Study on the Pickering emulsions stabilized by SiO2 nanoparticles for enhanced oil recovery

In high-temperature and high-salt environments, emulsions stabilized by surfactants are susceptible to instability phenomena, such as droplet coalescence, thereby limiting their utility in tertiary oil recovery. The Pickering emulsions, which are stabilized by solid particles, have been proved to exhibit good stability. This study demonstrated that the nonionic surfactant C16E20 can adsorb onto SiO2 nanoparticles with an efficiency exceeding 99%, rendering C16E20 suitable for modulating the wettability of SiO2 nanoparticles. By adjusting the proper surfactant-to-nanoparticle ratio, such as 0.1%:1.0%, a hydrophilic-lipophilic equilibrium is obtained, which is beneficial for the preparation of Pickering emulsions. Laser confocal and cryo-scanning electron microscopy results indicated that SiO2 nanoparticles in Pickering emulsions were dispersed at the oil-water interface, forming a network structure between the emulsion droplets. Further experiments illustrated that the Pickering emulsions showed excellent stability for at least 180 days at 80 degrees C. Conventional emulsions behave as Newtonian fluids at lower oil-phase ratios, while Pickering emulsions exhibit non-Newtonian fluid properties, with their viscosity capable of increasing by over 100 times. Additionally, Pickering emulsions were found to exhibit thixotropy, attributed to the reversible formation and destruction of droplet bridging structures. Overall, Pickering emulsions are regarded as potential agents for Enhanced Oil Recovery in oilfield development.