Molecular insight into oil displacement by CO₂ flooding in water-cut dead-end nanopores

Understanding the mechanisms underlying residual oil displacement by CO₂ flooding is essential for CO₂-enhanced oil recovery. This study utilizes molecular dynamics (MD) simulations to investigate the displacement of residual oil by CO₂ flooding in dead-end nanopores, focusing specifically on the water-blocking effect. The findings reveal that oil displacement does not commence until the water film is breached. The dissolution of CO₂ molecules in water and the hydrogen bond interactions between water and rock are the primary factors that disrupt the hydrogen bond network among the water molecules, facilitating the breakthrough of the water film. Additionally, the displacement process can be delineated into four distinct stages - encompassing water film rupture, oil swelling, massive oil displacement, and displacement completion - as evidenced by the oil recovery-displacement time curves. Moreover, a cutting-edge oil recovery-displacement time model precisely quantifies crucial stages in the displacement process. For example, when t < δ, trapped oil is impeded by the water film, while when t > δ + 3τ, displacement culminates successfully. Altogether, this research bolsters comprehension of residual oil displacement in the presence of water blocking and advocates for sustainable oil production strategies in oilfields.