Ternary composite oil displacement agent and preparation method thereof

The invention discloses a ternary composite oil displacement agent and a preparation method thereof, and belongs to the field of oilfield chemistry. The ternary composite oil displacement agent comprises petroleum sulfonate, an emulsifier, a polymer and water, wherein the total mass percent of the petroleum sulfonate and the emulsifier is 0.05-0.3%, and the mass ratio of the petroleum sulfonate tothe emulsifier is (17-19):(1-3); the viscosity of the ternary composite oil displacement agent is 38-45 mPa.S; the emulsifier is prepared by the following steps: adding C14-16 fatty alcohol and a catalyst into a reactor, introducing nitrogen into the reactor, heating the reactor to a first preset temperature, stopping introducing nitrogen, dropwise adding ethylene oxide into the reactor, carryingout a polymerization reaction, heating the reactor to a second preset temperature, carrying out heat preservation, and then cooling to a third preset temperature to obtain the emulsifier; and the mass ratio of the fatty alcoh