煤层瓦斯渗流过程中压力分布的滑脱效应

 气体在多孔介质中渗流时,不仅需克服启动压力梯度,而且受气体滑脱效应的影响。基于煤层瓦斯的渗流特性,建立考虑滑脱效应的煤层瓦斯渗流模型,并对煤层瓦斯渗流过程的压力分布进行数值模拟。计算结果表明,在一定煤层深度内,与不考虑滑脱效应时煤层瓦斯压力分布相比,考虑滑脱效应对其影响显著,且随着暴露时间增长和距煤壁距离增大,其差别更为明显。滑脱因子的变化将直接影响煤层内部气体压力的分布,随着滑脱因子的增大,气体压力减小,滑脱越明显。与不考虑滑脱效应(Darcy 解)瓦斯压力分布相比,考虑滑脱效应时煤层瓦斯压力分布曲线更接近实测数据,表明在研究煤层渗流过程中须考虑滑脱效应。

Effect of coal seam gas seepage on gas pressure distribution

Many experiments indicate that for the gas seepage in the porous media, not only the threshold pressure gradient is important, but also the slippage effects should be considered. Based on the characteristics of the gas seepage in coal seams, a nonlinear seepage mathematical model through the coal seam is built, with consideration of the threshold pressure gradient and the slippage effects, to numerically simulate the gas pressure distribution in the process of the coal seam gas seepage. It is shown that the slippage has a larger effect on the gas pressure in a certain coal seam depth, and with the increase of the depth and the passing of the time, the difference gets more obvious. The change of the slip factor b directly affects the gas pressure distribution in the coal seam, and with the increase of the slip factor, the gas pressure reduces and the slippage gets more obvious. As compared with the case without considering the slippage effect (the Darcy solution), the gas pressure distribution curves in the coal seam, with considering the slippage effect, are closer to the measured data, as is consistent to the actual gas seepage, which indicates that the slippage effect is very important in the process of the coal seam gas seepage. Some internal structural characteristics and the slippage flow mechanism in the coal seam are revealed, which will help for the theoretical prediction of the lane coal seam emission's width and for the coalbed methane industrialization in hypotonic reservoirs.