Behavior of Cross‐Linked Polyacrylic Acid Microspheres in Drilling Fluids

ABSTRACT To develop a temperature‐resistant and salt‐resistant drilling fluid filtrate reducer that meets diverse application requirements and to enrich the understanding of the structure–property relationships of cross‐linked polymer microspheres, a cross‐linked polyacrylic acid microsphere (CPAA) drilling fluid loss agent was prepared by water dispersion polymerization using acrylic acid as the monomer. The structural characteristics of CPAA were investigated, and its behavior in drilling fluids was evaluated. The findings reveal that CPAA, a cross‐linked polyacrylic acid microsphere with abundant carboxyl hydration groups and a simple composition, has an average particle size of approximately 700 nm and an initial thermal decomposition temperature of 266°C. CPAA exhibits excellent filtration loss reduction and viscosity‐increasing effects in drilling fluids, showing superior temperature and salt resistance. When 0.8 wt% CPAA was added to a 4 wt% bentonite drilling fluid, the apparent viscosity increased to 116 mPa·s, and the fluid loss decreased to 5 mL. After aging at 180°C for 16 h, the fluid loss remained at 8 mL, and it was maintained at 14 mL after adding 20 wt% NaCl. Finally, the temperature and salt resistance of CPAA were compared with those of different polymer microspheres, and the possible mechanisms were discussed.