Alberta, Canada contains about 170 Gbbl of recoverable heavy oil and bitumen; most of it with in situ viscosities in the hundreds of thousands to millions of cP. To mobilize and produce this oil, steam-based recovery methods such as Cyclic Steam Stimulation and Steam-Assisted Gravity Drainage are used. Given the large energy requirements and volumes of emitted greenhouse gas from these processes, there is strong motivation to develop enhanced recovery processes with lower energy and emission intensities. One incremental move to achieve this is by using steam-solvent hybrid processes such as ES-SAGD where solvent is co-injected with steam. Steam- solvent processes are the next generation of reduced emission to atmosphere recovery processes for heavy oil and bitumen reservoirs beyond current steam recovery methods. The controlling feature of these processes is the mobilization and drainage of oil at the depletion chamber edge. Furthermore, both oil phase viscosity – mobility and density – drainage – depend strongly on temperature and solvent concentration. Here, a simple model is derived to describe dynamics of thermo-solvent coupling effects in the mobile oil zone at the edge of a steam-solvent chamber. A double front system evolves: compositional and thermal fronts result with different length scales. They are coupled through velocity and viscosity fields. We investigate the extent to which these fronts affect oil mobility at the edge of the chamber. The solvent provides an additional means to raise oil phase mobility beyond that achieved with heat. The enhanced mobility is due to 1. lowered viscosity because of solvent dilution and 2. slightly raised oil saturation due to addition of solvent (raises the oil effective permeability). Due to synergistic interactions between heat transfer and solvent diffusion, the oil zone has higher mobility in the solvent-steam system over that of the steam-only one. Therefore, steam-solvent systems lead to lower energy and emission intensity thus "greening", to some extent, heavy oil and bitumen recovery technologies.

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