Although coal swelling/shrinking during coal seam gas extraction has been studied for decades, its impacts on the evolution of permeability are still not well understood. This has long been recognized, but no satisfactory solutions have been found. In previous studies, it is normally assumed that the matrix swelling/shrinking strain can be split between the fracture and the bulk coal and that the splitting coefficient remains unchanged during gas sorption. In this study, we defined the fracture strain as a function of permeability change ratio and back-calculated the fracture strains at different states. In the equilibrium state, the gas pressure is steady within the coal; in the non-equilibrium state, the gas pressure changes with time. For equilibrium states, the back-calculated fracture strains are extremely large and may be physically impossible in some case. For non-equilibrium states, two experiments were conducted: one for a natural coal sample and the other for a reconstructed one. For the fractured coal, the evolution of permeability is primarily controlled by the transition of coal fracture strain or permeability from local matrix swelling effect to global effect. For the reconstituted coal, the evolution of pore strain or permeability is primarily controlled by the global effect.

中文翻译：

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瓦斯吸附引起的煤压裂应变数据的演变与分析

尽管已经研究了煤层瓦斯抽采期间的煤溶胀/收缩，但数十年来，其对渗透性演变的影响仍未得到很好的理解。早已认识到这一点，但是没有找到令人满意的解决方案。在以前的研究中，通常假设基质膨胀/收缩应变可以在裂缝和散装煤之间分配，并且在气体吸附过程中，分离系数保持不变。在这项研究中，我们将断裂应变定义为渗透率变化率的函数，并反算了不同状态下的断裂应变。在平衡状态下，煤中的气压稳定。在非平衡状态下，气压随时间变化。对于平衡态，反算的断裂应变非常大，在某些情况下在物理上可能是不可能的。对于非平衡态，进行了两个实验：一个用于天然煤样品，另一个用于重建样品。对于压裂煤，渗透率的演化主要受煤压应变或渗透率从局部基质膨胀作用到整体作用的过渡控制。对于再生煤，孔隙应变或渗透率的演化主要受整体效应控制。渗透率的演化主要受煤层破裂应变或渗透率从局部基质膨胀作用到整体作用的控制。对于再生煤，孔隙应变或渗透率的演化主要受整体效应控制。渗透率的演化主要受煤裂缝应变或渗透率从局部基质膨胀作用到整体作用的转变控制。对于再生煤，孔隙应变或渗透率的演化主要受整体效应控制。