Condensing solvent heavy oil recovery processes, such as NSolv, are a potential lower-energy and less GHG-intensive alternative to the currently employed thermal methods. In a condensing solvent process, n-alkane solvents are injected instead of steam and the bitumen viscosity is reduced mainly via mass transfer rather than heat transfer. One challenge with using n-alkane solvents is the precipitation and deposition of asphaltenes, which can reduce permeability and limit recovery rates. The objective of this study was to investigate the impact of asphaltene deposition on the mechanisms governing mass transfer and gravity drainage in condensing solvent processes using n-heptane and n-pentane. Gravity drainage experiments were conducted in a packed Hele-Shaw cell using glass beads and silica sands with permeabilities ranging from 96 to 225 D. In these experiments, a layer of solvent was flowed over an inclined bitumen surface. Liquid n-alkanes were injected at flow rates from 0.5 to 10 cm3/min, and bitumen production rates, mass transfer rates, residual bitumen saturations, and the extent of deasphalting were measured. Compared to experiments using toluene, the bitumen mass fluxes with n-alkanes were 35–50% lower due to lower diffusivity and reduced permeability from asphaltene deposition. Previously developed analytical and numerical models based on diffusive mass transfer and Darcy drainage flow were adapted to include asphaltene deposition and permeability reduction. The impact of deposition was accounted for by introducing the measured residual bitumen saturation and by tuning an effective permeability ratio. Asphaltene deposition was found to reduce the absolute permeability to 9% of its original value with n-pentane and to 33% with n-heptane. The mass fluxes were shown to scale to the square root of the effective permeability. The scaled mass fluxes were of similar magnitude to those calculated from the NSolv pilot data.
Núñez-Méndez et al. (Fri,) studied this question.