Coalbed methane (CBM) resources cannot be efficiently explored and exploited without a robust understanding of the permeability of fracture-size heterogeneities in coal. In this study, two sister coal samples were imparted with pre-developed cleat and connected fractures, and the permeability of the coal samples was measured under different conditions of controlled confining and gas pressures. Furthermore, the implications of the results for CBM exploration and exploitation were discussed. The permeability of coal with cleat development ranged from 0.001–0.01 mD, indicating ultra-low permeability coal. The gas migration in this coal changed from a linear flow to a non-linear flow, with the increase in gas pressure (>1 MPa). Thus, the permeability of the coal initially increased and then decreased. However, the Klinkenberg effect does not exist in this ultralow-permeability coal. For the coal sample with connected fracture, permeability ranged from 0.1–10 mD, which is larger by hundred orders of magnitude than that of the sample with cleat. For this coal, with a decrease in gas pressure (<1 MPa), the Klinkenberg effect significantly increased the permeability of the coal. With an increase in the applied confining pressure, both the Klinkenberg coefficient and permeability of the coal presented a decreasing trend. It is suggested that field fracture investigation is a prerequisite and indispensable step for successful CBM production. The coal beds that cleat network is well conductive to the connected fracture can be an improved target area for CBM production. During CBM production, a variety of flow regimes are available owing to the decrease in CBM reservoir pressure. In particular, under the low CBM reservoir pressure and low in situ geo-stress conditions, the gas migration in the CBM reservoir with connected facture development exhibits remarkable free-molecular flow. Thus, the reservoir permeability and predicted CBM production will be enhanced.

如果不深入了解煤中裂缝尺寸非均质性的渗透率，就无法有效地勘探和开发煤层气 (CBM) 资源。在这项研究中，两个姊妹煤样被赋予了预先发育的割理和连接裂缝，并在不同的控制围压和瓦斯压力条件下测量了煤样的渗透率。此外，还讨论了结果对煤层气勘探和开发的影响。割理发育煤的渗透率为0.001～0.01 mD，为超低渗透煤。随着瓦斯压力的增加（>1 MPa），该煤中的瓦斯运移由线性流动变为非线性流动。因此，煤的渗透率先升高后降低。然而，在这种超低渗透煤中不存在克林伯格效应。对于裂缝相连的煤样，渗透率在0.1-10 mD之间，比割理样品的渗透率高数百个数量级。对于这种煤，随着瓦斯压力的降低（<1 MPa），克林伯格效应显着增加了煤的渗透率。随着施加围压的增加，煤的克林伯格系数和渗透率均呈下降趋势。认为现场裂缝调查是煤层气成功生产的先决条件和必不可少的步骤。割理网络对连通裂缝具有良好传导性的煤层可成为煤层气生产的改进目标区。在煤层气生产过程中，由于煤层气储层压力的降低，可以使用多种流态。特别是在低煤层气储层压力和低地应力条件下，裂缝发育相连的煤层气储层中的气体运移表现出显着的自由分子流动。因此，将提高储层渗透率和预测的煤层气产量。