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<p>When using cavities created by anhydrite mining as underground oil storage spaces, the long-term exposure of surrounding rock to oil can alter its mechanical properties, potentially affecting the stability of the storage facility. To investigate this phenomenon, this study prepared anhydrite rock samples with varying oil immersion durations (0 days, 15 days, and 30 days). By combining results from uniaxial and triaxial compression tests with PFC<sup>2D</sup> numerical simulations, the macroscopic and microscopic damage characteristics of the anhydrite rock under different oil immersion periods were analyzed. The study's findings reveal that: (1) As the oil immersion time increases, the peak stress of the anhydrite rock gradually decreases. Additionally, the greater the confining pressure, the smaller the impact of oil immersion on the compressive strength of the rock samples. This suggests that higher confining pressure can mitigate the effects of oil immersion on the anhydrite rock. (2) Oil immersion alters the failure mode of the samples. As the immersion time increases, the shear failure angle gradually increases, and the failure mode transitions from shear failure to tensile failure. (3) PFC<sup>2D</sup> discrete element simulation analysis explains the changes in the mechanical properties of oil-impregnated anhydrite rock. Oil impregnation progressively weakens internal particle strength and the bonding strength between particles, leading to a significant concentration of internal force chains. A larger number of strong force chains become coarser and more concentrated, increasing the inhomogeneity and anisotropy of the rock samples and reducing their overall load-bearing capacity. (4) As the oil immersion time increases, the total number of microcracks in the rock samples after failure decreases. Notably, the proportion of tensile cracks experiences a sudden shift and rapidly increases after 15 days of oil immersion. This shift is a key reason for the transition of the macroscopic failure mode from shear failure to tensile failure.</p>

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Study on macro–microscopic damage characteristics of anhydrite under oil immersion

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2025年8月26日

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  • Congrui Zhang,
  • Wenguang Lu,
  • Yongxiang Ge,
  • Gaofeng Ren,
  • Haoyu Wang,
  • Fuhong Xu

摘要

When using cavities created by anhydrite mining as underground oil storage spaces, the long-term exposure of surrounding rock to oil can alter its mechanical properties, potentially affecting the stability of the storage facility. To investigate this phenomenon, this study prepared anhydrite rock samples with varying oil immersion durations (0 days, 15 days, and 30 days). By combining results from uniaxial and triaxial compression tests with PFC2D numerical simulations, the macroscopic and microscopic damage characteristics of the anhydrite rock under different oil immersion periods were analyzed. The study's findings reveal that: (1) As the oil immersion time increases, the peak stress of the anhydrite rock gradually decreases. Additionally, the greater the confining pressure, the smaller the impact of oil immersion on the compressive strength of the rock samples. This suggests that higher confining pressure can mitigate the effects of oil immersion on the anhydrite rock. (2) Oil immersion alters the failure mode of the samples. As the immersion time increases, the shear failure angle gradually increases, and the failure mode transitions from shear failure to tensile failure. (3) PFC2D discrete element simulation analysis explains the changes in the mechanical properties of oil-impregnated anhydrite rock. Oil impregnation progressively weakens internal particle strength and the bonding strength between particles, leading to a significant concentration of internal force chains. A larger number of strong force chains become coarser and more concentrated, increasing the inhomogeneity and anisotropy of the rock samples and reducing their overall load-bearing capacity. (4) As the oil immersion time increases, the total number of microcracks in the rock samples after failure decreases. Notably, the proportion of tensile cracks experiences a sudden shift and rapidly increases after 15 days of oil immersion. This shift is a key reason for the transition of the macroscopic failure mode from shear failure to tensile failure.