Based on analogy between isothermal drying of porous media and molecular diffusion in a single-block model containing a volatile liquid during lean gas injection, a detailed procedure is presented for two-dimensional quasi-static pore network modelling of diffusion. A modified invasion percolation algorithm is used to account for evaporation of liquid clusters formed during gas injection process. Diffusion in gas phase, capillaryinduced flow in liquid phase, and evaporation in gas-liquid interface were modelled to trace the movement of gas-liquid interface and desaturation profile. Using a set of throat sizes with normal distribution, 15 cases of a regular pore network model were proposed by rearranging throat positions in the model. Results of this study indicate that diffusion time, breakthrough time, vapour partial pressure gradient, liquid saturation gradient, liquid cluster frequency, gas-liquid interface frequency, and evaporation potential are strong functions of throat sorting. Correlation coefficient of throat size with position was used to capture the disorder of porous medium. It was shown that such a correlation coefficient is not capable of describing diffusion characteristics.