Investigation into the temperature resistance of saturated cardanol surfactants in crude oil-water systems: a molecular dynamics simulation.

Abstract

<h4>Context</h4>Surfactant flooding represents one of the critical methods in chemical enhanced oil recovery (EOR) technology. However, under high-temperature and high-salinity conditions, the interfacial properties of surfactants are prone to alteration, leading to reduced interfacial activity. In this study, three distinct types of surfactants derived from saturated cardanol were selected: 8EO8POH (nonionic surfactant), 8EO8POC2SO₃ (sulfonate surfactant), and 8EO8POSO₃ (sulfate surfactant). A high-temperature (30 ~ 180 ℃) and high-salinity (NaCl + CaCl₂ concentration of 1.0 mol/L) system model was constructed through molecular dynamics simulations to evaluate their thermal resistance. The results indicate that an increase in temperature enhances the aggregation of water molecules and crude oil components around the surfactant molecules, thereby strengthening weak interactions. Under these conditions, the balance between hydrophilic and lipophilic effects becomes the predominant factor determining the superior interfacial performance of the surfactants. Consequently, the order of heat resistance is as follows: 8EO8POC2SO₃ > 8EO8POSO₃ > 8EO8POH.<h4>Method</h4>In this study, Packmol was employed to construct the model, and Gromacs was used to perform molecular dynamics simulations under the GAFF force field. The simulated pressure was set to 1115.0 kPa. The temperatures were set at 303.15 K, 333.15 K, 363.15 K, 393.15 K, 423.15 K, and 453.15 K, respectively. The time step for all simulations was set to 2 fs. In the 1 ns and 15 ns NPT simulations, the Berendsen and Parrinello-Rahman methods were employed to maintain system pressure, and the temperature control was achieved through velocity-rescale. The LINCS algorithm was utilized to constrain molecular bond lengths. Short-range and long-range were used Lennard-Jones potential and Particle-Mesh Ewald (PME) summation method.