Retaining entrapped oil in carbonate reservoirs is a critical challenge in the oil industry. However, the mechanisms governing wettability alteration for enhanced oil recovery (EOR) on carbonate surfaces remain poorly understood. This study uses molecular simulations to explore the mechanisms behind wettability alteration by modifying reservoir rock parameters and examining the resulting changes in contact angle. Using the UNIVERSAL force field, a solution is proposed to improve wettability in the EOR process. The research investigates the influence of water, NaCl ions, and sodium dodecyl sulfate (SDS) on wettability modification under varying pressure and temperature conditions. Increasing NaCl concentration from 1.5% to 10% enhances ion absorption, thickens the water layer, and reduces the oil–calcite contact angle from 34° to 27°. Conversely, increasing the SDS molecular ratio to 10% raises the contact angle to 53°. Furthermore, the simultaneous addition of NaCl and SDS molecules significantly affects the interaction between the droplet and the matrix. This process causes the droplet contact angle to vary from 39° to 48°. This study establishes a molecular dynamics (MD) framework for investigating wettability behavior, laying the groundwork for future research on the fundamental mechanisms of wettability alteration. A deeper understanding of these processes is essential for optimizing oil recovery and has significant implications for the oil industry.
