Zwitterionic-hydrophobic associating polymer for enhanced rheology and fluid-loss control in high-temperature, high-salinity water-based drilling fluids

In deep oil and gas drilling, high-temperature and high-salinity conditions have posed severe challenges to water-based drilling fluids. These harsh environments can impair the performance of drilling fluids, increase fluid loss, and lead to frequent downhole accidents. In view of the above problems, this study combines the advantages of zwitterionic and hydrophobic association to prepare a zwitterionic hydrophobic association polymer (P-DADL) with high temperature and salt resistance. The chemical structure and properties were characterized and evaluated by in-situ infrared spectroscopy, nuclear magnetic resonance, thermogravimetry, SEM and other experimental methods. The results show that the thermal decomposition temperature of P-DADL is greater than 297 ℃, and it has a spatial network structure in aqueous solution, which exhibits strong clay-particle adsorption and suspension stability. After aging at 180 ℃ for 16 h, the apparent viscosity of the drilling fluid containing 2 wt% P-DADL is 62 mPa·s, the viscosity retention rate is 70.86%, and the FL_API is only 7.4 mL. Under the conditions of 180 ℃ and 35 wt% NaCl, the FL_API was further reduced to 6.4 mL, reflecting the salt synergistic filtration reduction characteristics. In addition, the suspension stability of saturated brine drilling fluid is greater than 98% within 48 h. P-DADL can effectively enhance the temperature resistance and salt resistance of water-based drilling fluid. Compared with commercial products, P-DADL exhibited a 78.4% improvement in filtration performance relative to commercial products. These findings highlight the potential of P-DADL as a multifunctional additive for high-salinity, high-temperature drilling operations.