Dispersion of a solvent into heavy oil and bitumen in porous media has special significance in the context of solvent-based as well as solvent-aided versions of SAGD and CSS recovery processes. While solvent is injected with steam, the mixture condensation temperature changes based on solvent partial pressure. In addition, water condensate creates a film which acts as a barrier and impacts solvent dissolution in oil. The solvent, which is not soluble or has very low solubility in water, may not be able to diffuse in the oleic phase due to the presence of the water film. The objective of the present study is to investigate the pore-scale solvent diffusion in oil for solvent-based and hybrid (steam + solvent) processes through the following steps:
Developing a pore-scale simulator, capable of handling steam and solvent condensation as well as mass transfer in porous media.
Investigating solvent dissolution in the oleic phase at the pore-level considering the asynchronous condensation of solvent and steam.
Investigating the dissolution of solvent, either in gaseous phase or in the form of liquified thin bulk films of condensed solvent and water condensate, in the oleic phase.
A pore-scale simulator was developed with the capability of modelling solvent mass transfer and condensation of both solvent and steam, along with a Navier-Stokes type solution for the velocity field. In addition, conjugate heat transfer was included in the model that takes into account the heat transfer from solvent and steam to the solid grains by considering the two media (i.e. solid and fluid) for the solution. A realistic description of a 2-dimensional porous medium is used for direct numerical simulation (DNS). The properties of a typical heavy oil and solvent were implemented in the model with diffusion coefficient as functions of both temperature and solvent concentration.
After model setup, the newly added features of mass transfer and conjugate heat transfer were validated by comparison with analytical models. For mass transfer validation, the numerical results were in agreement with analytical solution for a capillary whereas the model performance for conjugate heat transfer were inline with the analytical solution proposed for heat flow over a slab. The pore-scale simulator was then used to model two-dimensional pore-scale experiments of solvent co-injection with steam. To reproduce the experimental results, the interface advancement velocity was calculated as an evidence of the chamber growth. The 2D numerical simulation results were in agreement with the experimental data. The condensation of solvent vapor and steam also changes fluid flow and flow pathways of solvent at the pore-scale which results in some complex fluid flow and behavior such as excessive unexpected channeling.
The present study is the first of its kind which considers condensation of steam and solvent vapor at the pore scale. The model is used to investigate solvent vapor condensation in competition with steam at the pore-scale and to study the impact of solvent type and operating conditions such as pressure. The outcome of the present study improves our understanding of mass transfer in porous media for solvent- based and solvent-aided thermal recovery processes.