Mechanical properties of fractured sandstone after cyclic thermal shock

The stimulation of thermal reservoir in sandstone and long-term stability evaluation are of great significance to the development of geothermal energy. The mechanical properties of fractured sandstone under 0-8 thermal shocks are studied in this paper. The experimental results show that the P-wave velocity, uniaxial compressive strength and elastic modulus of the fractured sandstone all decrease gradually with the increase of the number of thermal shocks under two types of cooling methods. Compared with cooling method in water, the natural cooling method in air has less damage to mechanical properties of fractured sandstone. The uniaxial compressive strength and elastic modulus of fractured sandstone show a good exponential function relationship with the number of thermal shocks. Both the P-wave velocity and the elastic modulus can be used to describe the damage of the fractured sandstone with the number of thermal shocks. The first thermal shock weakens the mechanical properties of fractured sandstone most severely, and the deterioration effect of mechanical properties is significantly slowed down when the number of thermal shocks exceeds 4. In addition, the uniaxial compressive strength and elastic modulus of fractured sandstone also have a good exponential function relationship with the P-wave velocity. Finally, the thermal shock process of sandstone samples is simulated in COMSOL Multiphysics, and the effects of heat transfer coefficient and prefabricated cracks on the internal temperature field and stress field of sandstone are discussed, revealing the mechanism of thermal cracking in sandstone under thermal shock effect.