The permeability coefficient of coal seam is a key parameter for assessing the performance of underground coal bed methane extraction. First, compared with the widely accepted radial flow method, the related error range can be achieved by adapting the borehole pressure buildup method to calculate the permeability coefficient of coal seam at different positions of the same hard-soft composite coal seam. Second, the changing law shows that the permeability coefficient of coal seam varies in accordance with time and the different positions in hard-soft composite coal seam. The results indicate that the changing law is basically consistent in the permeability coefficient of coal seam, presenting a decreasing power function with time. The decay processes consist of three stages: rapid decay, slow decay, and stable process. At the early stage, the soft layer’s permeability coefficient is greater than that of the hard-soft interbedding, and the hard layer has the smallest coefficient. The decay rate of the permeability coefficient of the soft layer is greater than that of the hard layer and the hard-soft interbedding, which increases as time goes, resulting in the smallest permeability coefficient for the soft layer. It provides a new method for gas extraction in the hard-soft composite coal seam.

煤层渗透系数是评价地下煤层气抽采效果的关键参数。首先，与广为接受的径向流法相比，通过采用钻孔压力累积法计算同一硬软复合煤层不同位置的煤层渗透系数，可以得到相关误差范围。其次，变化规律表明，煤层渗透系数随时间和软硬复合煤层不同位置的变化而变化。结果表明，煤层渗透系数变化规律基本一致，呈现随时间递减的幂函数。衰变过程包括三个阶段：快速衰变、缓慢衰变和稳定过程。在早期阶段，软层渗透系数大于硬软互层，硬层渗透系数最小。软层渗透系数的衰减率大于硬层和硬软互层的衰减率，随着时间的推移逐渐增大，软层渗透系数最小。为硬软复合煤层瓦斯开采提供了一种新方法。