Multiscale Mechanistic Investigation of Polyacrylamide Nanosphere Degradation Under High‐Temperature and High‐Salinity Reservoir Conditions

ABSTRACT In deep reservoir environments, the effectiveness of polymer gel systems for enhanced oil recovery (EOR) is often compromised by extreme conditions of high temperature, high salinity, and elevated pressure. As the most extensively used polymer gel, polyacrylamide‐based gel particles have shown great promise but suffer from limited thermal and chemical stability under harsh conditions. The multiscale degradation mechanisms governing their breakdown remain poorly understood. In this study, we systematically investigate the degradation behavior of polyacrylamide nanospheres, a model system with controlled particle size under representative reservoir conditions (150°C, 5 MPa, up to 100 g/L salinity). Through a combination of thermal analysis, structural and surface characterization, gas‐phase product profiling, in situ high‐pressure IR spectroscopy, and density functional theory (DFT) calculations, we map out the key degradation pathways and their molecular origins. Results show that salinity promotes hydrolysis of amide groups, particularly at MBA crosslinking sites, while high‐pressure oxygen accelerates deamination and chain scission. In situ IR confirms the evolution of functional groups into carboxylic acids, and DFT results reveal that carboxyl‐rich environments significantly reduce the activation energy for bond cleavage, initiating autocatalytic degradation. Importantly, oxidative degradation under air proves more damaging than ionic effects alone. This comprehensive, multiscale approach not only clarifies the intertwined roles of heat, salt, and oxygen in destabilizing polymer gels but also provides a mechanistic foundation for developing salt‐tolerant, oxidation‐resistant gel formulations for high‐temperature reservoir applications.