Oil-in-water nanoemulsions are a particular class of emulsions where nanometric solvent droplets are dispersed in water using proper surfactant mixtures. Nanoemulsions can be formed with different techniques including high energy or low energy methods and, if properly formulated, can show very high kinetic stability as a direct consequence of monodispersity that minimize Ostwald Ripening effect and of the small droplet size that eliminates separation processes based on density difference.
Their unique characteristics and physic-chemical properties suggested their use as a "smart" displacing fluid for enhanced oil recovery (EOR).
Even though the mechanism of residual oil mobilization is still not well known, the coexistence, in nanoemulsions, of small droplets size, surfactants mixture and solvent could favorably impact on critical parameters such as oil/water interfacial tension, wettability, oil viscosity. All these considerations induce to compare nanoemulsion flooding technology with the most common chemical EOR methods.
This study presents examples of nanoemulsions prepared using a low energy proprietary method and a commercial surfactants mixture specifically tailored; this particular method allows to obtain very stable and, in many cases, mono-dispersed nanoemulsions using brines with different compositions (in order to mimic real field conditions) and a wide range of solvents with different features. These emulsions have been characterized in terms of physicochemical properties and size distribution of the dispersed oil droplets in water phase.
Together with the basic characterization, core-flooding experiments have been carried out in order to evaluate the effectiveness of the nanoemulsions as displacing fluid for enhanced oil recovery and to investigate the mechanisms of mobilization of the residual oil in comparison with the classical chemical EOR methods.