Synthesis and Performance Evaluation of a Cellulose Nanofiber‐Reinforced Filtrate Reducer for Water‐Based Drilling Fluids

To improve the filtration‐control performance and stability of cellulose ether‐based additives under high‐temperature and high‐salinity conditions, a cellulose‐based composite filtrate reducer (HASF) was developed for water‐based drilling fluids. HASF was synthesized by free‐radical graft polymerization of hydroxypropyl methylcellulose (HPMC) with acrylamide, 4‐acryloylmorpholine, and sodium p ‐styrene sulfonate, followed by incorporation of carboxylated cellulose nanofibers (CNF). Synthesis parameters were screened by an L16(4 5 ) orthogonal experimental design with the high‐temperature high‐pressure (HTHP) filtration loss as the response. FT‐IR and 1 H NMR results were consistent with the expected functional groups, and thermogravimetric analysis showed the main mass‐loss process above approximately 200°C. After aging at 160°C for 16 h, the HASF‐containing mud (1 wt% HASF) exhibited an API filtration loss of 8.1 mL versus 92 mL for the base mud, a reduction of approximately 91%, and an HTHP filtration loss of 22 mL. Within the tested ranges (up to 15 wt% NaCl, 1.5 wt% CaCl 2 , or 3 wt% KCl), FL API remained at or below 11 mL. Sand‐disk plugging tests showed reduced filtrate volumes, and SEM revealed a more compact filter cake, indicating the potential of HASF within the temperature, salinity, and formulation ranges investigated.