Study of Rheological Properties and Micro-mechanism of Heavy Oil Emulsion Prepared via Ultrasonic Dispersion

An emulsion is a dispersion with a complex mechanism of formation and a poor stability. In the preparation of emulsions, the used surfactant concentration, oil–water ratio, and kinetic conditions affect the type, microscopic characteristics, and rheological properties of the emulsions. As a result of its high viscosity, it is difficult to disperse the heavy oil with mechanical agitation, and the stability of the emulsion system formed is poor; hence, it is challenging to study its rheological properties. Therefore, herein, the ultrasonic dispersion method was employed to prepare the emulsion, and the microscopic characteristics of the emulsion were observed using an optical microscope and nanoparticle size analyzer. The conductivity of the emulsion system was studied by a conductivity meter. The effects of different surfactant concentrations, oil–water ratios, and kinetic conditions on the emulsion type and micro-characteristics were obtained. The experiments were performed to study the rheological properties of oil-in-water (O/W) and water-in-oil (W/O) emulsions. The results indicate that the emulsion prepared using an ultrasonic dispersion method was O/W-type when the mass percentage of a surfactant solution was higher than 0.1 wt % and the oil–water ratio was less than 1:3. The droplet size reaches a nanometer level and increases with a higher surfactant concentration. The particle size no longer decreases when the critical micelle concentration of the surfactant is reached. The droplet size corresponding to the peak of size frequency distribution was 70 nm, and the rheological curve was a shear-thickening dilatant fluid. When the mass percentage of a surfactant solution was lower than 0.1 wt % and the oil–water ratio was higher than 1, a W/O emulsion was formed with the droplet size of 10 μm. When the shear rate was less than 50 s–1, the emulsion was a pseudo-plastic fluid with shear-thinning behavior. As the shear rate increased, the emulsion gradually exhibited Newtonian fluid behavior.