Alternative chemical agents for alkalis, surfactants and polymers for enhanced oil recovery: Research trend and prospects

Chemical Enhanced Oil Recovery (CEOR) techniques include alkaline, surfactant, and polymer flooding, as well as their binary and ternary combination such as alkali-surfactant (AS) and alkali-surfactant-polymer (ASP) flooding. However, the conventional synthetic chemical agents deployed in chemical flooding are confronted with several challenges, mainly the high cost and environmental related issues. Moreover, various technical limitations also affect the economic feasibility of the implementation of these methods. Green alternatives, such as organic alkalis, biopolymers and biosurfactants have been proposed and studied in literature as environmentally friendly and economically feasible options. They have also been proven to be stable in harsh reservoir conditions and in the presences of divalent cations. This review, therefore, presents an overview of available works on potential alternative chemical agents for conventional CEOR chemical agents. The various reports are compared to certify findings that are strong enough to facilitate field implementation. Then, recommendations are made on findings that require substantiation by further studies and areas that require more investigation. New research approaches are also recommended to improve the understanding of the flooding process of these alternative chemical agents. Reported works on organic alkalis show that ethanolamine proves to be the most effective alternative to inorganic alkalis. Plant oil-based surfactants that have been synthesized recently, outperform conventional synthetic surfactants in addition to their environmental friendliness. Ionic liquids, on the other hand, have enhanced functionality in harsh reservoir conditions contrary to conventional surfactants. Biopolymers are more stable and have reduced adsorption under harsh reservoir conditions. However, further studies are required to deepen the knowledge on wettability alteration by organic alkalis and the adsorption of biodegradable anionic surfactants. Studies are required to also improve the injectivity of biopolymers and suppress their biodegradability during flooding. This review will help improve the knowledge on alternatives chemicals to facilitate their field scale application.