Nano-SiO2 Grafted with Temperature-Sensitive Polymer as Plugging Agent for Water-Based Drilling Fluids

Combining smart polymers and nano-silica is an effective method to prevent free water intrusion into micro-nanopores of shale, maintaining the wellbore stability in the drilling process. A core-shell structure nano-plugging agent (NPA) for water-based drilling fluid was synthesized through modifying nano-SiO2 by using N-isopropylacrylamide, 2-acrylamide-2-methylpropane-sulfonic acid and KH-570. The structure and properties of NPA were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, particle size distribution, and transmission electron microscopy methods. Results show that NPA presents a good thermal stability with the decomposition temperature of 370 degrees C. The median particle size of NPA is 193 nm. The results of the pressure transfer experiments indicate that NPA presents a good sealing performance. The permeability of the cores after NPA sealing was significantly reduced to 0.031 x 10(-7) mu m(2). After reaching the response temperature, the wetting angle of the shale surface treated by NPA is 77.22 degrees. After aging at 150 degrees C for 16 h, the FLHTHP of the water-based drilling fluid system was controlled within 5 mL. NPA can enhance wellbore stability and effectively reduce the leakage of the drilling fluid during drilling process.