Research progress on microscopic mechanisms of nanoparticle-assisted oil displacement based on molecular dynamics simulations and prospects

With the growing demand for petroleum resources and the increasing difficulty of reservoir development， the need for enhanced oil recovery （EOR） has become more urgent. Thanks to their unique advantages， such as small size， large specific surface area， and strong environmental compatibility， nanoparticles （NPs） have attracted extensive attention in tertiary oil displacement， yet their deep-seated microscopic mechanisms of oil displacement still require further investigation. Molecular dynamics （MD）， an advanced microscopic simulation technique， has become an important tool in reservoir-development research. This paper systematically reviewed key concepts in MD simulations， including equilibrium and non-equilibrium molecular dynamics， force fields， ensemble theory， and boundary conditions， and it discussed the application of commonly used NPs such as TiO2， SiO2， and carbon nanotubes （CNTs） in improving oil recovery. Microscopic mechanisms of NPs-assisted oil displacement were analyzed， including reduction of oil and water interfacial tension （IFT）， decrease of crude oil viscosity， improvement of the oil and water mobility ratio， and wettability alteration， as well as auxiliary mechanisms such as enhanced foam stability and improved polymer solution rheology. Future directions for MD-based NPs-assisted oil displacement research were outlined： designing simpler and greener NP synthesis/modification schemes via MD， combining MD simulations with laboratory experiments to study the effect of NPs on displacement efficiency， and integrating quantum mechanics （QM） to increase simulation accuracy.