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<p>To explore change of multiscale pores in coal and its impact on permeability during mining, an experimental study was conducted on the real-time evolutions of stress, pore structure, and permeability of coal under various stress paths with a novel low-field nuclear magnetic resonance testing system. The following results were yielded. (1) Under the stress-constant confining pressure (LASCCP) and constant axial stress-unloading confining pressure (CASUCP) paths, the proportion of macropores drops first, then rises, and leaps when the coal fails. Correspondingly, the proportions of mesopores and micropores fall rapidly. Under the loading axial stress-constant confining pressure (LASCCP) path, initially, the proportion of macropores fluctuates between 7.1% and 7.4%, while that of mesopores goes up with fluctuations. Upon coal instability, the proportion of macropores expands noticeably, while those of mesopores and micropores plunge. (2) The cumulative contribution rates (CRs) of micropores and mesopores to permeability are minimal, while that of macropores exceeds 99.99%. Among macropores, Ma-1 and Ma-2 contribute less than 2%. Under the LASCCP path, the CR of Ma-3 ranges from 29.57% to 46.42%, showing a growth trend, while that of Ma-4 exhibits an opposite trend. Under the CASUCP path, the CR of Ma-3 falls from the initial value 34.22% to 26.23% when instability occurs, while that of Ma-4 rises from 63.70% to 72.74%. Under the LASUCP path, the CR of Ma-3 ascends initially and then falls, quickly plummeting to 25.70% upon instability. In contrast, that of Ma-4 grows from 65.31% to 73.34% at the point of failure. The results of this study conduce to revealing the mechanism of pressure relief and permeability enhancement of coal seams, investigating how the pore-fracture structure in coal controls the seepage process, and advancing the detailed scientific classification and research of multi-scale pores in coal.</p><p><b>Highlights</b><UnorderedList Mark="Bullet"> <ItemContent> <p>A novel low-field nuclear magnetic resonance method was adopted.</p> </ItemContent> <ItemContent> <p>Evolution of multiscale pores in coal under multiple stress path was detected.</p> </ItemContent> <ItemContent> <p>Contribution of multiscale pores to permeability was quantified.</p> </ItemContent> </UnorderedList></p>

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Evolution of Pore-Fractures in Coal Under Multiple Stress Paths and Its Effect on Seepage Based on LF-NMR

  • 期刊论文

  • 发表日期：

    2025年3月31日

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  • Ting Liu,
  • Kunlong Liu,
  • Baiquan Lin,
  • Jianfeng Li,
  • Jianhao Wang,
  • Mingyang Li,
  • Jizhao Xu,
  • Jin Zhang

摘要

To explore change of multiscale pores in coal and its impact on permeability during mining, an experimental study was conducted on the real-time evolutions of stress, pore structure, and permeability of coal under various stress paths with a novel low-field nuclear magnetic resonance testing system. The following results were yielded. (1) Under the stress-constant confining pressure (LASCCP) and constant axial stress-unloading confining pressure (CASUCP) paths, the proportion of macropores drops first, then rises, and leaps when the coal fails. Correspondingly, the proportions of mesopores and micropores fall rapidly. Under the loading axial stress-constant confining pressure (LASCCP) path, initially, the proportion of macropores fluctuates between 7.1% and 7.4%, while that of mesopores goes up with fluctuations. Upon coal instability, the proportion of macropores expands noticeably, while those of mesopores and micropores plunge. (2) The cumulative contribution rates (CRs) of micropores and mesopores to permeability are minimal, while that of macropores exceeds 99.99%. Among macropores, Ma-1 and Ma-2 contribute less than 2%. Under the LASCCP path, the CR of Ma-3 ranges from 29.57% to 46.42%, showing a growth trend, while that of Ma-4 exhibits an opposite trend. Under the CASUCP path, the CR of Ma-3 falls from the initial value 34.22% to 26.23% when instability occurs, while that of Ma-4 rises from 63.70% to 72.74%. Under the LASUCP path, the CR of Ma-3 ascends initially and then falls, quickly plummeting to 25.70% upon instability. In contrast, that of Ma-4 grows from 65.31% to 73.34% at the point of failure. The results of this study conduce to revealing the mechanism of pressure relief and permeability enhancement of coal seams, investigating how the pore-fracture structure in coal controls the seepage process, and advancing the detailed scientific classification and research of multi-scale pores in coal.

Highlights

A novel low-field nuclear magnetic resonance method was adopted.

Evolution of multiscale pores in coal under multiple stress path was detected.

Contribution of multiscale pores to permeability was quantified.