The diffusion coefficient is a key parameter to describe promising solvent - based technologies for heavy oil and bitumen recovery. In this work, an extended diffusion model considering the volume changes on mixing was used to calculate the mutual diffusion coefficients for the heavy oil -hydrocarbon solvent system. The approach requires not only concentration profiles, but also data on volume changes in the process of mixing. The concentration profiles were obtained from diffusion laboratory experiments in which X-ray Computer Assisted Tomography (CAT) was used to measure the density distributions at different times. In addition, the volume changes data was obtained by performing heavy oil and hydrocarbon solvent mixing experiments at different content of solvent in heavy oil.
By comparing the diffusion coefficient versus concentration curves based on the extended diffusion model and on the usual diffusion model (1), it was concluded that the volume changes due to mixing make significant differences to the diffusion coefficient determination in heavy oil – hydrocarbon solvent system, and the mutual diffusion coefficients are strong functions of concentration, which is consistent with previous literature.