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<p>CO<sub>2</sub>-enhanced coalbed methane (CO<sub>2</sub>–ECBM) recovery can simultaneously achieve the dual objectives of efficient unconventional resources development and CO<sub>2</sub> geological sequestration. During the initial hydrophobic depressurization phase, residual water within the coal matrix significantly influences subsequent CO<sub>2</sub> injection, displacement, and sequestration processes. Quantifying the impact of coal hydration reactions in a CO<sub>2</sub> environment on coal structure damage and failure mechanisms is crucial for optimizing CO<sub>2</sub> injection parameters. This study examined the effects of varying hydration reaction durations in a CO<sub>2</sub> atmosphere on the structural integrity. Coal samples were subjected to X-ray diffraction, uniaxial compression tests, acoustic emission monitoring, and surface strain analysis after exposure to different reaction cycles. The findings indicated that the coupling reaction of CO<sub>2</sub>–H<sub>2</sub>O–coal induced an acid erosion effect, altering the mineral composition of the coal. As immersion time increased, clay mineral particles were generated, weakening its mechanical strength. Specifically, compared to the original sample, a 15-day immersed sample exhibited a 39.39% reduction in UCS, a 46.92% decrease in elastic strain range, and a 25.38% decline in elastic modulus. Acoustic emission results showed that maximum energy decreased with increasing immersion time. During compression, the distribution of acoustic emission energy shifted from 90–100% to 60–90%. Kernel density estimation and normalization methods applied in ringing amplitude (RA)–average frequency (AF) analysis revealed that the proportion of tensile failure increased from 47.3% to 84.1% post-reaction. Strain rate variation maps were obtained and a correlation was established between strain and acoustic emission ringing count signals. As the reaction progressed, the relative area proportion of high-strain rate regions in shear strain rate maps decreased, consistent with the RA–AF analysis. Energy analysis indicated that the combined CO<sub>2</sub>–H<sub>2</sub>O–coal reaction led to the increasing internal damage, higher dissipated energy, a greater brittleness index, and enhanced plastic deformation and failure extent. These experimental results provide valuable insights for advancing CO<sub>2</sub>–ECBM practices and expanding coalbed methane extraction.</p>

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Mechanical Response and Damage Mechanism of Coals Under the Hydration Reaction in the Atmosphere of CO2

  • 期刊论文

  • 发表日期：

    2025年7月6日

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  • Jizhao Xu,
  • Hongchang Liu,
  • Sheng Qian,
  • Hexiang Xu,
  • Hongda Wen,
  • Ting Liu,
  • Zihao Wei,
  • Zijian Yu,
  • Zhibo Xing,
  • Cheng Zhai

摘要

CO2-enhanced coalbed methane (CO2–ECBM) recovery can simultaneously achieve the dual objectives of efficient unconventional resources development and CO2 geological sequestration. During the initial hydrophobic depressurization phase, residual water within the coal matrix significantly influences subsequent CO2 injection, displacement, and sequestration processes. Quantifying the impact of coal hydration reactions in a CO2 environment on coal structure damage and failure mechanisms is crucial for optimizing CO2 injection parameters. This study examined the effects of varying hydration reaction durations in a CO2 atmosphere on the structural integrity. Coal samples were subjected to X-ray diffraction, uniaxial compression tests, acoustic emission monitoring, and surface strain analysis after exposure to different reaction cycles. The findings indicated that the coupling reaction of CO2–H2O–coal induced an acid erosion effect, altering the mineral composition of the coal. As immersion time increased, clay mineral particles were generated, weakening its mechanical strength. Specifically, compared to the original sample, a 15-day immersed sample exhibited a 39.39% reduction in UCS, a 46.92% decrease in elastic strain range, and a 25.38% decline in elastic modulus. Acoustic emission results showed that maximum energy decreased with increasing immersion time. During compression, the distribution of acoustic emission energy shifted from 90–100% to 60–90%. Kernel density estimation and normalization methods applied in ringing amplitude (RA)–average frequency (AF) analysis revealed that the proportion of tensile failure increased from 47.3% to 84.1% post-reaction. Strain rate variation maps were obtained and a correlation was established between strain and acoustic emission ringing count signals. As the reaction progressed, the relative area proportion of high-strain rate regions in shear strain rate maps decreased, consistent with the RA–AF analysis. Energy analysis indicated that the combined CO2–H2O–coal reaction led to the increasing internal damage, higher dissipated energy, a greater brittleness index, and enhanced plastic deformation and failure extent. These experimental results provide valuable insights for advancing CO2–ECBM practices and expanding coalbed methane extraction.