Correlation for the Diffusivity of Gaseous and Liquid Hydrocarbons with Bitumen

The oil production rate of in situ heavy oil recovery processes involving the injection of gaseous or liquid hydrocarbon solvents depends strongly on the mutual diffusivity of the solvent and bitumen. Data for these diffusivities, particularly above the ambient temperature, are relatively scarce because they are time-consuming to measure. In this study, the diffusion and solubilities of gaseous toluene, n-pentane, and n-heptane in a Western Canadian bitumen and its maltenes were measured at temperatures from 150 to 180 degrees C using a pressure decay method. The diffusivities were determined as a function of viscosity from a numerical model of the experiments. A previously developed correlation for the infinite dilution viscosity of solvent into bitumen, originally proposed for gas/bitumen systems with low solvent solubility in bitumen, was extended to higher solubility gases and to liquid hydrocarbon/bitumen systems. The correlation was updated using gas/bitumen diffusivities and liquid hydrocarbon/bitumen diffusivities from the literature, and the gas/bitumen data were obtained in this study. Tuned correlation parameters for solvent diffusion in bitumen and in maltenes are provided. The numerical model with the proposed correlations matches the measured cumulative mass transfer from the pressure decay experiments in this study to within +/- 18% and the measured concentration profiles from liquid solvent/crude oil experiments to within +/- 4 wt %.