Mass transfer of solvents in bulk heavy oil and bitumen was monitored successfully using X-ray Computer Assisted Tomography (CAT). Concentration gradients were obtained from analysis of bulk density maps as a function of location and time. Analysis of the data using Fick's Law provided apparent diffusion coefficients, which were consistent with previously published data using different solvents and different oils.
A second series of experiments was then performed whereby the heavy oil was mixed with sand at a level that is similar to what expected in heavy oil reservoirs. There was no connate water in the system. Different solvents were then placed on top of the oil/sand mixtures and the diffusion of the solvent into the sand pack was observed. X-ray CAT was used to monitor density and concentration profiles. Oil concentration profiles in solvent were clearly observed but the solvent concentration in the sand pack proved to be more challenging. The same Fickian approach that was used in bulk oil systems was applied to predict apparent diffusion coefficients for the liquid volume portion of the experiment. Preliminary results showed that the apparent diffusion coefficients are of the same order of magnitude as in the bulk oil systems.