Abstract
Chemical enhanced oil recovery (EOR) plays an important role in improving hydrocarbon production from mature reservoirs, where conventional recovery methods leave a large fraction of oil unrecovered. Among chemical EOR approaches, polymer flooding is widely used to improve mobility control and sweep efficiency. However, conventional polymers such as partially hydrolyzed polyacrylamide (HPAM) often suffer from viscosity loss, chain degradation, and poor stability under high-temperature, high-salinity, high-hardness, and high-shear reservoir conditions. This review discusses recent advances in polymer-based EOR, with particular focus on polyampholytes as next-generation mobility-control agents. Polyampholytes contain both anionic and cationic groups along the polymer backbone, enabling ionic association, salt-responsive chain conformation, and enhanced tolerance to harsh brine environments. Their antipolyelectrolyte behavior can promote chain expansion and viscosity retention at elevated salinity, distinguishing them from conventional polyelectrolytes. The review summarizes the molecular architecture, rheological behavior, reservoir interactions, and oil-displacement mechanisms of polyampholytes, including their integration with surfactants, foams, and nanoparticles. Key challenges related to synthesis, cost, injectivity, adsorption, long-term stability, and field-scale implementation are also discussed. Future perspectives emphasize the design of cost-effective, environmentally sustainable, and stimuli-responsive polyampholyte systems for demanding reservoir conditions.