Steam injection, in various forms, has been commercially successful for in situ recovery from the oil sands. One of the recovery methods being tested – with an aim to reduce steam requirement – involves the injection of a suitable solvent, by itself, or in combination with steam. Solvents are being utilized at a pilot scale in both cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD) processes. The present study examines the mixing of a solvent with bitumen at the pore scale, using an analytical model with typical field data.
The convective diffusion equation is solved for a spherical geometry, and applied to a drop of bitumen is a pore space. Calculations are done for a number of solvents, viz. pentane, and hexane. The rate of bitumen dissolution is determined for both static and dynamic conditions, for a number of velocities corresponding to typical field injection rates. The diffusion coefficients are taken from the latest laboratory data reported. Calculations are also done for heating of the bitumen (without solvent) for the same conditions. The resulting bitumen viscosity is compared as a function of time, for both solvent injection and heating.
Results show that the time of solution of a bitumen drop in the solvent is of the order of days. The time varies with the type of solvent (largest for pentane), and the injection velocity. The times to attain the same viscosity by solvent injection in one case, and conduction heating in the other, respectively, differ by orders of magnitude. The significance of this finding for field application of solvents is discussed.
The outcome of this research will improve our understanding about solvent diffusion and dispersion process for bitumen in porous media. This will help us to modify the current modelling approach to capture more realistic mass transfer and solvent/bitumen interaction in porous media.