The strong heterogeneity and complicated pore structure of low-permeable tight sandstone with nano-and micro-scale pore-throats could not be accurately covered by using current core testing methods.Micro-scale flowing simulation based on digital core theories was then introduced to study the gas flowing in such stones.Samples taken from the Shaximiao Formation in Western Sichuan Basin were scanned with CT to build up three-dimensional (3D) digital cores.Methods such as pore-throat identification

pore topology simplification and throat adjustment

were also resorted to establish 3D pore network models with various throat distribution patterns.Considering the complexities of gas flow in such nano-and micro-scale pore-throats

we also established a multi-mechanism flow equation that takes Darcy flow

gas slippage effect and Knudsen diffusion into consideration

and tried to solve discretely the equation by combining it with the pore network models.Numerical simulations were then carried out to study the influence of various transport mechanisms upon gas migration under different pressures.Results indicate that smaller pore-throat size and lower pore pressure mean a stronger non-linear gas flow.Gas flow was observed to basically follow the Darcy's law when pore pressure higher than 10MPa and average throat radius larger than 0.1 μm.While in samples with average pore-throat radius less than 0.1 μm and pore pressure less than 10 MPa

gas flow was dominated by gas slippage and Knudsen diffusion

a phenomenon worthy of considering during gas production.