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<p>Hot dry rock (HDR) is a deep geothermal resource. Liquid nitrogen can effectively increase fracture complexity in HDR reservoirs. In this study, to quantify the damage evolution of liquid nitrogen-cooled rocks and to determine the theoretical relationships among the sample conditions, internal damage states, and macroscopic nonlinear mechanical behavior, the effects of air cooling and liquid nitrogen cooling on granite samples were compared through triaxial compression testing (0–60&#xa0;MPa range) and acoustic emission (AE) localization analysis. The internal structural changes induced by liquid nitrogen cooling in the rock were analyzed through ultrasonic testing and numerical simulations. Quantitative analysis of AE distribution during rock failure following liquid nitrogen cooling was conducted using the defined characteristic size and density of the AE events. The damage evolution during the rock failure process after liquid nitrogen cooling was analyzed via an established statistical damage constitutive model. The results revealed that liquid nitrogen cooling decreased the longitudinal wave velocity. The large temperature gradient and mismatched deformation characteristics between different minerals resulted in complex distributions of thermal stresses in heterogeneous materials. The characteristic density of the AE events under loading was greater after liquid nitrogen cooling than after air cooling. The peak stresses were lower after liquid nitrogen cooling than after air cooling. Under confining pressures of 0–60&#xa0;MPa, the peak stress induced by liquid nitrogen cooling was reduced by 2.51–10.97%, 3.75–9.27%, and 3.27–32.36% for samples at 25, 200, and 400&#xa0;°C, respectively. Compared with air cooling, liquid nitrogen cooling caused greater thermal damage and total damage but resulted in a lower damage evolution rate in the deformation and failure processes. High temperatures contributed to deterioration effects, whereas a high confining pressure weakened the deterioration effects. In this study, quantitative and dynamic tracking of the progressive evolution of damage in liquid nitrogen-cooled granite under mechanical loading and different confining pressures was achieved.</p>

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Impact of Cryogenic Cooling with Liquid Nitrogen on the Mechanical Properties and Damage Evolution of High-Temperature Granite under Different Confining Pressures

  • 期刊论文

  • 发表日期：

    2026年4月5日

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  • Chengzheng Cai,
  • Chunbo Zhou,
  • Zhongwei Huang,
  • Shouceng Tian,
  • Haizhu Wang,
  • Zhengchao Zhu,
  • Bo Wang,
  • Jiacheng Li

摘要

Hot dry rock (HDR) is a deep geothermal resource. Liquid nitrogen can effectively increase fracture complexity in HDR reservoirs. In this study, to quantify the damage evolution of liquid nitrogen-cooled rocks and to determine the theoretical relationships among the sample conditions, internal damage states, and macroscopic nonlinear mechanical behavior, the effects of air cooling and liquid nitrogen cooling on granite samples were compared through triaxial compression testing (0–60 MPa range) and acoustic emission (AE) localization analysis. The internal structural changes induced by liquid nitrogen cooling in the rock were analyzed through ultrasonic testing and numerical simulations. Quantitative analysis of AE distribution during rock failure following liquid nitrogen cooling was conducted using the defined characteristic size and density of the AE events. The damage evolution during the rock failure process after liquid nitrogen cooling was analyzed via an established statistical damage constitutive model. The results revealed that liquid nitrogen cooling decreased the longitudinal wave velocity. The large temperature gradient and mismatched deformation characteristics between different minerals resulted in complex distributions of thermal stresses in heterogeneous materials. The characteristic density of the AE events under loading was greater after liquid nitrogen cooling than after air cooling. The peak stresses were lower after liquid nitrogen cooling than after air cooling. Under confining pressures of 0–60 MPa, the peak stress induced by liquid nitrogen cooling was reduced by 2.51–10.97%, 3.75–9.27%, and 3.27–32.36% for samples at 25, 200, and 400 °C, respectively. Compared with air cooling, liquid nitrogen cooling caused greater thermal damage and total damage but resulted in a lower damage evolution rate in the deformation and failure processes. High temperatures contributed to deterioration effects, whereas a high confining pressure weakened the deterioration effects. In this study, quantitative and dynamic tracking of the progressive evolution of damage in liquid nitrogen-cooled granite under mechanical loading and different confining pressures was achieved.