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Influence of Pore Structure Characteristics of Low Permeability Coal on Gas Nonlinear Seepage

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Abstract

Coalbed methane (CBM) mining has always been plagued by low mining efficiency. CBM-rich areas have high mining efficiency, but their formation is affected by CBM seepage. Through on-site mining, it is found that gas seepage in low-permeability areas presents nonlinear characteristics. In this paper, the causes and rules of nonlinear seepage are analyzed. The pore structure characteristic parameters such as pore size distribution, pore proportion and fractal dimension were obtained by nuclear magnetic resonance technology, and the pore structure characteristics of low permeability coal are analyzed. The results showed that the proportion of porosity was 6.30–11.02% and the proportion of percolation pores was 7.52–19.59%. Both total porosity and percolation pores had fractal characteristics. Aiming at the nonlinear problem of gas seepage law in low permeability coal, the permeability and gas flow data of coal samples under different gas pressures were measured by the self-designed coal core permeability automatic tester, and the gas seepage characteristics of low permeability coal samples are studied. The experiment showed that there was a starting pressure gradient in gas seepage in coal samples, and the relationship between gas permeability and gas pressure turned over at 1.25 MPa, indicating that there is a slip effect in coal pores. Considering the influence of pore structure parameters on the nonlinear seepage characteristics of CBM, the relationships between porosity, tortuosity, pore proportion, and fractal dimension and Kirschner permeability, slippage factor, and starting pressure gradient were fitted. The analysis showed that the pore size distribution characteristics with large proportion of micro-pores in low permeability coal made the pressure gradient required for the internal gas seepage larger, the influence of the slippage effect was enhanced, and the seepage of gas was nonlinear. To conclude, the influence of micro-pores developed in low permeability coal on nonlinear gas seepage was significant.

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Notes

  1. \({\text{1 mD }} = { 9}.{869233*1}0^{{ - {4}}}\,\upmu{\text{m}}^{{2}}\).

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Acknowledgment

This study was financially supported by the National Natural Science Foundation of China (Nos. 52274228, 51874236), and Shaanxi Provincial Department of Education Youth Innovation Team Building Research Project (No. 21JP073).

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Authors and Affiliations

  1. School of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an, 710054, Shaanxi, China

    Min Yan, Fan Yang, Haifei Lin & Shugang Li

  2. Key Laboratory of Western Mine Exploitation and Hazard Prevention, Ministry of Education, Xi’an University of Science and Technology, Xi’an, 710054, Shaanxi, China

    Min Yan, Fan Yang, Haifei Lin & Shugang Li

  3. Qingzhou City People’s Government Yunmen Mountain Sub-district Office, Qingzhou, 262500, Shandong, China

    Binbin Zhang

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  1. Min Yan
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  2. Fan Yang
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Correspondence to Min Yan or Haifei Lin.

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Yan, M., Yang, F., Zhang, B. et al. Influence of Pore Structure Characteristics of Low Permeability Coal on Gas Nonlinear Seepage. Nat Resour Res (2024). https://doi.org/10.1007/s11053-024-10325-5

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  • DOI: https://doi.org/10.1007/s11053-024-10325-5

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