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.

gas seepage  /  slippage effect  /  gas pressure  /  coal seam