Nano-silica/polymer composite as filtrate reducer in water-based drilling fluids

Wellbore instability and reservoir damage caused by filtrate of water-based drilling fluids (WDFs) invading the formation are extremely problematic issues in the process of oil excavation. Herein, we reported a novel polymer with core-shell structure based on modified silica nanoparticles as a filtrate reducer (NS-DA) in WDFs. Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (NMR) results revealed that the target product NS-DA had been gained. The results of thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of NS-DA occurred after 293 °C. Meanwhile, NS-DA exhibited the most outstanding filtration loss reduction ability compared to three commercially filtrate reducer (Driscal D. PAC-Lv and CMC) in the filtration loss test prescribed by the American Petroleum Institute. Specifically, the filtration loss of Driscal D/WDFs, PAC-Lv/WDFs and CMC/WDFs were 16.2 mL, 18.4 mL and 19.8 mL after hot rolling at 180 °C for 16 h, respectively, while the filtration loss of NS-DA/WDFs was only 5.6 mL. The mechanism of NS-DA in controlling filtration loss was investigated by Zeta potential measurements, particle size distribution analysis and mud cake analysis. The results showed that NS-DA molecular chains were firmly adsorbed on the surface of clay particles through hydrogen and ionic bonds, which reduced the zeta potential and the average particle size of clay particles, diminished the mud cake permeability, and thus enhanced the stability of the WDFs colloidal system. This work indicates that NS-DA has great potential for future oil excavation.