Permeability Enhancement of Granite Specimens through Hydroshearing Relevant to Enhanced Geothermal Systems

Abstract:

Hydraulic stimulation of an Enhanced Geothermal System (EGS) through injection-induced shear slip (commonly known as ‘hydroshearing’) has proven as an effective technique for permeability enhancement of a reservoir. During hydroshearing, pre-existing fractures (or faults) within the reservoir are slipped and dilated by injecting water at a pressure below the minimum principal stress, which increases permeability of the reservoir. In this study, a suite of triaxial flow through tests was conducted to induce a shear slip along a 45°tensile-fracture present in cylindrical granite specimens. Three tests at the temperature of 20°C, 65°C, and 130°C were conducted to investigate the effect of temperature on permeability enhancement of the specimens. Hydroshearing increased the permeability of the specimens by 1.6, 1.8, and 23 times under temperature of 20°C, 65°C, and 130°C, respectively. Fracture surface degradation under different temperature, which could affect the long-term permeability evolution, was also examined in the study. Inductively Coupled Plasma (ICP) test showed increased temperature led to enhanced mineral dissolution and higher dissolution rates in post-hydroshearing stage compared to pre-hydroshearing stage.