Synergistic effects of covalent crosslinking and hydrophobic association on enhancing thermal and salt resistance of polymeric filtrate reducer

Traditional linear polymeric filtrate reducers for water-based drilling fluids (WBDFs) are insufficient for drilling engineering requirements, even with adjustments in the type and proportion of functional groups in the copolymer, especially under high-temperature and high-salinity conditions. In this study, a dual cross-linked copolymer (named AAS-L 4% -M 0.5‰ ) was synthesized through free radical copolymerization using lauryl methacrylate (LMA) as hydrophobic associated segments and N, N ’-methylene bisacrylamide (MBA) as the chemical crosslinker. The synergistic effect of covalent micro-crosslinking and hydrophobic association in AAS-L 4% -M 0.5‰ were systematically investigated and demonstrated. After aging at 220 °C for 16 h, the WBDFs containing 1 % AAS-L 4% -M 0.5‰ exhibited high-temperature/high-pressure filtration loss (FL HTHP ) and American Petroleum Institute filtration loss (FL API ) of 34 mL and 10 mL, respectively, representing reductions of 50 % and 38 % compared to the linear polymer AAS-L 0 -M 0 . Even after aging at 200 °C in saturated salt solution conditions, the WBDFs containing AAS-L 4% -M 0.5‰ maintain excellent filtration properties with FL API value of 7.5 mL, achieving an 83 % reduction compared to AAS-L 0 -M 0 . Moreover, because of the three-dimensional spatial network structure formed by dual cross-linking, AAS-L 4% -M 0.5‰ effectively inhibits unwanted foaming caused by the polyelectrolyte effect. Therefore, this work provides a simple but effective approach to develop temperature-resistant and salt-tolerant filtrate reducers with excellent workability.