We used a combination of experimental, analytical and numerical approaches to examine the oil drainage rates obtained from VAPour EXtraction (VAPEX) process to recover heavy oil. In particular we investigated the influence of macroscopic scale heterogeneities through a series of experiments. These heterogeneities comprised layers, a quadrant model and two cases with discontinuous shale barriers above the injection well. All experiments were performed in well-characterized glass bead packs using glycerol and ethanol as analogues of heavy oil and solvent respectively. All the porous medium and fluid properties (including permeability, porosity, viscosity, density, diffusion and dispersion) were measured independently. The experimentally measured rates were compared to the estimates derived from the Butler-Mokrys analytical model. Numerical simulations were validated using the experimental observations from the homogenous and heterogeneous systems.

The findings confirmed the square root dependency of the oil rates on permeability (at least for the range of permeabilities used here) which is consistent with findings from previous studies. Despite that, the results indicated that the Butler-Mokrys derived expression under-predicts the physical oil rates, even when the effects of convective dispersion and end-point density difference (as suggested by other works) were factored in. Results from the heterogeneous models suggest that layering may not reduce VAPEX oil drainage rates significantly. They also showed that oil was not recovered from the lower permeability layers. For models with discontinuous shale barriers, the simulations tended to over-predict the oil rates compared with the experiments.

Overall the estimated rates from the simulations were more comparable to the physical rates than those estimated from the original Butler-Mokrys analytical derivation. Moreover the simulator was able to capture the pattern of solvent-oil distribution for both homogeneous models and heterogeneous models. This would suggest that the Butler-Mokrys model does not properly describe all the physical processes that are controlling the oil drainage rate even in homogeneous models.

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