A Hydroxypropyl Methyl Cellulose-Based Graft Copolymer with Excellent Thermothickening and Anti-salt Ability for Enhanced Oil Recovery

Thermothickening polymers are a novel type of material developed for enhanced oil recovery applications in high-temperature and high-salinity oil reservoirs. However, the existing synthesis process of thermoviscosifying polymers is complex and of high cost, both of which limit the wide application of thermoviscosifying polymers. In this study, a thermothickening water-soluble polymer (PHAD) with a low concentration was synthesized by a "graft from" method, with acrylamide and diacetone acrylamide as grafted monomers and hydroxypropyl methyl cellulose as the backbone chain. The basic parameters for PHAD copolymers were systematically studied in comparison with their homopolyacrylamide counterpart. The results show that the PHAD copolymers exhibited excellent thermothickening ability even when the polymer concentration was 0.2 wt % (total salinity is 9350.08 mg.L-1) upon increasing the temperature from 25 to 90 degrees C, where the apparent viscosity enhancement changes from 4.0 to 13.3 times with increasing the diacetone acrylamide content in PHAD copolymers. The PHAD copolymers also showed good salt tolerance, thermal stability, and viscoelastic properties under harsh reservoir conditions, which are attributed to the synergistic effect of the rigid heterocyclic ring structure and hydrophobic intermolecular association of thermoresponsive monomers within polymer chains. Moreover, the core displacement experiment and etched glass microscopic model show that the PHAD copolymers have good migration in porous media. Due to its high sweep efficiency, the PHAD copolymer has a higher recovery factor (14.0%) than polyacrylamide (4.3%), which makes it more suitable for salt-tolerant and temperature-tolerant tertiary oil recovery chemicals.