A mini-review of water-alternating-CO2 injection process and derivations for enhanced oil recovery and CO2 storage in subsurface reservoirs

Increasing carbon dioxide levels are significantly impacting the ecosystem, prompting the oil industry to explore innovative methods for reducing emissions and trapping CO₂ while enhancing oil recovery. Among these, the water-alternating-gas CO₂ (WAG-CO₂) injection process has emerged as a crucial technique for optimizing hydrocarbon extraction from subsurface reservoirs. WAG-CO₂ combines the benefits of water injection with the utilization of CO₂, enhancing oil production efficiency and offering a potential solution for CO₂ storage. This mini-review delves into the multifaceted aspects of WAG injection, including advanced variations such as surfactant alternating gas (SAG) and low-salinity water alternating gas (LS-WAG). Furthermore, it explores recent advancements in the field, such as CO₂ alternating nano water (NWAG) and foam assisted WAG (FWAG) injections, underscoring the evolution of these techniques. The integration of WAG with polymer injection and mobility control technologies produces synergistic effects, expanding the applicability of WAG methods. This review provides a comprehensive analysis of the potential of WAG and its derivatives for enhanced oil recovery (EOR) while addressing current challenges and future trends, thereby contributing to the sustainable development of the oil industry.