Screening and Evaluation of CO₂ Thickening Agents Based on Molecular Dynamics Simulation Technology

CO₂ is one of the main methods for improving recovery. The low viscosity and density of CO₂ lead to issues such as viscous fingering and gravitational override during the displacement process, which can cause gas channeling and premature breakthrough in reservoirs. These problems severely affect sweep and displacement efficiencies, thereby reducing the recovery of CO₂ flooding. Addressing the challenge of increasing CO₂ viscosity to mitigate these issues is crucial for improving CO₂ flooding technology. This study conducts a feasibility analysis on the use of polymers to enhance the viscosity of CO₂ through molecular dynamics simulations. Models of five CO₂ + polymer systems (P-1-D, PVEE, PVAEE, Piso-BVE, and four-armed PVAc) were established. The results indicate that the presence of functional groups such as ether, acetate, and ester in the polymers enhances intermolecular interactions, which restricts the free movement of CO₂ molecules and significantly reduces intermolecular forces among them. This results in an increase in CO2 viscosity. Among the polymers, the four-armed PVAc increases the viscosity of the supercritical CO₂ system by 5.29 times, although it has the poorest solubility. In comparison, P-1-D increases the viscosity by 4.75 times while exhibiting moderate solubility.