Dynamic Oil-Film Detachment Induced by Amphiphilic Magnesium-Based Nanosheets for Enhanced Residual Oil Mobilization

After long-term waterflooding, considerable adhered residual oil remains trapped in reservoir pores, and its mobilization is jointly restricted by capillary forces, oil–solid adhesion, and local wettability. Herein, amphiphilic magnesium-based nanosheets (AMN) were prepared via amino functionalization and hydrophobic-chain grafting to improve the mobilization of adhered residual oil after waterflooding. AMN exhibited a two-dimensional sheet-like morphology, with a lateral size of approximately 70–160 nm and a thickness of 12–13 nm. Interfacial tests demonstrated that AMN reduced the oil–water interfacial tension, altered the wettability of oil-wet surfaces, and improved emulsion stability. To further reveal the dynamic detachment mechanism of adhered oil films, a dynamic oil-film shrinkage evaluation method was developed, and a comprehensive detachment index, F detach, was established by integrating oil-film area detachment, shrinkage kinetics, apparent adhesion release, and interfacial tension reduction capability. The results showed that AMN rapidly induced oil-film boundary recession and contact-angle increase, transforming adhered oil films from a spreading state into a contracted, weakly adhered, and more mobilizable state. The F detach value of AMN reached 0.9232, which was significantly higher than those of SDBS and water, and random-weight sensitivity analysis confirmed the robustness of this evaluation. Microscopic displacement experiments showed that AMN effectively mobilized multiple types of residual oil, achieving a final microscopic recovery of 93.08%. Core flooding further confirmed that AMN achieved a final recovery of 41.40% and an incremental recovery of 21.21%, approximately 2.25 times that of SDBS. These results demonstrate that AMN enhances adhered residual oil mobilization through the synergistic effects of interfacial tension reduction, wettability regulation, emulsion stabilization, and dynamic oil-film detachment, providing guidance for the design and evaluation of nanosheet-based oil-displacing agents.