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气体在致密多孔介质中的运移受多种因素的影响,如孔隙结构、气体的赋存方式、温度和压力等。地层压力大,气体密度高,应属于稠密气体;另外,在页岩、煤岩、致密砂岩等多孔介质中发育了丰富的纳米级孔隙,使气体的运移机制极为复杂。详细研究了气体在致密多孔介质中的运移机理,并引入稠密气体理论,通过计算分子平均自由程,发现直径大于2nm的孔隙中,压力大于1.135MPa时(76.85℃),气体不会发生Knudsen型扩散,Fick型扩散和表面扩散可能是主要的扩散方式;并得到Knudsen渗透率修正因子随压力增加而减小,随温度的升高而增加,随孔隙半径的减小而增加,在较小孔隙中温度的影响更显著;气体从小孔扩散至大孔和裂缝系统是多种扩散机制的结果,孔隙的大小、气体的赋存方式和压力直接关系到气体的运移机理。对比分析Klinkenberg渗透率和Knudsen渗透率修正因子,发现Knudsen渗透率模型是更精确的渗透率模型,Klinkenberg渗透率修正因子可以看作是Knudsen渗透率修正因子的一级修正。
Gas migration in dense porous media is affected by many factors, such as pore structure, the manner in which gas is deposited, temperature and pressure. The formation pressure is high, and the gas density is high, so it belongs to the dense gas. In addition, rich nano-scale pores are developed in the porous media such as shale, coal and tight sandstone, which make the gas migration mechanism extremely complicated. The mechanism of gas migration in dense porous media is studied in detail, and the theory of dense gas is introduced. By calculating the mean free path, it is found that when the pressure is greater than 1.135MPa (76.85 ℃) Type diffusion, Fick type diffusion and surface diffusion may be the main diffusion modes. The Knudsen permeability correction factor decreases with increasing pressure, increasing with increasing temperature, increasing with decreasing pore radius, The influence of temperature on the pore is more significant. The diffusion of gas from the pores to the macropores and the fracture system is the result of various diffusion mechanisms. The size of the pores, the mode of gas storage and the pressure are directly related to the gas migration mechanism. By comparing Klinkenberg permeability with Knudsen permeability correction factor, it is found that the Knudsen permeability model is a more accurate permeability model and the Klinkenberg permeability correction factor can be regarded as a first-order correction of the Knudsen permeability correction factor.