Development of Hydrophobic-Modified Nanosilica for Pressure Reduction and Injection Increase in an Ultra-Low-Permeability Reservoir

A low-permeability reservoir contains many fine pore throat structures, which result in excessive injection pressure of the water injection well and difficult water injection in the production process of a low-permeability reservoir. In this study, a new silane coupling agent was synthesized via the ring-opening reaction between dodecyl amine and KH-560 (γ-propyl trimethoxysilane). The modified KH-560 was reacted with nano-SiO2to synthesize the modified nano-SiO2as an antihypertensive additive. Fourier infrared spectroscopy, thermogravimetric analysis and laser scattering were used to characterize this modified nano-SiO2. The results show that the particle size of the modified nano-SiO2is less than 60 nm. The test results of the water contact angle show that the dispersion system can increase the rock contact angle from 37.34° to 136.36°, which makes the rock surface transform from hydrophilicity to hydrophobicity and reduce the binding effect of rock with water. The dispersion test shows that the modified nano-SiO2has good dispersion stability under alkaline conditions with TX-100 (Polyethylene glycol octylphenyl ether) as the dispersant. The antiswelling test results show that the antiswelling rate of this modified nano-SiO2is 42.9%, which can efficiently prevent the clay expansion in the formation to reduce the injection pressure. The core displacement test results show that its depressurization rate reaches 49%. The depressurization rate still maintains 46% at a 20 PV water flow rate, indicating that its depressurization effect is remarkable and it has excellent erosion resistance.Keywords:nano-SiO2;hydrophobicity;ultra-low-permeability reservoir;pressure reduction