Natural deep eutectic solvent for exclusive and assured green enhanced oil recovery and other oil and gas applications: a review

The growing global demand for oil necessitates extraction beyond primary and secondary recovery, making tertiary recovery methods essential for meeting energy requirements. As a result, enhanced oil recovery (EOR) is expected to play a more significant role in the coming years. While physical gas injection and thermal techniques have been widely used, their high costs and limited applicability present challenges. Consequently, chemical-based EOR methods have gained prominence due to their efficiency, economic feasibility, and lower capital investment. Therefore, the development and optimization of eco-friendly and efficient chemical compounds are crucial for the oil and gas industry to enhance reservoir productivity and achievement of sustainability goals. Use of Ionic liquids (ILs) in chemical EOR have proved efficient on a commercial scale but their toxicity is a major environmental concern. Natural deep eutectic solvents (NADES) are emerging as sustainable and eco-friendly alternatives to conventional ILs and deep eutectic solvents (DES) in various industrial applications, particularly in the oil and gas sector. Synthesized from plant-based and biodegradable materials, NADES are non-toxic, renewable, customizable, and are consequently regarded as ideal solutions to environmental and economic challenges. This review highlights the potential of NADES in oil operations, specifically, in enhanced oil recovery. NADES can potentially alter rock wettability, inhibiting shale swelling. By virtue of their biocompatibility and low environmental impact, NADES also offer a cost-effective and sustainable option for various other applications like shale gas inhibition, fracturing fluid and natural gas dehydration. Extensive laboratory research is expected to realize the full potential of NADES as 100 % green solvents, driving the transition to more sustainable practices in the energy sector.