A method of preventing formation of a water and oil emulsion in a downhole formation containing oil, the method comprises preparing a dispersion of water and a plurality of nanoparticles, each nanoparticle in the plurality of nanoparticles having a size of at least 300 nanometers, and injecting the mixture downhole into contact with the oil downhole. Presence of the plurality of nanoparticles prevents formation of an emulsion between the injected water and the oil.