Abstract
Nanosilica-modified polymer (MNP) flooding significantly enhances crude oil recovery by increasing the sweep efficiency. However, their microscopic displacement mechanisms remain incompletely understood. This study employed a synthesized nanosilica-modified polymer (MNSP) as a displacement agent. Oil displacement efficiency and the remaining oil mobilization mechanisms were evaluated using core flooding experiments and microscopic visualization in etched models. The displacement mechanism was systematically elucidated based on interfacial tension modulation, emulsification efficiency, and wettability alteration. Microscopic displacement experiments demonstrated a recovery ratio of 91.60% for MNSP. Nuclear magnetic resonance displacement analysis revealed crude oil utilization rates of 65.00% in large pores, 25.78% in medium pores, and 9.22% in small pores. The core mechanism involves nanosilica synergistically cooperating with hydrophobic associations to form a three-dimensional network structure at the oil-water interface, reducing interfacial tension. Concurrently, nanosilica induces rock wettability reversal via wedge-film pressure, promotes stable emulsion formation, and enhances oil stripping efficiency. This work systematically elucidates the oil displacement mechanisms of MNSP, providing a theoretical foundation for further research on similar polymer oil displacement mechanisms.