煤层瓦斯多机制流固耦合模型与瓦斯抽采数值模拟分析

A fluid-solid coupling model of coal seam gas considering gas multi-mechanismflow and a numerical simulation analysis of gas drainage

为了更好地揭示瓦斯抽采过程中松软低透气性煤层瓦斯运移的本质和规律,基于孔隙-裂隙双重介质的假设,建立了全面考虑有效应力、煤层瓦斯多机制流动、真实气体效应和迂曲度影响的煤层瓦斯多机制流固耦合模型。基于所建理论模型,以郑煤集团(河南)白坪煤业有限公司13181工作面为工程背景,利用COMSOL软件开展煤层瓦斯抽采数值模拟,全面分析了瓦斯压力随抽采时间的动态分布规律,结合现场实测结果验证了数值模拟有效抽采半径的准确性。系统开展了不考虑Klinkenberg效应、不考虑基质瓦斯扩散和不考虑煤层瓦斯多机制流动影响的瓦斯抽采数值模拟,对比分析了不同控制因素对煤层瓦斯运移的影响。研究结果表明:抽采结束后,煤层瓦斯压力以抽采钻孔为中心呈椭圆分布;煤层瓦斯压力和有效抽采半径的变化幅度随抽采时间逐渐减小,并趋于稳定;煤层瓦斯有效抽采半径的数值模拟结果与现场实测结果之间的平均误差为3.65%,验证了所建煤层瓦斯多机制流固耦合模型的有效性与合理性;与考虑煤层瓦斯多机制流动影响的模拟结果相比,不考虑Klinkenberg效应的有效抽采半径和渗透率偏小,而不考虑基质瓦斯扩散和瓦斯多机制流动的有效抽采半径和渗透率则明显偏大,表明Klinkenberg效应和基质瓦斯扩散对煤层瓦斯流动分别起促进和抑制之作用。

In order to better reveal the nature and law of gas migration in soft and low permeability coal seams during gas drainage,based on the dual medium of pore and fracture,a coupled fluid-solid model of gas multi-mechanism considering the influence of effective stress,multi-mechanism flow of coal seam gas,real gas effect and tortuosity is established.With the No.13181 working face of the Baiping Mine Coal Industry Co.,Ltd.of Zhengzhou Coal Group Industry(Henan)as the engineering background,the COMSOL software is used to carry out a numerical simulation of gas drainage based on the model established.The dynamic distribution law of gas pressure with the drainage time is fully analyzed,and the accuracy of the effective drainage radius of the numerical simulation is verified in combination with the on-site measurement results.Numerical simulations of gas drainage without considering the Klinkenberg effect,matrix gas diffusion and multi-mechanism flow of coal seam gas are carried out systematically,and the specific effects of different control factors on coal seam gas migration are compared and analyzed.The results show that the gas pressure of coal seam is elliptic with the center of the drainage hole after the drainage.The variation range of coal seam gas pressure and effective drainage radius gradually decreases with the drainage time and tends to be stable.The average error between the numerical simulation results and the on-site measurement results of effective drainage radius of coal seam gas is 3.65%,which verifies the effectiveness and rationality of the coupled fluid-solid model of coal seam gas multi-mechanism.Compared with the simulation results considering the effect of multi-mechanism flow of coal seam gas,the effective drainage radius and permeability without considering the Klinkenberg effect is smaller,while the effective drainage radius and permeability without considering the matrix gas diffusion and multi-mechanism flow are obviously larger,indicating that the Klinkenberg effect and matrix gas diffusion can promote and inhibit the coal seam gas flow respectively.