Review on Applications of Chelating Agents in Enhanced Oil Recovery: Advances and Outlook

Chelating agents have been found to be a promising multifunctional additive in chemical enhanced oil recovery (cEOR), offering unique abilities in altering rock wettability, reducing interfacial tension (IFT), and synergistically enhancing surfactant performance under challenging reservoir conditions. They can sequester multivalent cations and maintain stability in high-temperature, high-salinity environments for both sandstone and carbonate reservoirs. Several chelating agents are reported in the literature, such as EDTA, DTPA, HEDTA, and GLDA, as well as phosphonates like HEDP and NTMP, along with newer biodegradable chelating agents like GLDA. The available literature, which is reviewed, shows that chelating solutions can reduce IFT and alter the wettability of carbonate and sandstone rock surfaces from oil-wet to strongly water-wet, yielding additional oil recoveries of 20–30% of original oil in place under optimized pH, concentration, and different chemical strategies. The synergistic effect of the chelating agent and surfactant further enhances recovery by minimizing surfactant adsorption onto rock surfaces through stable metal-chelant complex formation, thereby preserving surfactant chemical availability in the pore space. Nevertheless, there is still an engaging debate on the extent to which chelating agents can be considered effective and reliable, as their performance is strongly influenced by concentration, mineralogy, pH, and reservoir conditions. The complexity of chelating agents has driven intense research and developmental efforts to understand their performance under field-scale conditions and diverse reservoir environments. Pilot studies need to be designed, supported by fluid-flow modeling and optimization for implementation on a large scale. Overall, chelating agents represent a versatile class of multifunctional EOR chemicals capable of improving oil recovery under harsh reservoir conditions while offering opportunities for environmentally compatible and economically viable operations.