Evaluation of the Synergistic Oil Displacement Effect of a CO 2 Low Interfacial Tension Viscosity-Increasing System in Ultra-Low Permeability Reservoirs.

In addressing the issue of poor control over gas permeability during the CO₂ flooding process in ultra-low permeability reservoirs, this study proposes the use of a low interfacial tension viscosity-increasing system as a substitute for water in CO₂–water alternating flooding to enhance CO₂ mobility control and increase oil recovery. The performance of the system was evaluated through tests of viscosity, interfacial tension, wettability, and emulsification properties, and the injection behavior and gas channeling prevention effect of the viscosity-increasing system with CO₂ alternate flooding were investigated. The results indicate that the low interfacial tension viscosity-increasing fluid exhibits good thickening properties, interfacial activity, hydrophilic wettability, and oil–water emulsification performance, also demonstrating strong environmental adaptability. The CO₂–low interfacial tension viscosity-increasing fluid alternate flooding shows good injectivity in ultra-low permeability cores (1.085 mD). Following water flooding in heterogeneous ultra-low permeability cores, the implementation of CO₂ low interfacial tension viscosity-increasing fluid alternate flooding can lead to a 15.91% increase in overall recovery compared to water flooding, outperforming CO₂ flooding and CO₂–water alternating flooding. The mechanisms by which the CO₂ low interfacial tension viscosity-increasing fluid enhances oil recovery include reducing interfacial tension, improving mobility ratio, altering rock surface wettability, and emulsification effects. The low interfacial tension viscosity-increasing systems demonstrate effective mobility control and oil displacement capabilities and synergistically enhance the efficiency of CO₂, presenting potential application prospects in the development of CO₂ flooding in ultra-low permeability reservoirs. [ABSTRACT FROM AUTHOR]