Rheology, Phase Stability, and Microstructure of Nanosilica-Assisted Partially Hydrolyzed Polyacrylamide

Partially hydrolyzed polyacrylamide (HPAM) is widely used for chemical enhanced oil recovery but its performance can be greatly reduced under harsh reservoir conditions. One proposed method of improving the performance of polymer flooding under reservoir conditions is the addition of functionalized nanoparticles (NPs). In this study, we systematically investigated the effects of adding hydrophobic or hydrophilic silica nanoparticles on the rheology, phase stability, and microstructure of HPAM solutions. Adding low concentrations of NPs slightly reduces the viscosity of the solutions but the presence of a high quantity of NPs (>0.5 wt %) makes the solution more viscous, elastic, and shear thinning. The results of dynamic light scattering reveal that these effects are mainly caused by the reversible formation of a large HPAM-NP network, which consists of HPAM chains weakly connected by NPs. When kept under static conditions, the NP-HPAM mixtures tend to undergo phase separation in a few days, but this issue is less likely to be a concern in field-scale polymer flooding during which the fluids are under constant flow. The findings of this study provide potential solutions to improve the performance of polymer flooding under high-salinity reservoir conditions.