Preparation of thickened P(AA-AMPS) copolymers by inverse emulsion polymerization and evaluation of fracturing and oil flooding performance

Polymer is an essential type of fracturing fluid. Nevertheless, issues such as slow dissolution, high initial viscosity, and challenges in storage, transportation and operation limit its application. To address these issues, a thickened copolymer P(AA-AMPS) was synthesized by inverse emulsion polymerization using acrylic acid (AA) and 2-acrylamide-2-methylpropanesulfonic acid (AMPS) as the monomers. Three P(AA-AMPS) copolymers were obtained by changing the weight ratio of AA and AMPS monomers. When the weight ratio of AA to AMPS monomers was 8.2:1.8, the P(AA-AMPS) copolymer solution exhibited the best interfacial activity, reducing the oil–water interfacial tension to 3.95 mN m⁻¹. The initial viscosity of the copolymer was only 66 mPa s, but its solution could reach a high viscosity of up to 817 mPa s. P(AA-AMPS) copolymers demonstrated good resistance for temperature and shear. For instance, the viscosity of copolymer solution still remained 300 mPa s with a shear rate of 170 s⁻¹ at 90 °C. Furthermore, P(AA-AMPS) copolymers had excellent gel-breaking capacity, sand suspension stability, wettability and oil displacement ability. Therefore, the integration of fracturing and oil flooding can be realized for the development of low permeability reservoirs by selecting appropriate copolymers. P(AA-AMPS) copolymers would play an important role due to their significant viscosity differences and easy operation on storage, transportation and application.