Coalbed methane (CBM) is a clean energy source that requires understanding of coal pore structures and flow behavior for efficient development. In deep formations with high gas content and low permeability, variations within coal pore structure influence methane extraction efficiency. This study explores the dynamic regulatory mechanisms influencing flow anisotropy in coal pore structures across varying degrees of metamorphism. The nonlinear responses of flow capacity and transition phenomena under different gas pressure conditions have been investigated using fluid intrusion methods, digital core technology, and numerical simulations. The results show that the interdependent coal pore parameters create anisotropic structures, with gas flow capacity initially decreasing and then gradually increasing with rising pressure differences. This nonlinear change may result from the dynamic adjustment of the internal pore structure, although some responses exhibit hysteresis. Low-rank coals exhibit four flow direction transitions within a pressure difference of 0.7–3.9 MPa, while high-rank coals demonstrate pore homogenization, characterized by high stability in flow direction without any transitions. The flow transition phenomenon in low-rank coals is attributed to the sensitivity of their loose molecular structure to pressure changes, whereas the dense structure of high-rank coals suppresses pressure response. These findings emphasize the impact of coal rank and pore interactions on flow behavior. Low-rank coals necessitate dynamic pressure regulation to capitalize on flow direction transitions, while high-rank coals require strategic placement following their inherently dominant direction. This study provides a theoretical foundation for efficient CBM development in complex geological conditions under high pressure.

中文翻译：

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原始煤孔隙系统中微流的各向异性特征：孔隙微观结构控制的转变

煤层气 （CBM） 是一种清洁能源，需要了解煤孔结构和流动行为才能实现高效开发。在含气量高、渗透率低的深层地层中，煤孔隙结构的变化会影响甲烷提取效率。本研究探讨了在不同变质程度下影响煤孔隙结构流动各向异性的动态调控机制。采用流体侵入法、数字核心技术和数值模拟研究了不同气压条件动容量和转变现象的非线性响应。结果表明，相互依赖的煤孔隙参数会产生各向异性结构，气体流动能力最初减小，然后随着压力差的增加而逐渐增加。这种非线性变化可能是由内部孔隙结构的动态调整引起的，尽管一些响应表现出滞后。低阶煤在 0.7–3.9 MPa 的压力差内表现出四个流向转变，而高阶煤表现出孔隙均质化，其特点是流向高度稳定，没有任何转变。低阶煤的流动转变现象归因于其松散分子结构对压力变化的敏感性，而高阶煤的致密结构抑制了压力响应。这些发现强调了煤等级和孔隙相互作用对流动行为的影响。低等级煤需要动态压力调节以利用流向转变，而高等级煤需要按照其固有的主导方向进行战略布局。 本研究为高压下复杂地质条件下的高效煤层气开发提供了理论基础。