Geological Model and Potential of Supercritical Geothermal Reservoir

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.