Hyperbranched Polymer‐Grafted Nano‐Silica for Fluid Loss Control in Water‐Based Drilling Fluids: Performance and Mechanism

ABSTRACT With the increasing shift toward deep and complex formations, there is a critical need for drilling fluid additives that can withstand high‐temperature and high‐salinity conditions. Conventional fluid‐loss reducers often undergo molecular degradation under such harsh environments, severely compromising wellbore stability. To address this, a novel hyperbranched polymer nanocomposite, PAAK (Poly(APE‐AM‐AMPS‐(KH570‐SiO 2 ))), was synthesized via free‐radical copolymerization using pentaerythritol triallyl ether (APE) as a branching core, along with acrylamide (AM), 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), and KH570‐modified nano‐silica. The resulting material exhibits excellent thermal stability, with an initial decomposition temperature of 336°C. After aging at 200°C, the API fluid loss (FL API ) of a saturated brine drilling fluid containing 2.0 wt% PAAK was reduced to only 6.6 mL, demonstrating outstanding filtration control under extreme conditions. Mechanistic analysis reveals that PAAK operates through a dual mechanism—adsorption of polymer chains onto clay surfaces and physical plugging by nano‐silica—which synergistically promotes the formation of a dense, low‐permeability filter cake. This work provides a new strategy for designing high‐performance water‐based drilling fluid additives.