Enhanced Oil Recovery in High-Temperature and High-Salinity Reservoirs: A Reservoir-Oriented Review of Screening Logic, Field Constraints, and Future Directions

High-temperature and high-salinity (HTHS) reservoirs remain challenging targets for enhanced oil recovery (EOR) because temperature, ionic strength, divalent ions, heterogeneity, and long residence time jointly impair chemical functionality, transport efficiency, and displacement performance. Rather than summarizing recent advances only by material class, this review reorganizes the field using a reservoir-oriented framework in which HTHS reservoirs are stratified into moderate, high, and ultra-HTHS severity windows, and candidate technologies are evaluated against four coupled performance processes: transport and injectivity, chemical retention and deactivation, mobility control and sweep improvement, and interfacial modification for residual-oil mobilization. The analysis shows that no single technology is universally optimal. Thermo-salt-tolerant polymers and alkali-free surfactant–polymer systems remain practical options in moderate-to-high HTHS settings when injectivity and functional persistence can be preserved; foam and deep-profile-control technologies become more valuable when heterogeneity and channeling dominate recovery loss; and many smart or nanoenabled systems remain promising but translationally immature because of unresolved constraints in injectivity, retention, response reliability, synthesis cost, and long-term stability. This review further argues that the central challenge in HTHS EOR is not only the design of new formulations but also the establishment of screening criteria that remain credible during scale-up. Accordingly, it emphasizes the lab-to-field gap, proposes a reservoir-oriented screening workflow, and identifies future priorities in functional longevity, salinity-dependent rheology, adsorption mitigation, transport evaluation, and pressure-window-controlled injection design.