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<p>While thermal-assisted stimulation can mitigate the ultra-low permeability of coal-bearing shales, the dynamic micro-reconstruction mechanisms of pore networks over extreme temperature ranges remain poorly understood. To bridge this gap, Carboniferous–Permian coal-bearing shales from the Ningwu Basin were thermally treated (25–1000&#xa0;°C) and systematically evaluated using low-temperature N₂ adsorption, scanning electron microscopy (SEM), and fractal theory. The results reveal that mesopores (2–50&#xa0;nm) consistently dominate the reservoir space. Total pore volume and specific surface area exhibit a non-linear trajectory, peaking optimally at 600&#xa0;°C before sharply declining due to macroscopic framework collapse. Fractal analysis indicates a fundamental temperature-dependent transition: from micropore surface roughening at low temperatures to extreme spatial tortuosity within larger pore networks at elevated temperatures. Mechanistically, organic matter pyrolysis and clay mineral dehydroxylation synergistically drive this microstructural reconstruction, generating extensive secondary fracture networks that substantially enhance permeability. Balancing pore capacity enhancement with structural stability, the 500–600&#xa0;°C range is definitively identified as the optimal thermal window for the in-situ recovery of coal-bearing shale reservoirs.</p>

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The impact of thermal treatment on pore structure evolution of coal-bearing shale

  • 期刊论文

  • 发表日期：

    2026年5月23日

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  • Zhenlong Ge,
  • Hong Niu,
  • Yuqian Guan,
  • Zhichao Hao,
  • Yixuan Jia,
  • Yi Zhang

摘要

While thermal-assisted stimulation can mitigate the ultra-low permeability of coal-bearing shales, the dynamic micro-reconstruction mechanisms of pore networks over extreme temperature ranges remain poorly understood. To bridge this gap, Carboniferous–Permian coal-bearing shales from the Ningwu Basin were thermally treated (25–1000 °C) and systematically evaluated using low-temperature N₂ adsorption, scanning electron microscopy (SEM), and fractal theory. The results reveal that mesopores (2–50 nm) consistently dominate the reservoir space. Total pore volume and specific surface area exhibit a non-linear trajectory, peaking optimally at 600 °C before sharply declining due to macroscopic framework collapse. Fractal analysis indicates a fundamental temperature-dependent transition: from micropore surface roughening at low temperatures to extreme spatial tortuosity within larger pore networks at elevated temperatures. Mechanistically, organic matter pyrolysis and clay mineral dehydroxylation synergistically drive this microstructural reconstruction, generating extensive secondary fracture networks that substantially enhance permeability. Balancing pore capacity enhancement with structural stability, the 500–600 °C range is definitively identified as the optimal thermal window for the in-situ recovery of coal-bearing shale reservoirs.