Synthesis and Evaluation of Fluorinated Styrene Copolymer Nanospheres for High-Temperature, Low-Permeability Enhanced Oil Recovery

Nanomaterial flooding is one of the key methods for enhancing oil recovery (EOR) in low-permeability reservoirs. This study addresses the EOR requirements for a high-temperature and low-permeability offshore oil field (reservoir temperature of 90 °C, core permeability of 50 mD). A novel temperature-resistant and salt-tolerant copolymer nanosphere (PFSN) containing fluorine atoms on its surface was synthesized via emulsion polymerization using 4-fluorostyrene (4-FSt) and styrene (St) as monomers. The synthesis conditions for PFSN were optimized based on particle size and the ability to alter core wettability. The recommended synthesis conditions are as follows: St/4-FSt mass ratio of 10:1, total monomer concentration of 6 wt %, emulsifier dosage of 1.0 wt %, initiator concentration of 3.0 wt %, n-butanol dosage of 2.0 wt %, reaction temperature of 65 °C, and reaction time of 3 h. It can be found that the PFSN exhibits a higher decomposition temperature than polystyrene (PS) by 11.2%. Core flood injection experiments demonstrated that the PFSN nanofluid exhibits favorable resistance and residual resistance factors. Oil displacement tests revealed that 2000 mg/L PFSN solution enhanced oil recovery by 25.74%. The primary EOR mechanisms involve the ability of PFSN to reduce oil/water interfacial tension and alter the core wettability to intermediate-wet. These effects collectively decrease the adhesion work of crude oil on the core surface, thereby improving the displacement efficiency.