Molecular dynamics simulation of crude oil detachment using ScCO₂ and miscible agents on SiO₂ surfaces

Carbon capture, utilization, and storage technology has garnered increasing attention across various industries. To further elucidate the mechanism of CO₂ enhanced oil recovery, an amphiphilic surfactant was designed based on β-cyclodextrin. The mechanism of oil detachment from SiO₂ was investigated through molecular dynamics simulations. Density distribution curves and diffusion coefficients of oil phase and CO₂ indicated improved miscibility following the addition of surfactants. Subsequent analysis of desorption efficiency for oil phase revealed that the enhanced miscibility between CO₂ and oil molecules facilitated desorption from solid surfaces. The C2-OAC7 system exhibited superior desorption effects due to lower energy levels associated with CO₂ + surfactant and oil interactions. The addition of surfactants promoted mutual dissolution of CO₂ and oil primarily through increased cavity space in β-cyclodextrin, enhancing van der Waals forces between CO₂-philic/oil-philic groups with CO₂ and octane respectively. This study provides valuable data references and theoretical foundations for structural design and action mechanisms of miscible surfactants.

In this study, Packmol was employed to construct the model, Gromacs was utilized for molecular dynamics simulations, and VMD was adopted for graphical visualization. Initially, the energy minimization of the two systems, namely "CO₂ + Surfactant" and "Oil + SiO₂-OH," was performed. Subsequently, 1ns NPT simulations were conducted on both systems under specific conditions: 313 K and 105 bar for the "CO₂ + Surfactant" system, and 298 K and 101.325 kPa for the "Oil + SiO₂-OH" system. Finally, a 10ns NPT simulation was carried out. The Berendsen and Parrinello-Rahman methods are used to maintain system pressure. The LINCS algorithm is employed to constrain molecular bond lengths, while the Lennard-Jones potential is applied to define the cutoff radius. Long-range electrostatic interactions are handled using the Particle-Mesh Ewald (PME) summation method.