Physicochemical Properties of Heavy Oil and Emulsification-Controlled Phase Inversion/Stability of Oil–Water Systems

Oil–water emulsions formed by heavy crude oil from Block A of the YT Oilfield during production and transportation are strongly influenced by the oil’s high viscosity and density and by its abundant resins and asphaltenes. Such emulsions can increase shear viscosity and flow resistance and may even undergo phase inversion. To clarify these behaviors, the rheology, viscosity–temperature characteristics, density, water cut, and SARA composition of the heavy oil were measured. The effects of emulsification temperature, stirring rate, salinity, and water cut on emulsion phase inversion and stability were then investigated. The oil exhibited weakly non-Newtonian behavior at 0–10 °C and Newtonian behavior at 20–60 °C. Its viscosity at 50 °C was 1323.4 mPa·s, and its density at 20 °C was approximately 0.96 g/cm3. The water cut was 0.05%, and the combined resin and asphaltene content was about 40%, with resins as the dominant fraction. With increasing water cut, the shear viscosity of the emulsion first rose and then declined, reaching a maximum at the phase inversion point. A higher emulsification temperature shifted the inversion point toward a higher water cut and increased the shear viscosity at inversion. Stirring rate and salinity did not change the position of the inversion point; however, a higher stirring rate increased the shear viscosity at inversion, whereas a higher salinity decreased it. Orthogonal range analysis showed that the factors affecting shear viscosity were ranked as follows: water cut > emulsification temperature > salinity > stirring rate. These findings provide an experimental basis for viscosity reduction, gathering and transportation optimization, and phase inversion control in the YT Oilfield.