Heavy oil separation and recovery by the self-assembly of polymers and silica particles in hypersaline water

Emulsification and separation are of great significance in oil recovery. Herein, we report a synergic system of polymers and silica particles, which can achieve the emulsification and separation of heavy oil through the alkaline/acidic solution. Since the high salinity of formation water is an inevitable issue for chemical waterflooding, the effects of salinity on the properties of heavy oil emulsions were investigated by the zeta potential, interfacial tension (IFT), separation efficiency, dynamic light scattering (DLS), and rheology in experiments. The results show that heavy oil emulsions at extreme salinity (up to 50 g/L) remain stable under alkaline conditions. But conversely, the separation process of heavy oil emulsions is expedited under acidic conditions. Furthermore, the interaction mechanism is also elucidated by molecular dynamics simulations to provide a well-researched interpretation of the experimental phenomena. The self-assembly between the polymer and silica particles is seriously affected by the salt ions through the electrostatic screening effect, with increasing zeta potential values from -52.5 mV to -18.1 mV, and the interfacial films are crippled, exhibiting more viscous properties, which induces the separation of heavy oil emulsions. However, it can be stable under alkaline conditions with separation efficiencies of less than 14.3% in 24 h. This novel reversible PS system is used in hypersalinity (30 g/L) to realize emulsification and separation without any demulsifiers, breaking through the current salinity limit of polymer waterflooding (EOR increased by 15.51%). The findings of this study can help for a better understanding of the molecular mechanism of switchable heavy oil emulsions and develop a potential solution for EOR in reservoirs with high salinity.