STUDY OF HYDROTHERMAL CYCLING ON DETERIORATION AND DAMAGE MECHANISM OF SANDSTONE

Since water and high temperature are significant variables that control the strength of deep rock formations, it is vital for deep geological engineering to explore the mechanical behavior of reservoir rock under conditions of hydrothermal cycling. For deep sandstone samples that have undergone different hydrothermal cycles, a series of examinations, consisting of scanning electron microscopy, uniaxial compression, and nuclear magnetic resonance, were performed in this study to evaluate the mechanical properties and pore structure features. Moreover, the effect of hydrothermal cycles on the mechanical characteristics and microstructure of deep sandstone is investigated in this study. The results show that as the hydrothermal cycles progress, the micropore of the sandstone samples continues to increase, while mesopore and macropore show a decreasing trend, overall indicating an increase in porosity. Under the action of thermal stress and water-rock interaction, the fractal dimension of sandstone pores gradually decreases, indicating that the hydrothermal cycle reduces the complexity of pores. With an increase in cycles, the elastic modulus and uniaxial compressive strength of sandstone decreased to varying degrees. The damage variable D<sub>n</sub>, defined based on the elastic modulus, quantitatively reflects the evolution of sandstone resistance to deformation with the micropore structure to a certain extent. The modulus of elasticity parameter of sandstone decreases significantly as the damage variable D<sub>n</sub> increases. The evolution of pore structure and mechanical damage patterns in sandstone show a firm consistency. The water-rock interaction and thermal stress damage primarily influences the damage to sandstone. The findings of this study can provide theoretical guidance for the safe and efficient development of deep geothermal resources.