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

• We measure the CO2–water interfacial tension and contact angle with and without the surfactant.
• The surfactant lowers the interfacial tension from γfl ∼ 50 mN/m to γfl ∼ 4 mN/m at pressure P ≥ 7 MPa.
• The surfactant increases the contact angle for a CO2–water–SiO2 system from θ ∼ 20° to θ ∼ 70° at P ≥ 7 MPa.
• We conduct CO2 injection tests in a 2D pore micro-model and 2D pore-network simulations.
• Microscopic sweep efficiency of CO2 invasion roughly doubles when the surfactant is added.

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 γfl 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 γfl·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.