Preparation and Evaluation of Biopolysaccharide-Based Temperature-Resistant Drilling Fluid Additives

Xanthan gum (XG), valued for its environmental friendliness and multifunctionality, has been extensively utilized in drilling fluids. However, its inadequate thermal stability at elevated bottomhole temperatures encountered in deep drilling operations has constrained its broader application. In this study, we successfully synthesized a graft copolymer (XG-g-Nano SiO₂-AMPS) through grafting XG with KH570-modified nano-SiO₂ and thermally stable monomer AMPS. The modified product exhibited significantly reduced molecular weights, with number-average (M _n) and weight-average (M _w) molecular weights of 3.17 × 10⁵ g/mol and 3.88 × 10⁵ g/mol, respectively. Thermal analysis revealed a 31% mass loss at high temperature, representing an 14% reduction compared to native XG, while biotoxicity assessment showed an EC₅₀ value exceeding 10⁶ mg/L, indicating low toxicity. Performance evaluation demonstrated excellent viscosity-enhancing properties and superior filtration control, with API filtrate volumes (FL_API) of 3.0 mL (freshwater) and 3.4 mL (saturated brine), along with high-temperature/high-pressure filtrate volumes (FL_HTHP) of 12 and 15 mL, respectively, after 16 h of thermal aging at 150 °C. This breakthrough substantially improves XG's thermal resilience, extending its applicability in deep high-temperature wells.