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Solvent vapour extraction (VAPEX) process is an economically viable, technically sound, and environmentally friendly insitu heavy oil recovery method to exploit tremendous heavy oil and bitumen reserves. In this recovery process, significant heavy oil viscosity reduction is achieved through sufficient solvent dissolution and possible asphaltene precipitation. Over the past two decades, several researchers have carefully studied the effects of some major factors on the VAPEX process, such as the test pressure, reservoir porosity and permeability, solvent and heavy oil types, well configuration, and connate water saturation. However, it is unclear how waterflooding and solvent injection will affect a typical VAPEX process.In this paper, waterflooding and solvent injection effects are experimentally studied by using a visual rectangular sandpacked high-pressure VAPEX physical model with a low permeability. The physical model is packed and then saturated with a heavy oil sample at the connate water saturation. Pure propane and a mixture of n-butane and methane are used as respective solvents to extract two different heavy oil samples. The waterflooding effect is examined by performing a series of VAPEX tests with the initial waterflooding, prior to the subsequent solvent injection/soaking. In addition to the visual observation of the solvent chamber evolution, the heavy oil production rate, produced solvent-oil ratio, and asphaltene content of the produced heavy oil are measured during the waterflooding and solvent injection/soaking. It is found that the initial waterflooding causes an oil production reduction in the subsequent solvent injection. Also solvent breakthrough occurs earlier and a small amount of water is produced afterwards. This is because the initial waterflooding creates some lowresistance channels for the injected solvent to bypass the untouched heavy oil. As a result, the heavy oil is not diluted enough to be produced during the subsequent solvent injection/soaking. In the absence of waterflooding, however, solvent injection alone can increase the heavy oil production in comparison with the solvent-soaking process. Moreover, it is visually observed that solvent injection leads to less asphaltene deposition onto the porous media. This is quantitatively verified by a higher measured asphaltene content of the produced heavy oil at a higher solvent injection rate.

In this article, a new model is developed to determine the solvent convective dispersion coefficient in a solvent vapor extraction (VAPEX) heavy oil recovery process. It is assumed that solvent mass transfer by convective dispersion takes place along the transition zone between the solvent chamber and untouched heavy oil, whereas solvent mass transfer by molecular diffusion occurs in the direction normal to the transition zone. It is also assumed that the solvent-diluted heavy oil gravity drainage through the transition zone has a linear or quadratic velocity profile in order to obtain analytical solutions of the solvent convective dispersion coefficients for the solvent chamber spreading and falling phases. As a result, this analytical model correlates the solvent convective dispersion coefficient to the maximum apparent oil gravity drainage velocity at the interface between the solvent chamber and transition zone, solvent molecular diffusion coefficient, transition-zone thickness, and porosity of the porous medium. To determine the solvent convective dispersion coefficient, the maximum apparent oil gravity drainage velocity is calculated by using Darcy's law and the transition-zone thickness is obtained either from a previous study or by using a time similarity between the solvent molecular diffusion and oil gravity drainage. It is found that such a determined solvent convective dispersion coefficient is two to five orders larger than the solvent molecular diffusion coefficient, depending on the detailed experimental conditions of a specific VAPEX test. List of Symbols cSolvent mass fraction in the solvent-diluted heavy oil (g solvent/g heavy oil) C max Maximum solvent volume concentration at the interface between the solvent chamber and transition zone (vol.%) D Solvent molecular diffusion coefficient (m 2 /s) D app Apparent solvent molecular diffusion coefficient along x-axis (m 2 /s) D x Apparent solvent molecular diffusion coefficient along x-axis (m 2 /s) D y Solvent convective dispersion coefficient along y-axis (m 2 /s) g Local gravitational acceleration (m/s 2 ) H VAPEX physical model height (m) J x Solvent mass flux by molecular diffusion along x-axis (kg/m 2 s) J y Solvent mass flux by convective dispersion along y-axis (kg/m 2 s) k Absolute permeability of the VAPEX physical model (m 2 ) L VAPEX physical model length (m) P Constant operating pressure during the VAPEX test (kPa) P v Propane vapor pressure at T = 20.8 • C (kPa) Q s Solvent mass flow rate (kg/s) T Constant operating temperature during the VAPEX testInterstitial gravity drainage velocity of the solvent-diluted heavy oil along the transition zone (m/s) v ave Average apparent gravity drainage velocity of the solvent-diluted heavy oil along the transition zone (m/s) v max Maximum apparent gravity drainage velocity of the most diluted heavy oil at the interface between the solvent chamber and transition zone (m/s) xx-coordinate (m) y y-coordinate (m)Greek Symbols δ Transition-zone thickness (m) μ o Viscosity of the heavy oil (Pa s) μ o (C ma...

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