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

•A covalent micro-crosslinking and hydrophobic association dual cross-linked copolymer AAS-L4%-M0.5‰ was synthesized as filtration reducer in drilling fluid.•The synergistic effects of covalent crosslinking and hydrophobic association on enhancing the performance of polymeric filtrate reducers was explored.•The polymeric filtrate reducer maintains excellent filtration properties under conditions of 200 °C and 36 wt% NaCl.•The dual-crosslinked copolymer filtrate reducers could minimize the unwanted foaming. 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-L4%-M0.5‰) 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-L4%-M0.5‰ were systematically investigated and demonstrated. After aging at 220 °C for 16 h, the WBDFs containing 1 % AAS-L4%-M0.5‰ exhibited high-temperature/high-pressure filtration loss (FLHTHP) and American Petroleum Institute filtration loss (FLAPI) of 34 mL and 10 mL, respectively, representing reductions of 50 % and 38 % compared to the linear polymer AAS-L0-M0. Even after aging at 200 °C in saturated salt solution conditions, the WBDFs containing AAS-L4%-M0.5‰ maintain excellent filtration properties with FLAPI value of 7.5 mL, achieving an 83 % reduction compared to AAS-L0-M0. Moreover, because of the three-dimensional spatial network structure formed by dual cross-linking, AAS-L4%-M0.5‰ 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.