Revealing How to Prepare Polymer Gels under High-Temperature and High-Salinity Conditions

Abstract Polymer gel performance and stability under high-temperature, high-salinity conditions critically constrain their practical applications. While gels have been successfully formulated at temperatures exceeding 100 °C and brine salinities above 4 × 104 mg·L–1, the quantitative influence of temperature and brine salinity on gelation behavior remains poorly understood; consequently, evidence-based guidelines for polymer and cross-linker selection are lacking. This study used hydroquinone (HQ) and hexamethylenetetramine (HMTA) as cross-linkers and AM–AMPS polymers (AM: acrylamide; AMPS: 2-acrylamido-2-methylpropanesulfonic acid) with 25%, 47%, and 69% AMPS content as gelling agents (abbreviated as AMPS25, AMPS50, and AMPS70, respectively). Gelation behavior was tested at 110 and 130 °C and in brines with salinities of 4.15 × 104 mg·L –1 and 2.5 × 105 mg·L–1. The effects of temperature, brine salinity, polymer structure, and cross-linker dosage were analyzed. Results show that gel performance in brine is more sensitive to temperature than to brine salinity. AMPS25 forms stable gels at 110 °C under both low- and high-salinity conditions; AMPS50 demonstrates superior gelation performance compared to AMPS70 at 130 °C in brine with a salinity of 4.15 × 104 mg·L–1. This is because strong electrostatic repulsion between the polymer and cross-linker impedes the cross-linking reaction, resulting in unsatisfactory gel formation for the lower-concentration AMPS70 under these conditions. Under conditions of 130 °C and a brine salinity of 2.5 × 105 mg·L–1, the gel strength formed by AMPS70 was marginally lower than that of AMPS50, yet its gelation time was longer and thermal stability was enhanced. The study concludes that increasing cross-linker dosage or using higher-AMPS-content polymers helps control carboxylate ion formation during thermal treatment of polymer gels, a key approach to developing temperature- and salt-resistant gels.