# Progress on the Application of Nanomaterial Expansion in Oil Displacement
## 3 Nanomaterial Swelling Oil Displacement Mechanism
### The \"Rolling Up\" and \"Diffusion\" Phenomena
Nanoparticles can replace the original interface between oil and water, reduce the friction between the oil phase and the water phase, and further reduce the interfacial tension. The study of [PERSON] et al. [101] also shows that the presence of nanofluids will lead to changes in the morphology of rock surfaces. Figure 15, below, is a schematic diagram of the adsorption of nanoparticles on rock surfaces. The presence of nanofluids will cause the wedge-shaped film structure to form at the contact part of the oil-water and rock interface. The existence of the wedge-shaped structure separation pressure will cause the oil droplets on the rock to peel off, thereby rolling up the oil film. Figure 14: Effect of nano-oil displacement agent concentration on the contact angle [100]. Figure 15: Adsorption diagram of nanofluids on rock surface [101]. Based on the analysis results presented in the Principle of Enhanced Oil Recovery by Nanomaterials section, it can be seen that the nanofluid system has a significant synergistic effect in regulating the interfacial tension and improving the wettability of the rock surface. This synergistic effect is mainly achieved by changing the direction of the capillary force, thus providing kinetic advantages for the migration and diffusion of oil droplets [102]. [PERSON] et al. [103] found through experiments that amphiphilic-modified graphene oxide nanomaterials have excellent interfacial activity characteristics, and the nano-adsorption layer formed by them can reduce the oil-water interfacial tension to the order of 10 1 mN/m. This system can not only construct a super-hydrophilic interface on the surface of reservoir rock but also effectively control the wettability through the formation of nano-scale interfacial film. This multi-mechanism coupling provides a new technical path for enhancing oil recovery. The relevant research results have laid a theoretical foundation for the engineering application of nanofluids in the field of tertiary oil recovery. The mechanism of nanofluids' synergistic microscopic oil displacement effect can be summarized in three key elements: structural separation pressure, interfacial tension control, and rock wettability optimization. Among them, the presence of surfactants is the core condition that triggers the detachment of oil droplets. These substances promote the interfacial behavior of crude oil particles adsorbed on the pore surface by reducing the contact angle of the oil-rock interface. When the contact angle is less than the critical value, the oil droplets undergo morphological reconstruction under the action of capillary force to form larger aggregates, which is the \"rolling-up\" phenomenon of oil droplets [104]. The synergistic effect of the diffusion mechanism is reflected in the dynamic regulation of oil-water interfacial tension. The microbubble diffusion effect formed by the Brownian motion of nanoparticles can significantly reduce the interfacial tension between crude oil and displacement fluid, thereby improving the fluidity of crude oil. It is worth noting that there is a significant interaction between the two mechanisms: the large-sized oil droplets formed in the \"roll-up\" process provide a larger interface for diffusion, and the microbubbles generated by diffusion further promote the detachment of oil droplets by enhancing the interface disturbance. This dynamic synergistic effect makes nanofluids show better recovery efficiency than traditional oil displacement agents in porous media [105]. In oil exploitation engineering, entrainment and the diffusion effect constitute the core mechanism to improve the efficiency of crude oil migration. The entrainment effect significantly improves the flow performance of crude oil by changing the droplet shape parameters. The nanolayer formed by the diffusion effect enhances the migration efficiency of droplets in the pore throat by regulating the interaction between bubbles and fluids.