Abstract Fracture randomness and irregularities have a decisive effect on the gas reservoir and migration in overlying strata at different coal mining heights. To determine the boundary of a gas migration channel, its effect on gas storage, and migration in the overlying strata at different coal mining heights, this study integrated the two-dimensional (2D) physical similarity simulation of the calculated fractal dimensions to examine the results obtained using analytical techniques. With the increase of the mining height, the range of gas migration channels increased significantly. Moreover, we identified the primary parameters of the gas migration channel boundary in the mutant regions of bed separation and the broken fracture density. Apart from the increasing working distance, the fractal dimension increased when the fractal dimension of a working face side was larger than an open-off cut side. The fractal dimensions of a mine with a height of 6.0 m were 1.07 and 1.23 times of those for heights of 4.0 and 2.0 m, respectively. According to the variation principle of fractal characteristics and Reynolds number, the gas migration channel was divided into three regions, namely a gas active, gas circulation, and gas enrichment areas. On the basis of the fractal theory, an effective model was proposed to calculate the evolution characteristics of gas migration channels at different mining heights. Compared with the previous gas migration channel model, the proposed model could be appropriately estimated the position of high-level boreholes; the improved estimations can improve gas drainage efficiency and ensure safe and efficient mining.

中文翻译：

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不同采高瓦斯运移通道分形特征

摘要 裂缝的随机性和不规则性对不同采煤高度上覆地层的气藏和运移具有决定性影响。为确定瓦斯运移通道的边界、其对储气量的影响以及不同采煤高度上覆地层运移的影响，本研究结合计算分形维数的二维（2D）物理相似性模拟来检验结果使用分析技术获得。随着开采高度的增加，天然气运移通道范围显着增加。此外，我们确定了床分离突变区和破裂裂缝密度的气体运移通道边界的主要参数。除了增加工作距离，当工作面侧的分形维数大于开切侧的分形维数时，分形维数增加。6.0 m 高度矿井的分形维数分别是 4.0 m 和 2.0 m 矿井的 1.07 倍和 1.23 倍。根据分形特征和雷诺数的变化规律，将天然气运移通道划分为三个区域，即气体活动区、气体环流区和气体富集区。以分形理论为基础，提出了计算不同采高天然气运移通道演化特征的有效模型。与以往的天然气运移通道模型相比，该模型能够较好地估计高位井眼的位置；