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<p>To reveal the influence of effective stress on permeability during drainage of deep coalbed methane, five coals (depths: 1884–2558 m) were selected from the Daning–Jixian and Suide regions in China for effective stress loading and unloading experiments. It was found that the permeability loss rate (<i>PLR</i>) of natural coal exhibits staged variation with increasing effective stress. Below the threshold of 16.3 MPa, <i>PLR</i> remained relatively low under small incremental loading. Beyond this value, no significant difference in <i>PLR</i> was observed. Ultimately, the <i>PLR</i> reached 100% when the effective stress attained 22.3 MPa. For artificially fractured coal, when stepwise loading was applied with effective stress increments of 2 or 3 MPa, the final <i>PLR</i> reached approximately 86%; whereas increasing the stress increment to 6 or 9 MPa resulted in a final <i>PLR</i> exceeding 95%. The stress sensitivity coefficient, and fracture compressibility all increased with the increasing effective stress loading increments. The gas slip effect occurred throughout the entire loading and unloading process and increases with effective stress. When stepwise loading and unloading were conducted with effective stress increment of 2 MPa, the average irreversible permeability loss rate (<i>IPLR</i>) was 1.73% for artificially fractured coal and 30.45% for natural coal. Compared with shallow coal, deep coal exhibited lower stress sensitivity and lower <i>IPLR</i>. For natural coal, 16.3 MPa effective stress served as a critical threshold for adjusting for adjusting the effective stress increment; while for artificially fractured coal, a small effective stress increment was efficient in maintaining permeability.</p>

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Contrasting Stress Sensitivity of Natural vs. Artificially Fractured Deep Coals: Implications for Coalbed Methane Drainage Pressure Control

  • 期刊论文

  • 发表日期：

    2025年12月25日

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  • Junjie Xiong,
  • Zhenzhi Wang,
  • Yixin Zhao,
  • Yi Jin,
  • Jienan Pan

摘要

To reveal the influence of effective stress on permeability during drainage of deep coalbed methane, five coals (depths: 1884–2558 m) were selected from the Daning–Jixian and Suide regions in China for effective stress loading and unloading experiments. It was found that the permeability loss rate (PLR) of natural coal exhibits staged variation with increasing effective stress. Below the threshold of 16.3 MPa, PLR remained relatively low under small incremental loading. Beyond this value, no significant difference in PLR was observed. Ultimately, the PLR reached 100% when the effective stress attained 22.3 MPa. For artificially fractured coal, when stepwise loading was applied with effective stress increments of 2 or 3 MPa, the final PLR reached approximately 86%; whereas increasing the stress increment to 6 or 9 MPa resulted in a final PLR exceeding 95%. The stress sensitivity coefficient, and fracture compressibility all increased with the increasing effective stress loading increments. The gas slip effect occurred throughout the entire loading and unloading process and increases with effective stress. When stepwise loading and unloading were conducted with effective stress increment of 2 MPa, the average irreversible permeability loss rate (IPLR) was 1.73% for artificially fractured coal and 30.45% for natural coal. Compared with shallow coal, deep coal exhibited lower stress sensitivity and lower IPLR. For natural coal, 16.3 MPa effective stress served as a critical threshold for adjusting for adjusting the effective stress increment; while for artificially fractured coal, a small effective stress increment was efficient in maintaining permeability.