Cationic copolymer based vinylimidazolium for separating an emulsion oil-in-water

A method for separating an emulsion of oil-in-water, formed during the production of crude oil in an aqueous phase and an oily phase, comprising: adding 1 part per million (ppm) to 10,000 ppm of a cationic copolymer based vinylimidazolium to the emulsion oil in water, based on a total volume of the emulsion oil-in-water to form the aqueous phase and the oil phase; and separating the aqueous phase from the oil phase.