# Effect of Amphiphilic Polymer/Nano-Silica Composite on Shale Stability for Water-Based Muds
## 3 Results and Discussion  
### Characterization of the SMA/SiO\({}_{2}\)  
Figure 4 depicts FT-IR spectra of SiO\({}_{2}\), KH570/SiO\({}_{2}\) and SMA/SiO\({}_{2}\), and the characteristic peaks were observed. As shown in Figure 4a, the stretching band of O-H (3419 cm\({}^{-1}\)) in SiO\({}_{2}\) was significantly weakened after the surface modification of SiO\({}_{2}\). The new peaks at 2928 cm\({}^{-1}\) and 2844 cm\({}^{-1}\) were for the stretching vibrations of the methyl and methylene from KH570. Thus, KH570 was successfully grafted onto SiO\({}_{2}\). Figure 4b shows the FT-IR spectrum of SMA/SiO\({}_{2}\). The peaks at 3061 cm\({}^{-1}\) and 3026 cm\({}^{-1}\) were for the C-H in the benzene ring from St. The peaks at 1603 cm\({}^{-1}\), 1495 cm\({}^{-1}\) and 1452 cm\({}^{-1}\) were for the vibrations of the benzene skeleton from St. The peak at 1730 cm\({}^{-1}\) was for the stretching vibrations of C=O, while 1200 cm\({}^{-1}\) represented the stretching vibrations of C-O-C from MMA. The peak at 3429 cm\({}^{-1}\) represented the stretching vibrations of N-H from AM. In addition, the stretching vibrations of Si-O and Si-O-Si were located at 1117 cm\({}^{-1}\) and 1076 cm\({}^{-1}\) respectively. Therefore, the FT-IR spectra show that SMA/SiO\({}_{2}\) was successfully prepared.  
Figure 4: FT-IR spectra of (a) SiO\({}_{2}\), KH570/SiO\({}_{2}\) and (b) SMA/SiO\({}_{2}\).  
In order to further characterize the chemical structure of SMA/SiO\({}_{2}\), the \({}^{1}\)H-NMR spectra of SMA/SiO\({}_{2}\) is presented in Figure 5. The peaks corresponding to the protons in the copolymer were labeled. It can be concluded that St, MMA and AM were grafted onto KH570/SiO\({}_{2}\). Thus, the chemical structure of SMA/SiO\({}_{2}\) was further confirmed.  
The dispersion morphology of SMA/SiO\({}_{2}\) in aqueous solution was observed, and the TEM image is shown in Figure 6. The spherical nanoparticles exhibited good dispersivity in the aqueous solution. In addition, the average particle size of SMA/SiO\({}_{2}\) was about 75 nm, and the particle size distribution was mainly in the range of 50-90 nm.  
Figure 7 presents the PSD curves of SMA/SiO\({}_{2}\). The test results showed that the average particle size of SMA/SiO\({}_{2}\) was 72 nm, while the particle size was mainly distributed in the range of 43-122 nm. Due to a few nanoparticles in SMA/SiO\({}_{2}\) agglomerated, the larger particles were found in the PSD test results. Overall, the PSD test results corresponded with the TEM characterization results. The nanoscale diameter of SMA/SiO\({}_{2}\) was further confirmed. It could be inferred that SMA/SiO\({}_{2}\) was able to plug the shale pores and cracks in nano-scale.  
Figure 5: \({}^{1}\)H-NMR spectra of SMA/SiO\({}_{2}\).  
Figure 6: TEM image of SMA/SiO\({}_{2}\).  
Figure 8 shows the thermogravimetric curves of SMA/SiO\({}_{2}\). The weight loss was less than 0.3% for SMA/SiO\({}_{2}\) below the temperature of 120 \({}^{\circ}\)C due to the solvent evaporation. No significant weight loss was observed before the temperature reached 390 \({}^{\circ}\)C. Thermal stability is essential for plugging agents since WBMs withstand high-temperature stratum conditions. Through the results of TGA analysis, good high-temperature resistance of SMA/SiO\({}_{2}\) was confirmed.