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煤层作为富含孔隙和裂隙的多孔介质,其中赋存的瓦斯流动符合多孔介质中的流体渗流规律,即达西定律。当煤层上覆岩层和底部岩层为致密岩层、透气性极小时,可以认为完全不透气,则含瓦斯煤层为承压煤层;当煤层上覆岩层和底部含有一定的裂隙,其渗透系数与含瓦斯煤层相比虽然很小,但仍然有少量瓦斯通过透气性较低的上下岩层流入或流出含瓦斯煤层,此时含瓦斯煤层为半承压煤层。在承压煤层瓦斯流动的基础上,考虑半承压煤层瓦斯流动的特性,分别推导了渗透率各向同性和各向异性条件下半承压煤层瓦斯流动的微分方程,从而建立了半承压煤层瓦斯流动的数学模型。
The coal seam, as a porous medium rich in pores and fractures, contains gas flowing in accordance with the fluid seepage law in porous media, that is, Darcy’s law. When the coal seam overburden and the bottom of the rock is a tight rock formation, the gas permeability is extremely small, can be considered completely airtight, the gas containing coal seam is a pressure coal seam; when the overlying rock and bottom of the coal seam contains some cracks, the permeability coefficient and gas Although the coal seam is very small, a small amount of gas still flows into or out of the gas-bearing coal seam through the upper and lower strata with lower gas permeability. In this case, the gas containing coal seam is a semi-confined coal seam. Based on the gas flow in the confined coal seam and considering the characteristics of the gas flow in the semi-supporting coal seam, the differential equations of the gas flow in the semi-supporting coal seam under the conditions of permeability isotropy and anisotropy are derived respectively, Mathematical model of coal seam gas flow.