Porous media flooding mechanism of nanoparticle-enhanced emulsification system

Abstract

This study carried out interfacial tension (IFT) testing, sand surface element analysis and scanning electron microscope imaging, rock–oil–emulsification system interaction testing, and microstructure, droplet size distribution, and stability of oil in water (O/W) emulsion to clarify the porous media flooding mechanism of a hydrophilic nano-SiO2 enhanced emulsification system. The results show that by adding a small amount of nano-SiO2 (0.01 wt. %) into an anionic surfactant fatty alcohol polyoxyethylene ether sodium hydroxypropyl sulfonate (AEOSHS) solution (0.5 wt. %), the IFT of oil–water was effectively reduced, the adsorption loss of AEOSHS on the formation sand surface was reduced by more than 70%, and the droplet size of the formed O/W emulsion was reduced by 50%. This greatly improves the effective concentration of AEOSHS and emulsifies the heavy oil ability in the formation away from the injection well. Moreover, the spreading ability of oil on the core surface is greatly reduced, and the width of the diffusion zone is narrowed. Meanwhile, a very clear dividing line of oil can be seen, which shows that the wettability of the core has changed to water wet. The stability of the formed O/W emulsion was further enhanced, and the coalescence and migration process of the droplet is extremely slow. The oil recovery of the AEOSHS + nano-SiO2 system can effectively increase 21.95% of the original oil in place. Both the sand-packed tube experiment and the microscopic visual oil flooding experiment show that the system can not only expand the swept volume but also improve the oil displacement efficiency, which means that the combined system can significantly improve the oil displacement effect.