The effect of Knudsen diffusion and adsorption on shale transport in nanopores

Shale transport properties are investigated by numerical simulations of a simple, physics-based continuum model. Shale samples from the Yanchang Triassic Formation in Ordos Basin are tested to get the pore volume distribution of shale. Due to the existence of nanopores in shale reservoirs, there are great differences in gas transport mechanisms compared to those in conventional gas reservoirs. These mechanisms include Knudsen diffusion and adsorption. A physics-based continuum model is utilized to simulate the gas transport in a channel with nanoscale radius, where these mechanisms are taken into consideration by imposing a general boundary condition with two parameters. The correction factor which is the ratio between apparent permeability and intrinsic permeability is investigated for a wide pressure range, which shows it is always larger than 1, illustrating that Knudsen diffusion always plays a role in shale gas transport.