Abstract Diffusion and seepage play a significant role in the mine gas extraction, while their influence degree is dynamic with the change of time or location, showing a notable dynamic stage characteristic. Therefore, it is significant to master the conversion node of gas transport for improving the gas production. However, it is difficult to determine the conversion node and master controlling roles during mine gas extraction due to the lack of judgment index. In this work, a dual-porosity model was constructed to describe the gas transport in coal seam. Then, a transfer coefficient ratio between gas diffusion and gas seepage was used to define as the conversion node. Furthermore, our model was validated by comparing with the previous model, showing that our model can better describe the evolution of gas pressure under different stress conditions. The influence of stress, initial permeability and initial diffusion coefficient on the conversion node were investigated. Results showed that the initial permeability shows the most notable influence on the conversion node, followed by the stress. The initial diffusion coefficient has the relatively complex effect on the conversion node depending on the specific reservoir conditions. Finally, the transfer coefficient ratio was used to determine the best distance of boreholes for improving the gas production. The research results are important for CBM and mine gas extraction.

中文翻译：

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矿井瓦斯抽采过程中输气阶段演化特征——在井眼布置提高产气量中的应用

摘要 扩散渗流在矿井瓦斯开采中起着重要作用，其影响程度随时间或地点的变化而动态变化，呈现出显着的动态阶段特征。因此，掌握输气转换节点对提高产气量具有重要意义。然而，由于缺乏判断指标，很难确定矿井瓦斯开采过程中的转换节点和主控角色。在这项工作中，建立了双孔隙度模型来描述煤层中的气体输运。然后，将气体扩散和气体渗流之间的传递系数比定义为转换节点。此外，通过与之前的模型进行比较，我们的模型得到了验证，表明我们的模型可以更好地描述不同应力条件下气体压力的演变。研究了应力、初始渗透率和初始扩散系数对转换节点的影响。结果表明，初始渗透率对转换节点的影响最为显着，其次是应力。初始扩散系数对转换节点的影响取决于具体的储层条件。最后，利用传递系数比确定提高产气量的最佳钻孔距离。研究成果对煤层气和矿井瓦斯开采具有重要意义。结果表明，初始渗透率对转换节点的影响最为显着，其次是应力。初始扩散系数对转换节点的影响取决于具体的储层条件。最后，利用传递系数比确定提高产气量的最佳钻孔距离。研究成果对煤层气和矿山瓦斯开采具有重要意义。结果表明，初始渗透率对转换节点的影响最为显着，其次是应力。初始扩散系数对转换节点的影响取决于具体的储层条件。最后，利用传递系数比确定提高产气量的最佳钻孔距离。研究成果对煤层气和矿井瓦斯开采具有重要意义。