After a coal mine is abandoned, a large amount of coalbed methane (CBM) resources is still accumulated in the overlying and underlying coal strata. The structure of the coal/rock pore fracture, which is a key element for the development of CBM resources, changes significantly due to the influence of mining. In this study, the pore volume and pore size distribution (PSD) of six coals (three parallel bedding coals and three vertical bedding coals), three mudstones, and three sandstones before and after fracture are compared from the perspective of macro and micro using a triaxial compression experiment and high-pressure mercury intrusion porosimetry, and the pore-fracture evolution of the coal under different confining pressures is studied. By quantificationally characterizing the pore-fracture strain of fractured coal/rock, an equivalent model based on plastic deformation is proposed. Combined with the pore-fracture characteristics of coal/rock strata in abandoned mines, the influence of the coal/rock fracture on CBM migration is discussed. The results show that (1) the pore volumes of coal, mudstone, and sandstone are significantly reduced after the fracture. The compression of coal is more significant than that of other samples. The macropore (>50 nm) volume of coal and mudstone decreased sharply in the process of loading, while that of mesopores (2–50 nm) changed little. For sandstones, the macropore and mesopore volumes are compressed. (2) With the increase of effective stress, the compression degree of pores increases; especially, the volume of macropores decreases significantly. (3) The expansion of fracture is beneficial to the migration of CBM, while pore compression reduces the diffusion path. The ultimate performance of CBM migration in mining-disturbed strata is determined by the net effect of two competing effects. This study has a guiding role in improving the pore-fracture strain physical model of fractured coal/rock and revealing the CBM migration in abandoned mines.

中文翻译：

---

扰动煤系地层孔隙结构变化的实验研究：对废弃矿井煤层气发育的启示

废弃煤矿后，上层和下层煤层中仍积累了大量煤层气（CBM）资源。作为开采煤层气资源的关键因素，煤/岩石孔隙裂缝的结构由于开采的影响而发生了显着变化。本研究从宏观和微观角度比较了6种煤（3种平行顺层煤和3种垂直顺层煤），3种泥岩和3种砂岩在破裂前后的孔隙体积和孔径分布（PSD）。通过三轴压缩实验和高压压汞法，研究了煤在不同围压下的孔隙破裂演化规律。通过定量表征破裂的煤/岩石的孔隙断裂应变，提出了基于塑性变形的等效模型。结合废弃矿山煤／岩地层的孔隙破裂特征，探讨了煤／岩破裂对煤层气运移的影响。结果表明：（1）断裂后煤，泥岩和砂岩的孔隙体积明显减小。煤的压缩比其他样品的压缩更为显着。煤和泥岩的大孔（> 50 nm）在加载过程中急剧减少，而中孔（2–50 nm）的变化很小。对于砂岩，大孔和中孔的体积被压缩。（2）随着有效应力的增加，孔隙的压缩程度增加；特别是大孔的体积明显减少。（3）裂缝的扩展有利于煤层气的运移，而孔压缩减少了扩散路径。煤层气运移在受开采扰动的地层中的最终表现是由两个竞争效应的净效应决定的。这项研究对改善破碎煤/岩石的孔隙断裂应变物理模型以及揭示废弃矿井的煤层气运移具有指导作用。