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Supercritical CO2(scCO2)flooding,a promising and economical technique,can greatly improve water injectivity and enhance oil recovery.In this work,molecular dynamics simulation was performed to investigate the mechanism of scCO2 selective extraction inducing the wettability alteration of an oil reservoir,MD simulations were achieved using Materials Studio(MS)software package.The results indicate that scCO2 could disrupt the structure of crude oil,and a clear selectivity of scCO2 for extracting apolar components from the crude oil is observed.As a result,the polar components of crude oil remained on the oil reservoir rock surface.Next,the wettability of the rock surface was further investigated,and the results indicate that the wettability of the rock surface is altered from hydrophobic to hydrophilic after scCO2 flooding.Our study provides a comprehensive understanding of the wettability alteration of the oil reservoir rock surface and the improvement of the water injectivity rate after scCO2 injection.