A novel numerical simulation method and applications of CO₂ thickened flooding

CO₂-EOR (CO₂ Enhanced Oil Recovery) is currently one of the predominant techniques for improving oil recovery worldwide, offering significant production enhancement. However, during CO₂ flooding operations, challenges such as viscous fingering, gravity segregation, and reservoir heterogeneity often lead to severe gas channeling issues. Current mitigation strategies include water-alternating-gas (WAG) injection, CO₂ viscosity thickening, hydrogel plugging, foam blockage, and nanoparticle-based conformance control. Among these, CO₂ viscosity enhancement is considered a highly promising method for improving oil recovery. However, simulating CO₂ thickening has remained a significant challenge, with existing research primarily focused on laboratory experiments and limited numerical simulation studies. This study employs the CMG-GEM numerical simulation software, utilizing a modified typical heterogeneous "Egg Model" reservoir, to systematically investigate the mechanisms of CO₂ viscosity modification on recovery performance. To simulate CO₂ thickening, this paper proposes modifying the key viscosity parameter "[Formula: see text](viscosity)" to approximate the CO₂ thickening process. A series of injection schemes were designed, including continuous gas injection, alternating injection of thickened and unthickened CO₂, and water-alternating-gas (WAG) injection, to compare and evaluate the development performance under various conditions. The study systematically examines the effects of different thickening multiples, slug ratios, and reservoir heterogeneity levels. The results indicate that adjusting the viscosity parameter "[Formula: see text](viscosity)" can effectively simulate CO₂ thickening behavior. Furthermore, CO₂ viscosity enhancement demonstrates significant potential for improving oil recovery, providing both theoretical insights and practical guidance for numerical simulation studies of viscosity-modified CO₂ flooding.