Solvent Vapour extraction (Vapex) is a promising technology for in-situ heavy oil recovery from oil sands deposits. The prediction of oil recovery rates requires fundamental understanding of the pore-scale mechanisms and their impact on mass transfer and oil production. To bridge the gap between pore-scale mechanisms and macro scale recovery, a dynamic pore-network model for two-phase flow with mass transfer is developed. The impact of pressure gradient on two-phase flow pattern, mass transfer and oil production are investigated. It is found that at high capillary numbers, in viscous dominated flow, dissolved oil is moved in intermittent liquid clusters to the outlet of the network. This mechanism of interface renewal maintains a steep solvent mole fraction gradient at the interface and enhances mass transfer, resulting in high oil production. In capillary dominated flow, capillary fingering with low mass transfer and oil production are observed.