Influence of the Interfacial Properties on the Stability of Water in Heavy Oil Emulsions in Thermal Recovery Process

Under the conditions of thermal oil recovery, the heavy oil in a reservoir usually exists in the form of W/O emulsion with high water content, which has significant effect on oil recovery performance. The most important parameter on the stability of W/O emulsion is interfacial properties. Thus, in order to investigate the effect of interfacial properties on the stability of W/O emulsion in a heavy oil reservoir at elevated temperatures, experiments have been conducted to generate various emulsions with variations in the temperature; stirring rate; contents of asphaltene, resin, and wax of the simulated heavy oil; and water salinity based on a target heavy oil reservoir in China. Then, the properties of the W/O emulsions include viscosity, interfacial viscosity (IFV), interfacial tension (IFT), and dehydration rate; the microscopic morphologies are measured as well. The experimental results show evidently stable W/O emulsion of heavy oil and water generated in thermal processes due to the stable, thick, and indistinct interface between heavy oil and water, where the active molecules of asphaltene and resin are accumulated. The interface connects the central large droplet and the surrounding small droplets tightly. The results also indicate the size of the central droplet, and the indistinct interface can be enlarged with increasing temperature and increasing stirring rate. Compared to resin, it is noted that the larger asphaltene molecules have stronger connection because of their stronger intermolecular force, larger IFV, and less IFT. At the same time, the stability of W/O emulsion will be strengthened with increasing temperature and stirring rate and gradually weakened with increasing salinity. In conclusion, the stability of water in heavy oil emulsion is mainly related to the large interfacial viscosity of the interface with much more heavy components such as asphaltene and resin compared to thin oil.