A Population Balance Model for Emulsion Behavior of Alkaline Water-Heavy Oil Systems in Bulk Phase

Experimental and theoretical techniques have been developed to quantify the behavior of alkaline water-heavy oil emulsion systems at high pressures and elevated temperatures. Experimentally, initial emulsions were prepared by agitating either sodium carbonate (Na2CO3) solution or sodium hydroxide (NaOH) solution with heavy oil samples inside a visualized PVT cell. After being settled for a certain period of time, the phase volume of the in situ generated water-in-oil (W/O) emulsion was monitored, and the local water content distribution within each dual-emulsion system was measured. Experiments with the same composition and mixing condition, but with different settling times, were conducted to track the continuous water content distribution. Mathematically, two groups of population balance equations (PBEs) were modified and applied to quantify the phase behavior during the emulsion destabilization process with the consideration of coalescence, settling, and diffusion of the dispersed droplets as well as the mass transfer between emulsion phases. To quantify the mass transfer between the W/O and oil-in-water (O/W) emulsion phases, the measured emulsion inversion point (EIP) was used as the interface boundary condition of the dual-emulsion systems. Both the fixed-pivot technique and a semi-implicit finite difference approach were applied for discretizing the internal coordinate (droplet volume) and the external coordinates in time and space domains, respectively. By assuming the dispersed droplets as a log-normal distribution, the genetic algorithm (GA) was applied to optimize the coalescence efficiency by using the experimental measurements as well as the water droplet distribution in the W/O emulsion phase. Because of the corresponding changes of oil viscosity and interfacial tension (IFT), either an increase in temperature or a decrease in pressure leads to a smaller EIP and higher coalescence efficiency. As a weak alkali, Na2CO3 facilitates the stabilization of the emulsion and inhibits the influence of higher temperatures, while NaOH solution-heavy oil systems achieve emulsion inversion more easily.

Automated summary

Experimental and theoretical techniques have been developed to quantify the behavior of alkaline water-heavy oil emulsion systems at high pressures and elevated temperatures. The study found that changes in temperature and pressure affect the properties of emulsions, and the role of sodium carbonate and sodium hydroxide in the systems are different.