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 (gamma-propyl trimethoxysilane). The modified KH-560 was reacted with nano-SiO2 to synthesize the modified nano-SiO2 as 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-SiO2 is 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 degrees to 136.36 degrees, 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-SiO2 has 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-SiO2 is 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.