穿层钻孔瓦斯径向非稳态流动模型解析解
ANALYTICAL SOLUTION FOR THE UNSTEADY-STATE RADIAL FLOW MODEL OF GAS IN CROSS-MEASURE BOREHOLE
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摘要: 精准描述穿层钻孔瓦斯的径向非稳态流动规律, 是防治煤矿瓦斯灾害的关键理论依据. 然而, 该模型的解析解研究尚显薄弱. 为此, 基于柱坐标系与定压边界条件, 建立了相应的瓦斯流动模型. 利用Laplace变换与Bessel函数, 推导获得该模型的解析解, 并与数值解及传统指数积分函数式进行对比验证, 系统分析了关键参数对瓦斯抽采效能的敏感性. 研究表明: 解析解、数值解及传统指数积分函数式的计算结果随时间演化高度一致, 验证了解析解的正确性与可靠性, 其中解析解与数值解的吻合度优于指数积分函数式. 高透气性可显著强化初期抽采效果, 而强吸附特性则明显抑制抽采进程; 较高的原始瓦斯压力虽在初期提升抽采速率与压降幅度, 却会降低整体压降效率, 并加剧后期抽采速率的衰减; 增加抽采负压对抽采速率与效率的提升作用较为有限; 扩大钻孔半径会提高单孔抽采速率与累计抽采量, 但会导致单位面积抽采效率下降. 综合比较, 各参数对抽采效率的影响强度依次为: 原始瓦斯压力 > 吸附特性≈透气性 > 钻孔半径 > 抽采负压. 研究结果为穿层钻孔中瓦斯非稳态径向流动行为提供了更深入的理论认识, 并为优化瓦斯抽采策略、提高抽采效率以及保障煤矿安全生产提供了重要理论支撑.Abstract: Accurate characterization of the radial transient gas flow in cross-measure boreholes is a fundamental theoretical basis for the prevention and control of coal mine gas disasters as well as for efficient coalbed methane extraction. However, analytical investigations of this process remain limited. In this study, a novel gas flow model was established based on cylindrical coordinates and constant-pressure boundary conditions. By employing Laplace transforms and Bessel functions, an analytical solution for this model was derived, which was further validated through comparisons with numerical solutions and traditional exponential integral functions. The sensitivity of key parameters to gas extraction efficiency was systematically analyzed. The study demonstrates that the analytical solution, numerical solution, and traditional exponential integral function exhibit highly consistent temporal evolution, validating the accuracy and reliability of the analytical solution. The agreement between the analytical and numerical solutions significantly outperforms that of the exponential integral function. High permeability significantly enhances initial extraction efficiency, while high adsorption exhibits an inhibitory effect. Higher initial gas pressure aids in increasing initial extraction rate and pressure drop magnitude but reduces overall pressure drop efficiency, leading to more pronounced rate decay in the later extraction phase. Increasing drawdown pressure enhances suction but yields limited gains in extraction rate and efficiency. Increasing the borehole radius enhances the extraction rate and cumulative extraction volume per borehole but reduces the extraction efficiency per unit area. The influence of each parameter on extraction efficiency is ranked as follows: initial gas pressure is greater than adsorption properties, which is greater than or equal to permeability, followed by borehole radius, and extraction negative pressure is the smallest. The findings provide deeper theoretical insight into the transient radial flow behavior of gas in cross-seam boreholes and offer an analytical framework for optimizing gas drainage strategies, improving extraction efficiency, and ensuring safe coal mine production.
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