Smart Water–Polymer Hybrid Flooding in Heavy Oil Sandstone Reservoirs: A Detailed Review and Guidelines for Future Applications

The application of smart water–polymer hybrid flooding in sandstone reservoirs has gained significant attention in recent years. This study provides a comprehensive review of the smart water–polymer flooding concept, including the underlying mechanisms, necessary conditions, and specific applications in heavy oil sandstone reservoirs. Screening criteria and required conditions for each method are investigated thoroughly to ensure the possibility of their synergy. The study also addresses smart water deficiency as a single Enhanced Oil Recovery (EOR) process for heavy oil heterogeneous sandstone reservoirs. The effectiveness of smart water–polymer hybrid flooding in terms of enhancing oil recovery mechanisms, various injection scenarios, economic profitability, and associated risks such as injectivity decline and viscosity loss is thoroughly examined and compared in different experimental and simulation studies. Based on the literature, it is concluded that wettability alteration and mobility control are the main controlling mechanisms. The synergistic effect of these mechanisms can lead to an increase in oil recovery equal to or higher than the summation of each method separately, with more effective results for heavy oil reservoirs. Notably, among the various injection scenarios explored, smart water injection followed by a tertiary smart water–polymer flood demonstrated the highest ultimate oil recovery. Despite numerous experimental studies on this subject, a series of controversial results have been observed concerning issues such as injectivity, polymer retention, and cation exchange between the polymer and aqueous phase. This indicates the necessity for more detailed investigations on this hybrid EOR method in the future. Simulation and optimization studies, particularly by applying proxy models such as artificial-intelligence-based methods, seem to have a high potential for further field study in this topic.