Permeability models for single-phase gas transport though nanotubes and nanoslits were established by a weighted
superposition of slip flow and molecular diffusion (the inorganic pores were regarded as the nanoslits; the organic pores were
regarded as the nanotubes). Besides, the influence of water saturation on the gas transport was quantified by considering its distribution
characteristic inside the inorganic pores and the organic pores of actual shale formations. The results show that the effect
of water saturation on the gas flow capacity at a nanoscale is mainly controlled by a Knudsen number (Kn); as Kn increases,
the impact of nano-scale effect (slip and diffusion) begins to grow, and the decrease in gas flow capacity caused by the bound
water weakens. For slit-shaped pores (e.g. inorganic pores), when Kn < 0.001 (the nano-scale effect is not obvious), the gas-phase
permeability decreases by as high as 51% with an irreducible water saturation of 30%; instead, when Kn > 1.0 (the nano-scale
effect is significant), the gas-phase permeability reduces by about 33% in the same water saturation condition. Therefore, with the development of shale gas reservoirs, the reservoir pressure gradually reduces and the Kn gradually increases, leading to a
weakening effect of the bound water on gas flow; however, this effect still cannot be ignored. This paper provides a theoretical
basis for reasonable evaluations and predictions of gas production from actual shale formations with initial water saturation.
