A composite system of amphoteric copolymer nanosphere and betaine surfactant for enhanced oil recovery application

The combination of nanomaterial and surfactant is one of the important methods to enhance the oil recovery of surfactant flooding . In view of the conditions of a high-temperature and low-permeability offshore oilfield (temperature 90 °C, gas permeability 100 mD), a novel amphoteric copolymer (PMSN) nanosphere was prepared through emulsion polymerization by using methacrylic acid, styrene and cationic phenylamine monomer as the monomers. In aim to enhance oil recovery, the composition of copolymer monomers and betaine type were optimized, and a new composite oil displacement system of PMSN nanosphere and cocoamidopropyl betaine (CAB) was proposed in this work. The oil displacement experiment results showed that when the mass ratio of PMSN nanosphere to CAB was 1:2 and the total concentration was 3000 mg/L, the enhanced oil recovery was by 26.69 %, which was 5.66 % higher than that of 3000 mg/L CAB. The study of oil displacement mechanism showed that PMSN nanosphere can cooperate with CAB to further reduce the O/W interfacial tension and change the wettability of the core surface, thereby effectively reducing the adhesion work of crude oil on the core surface and improving the oil displacement efficiency of CAB. • Amphoteric PMSN nanosphere used for EOR was prepared. • PMSN nanosphere + CAB had better EOR performance than that of CAB. • PMSN nanosphere can synergistically reduce IFT and alter wettability with CAB.