Accurately identifying the source of coalbed methane is of great practical significance in preventing gas concentration overruns and improving extraction efficiency. At present, it is widely believed that underground gas mainly comes from coal desorption, and the mechanism of gas flow inside the coal seam is explored in depth, while the gas released inside the rock is often neglected, and there is insufficient understanding of its internal transportation law. In this study, the density gradient theory (FGDGD) in the coal matrix was used as a guide to characterize the adsorption and transport properties of gases within the rock. The anthracite and mudstone from the same roadway in Yuxi mine were selected for the experiments, and coal rock samples with particle sizes of 0.425 mm–0.25 mm were ground. The adsorption constant test and adsorption process experiments were carried out under the constant volume condition, and the transport behavior of gas within the rock was simulated and numerically solved, and the content and flow behavior of gas in the rock were discussed in detail. The results are as follows: (i) The simulation curves based on the density gradient model fit well with the experimental data for both coal and rock downholes, indicating that the gas transport law inside the rock downhole is also in accordance with the density gradient theory, which broadens the scope of application of the theory. (ii) The free gas diffusion coefficients (rock) are smaller than (coal) for the gases in the rock matrix and coal matrix, which may be due to the difference in the pore structure of the rock matrix, resulting in lower adsorption sites than those of the coal. (iii) Although the gas content inside the rock is relatively low compared with that of coal, it is significant for reducing the prediction error of gas influx in engineering practice. Therefore, it is necessary to consider the storage of gas in rocks and its migration behavior when studying the sources of gas emissions in engineering fields.

中文翻译：

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基于自由气体扩散理论的顶板岩石气体输运模型及数值解

准确识别煤层气来源对于防止瓦斯浓度超标、提高抽采效率具有重要的现实意义。目前人们普遍认为地下瓦斯主要来源于煤的解吸，并对煤层内部瓦斯流动机理进行了深入探索，而对岩石内部释放的瓦斯却往往忽视，对其内部认识不足。运输法。在本研究中，以煤基质中的密度梯度理论（FGDGD）为指导来表征岩石内气体的吸附和传输特性。试验选取玉溪矿同巷无烟煤和泥岩，磨碎粒度为0.425 mm~0.25 mm的煤岩样品。在定容条件下进行了吸附常数测试和吸附过程实验，对岩石内气体的输运行为进行了模拟和数值求解，详细讨论了岩石中气体的含量和流动行为。结果如下： (i) 基于密度梯度模型的模拟曲线与煤岩井下的实验数据吻合良好，表明井下岩石内部的瓦斯输运规律也符合密度梯度理论，拓宽了该理论的应用范围。 (ii) 岩石基质和煤基质中气体的自由气体扩散系数（岩石）小于（煤），这可能是由于岩石基质孔隙结构的差异，导致其吸附位点较低。那些煤炭。 (iii)虽然岩石内部瓦斯含量与煤相比较低，但对于工程实践中减少瓦斯涌量预测误差具有重要意义。因此，在研究工程领域瓦斯排放源时，需要考虑气体在岩石中的储存及其运移行为。