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<p>In coal-oil-gas co-storage zones, long-term oil and gas seepage significantly alter the intrinsic properties of coal, thereby posing substantial challenges to safe coal extraction. However, the mechanisms governing the evolution of coal properties under such conditions remain insufficiently understood. This study therefore investigated coal specimens collected from a coal seam by integrating high-resolution CT scanning, uniaxial compression testing, synchronous acoustic emission (AE) monitoring, and fractal analysis to quantitatively evaluate seepage-induced damage and its effects on fracture evolution and mechanical behavior of coal. The results indicate that fracture density, cumulative fracture length, and box-counting fractal dimension decrease monotonically with increasing distance from legacy oil wells, demonstrating a negative correlation between seepage-induced damage and well distance. Coal specimens located closer to oil wells exhibit more pronounced mechanical deterioration, as reflected by lower peak strength, elastic modulus, and peak strain, and their failure is predominantly characterized by shear-dominated failure. In contrast, specimens farther from the wells gradually transition toward mixed shear-tensile failure. AE analysis during uniaxial compression identifies four distinct deformation stages: compaction, elastic deformation, rapid crack propagation, and post-peak softening. High-amplitude AE events characterized by high RA values (rise angle) and low AF values (average frequency) may serve as reliable precursors to imminent coal ins ility. Seepage-induced deterioration facilitates the development of migration pathways for oil and gas hazards, whereas the associated stress-relief effect may reduce the likelihood of mining-induced dynamic disasters. These findings provide theoretical support for hazard prevention and the safe extraction of coal in coal-oil-gas coexisting reservoirs.</p>

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Fracture evolution and mechanical response of coal with damage induced by oil-gas seepage

  • 期刊论文

  • 发表日期：

    2026年7月1日

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  • Yawu Shao,
  • Wei Yao,
  • Lei Zhu,
  • Gang Han,
  • Haifei Lin,
  • Hu Liu,
  • Jiahao Xie,
  • Mingming Sun,
  • Jin Wang

摘要

In coal-oil-gas co-storage zones, long-term oil and gas seepage significantly alter the intrinsic properties of coal, thereby posing substantial challenges to safe coal extraction. However, the mechanisms governing the evolution of coal properties under such conditions remain insufficiently understood. This study therefore investigated coal specimens collected from a coal seam by integrating high-resolution CT scanning, uniaxial compression testing, synchronous acoustic emission (AE) monitoring, and fractal analysis to quantitatively evaluate seepage-induced damage and its effects on fracture evolution and mechanical behavior of coal. The results indicate that fracture density, cumulative fracture length, and box-counting fractal dimension decrease monotonically with increasing distance from legacy oil wells, demonstrating a negative correlation between seepage-induced damage and well distance. Coal specimens located closer to oil wells exhibit more pronounced mechanical deterioration, as reflected by lower peak strength, elastic modulus, and peak strain, and their failure is predominantly characterized by shear-dominated failure. In contrast, specimens farther from the wells gradually transition toward mixed shear-tensile failure. AE analysis during uniaxial compression identifies four distinct deformation stages: compaction, elastic deformation, rapid crack propagation, and post-peak softening. High-amplitude AE events characterized by high RA values (rise angle) and low AF values (average frequency) may serve as reliable precursors to imminent coal ins ility. Seepage-induced deterioration facilitates the development of migration pathways for oil and gas hazards, whereas the associated stress-relief effect may reduce the likelihood of mining-induced dynamic disasters. These findings provide theoretical support for hazard prevention and the safe extraction of coal in coal-oil-gas coexisting reservoirs.