Effect of Charge Density of Reverse Emulsion Breaker on Demulsification Performance for Steam-Assisted Gravity Drainage (SAGD) Emulsions under High Temperature and High Pressure

Reverse emulsion breakers (REBs) play a crucial role in the demulsification of complex water-in-oil-in-water (W/O/W) emulsions in steam-assisted gravity drainage (SAGD) production of oil sands. Developing effective REBs remains challenging due to the poor understanding of influencing factors and demulsification mechanisms. In particular, despite the recognition of the vital role of charge density of the REBs in their demulsification performance, the available literature is limited. Herein, we investigated the correlation between the charge density of commercial REBs and their demulsification performance for complex emulsions under simulated SAGD operation conditions (100–200 °C and 0.3–1.4 MPa) by employing an in-house-built bottle test system. It is demonstrated that a high charge density of the REBs not only promotes the qualities of produced water and oil but also significantly accelerates the speed of oil/water phase separation. At the microscale, the REB with a high charge density is capable of reducing the amount and size of residual oil droplets in produced water. The interactions of the species involved during the demulsification process were investigated by employing multiple techniques including optical microscopy imaging, ζ potential measurement, and dynamic light scattering. The results suggest that the cationic REBs are adsorbed at the oil/water interface, neutralize negative surface charge of oil droplets, and replace interface-active species originally present at the oil/water interface. Multilayer adsorption of REBs may be generated after demulsification, and the adsorbed REBs could partially desorb from the surface of oil droplets with increasing temperature. This work has delineated the influence of the charge density of REBs on their demulsification performance and improved the fundamental understanding of the interactions of the constituent species in SAGD emulsions and REBs, which provides useful information on the development and applications of efficient and cost-effective chemicals in oil sands exploitation and emulsion treatment.