Core-Flooding Evaluation of Biobased Winsor IV Microemulsions with and Without Added Silica Nanoparticles for Enhanced Oil Recovery in Sandstone

Effective enhanced oil recovery (EOR) formulations should avoid compositional complexity. Biobased Winsor IV microemulsions were prepared using saponified coconut oil (surfactant), pine oil (nonpolar phase), isopropyl alcohol (cosurfactant), and either glycerol (MEG series) or aqueous 2% (w/v) NaCl (MES series) as the polar phase. Viscosity, conductivity, and oil–water interfacial tension (IFT) were measured at 60 °C. Displacement was evaluated in Botucatu sandstone plugs, using 2% (w/v) NaCl brine for core saturation and waterflooding. MEG3 and MES3, the highest-recovery formulations within their respective series, yielded recoveries of 79.1% and 77.4% of original oil in place (OOIP). With 100 ppm unfunctionalized SiO2, final recoveries were 77.4% and 75.2%, respectively. Incremental recovery as % OOIP was slightly higher in the SiO2 runs (27.4% and 26.8% vs. 26.7% and 26.2%), whereas residual-oil-normalized recovery efficiency was lower (54.8% and 51.9% vs. 56.1% and 53.7%). Each condition was tested once (n = 1) using separate plugs with different initial oil saturations. Thus, the comparison is descriptive and preliminary and establishes neither statistical differences nor equivalence. Because particle size, zeta potential, and colloidal stability were not characterized, the contribution of SiO2 to recovery remains undetermined.