Thermosensitive polymer/nanosilica hybrid as a multifunctional additive in water-based drilling fluid: Rheologicalproperties and lubrication performance as well as filtration loss reduction capacity

Abstract

In previous studies, for obtaining a flat rheological drilling fluid, binary and ternary thermosensitive silica (SiO₂) nanohybrids as rheological modifiers were synthesized using N-isopropylacrylamide with a thermal association temperatureof 32–33 °C as the thermosensitive monomer [J. Petrol. Sci. Eng. 219 (2022), 111096; Geoenergy Science and Engineering 228 (2023), 211934]. However, the as-synthesized SiO₂ nanohybrids exhibited limited performance and low thermal transition temperature. Thus surface initiated atom transfer radical polymerization was utilized to graft hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) onto SiO₂ surface to obtain PEGMA/SiO₂ nanohybrids with an elevated thermal association temperature of 75 °C. The morphology and structure of the as-synthesized PEGMA/SiO₂nanohybrid were characterized by infrared spectroscopy and transmission electron microscopy; and its effects as a thermosensitive multifunctional additive on the rheological properties and lubrication performance as well as filtration loss reduction capacity of a water-based drilling fluid were investigated. Results indicate that the drilling fluids with 1.0% PEGMA/SiO₂ nanohybrids exhibited obvious thermal thickening behavior in the temperature range of 70–80 °C; at low temperatures, however, they had a significant viscosity reduction effect therein. At room temperature, the apparent viscosity and plastic viscosity were reduced by 68% and 50%, respectively. Besides, due to the tightly packed plugging layer formed by PEGMA/SiO₂ nanohybrids and bentonite, the filtration loss of the drilling fluids containing 1.0% PEGMA/SiO₂ nanohybrid was reduced by 37% as compared with that of the base slurry; and the lubrication coefficient was decreased by up to 50%. Moreover, the high-temperature aging process promoted the intermolecular interactions of the nanohybrids and their interaction with bentonite flakes, thereby further improving the rheological behavior, filtration reduction ability, and lubricity of the drilling fluids. The as-synthesized thermosensitive PEGMA/SiO₂ nanohybrids with excellent multifunctionality could find promising application in water-based drilling fluids.