EXPERIMENTAL STUDY OF SLIPPAGE EFFECTS AND KNUDSEN DIFFUSION IN SHALE NANOPORES

In addition to Darcy flow, slippage effect and Knudsen diffusion are also the main flow modes of shale gas in nanopores. It is necessary to find out their characteristics, changing trend and influencing factors for shale gas exploitation. In this study, five Carboniferous shale samples are collected from the eastern Qaidam Basin to test the physical and chemical properties such as TOC, R_o, pore size and mineral compositions. The experiment is designed on the basis of Darcy principle. Combined with mass flux model and apparent permeability formula, the permeability contribution values, distribution coefficients and the trend of mass flux with pressure of Darcy flow, slippage effect and Knudsen diffusion are obtained to analyze the effects of such physicochemical properties. The results show that the permeability contribution value of slippage effect is the largest when the pressure is small, and then gradually decreases, with a little change in mass flux. The proportion of Knudsen diffusion is small and decreases with the increase of pressure. The permeability contribution value of Darcy flow remains unchanged, while the proportion and mass flux increase. The TOC and R_o have great effect on shale gas flow in real formation, and mineral content and pore size have direct influence on seepage.