Rheological characterization and shear viscosity prediction of heavy oil-in-water emulsions

The rheology of oil-in-water emulsion is a key issues in heavy oil development, storage, transport, and processing. Based on single-factor experiments, the effect of shear rate (γ), dispersed-phase volume fraction (φ), continuous-phase viscosity (ηc), and droplet size (D50) on the rheological properties of heavy oil-in-water emulsions were evaluated through microscopic observation and rheological experiments. Furthermore, a 10-factor/3-level experiment was designed to investigate the sensitive factors affecting shear viscosity. The experimental results indicated that, when the volume fraction of dispersed-phase was higher than 0.3, the rheological characteristics of the prepared emulsions exhibited an obvious shear-thinning behavior, and the droplet size had a significant influence on shear viscosity at shear rates between 0.3 and 100 s−1. When the volume fraction of the dispersed-phase was less than 0.3, the emulsions behaved as Newtonian liquids. As the shear rates increase, the droplets disperse to a greater extent, leading a reduction in viscosity, and ultimately causing the emulsion to exhibit the characteristics of a Newtonian fluid. Owing to the strong hydration effect of small droplets, the viscosity of small droplet-size emulsions increases at a constant dispersed-phase volume fraction. Emulsions exhibit obvious shear-thinning behavior with an increase in shear rate, as a result of a low effective dispersed-phase volume fraction under a high shear rate. Finally, the volume coefficient of the Sibree model was corrected by considering correlation factors from the experiments, and the Sibree model was improved. The improved shear viscosity model better fits the experimental data for all the studied heavy oil-in-water emulsion, with the mean relative error of 9.3%. Therefore, the improved model can predict the effects of all factors affecting shear viscosity.