# Progress on the Application of Nanomaterial Expansion in Oil Displacement
## 3 Nanomaterial Swelling Oil Displacement Mechanism
### Pressure Oil Displacement by Structural Separation
[PERSON] et al. [87] observed the self-assembly phenomenon of nanoparticles in the three-phase contact wedge region formed on a nanofluid-bubble-solid surface using a reflective light digital video microscope. On this basis, the dynamic process of nanofluid displacement of oil droplets on the glass surface was further studied. Two contact lines were also formed during the displacement process. One was the outer line formed between the oil droplets, the solid surface, and the micelle solution, and the other was the inner line formed between the oil droplets, the solid surface, and the liquid film. The thickness of the liquid film increased with the extension of the diffusion time, and the shrinkage rate of the inner contact line was greater than that of the outer contact line. Finally, the oil  
Figure 11: Photomicrograph taken using reflected light interferometry depicting the inner and outer contact lines and the nanofluid film region [87]. droplets were completely detached from the glass surface under the action of a ripple-like water-based film [90]. After research, [PERSON] et al. [87] found that nanoparticles form a certain structure under the action of wedge constraints and have a high tension at the apex of the film. When the tension of the membrane increases towards the wedge vertex, the nanofluid will move in the three-phase contact line, which leads to the enhancement of the dynamic diffusion behavior of the nanofluid. The nanoparticle structure in the wedge membrane leads to the structural separation pressure gradient at the wedge apex, as shown in Figure 12. With the injection of nanofluids, the size of the wedge-film will gradually increase. At the same time, the wedge membrane will continue to move forward under the action of the driving force, and the separation pressure will be generated under this movement. In addition, [PERSON] et al. [91] used a theoretical model to verify that changes in the physical and chemical properties of nanoparticles, such as size, temperature, and concentration, will have a certain effect on the separation pressure. In summary, due to the existence of electrostatic repulsion and Brownian motion between molecules, nanofluids will lead to the formation of a wedge-shaped, film-like structure at the contact surface between the three phases of oil, water, and solid, and the wedge-shaped film structure will continue to move forward due to the presence of the driving force, resulting in separation pressure and improving the wettability of the rock surface. Through the discussion of the Principle of Enhanced Oil Recovery by Nanomaterials section of this paper, we know that the change in wettability can greatly affect the efficiency of oil exploitation. The structure separation pressure displacement mechanism is one of the important mechanisms of nanofluid flooding, involving the pressure of the wedge area of the contact line, and this mechanism also provides a new explanation of the microscopic process of crude oil stripping. The combination of the structural pressure separation mechanism and the reduction in interfacial tension and wettability conversion is an important factor affecting mining efficiency. In the process of nanofluid flooding, the generation of structural pressure is closely related to the behavior of nanofluids at the interface between oil and water phases. Nanoparticles can change the nature of the interface between oil and water, so they can affect the stripping and movement of crude oil droplets. The mechanism of structural separation pressure flooding involves the adsorption and spreading of nanoparticles at the interface and also involves the structure and dynamic behavior of nanoparticles affecting the oil-water interface. By affecting the interface and the micro level, nanofluids can affect the fluidity of crude oil and thus greatly affect the efficiency of oil exploitation. Figure 12: Nanoparticle structuring in the wedge-film resulting in structural disjoining pressure gradient at the wedge vertex [87].