# Progress on the Application of Nanomaterial Expansion in Oil Displacement
## 2 Principle of Enhanced Oil Recovery by Nanomaterials
### Lower Oil Viscosity
The results show that the adsorption efficiency of alumina nanoparticles on asphaltene is 48 mg/g at below 250 \({}^{\circ}\)C, and the complete conversion time of the catalytic decomposition of asphaltene is only 90 min, which is better than that of cerium dioxide and silica nanoparticles. When the concentration of nanoparticles and surfactants in the nanofluids was 0.05 wt%, the oil viscosity decreased by 90%. Dynamic tests showed that when steam injection was combined with naphtha and nanofluids, the oil recovery rates were 64% and 75%, respectively. The API weight of the recovered oil increased from 11.9\({}^{\circ}\) to 34\({}^{\circ}\), and the viscosity decreased to less than 100 cP. The mechanism of action includes the destruction of the viscoelastic network formed by asphaltene-resin by nanoparticles, the catalytic cracking of heavy components to generate light compounds, and the enhancement of the heat transfer  
Figure 6: The relationship between the number of siloxane and silanol groups on silica nanoparticles and DVR, asphaltene adsorption capacity [61]. efficiency of the injected fluid to achieve efficient heat transfer, thereby effectively reducing oil viscosity and improving oil quality, showing the application potential of alumina-based nanofluids in heavy oil recovery and upgrading. [PERSON] et al. [63] confirmed that a nano-ceramic added to the HPAM solution has a better effect on the viscosity of the aqueous phase. The entry of nanomaterials in the oil displacement agent reduces the viscosity of the oil phase mainly by adsorption. The mechanism destroys the connection structure between crude oils and reduces the viscosity between crude oils. Nanofluids increase the viscosity of the aqueous phase, increase the mobility ratio between oil and water, increase the sweep efficiency, and achieve the purpose of improving the efficiency of oil production by means of physical and chemical combination. In the process of heavy oil reservoir exploitation, an effective way to maintain a favorable mobility ratio is to reduce the viscosity of crude oil. One of the principles of using a nano-oil displacement agent based on metal nanomaterials to improve oil recovery is to increase the viscosity of displacement fluid. Experiments have confirmed that the rheological properties of the nano-oil displacement system are significantly regulated by multi-physical field coupling effects such as the concentration gradient, thermodynamic conditions, shear rate, and salinity gradient. These key parameters directly affect the reservoir seepage dynamics by changing the fluid microstructure. Therefore, the establishment of a quantitative response model of oil displacement agent viscosity-seepage efficiency has important theoretical guidance value for the intelligent optimization of heavy oil recovery process parameters [64]. The mobility ratio (M) is a function of the relative permeability and viscosity of the displacement phase and the displaced phase, which is used to represent the difference in the flow capacity between the oil displacement agent and the crude oil and is related to the wettability of the rock and the interfacial tension. The formula for mobility ratio (M) is  
\[\mathrm{M}=\frac{\lambda_{\mathrm{w}}}{\lambda_{\mathrm{o}}}=\frac{K_{\mathrm{ w}}}{\mu_{\mathrm{w}}}\Big{/}\frac{K_{\mathrm{o}}}{\mu_{\mathrm{w}}}\]  
In the formula: M--flow ratio;  
\(\lambda_{\mathrm{w}}\), \(\lambda_{\mathrm{o}}\)--water and oil mobility, D/(mPa\(\cdot\)s);  
\(K_{\mathrm{w}}\), \(K_{\mathrm{o}}\)--water- and oil-phase permeability, D;  
\(\mu_{\mathrm{o}}\), \(\mu_{\mathrm{w}}\)--viscosity of oil and water, mPa\(\cdot\)s.  
In the case of a high mobility ratio (M > 1), it is easy to cause the displacement phase to point to the inside of the crude oil [65]. There will be viscosity in the residual oil at the front end of the injected fluid, which often occurs in the process of enhanced oil recovery, such as water flooding and CO\({}_{2}\) flooding, which is not conducive to crude oil recovery.