Engineered CO₂ injection: The use of surfactants for enhanced sweep efficiency

Poor CO₂ displacement efficiency can exacerbate hydro-chemo-mechanically coupled phenomena in CO₂ storage reservoirs, increase the area affected by CO₂ in the reservoir, and negatively impact the long-term geological storage of CO₂. The injection of CO₂ can be engineered using surfactants to improve displacement efficiency. Pendant and sessile drop tests show that a surfonic copolymer decreases the interfacial tension γ_fl and increases the contact angle θ under reservoir conditions. The combined changes in surface tension and contact angle have a pronounced effect on the capillary factor γ_fl·cosθ. Injection tests using micro-models and pore network simulations show that a smaller capillary factor transforms the displacement pattern and enhances the pore-scale sweep efficiency of CO₂, surpassing 40% in 2-D applications. Surfactant cost may offset the technical advantages identified in this study.