| Abstract |
Geological models and the properties of supercritical geothermal reservoirs are described with respect to characteristics of supercritical geofluids and mechanical behaviors of reservoir rocks. Mechanical conditions at the elastic-plastic boundaries of granitic rocks, in terms of permeability, indicate potentially exploitable supercritical geothermal resources. Tensile fracturing is possible even in ductile rocks, and some permeability-depth relations proposed for the continental crust show no drastic permeability reduction at the BDT (Brittle-Ductile Transition). The reservoir permeability ( more than 10-16 m2) could be maintained even under supercritical conditions. The permeable-impermeable boundary of the crust and geothermal reservoirs were affected by water-rock interaction such as dissolution and precipitation of silica minerals. Geochemical processes are a significant influence on the creation of a permeable-impermeable boundary in the crust. Possible tectonic settings for supercritical geothermal resources are classified into subduction zones, ridges, rifts, and hot spots. Geological model (particularly Granite-Porphyry system) and its geothermal potential was described. NE Japan is representative of an Island-Arc setting in a subduction system, and it is highly possible that exploitable supercritical geothermal resources. |