Study on the Enhanced Oil Recovery Properties of the Pickering Emulsions for Harsh Reservoirs

Pickering emulsions stabilized by surfactant-modified SiO₂ nanoparticles demonstrate good stability against droplet coalescence, showing application potential for enhanced oil recovery in high-temperature and high-salinity environments. Adjusting the adsorption ratio of surfactant on the nanoparticles significantly affects the wettability of nanoparticles and therefore regulates the microstructure and properties of Pickering emulsions. In this study, a saturated monolayer adsorption occurs at a surfactant-to-nanoparticles ratio of 0.1:1.0%, where an optimal hydrophilic-hydrophobic balance is achieved. However, below or above this ratio, the SiO₂ nanoparticles become more hydrophilic with the decreasing or increasing surfactant concentration. Pickering emulsions stabilized by the intermediate wet nanoparticles exhibit the best stability and highest viscosity. Laser confocal scanning microscopy and cryo-scanning electron microscopy reveal that the SiO₂ nanoparticles can form a bridge-structure network among the droplets of these emulsions. Microfluidic experiments and sand pack experiments show that Pickering emulsions provide greater permeation resistance than conventional emulsions stabilized solely by surfactant solely. In addition, microscopic experiments show that Pickering emulsions enhance oil recovery by 20% after second waterflooding, compared to a 12% recovery rate with conventional emulsions. It is found that the Pickering emulsions with bridge-structures may be accumulated in and plug channels much larger than their droplets, which results in higher properties of conformance control.