Thermal stimulation mechanical response and shear dilatation predictive model improvement of granite fractures in an enhanced geothermal system

The exploitation of shear dilatation behavior exhibited by natural rock fractures can serve as an effective strategy for stimulating reservoirs in the enhanced geothermal systems (EGS). However, few studies have considered the shear dilatation characteristics of rock fractures treated by real-time high temperature. Firstly, the self-developed Mechanical(M)-Thermal(T) coupling shear test cell and the MTS816.01 rock shear test system were used to carry out the direct shear tests of granite fractures. The M-T coupling effect on granite's physical properties such as cohesion, the mechanical properties such as shear strength, and strain energy characteristics such as dissipated strain energies were analyzed. On these Base, the shear dilatation mechanism of granite fractures treated by realtime high temperature is further revealed. Subsequently, based on the dynamic changes in the area degradation degree of granite fractures, the shear dilatation model of rock fractures treated by real-time high temperature were improved and verified. The results reveal that the M-T coupling effect can considerably impair the shear dilatation behavior of granite fractures. The temperature undermines the shear dilatation behavior of granite fractures by negatively affecting their physical and mechanical properties, while the normal stress deteriorates their shear dilatation behavior by constraining the normal displacement of the rock fractures. The modified shear dilatation model of rock fractures exhibits high accuracy and can accurately represent the shear dilatation behavior of rock fractures under M-T coupling effects. The novel insights provided in this paper contribute to a more comprehensive understanding of the wellbore stability and permeability improvement mechanism of EGS.