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基于滑脱流动和努森扩散,分别以分子之间碰撞频率和分子与壁面碰撞频率占总碰撞频率的比值作为滑脱流动和努森扩散的权重系数,进行权重叠加,建立了页岩气复杂孔裂隙气体传输模型.该模型综合考虑了滑脱效应和真实气体效应,同时还分别考虑了截面类型(圆形和矩形)和形状对气体传输的影响.用公开发表的分子模拟数据验证模型.结果表明:(1)本文模型能够合理地描述页岩气复杂孔裂隙气体传输机理,包括连续流动、滑脱流动和过渡流动;(2)页岩气孔裂隙截面类型和形状影响气体传输能力,相同截面面积,圆形截面孔裂隙气体传输能力大于矩形截面孔裂隙气体传输能力,矩形截面孔裂隙气体传输能力随纵横比增大而减小;与截面类型相比,截面形状对气体传输能力的影响更大;(3)真实气体效应提高了气体传输能力,且这种影响随压力增大而增大,随孔裂隙尺度减小而增大;(4)与圆形截面相比,真实气体效应对矩形截面气体传导率影响更大,且随矩形截面纵横比增大而增大.本文模型能为页岩气准确数值模拟奠定一些理论基础.
Based on the slip-flow and Knudsen diffusion, the collision frequencies between molecules and the ratio of molecular-wall collision frequency to the total collision frequency were respectively used as the weight coefficients of slip flow and Knudsen diffusion. Gas transport model.The model takes into account the slippage effect and the real gas effect, and also considers the influence of cross-section type (circle and rectangle) and shape on the gas transport separately.The model is verified by the published molecular simulation data.The results show that: (1) The model can reasonably describe fracture gas transmission mechanism in shale gas complex fractures, including continuous flow, slippage flow and transitional flow; (2) The type and shape of the fractured pores in shale gas affect the gas transmission capacity, the same cross-sectional area, The cross-sectional pore gas transmission capability is larger than that of the rectangular cross-section hole fracture gas, and the fracture gas transmission capacity decreases with the increase of the aspect ratio. The cross-sectional shape has a greater influence on the gas transmission capacity than the cross-sectional type. ( 3) The real gas effect increases the gas transmission capacity, and this effect increases with increasing pressure, decreasing with the pore size (4) Compared with the circular section, the real gas effect has a greater influence on the gas conductivity of the rectangular section, and increases with the aspect ratio of the rectangular section.Our model can lay the foundation for accurate numerical simulation of shale gas Some theoretical basis.