Microemulsions stabilized by in-situ synthesized nanoparticles for enhanced oil recovery

Nanoparticles (NPs) have been recently proposed to stabilize microemulsions (MEs) to improve their stability under harsh conditions, i.e., high temperature and high salinity as in hydrocarbon reservoirs. This work developed a novel method to produce iron oxide nanoparticles (IONPs) in-situ in oil-in-water (o/w) MEs, and examined their performance in improving oil recovery. IONPs were in-situ synthesized in MEs containing brine, n-hexane, mixture of SDS and Span 80 as the surfactants, and propyl alcohol as the co-solvent. The enhanced oil recovery (EOR) potentials of MEs and MEs containing different concentrations of IONPs (MEIN) were investigated in a core flooding system. The results indicated that the use of MEIN can significantly increase the oil recovery efficiency, i.e., jumping from 10% for ME without being stabilized NPs to 28.9% at a NPs concentration of 6400 ppm. Moreover, MEIN achieved much lower and more stable pressure profile (i.e. nearly one order of magnitude smaller) during the flooding and post-flooding stage, showing its excellent injection applicability. Four potential EOR mechanisms were examined and the formation of stable MEs synergistically stabilized by NPs and surfactants was considered as the main reason, supplemented by less formation of viscous phase, more stable IFT and increased viscosity for better mobility control