This paper describes the modelling of two important aspects in the simulation of the Vapex process for heavy oil: (1) dispersive mixing and (2) asphaltene precipitation.

The growth of the solvent chamber in the Vapex process is controlled by molecular diffusion and convective dispersion. It is shown that transverse dispersion is the dominant mechanism for fluid mixing at the solvent-oil interface. Simulation results obtained with both longitudinal and transverse dispersion, and with transverse dispersion only are illustrated and discussed.

The asphaltene precipitate is modelled as two solids: solid 1, which is in equilibrium with the asphaltene component in the oil phase, and solid 2, which is formed from solid 1 through a chemical reaction. Solid 2 can be used to represent the association of asphaltene and resins molecules and its precipitation can be made irreversible.

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