In the solvent vapor extraction of heavy oil and bitumen, commonly known as the Vapex process, viscosity of the oil is reduced by dilution with solvent. Although laboratory experiments are generally carried out using single component solvents, in the field application the commercially available solvents always contain impurities. These components distribute in the in situ oil at different proportions depending on their solubility at the operating conditions and their concentration in the injected mixture. In general it is expected that the non-condensable solvent components hinder the process.

This paper presents the results of a simulation study to investigate partitioning of solvent components inside the vapor chamber in the Vapex process. It appears that the non-condensable solvent components accumulate at the solvent vapor-viscous oil interface. The solvent component diffuses through this vapor boundary layer to the oil interface. However, the rate of diffusion in the gaseous phase is much faster than that of the molecular diffusion in the liquid phase. The later is the rate controlling step and dominates the performance of the process.

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