Methane flow in coal is associated with the content of both organic matter (OM) and inorganic matter (IOM). Coal matrix contains nanopores ranging in size from a few to hundreds of nanometers, which leads to a non-Darcy effect where the measured permeability of a gas (apparent permeability) is higher than that of a liquid (intrinsic permeability). In this study, a generalized Lattice Boltzmann model (GLBM) is employed for gas flow through the reconstructed coal matrix consisting of OM, IOM, and fractures. The apparent permeability model is proposed to calculate the total flow flux accounting for multiple transport mechanisms including viscous flow, slip flow, transitional flow, and the Knudsen diffusion. The impact of effective pore radius and gas surface diffusion on permeability in the gas adsorption-desorption process is also considered in the model. What’s more, the weighting factors are adopted to adjust the contribution of the viscous flow and the Knudsen flow. The effect of total organic/inorganic content and the development of fractures on the apparent permeability of the reconstructed coal matrix is also studied. It is found that the apparent permeability is extremely low when a fracture is nonexistent, and varies almost linearly with the total organic/inorganic content. A fracture plays a significant role in determining apparent permeability and the velocity distribution of the coal matrix.

中文翻译：

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考虑非达西效应的广义格子Boltzmann模型煤基表观渗透率预测

煤中的甲烷流动与有机物 (OM) 和无机物 (IOM) 的含量有关。煤基质包含大小从几纳米到数百纳米不等的纳米孔，这会导致非达西效应，其中气体的测量渗透率（表观渗透率）高于液体的渗透率（固有渗透率）。在这项研究中，采用广义格子玻尔兹曼模型 (GLBM) 来分析通过由 OM、IOM 和裂缝组成的重建煤基质的气流。提出了表观渗透率模型来计算考虑多种传输机制的总流量通量，包括粘性流、滑移流、过渡流和 Knudsen 扩散。模型还考虑了有效孔隙半径和气体表面扩散对气体吸附-解吸过程渗透率的影响。更重要的是，采用加权因子来调整粘性流和克努森流的贡献。还研究了总有机物/无机物含量和裂缝发育对重建煤基质表观渗透率的影响。发现当裂缝不存在时，表观渗透率极低，并且几乎与总有机/无机含量呈线性变化。裂缝在确定表观渗透率和煤基质的速度分布方面起着重要作用。还研究了总有机物/无机物含量和裂缝发育对重建煤基质表观渗透率的影响。发现当裂缝不存在时，表观渗透率极低，并且几乎与总有机/无机含量呈线性变化。裂缝在确定表观渗透率和煤基质的速度分布方面起着重要作用。还研究了总有机物/无机物含量和裂缝发育对重建煤基质表观渗透率的影响。发现当裂缝不存在时，表观渗透率极低，并且几乎与总有机/无机含量呈线性变化。裂缝在确定表观渗透率和煤基质的速度分布方面起着重要作用。