A comprehensive review on chemically enhanced water alternating gas/CO2 (CEWAG) injection for enhanced oil recovery

Mobility control is a major concern in gas flooding process, and water-alternating-gas injection (WAG) for enhanced oil recovery (EOR), which can be improved by simultaneous injection of chemicals. Chemically enhanced water alternating gas injection (CEWAG) is getting significance importance in EOR after WAG due to its ability to improve both the displacement and sweep efficiency. The unique feature of the process includes use of alkaline, surfactant, and polymer as a chemical slug during the CEWAG process to reduce the interfacial tension (IFT) with simultaneous improvement of mobility ratio. The paper reviews the mechanism of CEWAG injection for EOR and the advantages of the method over other conventional methods. Role of different chemicals and gases, modes and patterns of the injection, mobility control and capillary mechanisms along with different laboratory studies and field implications have been discussed. Different challenges associated with CEWAG process and their solutions have been demonstrated. Finally future development and conclusion have been drawn on the basis of reported research in the relevant field.