Molecular Dynamics Study on the Thickening Mechanisms of Pure and Nanoparticle-Enhanced Hydrolyzed Polyacrylamides

Partially hydrolyzed polyacrylamides (HPAMs) have been gaining attention in enhanced oil recovery, with recent studies showing that adding nanoparticles (NPs) can boost the HPAMs flooding efficiency. Here, molecular dynamics (MD) simulations were utilized to explore the viscosity enhancement mechanism of HPAMs and the silica nanoparticle composite system. The results demonstrated that during the HPAMs self-assembly process, polymer ends formed hydrogen bonds, creating a network structure that increased the viscosity of the system. The simulations identified multiple hydrogen bonding units formed between amide hydrogen atoms and carboxyl carbonyl oxygen atoms, enhancing polymer network stability and improving fluid transport and recovery rates in reservoirs. The introduction of nanoparticles increased the cross-linking points within the polymer network and restricted the movement of the HPAMs molecular chains, thereby reducing the relative slippage between polymer chains. On the other hand, the introduction of silica nanoparticles not only restricted the movement of polymer chains but was also restricted by the surrounding polymer network, greatly reducing their range of movement. The dual restrictive effect of these nanoparticles on polymer chains and of polymer chains on nanoparticles further enhanced the overall viscosity of the system. The findings aim to leverage these findings to enhance oil field recovery, particularly under extreme conditions, by improving the polymer flooding efficiency through nanoparticle integration.