Coal reservoir is a typical double pore medium, and the magnitude of its permeability is controlled by the parameters of the fracture pore structure. However, the relationship between fracture-pore parameters and permeability is not yet clear. Based on the fractal geometry theory, the fracture-pore morphology of coal body is characterized by tree bifurcation network and tortuous capillary bundle. This study also established a coal gas seepage flow model based on the fracture-pore fractal structure characteristics. The model includes the influence of coal structure parameters, different levels of original coal seam stress, and gas pressure on the gas seepage characteristics. Each parameter in the model has definite physical meaning and does not contain any empirical constants. Finally, the applicability of the model is evaluated by gas radial seepage experiment. It is shown that the gas permeability in the model is a function of fractal dimensions and structural parameters, and based on the sensitivity analysis of each parameter in the model, it is found that the tree diameter ratio and length ratio of the bifurcation network have a significant impact on the permeability. When increases from 0.1 to 0.9, the model permeability increases by 12 orders of magnitude. However, changes in the characteristic parameters of the pore structure have little effect on gas permeability. For dual porous media such as coal, the permeability of the fracture network dominates the overall permeability of the model, and small changes in the geometric structure of the fracture bifurcation network can lead to significant changes in permeability. The construction of this theoretical model provides a reliable basis for further improving coal-rock porous medium structure seepage models, as well as to better characterize the effect of gas drainage.

中文翻译：

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基于裂缝-孔隙分形结构特征的煤瓦斯渗流新模型


煤储层是典型的双孔隙介质，其渗透率的大小受裂缝孔隙结构参数的控制。然而，裂缝-孔隙参数与渗透率之间的关系尚不清楚。基于分形几何理论，煤体裂隙孔隙形态表现为树状分叉网络和曲折的毛细管束。本研究还建立了基于裂缝-孔隙分形结构特征的煤瓦斯渗流模型。模型包括煤体结构参数、不同水平的原始煤层应力、瓦斯压力对瓦斯渗流特性的影响。模型中的每个参数都有明确的物理意义，不包含任何经验常数。最后通过气体径向渗流实验评价了模型的适用性。结果表明，模型中的气体渗透率是分形维数和结构参数的函数，并且基于对模型中各参数的敏感性分析，发现分叉网络的树径比和长度比具有渗透率影响显着。当从 0.1 增加到 0.9 时，模型渗透率增加 12 个数量级。但孔隙结构特征参数的变化对气体渗透率影响不大。对于煤等双多孔介质，裂缝网络的渗透率主导模型的整体渗透率，裂缝分叉网络几何结构的微小变化可能导致渗透率的显着变化。 该理论模型的构建为进一步完善煤岩多孔介质结构渗流模型、更好地表征瓦斯抽采效果提供了可靠的依据。