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<p>One important factor influencing the gas/water two-phase seepage during coalbed methane extraction is the absolute permeability of coal reservoirs. The sensible design of a surface coalbed methane drainage system and the enhancement of drainage efficiency depend heavily on the quick and precise prediction of this parameter. The Huanglong Jurassic No. 4 coal seam sample from the Dafosi Coal Mine in the Binchang Mining Area serves as the research object for this study, which employs low-field nuclear magnetic resonance (LF-NMR) technology and high-temperature and high-pressure displacement equipment. The LF-NMR technique was employed to test coal reserves under thermal–mechanical coupling conditions. In conjunction with fractal theory, the association between the absolute permeability and the fractal dimension of coal reservoirs was examined, as well as the dynamic evolution features of the fractal dimension of the pore structure of coal reservoirs under thermal coupling settings. The fractal dimension of the pore structure was used to create a permeability prediction model. According to the study, the fractal map of the coal reservoir’s pore structure in its initial form contains clear inflection points that allow one to differentiate between the almost straight and curved segments. The fractal dimension <i>D</i><sub>1</sub> of the bound pore segment is linearly negatively correlated with the absolute permeability. By contrast, the <i>D</i><sub>2</sub> of the connected pore segment is exponentially negatively correlated with the absolute permeability. By identifying the inflection points in the diagram, <i>T</i><sub>2<i>cut-off</i></sub> can be rapidly ascertained to avoid the centrifugation test operation process. The absolute permeability prediction model based on the fractal dimension of the pore structure determined in this work may significantly streamline the experimental procedures while maintaining the accuracy of the prediction findings compared to the conventional NMR absolute permeability model. With just the NMR T<sub>2</sub> spectrum of the saturated sample, the model can determine its absolute permeability in real-time.</p>

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Characterization of coal reservoir permeability evolution under thermo-mechanical coupling based on fractal theory

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年7月1日

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  • Kaide Liu,
  • Qiyu Wang,
  • Songxin Zhao,
  • Wenping Yue,
  • Chaowei Sun,
  • Yu Xia

摘要

One important factor influencing the gas/water two-phase seepage during coalbed methane extraction is the absolute permeability of coal reservoirs. The sensible design of a surface coalbed methane drainage system and the enhancement of drainage efficiency depend heavily on the quick and precise prediction of this parameter. The Huanglong Jurassic No. 4 coal seam sample from the Dafosi Coal Mine in the Binchang Mining Area serves as the research object for this study, which employs low-field nuclear magnetic resonance (LF-NMR) technology and high-temperature and high-pressure displacement equipment. The LF-NMR technique was employed to test coal reserves under thermal–mechanical coupling conditions. In conjunction with fractal theory, the association between the absolute permeability and the fractal dimension of coal reservoirs was examined, as well as the dynamic evolution features of the fractal dimension of the pore structure of coal reservoirs under thermal coupling settings. The fractal dimension of the pore structure was used to create a permeability prediction model. According to the study, the fractal map of the coal reservoir’s pore structure in its initial form contains clear inflection points that allow one to differentiate between the almost straight and curved segments. The fractal dimension D1 of the bound pore segment is linearly negatively correlated with the absolute permeability. By contrast, the D2 of the connected pore segment is exponentially negatively correlated with the absolute permeability. By identifying the inflection points in the diagram, T2cut-off can be rapidly ascertained to avoid the centrifugation test operation process. The absolute permeability prediction model based on the fractal dimension of the pore structure determined in this work may significantly streamline the experimental procedures while maintaining the accuracy of the prediction findings compared to the conventional NMR absolute permeability model. With just the NMR T2 spectrum of the saturated sample, the model can determine its absolute permeability in real-time.