Gas flow characteristics in shales nanopores

Gas flow characteristics directly influence the productivity of shale gas reservoir and production evaluation. And shale gas flow characteristics are directly related to the pore distribution of shale. Pore sizes of 4-6 nanometers were mainly found in Long maxi and Wufeng shales formations of Zhao tong area using nitrogen isothermal adsorption. The calculation of apparent permeability of shale is made by using Kn number and Beskok-Karniandakis equation. The influence of temperatures, pressure and gas adsorption to the gas flow characteristics was analyzed. The ratio of apparent permeability to Darcy permeability reaches as much as 30 in the nanopores with diameter less than 10 nm. Gas adsorption layer will reduce pore diameters, the apparent permeability of pores with diameter less than 10 nm increases as the adsorption layer increases. The apparent gas permeability of nanopores is relevant to Kn number which is affected by temperature and pressure. Without considering of adsorption layer, the gas apparent permeability decreases as pressure increases and temperature increases. The ratio of apparent permeability to Darcy permeability with the consideration of adsorption layer and without consideration adsorption layer increases as the pressure increases and the temperature decreases.