近距离上保护层开采瓦斯运移规律数值分析

采动裂隙是瓦斯运移的通道,搞清瓦斯运移规律是瓦斯治理的前提。在考虑岩石动态破坏过程和含瓦斯煤岩渗流-应力-损伤耦合的基础上,结合平煤五矿实际地质条件和开采工艺,建立了数值计算模型,应用RFPA-Gas程序模拟了近距离上保护层采动顶底板岩层变形破坏、裂隙演化规律与瓦斯运移规律。模拟结果较好地再现了保护层开采过程中煤岩层应力变化、顶底板损伤及裂隙演化过程,得到了上覆岩层移动的"上三带"(冒落带、裂隙带和弯曲下沉带)和底板变形的"下两带"(底板变形破坏带和弹塑性变形带)。得到了被保护层瓦斯流量分布、瓦斯压力分布和透气系数的变化规律,卸压煤层瓦斯透气性增大了2500倍,得到了煤壁下方压缩区和膨胀区之间的张剪瓦斯渗流通道,并将保护层底板压缩区和膨胀区的瓦斯渗流特征提炼出来:压缩区对应的是渗流减速减量区、膨胀区由卸压膨胀陡变区和卸压膨胀平稳区组成,分别对应着渗流急剧增速增量区和渗流平稳增量区。指出卸压膨胀陡变区是瓦斯突出危险区,为近距离保护层开采瓦斯治理指明了方向。实践表明,瓦斯治理效果显著。

Numerical analysis of gas flow law with short distance upper protective layer gas extraction

Mined fracture is the passage of gas flow, and gas flow law is the precondition of control gas disaster. Based on the dynamic failure process and coupled fluid-solid interaction between gas flow and solid deformation, considering geologic condition and excavating technique in Mine No. 5 in Pingdingshan, a numerical simulation model is established with the gas-solid coupling rock failure process analysis system RFPA-Gas to simulate the stress variation law, roof and floor deformation, fracture evolution law, displacement in the protected seam, change in gas permeability and gas flow law during upper protective layer extraction. The simulation results reproduced stress variations in coal and rock strata, roof and floor deformation and fracture evolution process during protective layer extraction. The movement of rock strata were characterized by upper three zones and lower two zones: caving zone, fracture zone and bending subsidence zone in the vertical direction in the overlying stratum; floor deformation and failure zone and elasto-plastic deformation zone in the vertical direction in the underlying stratum. The gas flux, gas pressure and gas permeability change with the upper protective extraction. And the gas permeability of protected coal seam dramatically increases about 2 500 times. The tensile-shear gas flow passages appear under the pillar between compression zone and expansion zone. The gas flow speed and the flux reduce at the stress-concentration zone. The expansion zone is composed of stress relief and sudden expansion zone and stress relief and steady expansion zone. The gas flow speed and the flux increase dramatically at stress relief and sudden expansion zone. The gas flow speed and the flux increase slowly at stress relief and steady expansion zone. The gas outburst often occurs at stress relief and sudden expansion zone. The results provide a clear direction for gas control in the protective layer. The simulation results are in good agreement with the stress-relief effects in field.