ASSESSING POLYMER ASSOCIATION VIA SOLUTION PROPERTIES OF A TERPOLYMER FOR ENHANCED OIL RECOVERY UNDER HIGH SALINITY AND TEMPERATURE

Thermoviscosifier polymers are crucial in enhanced oil recovery due to their ability to increase viscosity with temperature by incorporating a lower critical solution temperature (LCST) side chain into a water-soluble polymer backbone. We investigated a copolymer of acrylamide (AM) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS), comparing it to a modified terpolymer with an LCST-grafted monomer (G). The solution properties of both polymers in brine were evaluated between 25 and 85 °C to assess the impact of the LCST modification. Rheological tests showed that the viscosity of AM-AMPS decreased steadily with temperature, while AM-AMPS-G exhibited a viscosity increase after reaching a critical temperature (T_c) and polymer concentration (c_c), indicating significant polymer-polymer intermolecular interactions likely due to physical crosslinking driven by hydrophobic interactions. Viscometry data revealed that hydrophobic interactions in the AM-AMPS-G system became more pronounced as temperature rose, enhancing both hydrophobicity and the number of hydrophobic grafts. In the dilute regime, only intramolecular interactions occur, preventing association; however, in the semi-dilute regime, interpolymer interactions facilitate crosslinking, although low graft content reduces interaction probabilities near c*. Notably, significant viscosity changes may not occur despite crosslinking, as viscosity depends on both the strength of hydrophobic interactions and crosslink density. Our findings indicate that hydrophobic interactions initiate earlier, with T_c and c_c marking when crosslinking substantially influences viscosity. Crosslinking progresses with increasing temperature, forming a more robust network that further increases viscosity.