Oil Detachment Mechanism in Natural Surfactant Flooding from Silica Surface: Molecular Dynamics Simulation

Summary International regulations have compelled Europe and the United States to phase out certain traditional surfactants to mitigate the use of toxic and nonbiodegradable chemicals. Sodium cocoyl propionate (SCA), as a natural surfactant with high performance, has been proved to have the potential to replace traditional surfactants in previous studies. However, its performance has not fully met practical application requirements. Therefore, in this paper, molecular dynamics (MD) simulation was used to study the detachment behavior and mechanism of SCA, lauryl dimethylamine oxide (OA-12), emulsifier OP-10, and SOO (combination of SCA, OA-12, and OP-10) on crude oil (dodecane, C12) at different temperatures (80–120°C) and salinities (20 000–200 000 mg/L). The complex interaction mechanism between surfactant molecules and C12 molecules was revealed by analyzing the simulated snapshot, radial distribution function (RDF), mean square displacement (MSD), and interaction energy. The simulated snapshot captures the conformational evolution of surfactant molecules at different time points, emphasizing the spatiotemporal and spatial changes of their dynamic behavior. A comparison of two desorption modes reveals that dispersive adsorption displacement and concentrated adsorption displacement are two possible desorption mechanisms. RDF analysis shows that the probability of SOO molecules near C12 remains high even at high-salinity and -temperature conditions. MSD analysis showed that the diffusion capacity of SOO was the highest at 100°C, reaching 1.52867×10 –5 cm2/ps. The calculation of interaction energy results reveals that SOO has a strong adsorption capacity for C12, which is mainly due to the effect of van der Waals (vdW) force. This is because the C12 molecules are inert, and their molecular movement is mainly determined by the polar groups of the surfactant. The main contribution of this study is to provide a natural surfactant with superior performance as a viable alternative, offering experimental settings for further improvement in SCA performance. This research provides theoretical guidance for on-site applications of SCA and SOO to enhance oil recovery.