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<p>To investigate the effect of rock microstructure on its macroscopic properties under instantaneous high temperature, we employed nuclear magnetic resonance and triaxial apparatus to examine the microstructure and macroscopic characteristics of samples. Additionally, Shannon entropy was introduced as a measure for characterizing microscopic pore and fragment distribution characteristics. We explored the relationship between pore proportion, density, pore size distribution entropy (PSDE), and fragment distribution entropy (FDE) with temperature variations. Furthermore, we utilized entropy weight to assess the thermal sensitivity of pores and calculate the damage coefficient. Finally, we extensively investigated the intrinsic relationship between PSDE and peak intensity, permeability, as well as dissipated energy. The results demonstrate that the microstructure of red sandstone undergoes a significant change after 400&#xa0;℃. Beyond this temperature, <i>T</i><sub>2</sub> exhibits substantial variations, with the proportion of micropores transitioning from an increasing to decreasing trend and the proportion of mesopores shifting from a decreasing to increasing pattern. Except at 400&#xa0;℃, there is an overall increase in pore density. Additionally, after 400&#xa0;℃, the distribution entropy decreases for micropores, macropores, and total pore diameter, while it increases for mesopores. The peak intensity and permeability of PSDE follow an exponential function, whereas its dissipative energy conforms to a linear relationship. Before 400&#xa0;℃, micropores exhibit the highest thermal sensitivity; however, macropore thermal sensitivity becomes dominant after this point, while both macropore and mesopore sensitivities increase significantly as micropore sensitivity declines notably. Employing entropy weight calculations effectively enhances accuracy when determining damage degree based on <i>T</i><sub>2</sub> peak area measurements. FDE and fracture area show an upward trend with increasing temperature until reaching their maximum value at 200&#xa0;℃ before rapidly declining after that; conversely, fractal dimension of fragments displays an opposite behavior. This study aims to provide fundamental insights into the stability assessment of surrounding rock in underground coal gasification and geothermal mining.</p>

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Revealing the Effect of Pore Size Distribution Characteristics on Macroscopic Properties of Red Sandstone Under Instantaneous High Temperature Through the Lens of Shannon Entropy Theory

  • 期刊论文

  • 发表日期：

    2025年2月7日

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  • Lin Ning,
  • Jing Bi,
  • Yu Zhao,
  • Chaolin Wang,
  • Yongfa Zhang,
  • Yang Li,
  • Yuhang Zhao,
  • Xiaojiang Deng

摘要

To investigate the effect of rock microstructure on its macroscopic properties under instantaneous high temperature, we employed nuclear magnetic resonance and triaxial apparatus to examine the microstructure and macroscopic characteristics of samples. Additionally, Shannon entropy was introduced as a measure for characterizing microscopic pore and fragment distribution characteristics. We explored the relationship between pore proportion, density, pore size distribution entropy (PSDE), and fragment distribution entropy (FDE) with temperature variations. Furthermore, we utilized entropy weight to assess the thermal sensitivity of pores and calculate the damage coefficient. Finally, we extensively investigated the intrinsic relationship between PSDE and peak intensity, permeability, as well as dissipated energy. The results demonstrate that the microstructure of red sandstone undergoes a significant change after 400 ℃. Beyond this temperature, T2 exhibits substantial variations, with the proportion of micropores transitioning from an increasing to decreasing trend and the proportion of mesopores shifting from a decreasing to increasing pattern. Except at 400 ℃, there is an overall increase in pore density. Additionally, after 400 ℃, the distribution entropy decreases for micropores, macropores, and total pore diameter, while it increases for mesopores. The peak intensity and permeability of PSDE follow an exponential function, whereas its dissipative energy conforms to a linear relationship. Before 400 ℃, micropores exhibit the highest thermal sensitivity; however, macropore thermal sensitivity becomes dominant after this point, while both macropore and mesopore sensitivities increase significantly as micropore sensitivity declines notably. Employing entropy weight calculations effectively enhances accuracy when determining damage degree based on T2 peak area measurements. FDE and fracture area show an upward trend with increasing temperature until reaching their maximum value at 200 ℃ before rapidly declining after that; conversely, fractal dimension of fragments displays an opposite behavior. This study aims to provide fundamental insights into the stability assessment of surrounding rock in underground coal gasification and geothermal mining.