, are designed to utilize natural and artificial subsurface fractures for the heat exchange between water and hot rock. Numerical analysis of water flow and heat transfer in fractured geothermal reservoir is strongly needed to estimate the heat mining performance of these systems.In this study, first of all, HDR/HWR geothermal reservoirs were characterized by fracture network based on fractal geometry which is getting popular to assess subsurface fractures. By using fracture network geothermal reservoir model, the mithodology to analyze water flow and heat transfer in reservoirs has been established. The changes of fracture apertures has significant influence on fluid flow, and it is important to estimate fracture behavior during water circulation. The mechanical and chemical interaction between water and rock was included into the program. Share dilation of each fracture caused by water pressure was calculated based on rock mechanics theory. Rock dissolution and precipitation experiments in high pressure and temperatures have been performed. Water/Rock interaction rate was obtained as a function of temperature and surface water velocity.Short-term water circulation test was conducted at Ogachi field, one of HDR/HWR test sites in Japan. The profile of production temperature was analyzed by the program developed in this study, and the results has shown good agreement with the actual data. Furthermore this analysis could give a stochastic estimation of long-term performance of Ogachi reservoir.