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Computed tomography imaging-based quantification of microstructural heterogeneity in coal under uniaxial loading: Insights into pore-scale gas flow behavior

Author

Listed:
  • Fan, Nan
  • Qiao, Yonggang
  • Wang, Hongyu
  • Liu, Changhua
  • Fan, Chaojun
  • Zhang, Shida
  • Mu, Yongliang
  • Deng, Cunbao
  • Wang, Aiguo

Abstract

The stress-induced evolution of the microscopic pore-fracture structure of coal is of immense significance for understanding the mechanisms governing gas flow behavior. In this study, X-ray micro-computed tomography (micro-CT), combined with uniaxial compression tests, is used to quantitatively characterize the mechanical response, acoustic emission (AE) characteristics, and microscopic pore-fracture structure of coal during loading. Further, a skeleton model (SM) and an equivalent pore network model (PNM) with topological features are constructed by extracting the connected pore-fracture structure. Based on the actual pore-fracture structure of the loaded coal, microscale gas flow simulations are conducted to quantify the flow velocity and permeability variations under different pressures. The effect of pore-throat structural parameters on permeability is also investigated. The mechanical response analysis of coal under stress reveals an initial slow increase in the accumulated AE energy with the increase in axial stress, followed by a steady phase and, ultimately, a sharp rise. The evolution of the pore-fracture structure is characterized by secondary fracture expansion and the activation of isolated pores, which in turn leads to a sudden increase in the number of pores, concurrent reductions in throat radius and length, and improved pore connectivity. The permeability of the loaded coal samples gradually decreases with the increase in pressure difference, and the higher the pore pressure, the more significant the decrease in permeability due to increased flow resistance. Among the micro-topological parameters, coal permeability is positively correlated with the effective porosity, average throat radius, and average coordination number, while it is negatively correlated with the pore-throat ratio. Overall, the findings of this study provide useful insights into the mass transfer process and gas transport mechanisms within real pore structures.

Suggested Citation

  • Fan, Nan & Qiao, Yonggang & Wang, Hongyu & Liu, Changhua & Fan, Chaojun & Zhang, Shida & Mu, Yongliang & Deng, Cunbao & Wang, Aiguo, 2025. "Computed tomography imaging-based quantification of microstructural heterogeneity in coal under uniaxial loading: Insights into pore-scale gas flow behavior," Energy, Elsevier, vol. 338(C).
    • Handle: RePEc:eee:energy:v:338:y:2025:i:c:s0360544225045189
    DOI: 10.1016/j.energy.2025.138876
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    References listed on IDEAS

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    1. Sun, Lulu & Wan, Fuqian & Wang, Gang & Duan, Shoulei & Huang, Qiming & Li, Wenlin, 2024. "Pore-fracture structures and seepage flow characteristics during spontaneous coal combustion based on CT 3D reconstruction," Energy, Elsevier, vol. 305(C).
    2. Liu, Haizhou & Mao, Lingtao & Ju, Yang & Hild, François, 2023. "Damage evolution in coal under different loading modes using advanced digital volume correlation based on X-ray computed tomography," Energy, Elsevier, vol. 275(C).
    3. Cai, Jianchao & Zhang, Zhien & Wei, Wei & Guo, Dongming & Li, Shuai & Zhao, Peiqiang, 2019. "The critical factors for permeability-formation factor relation in reservoir rocks: Pore-throat ratio, tortuosity and connectivity," Energy, Elsevier, vol. 188(C).
    4. Zhou, H.W. & Liu, Z.L. & Zhong, J.C. & Chen, B.C. & Zhao, J.W. & Xue, D.J., 2022. "NMRI online observation of coal fracture and pore structure evolution under confining pressure and axial compressive loads: A novel approach," Energy, Elsevier, vol. 261(PA).
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