Interfacial Regulation Behavior of Biosurfactants in Nanoconfined Environments and Their Enhanced Oil Recovery Mechanisms

Nanoscale pores are common in low-permeability and tight reservoirs, where confinement can alter molecular organization, diffusion, and adsorption at oil–water-mineral interfaces. Here, rhamnolipids (RLs) and sophorolipids (SLs) were compared in calcite-water–oil models using molecular dynamics simulations and quantum-chemical calculations. RLs preferentially accumulated at the oil–water interface, whereas SLs were more abundant in the oil phase and associated with heavy crude-oil components. The computed interaction-energy decomposition was dominated by van der Waals contributions. RLs showed their strongest association with asphaltenes, whereas the dominant SL association depended on model composition, with prominent resin association in model 3 and asphaltene association in model 4. Radial distribution functions supported stronger local association of SLs with resin- and asphaltene-rich domains, while diffusion analyses showed that heavy components and surfactants remained less mobile than light components and water. Electronic-structure analyses identified polar headgroups as potential sites for electrostatic and hydrogen-bond interactions and hydrophobic segments as the principal regions for dispersion interactions. These results define local molecular mechanisms by which RLs and SLs can modify interfacial organization under confinement. They should be interpreted as mechanistic descriptors rather than as direct predictions of field dosage or reservoir-scale recovery.