Modelling of dynamic mass transfer in a vapour extraction heavy oil recovery process

ABSTRACT Viscosity reduction through solvent dissolution into heavy oil is one of the most important recovery mechanisms of a vapour extraction (VAPEX) process. Existing analytical models can neither accurately describe the mass transfer between solvent vapour and heavy oil nor predict the solvent chamber evolution. Simulation models are confounded by numerical dispersion and have difficulty in accurately characterizing fluid properties in VAPEX. This study first develops a mass transfer model to describe a dynamic heavy oil‐solvent mixing process. This model is then incorporated into a VAPEX model to estimate solvent chamber development and an oil production rate. Diffusivity is determined through history matching theoretically calculated and experimentally measured cumulative oil production data. It is found that both constant and variable diffusivities can achieve an excellent match in cumulative oil production data. However, their respective characterization of the fluid properties in the VAPEX transition zone is very different. This study also proposes a method to convert constant diffusivity into its equivalent variable diffusivity for VAPEX by using some regressed correlations. Moreover, the back‐calculated effective diffusivity is found to be about 10–30 times of the corresponding molecular diffusivity measured in the laboratory.