考虑稀薄效应的页岩视渗透率研究

页岩孔隙细小,页岩气在页岩孔隙中的渗流会受到稀薄、克努森扩散、滑移效应的影响。为了表征页岩中气体渗流能力,在考虑稀薄效应对气体黏度影响的基础上,对气体质量通量方程进行了修正,得到了考虑稀薄效应、克努森扩散、滑移效应和孔隙壁面粗糙度的视渗透率计算模型。研究表明,当温度一定时,考虑稀薄效应影响的页岩视渗透率比不考虑稀薄效应的视渗透率大,两者间的差值随着压力的降低而减小。当压力一定时,考虑稀薄效应的页岩视渗透率比不考虑稀薄效应的视渗透率大,两者间的差值随着温度的增加而增大。当温度和压力都恒定时,考虑稀薄效应的页岩视渗透率比不考虑稀薄效应的视渗透率大,两者间的差值随着孔隙半径减小而增大。

Study on the apparent permeability of shales in consideration of rarefaction

The pore size of shales is so small that the gas flow is affected by the effect of rarefaction, Knudsen diffusion and slip effect. In order to characterize the seepage ability of the gas in shales, a new gas mass flux equation was derived on the basis of gas viscosity correction in consideration of the rarefaction effect. A new apparent gas permeability model was developed in consideration of the rarefaction effect, Knudsen diffusion, slip effect and wall roughness of pores. It is found that the apparent permeability of shale considering rarefaction effect is greater than that negligible rarefaction at the same temperature, the difference between the two apparent permeability decreases with the decreasing of pressure; the apparent permeability of shale considering rarefaction effect is greater than that negligible rarefaction at the same pressure, the difference between the two apparent permeability increase with the increasing of temperature; the apparent permeability of shale considering rarefaction effect is greater than that negligible rarefaction at the same temperature and pressure, the difference between the two apparent permeability increase with the decreasing of pores radius.