Enhanced Oil Recovery Analysis of Green Nanoemulsion Flooding for Sandstone Reservoirs

This paper presents a novel concept of using ester as a hydrophobic phase for the preparation of environmentally friendly and biodegradable nanoemulsions. This study comprehensively evaluates the efficacy of formulated environmentally friendly nanoemulsions designed for enhanced oil recovery. The formulations involve nonionic surfactants, namely Tween 40 and Tween 80, coupled with a biodegradable oleic phase (methyl ester) derived from edible oil. Nanoemulsions were meticulously prepared through a combination of low- and high-energy methods, and their stability was rigorously examined on macroscopic and mesoscopic scales at varied temperatures. The results indicate that the formulated nanoemulsions exhibit high kinetic stability with a zeta potential of around −33 mV and droplet sizes ranging between 59 and 150 nm. Interfacial tension (IFT) measurements demonstrated a significant decrease of IFT with increasing surfactant concentration (17 and 1.97 mN/m at 303 K for Tween 40 and Tween 80, respectively). Additionally, a phase behavior study established the critical parameters for optimal salinity, determining concentrations of 0.5 wt % for Tween 40-based formulations and 2 wt % for Tween 80-based formulations. Nanoemulsions showed remarkable results in enhancing oil recovery by transforming the wettability of sandstone rocks from oil-wet to water-wet. Further, the emulsions exhibited good miscibility with heavy crude oil and significantly reduced its viscosity, which improved the mobility of the oil. Injection of one pore volume of nanoemulsion slug, followed by a chase water flooding, exhibited a commendable 24.29% enhanced oil recovery over conventional water flooding.