Supercritical water/rock interactions and generation of artificial geothermal reservoirs in deep-seated high temperature rock masses

Laboratory results from simulated hydraulic stimulation tests on granite are presented where fracture and fluid flow behavior were examined under temperatures up to 600 °C and confining pressures up to 100 MPa at various injection rates. The results show that under high temperatures, fluid flow dominant behavior occurs for relatively lower injection rates, whereas macroscopic fracture tends to takes place at higher injection rates. Continuous injection tests under supercritical water conditions reveal that the fluid flow dominant behavior is due to the generation of a grain-scale extensive microcracks induced by the interaction between supercritical water and rock-forming minerals. It is proposed to utilize the discovered supercritical water-induced microcracking phenomenon in order to create an artificial reservoir in deep-seated rock masses whose temperature and pressure conditions exceed the critical point of water.