Preparation and action mechanism of temperature sensitive N-isopropylacrylamide/nanosilica hybrid as rheological modifier for water-based drilling fluid

A temperature-sensitive silica nanohybrid with a temperature response at 35 °C was prepared by copolymerization of temperature-sensitive monomer N-isopropylacrylamide (NIPAM) with reactive nanosilica (RNS-D).The rheological properties of the as-prepared NIPAM/nano-SiO2 nanohybrid as the rheological modifier of water-based drilling fluid were tested. Findings demonstrate that NIPAM/nano-SiO2 nanohybrid contributes to increasing the viscosity of the drilling fluid upon elevating temperature, and the drilling fluid fits to the Herschel-Bulkley model. The drilling fluid containing 1.0% (mass fraction) of NIPAM/nano-SiO2 nanohybrid exhibits significant thermally thickening performance at the critical association temperature (Tass) of NIPAM (Tass; 35 °C). In terms of the action mechanism of NIPAM/nano-SiO2 nanohybrid in drilling fluid, the amide group of NIPAM/nano-SiO2 nanohybrid can form hydrogen bond with bentonite, thereby being well adsorbed on the surface and edge of bentonite platelets or even entrapped into the interlay of the bentonite platelets. The resultant cross-linked structure can function to prevent the flocculation of bentonite platelets and increase the viscosity of the drilling fluid. After heating to Tass, the temperature-sensitive polymer molecular chains undergo hydrophilic to hydrophobic transformation and hydrophobic association to form cross-linked three-dimensional network structure and increase the viscosity of the drilling fluid. More importantly, the water-based drilling fluid with 1.0% NIPAM/nano-SiO2 nanohybrid still retains thermally thickening behavior and flat rheology even after being aged at 150 °C. Therefore, the temperature-sensitive NIPAM/nano-SiO2 nanohybrid could be a potential rheological modifier for flat rheology water-based drilling fluid.