Abstract: Under high temperature conditions,the degradation of polyacrylamide filtrate reducer molecules leads to a significant decrease in filtrate reduction efficiency.To address this issue,a high temperature resistant hyperbranched polymer filtrate reducer(JHPAS)was synthesized through copolymerization of hyperbranched monomer allyl pentaerythritol(APE)with 2-acrylamido-2-methylpropane sulfonic acid(AMPS),acrylamide(AM),and sodium styrene sulfonate(SSS).A novel clay-free water-based drilling fluid was formulated using JHPAS,and its filtrate reduction mechanism was analyzed.The rheological properties and filtrate performance under high temperature and high salt conditions were evaluated.The results demonstrate that JHPAS exhibits excellent thermal stability and has the ability to create a network structure in an aqueous solution. It adsorbs onto the surface of superfine CaCO₃,forming a compact filter cake in clay-free water-based drilling fluid,effectively plugging the pores on the filter cake and consequently reducing the filtrate loss of drilling fluid.The developed clay-free water-based drilling fluid maintains consistent rheological properties and demonstrates effective filtrate loss reduction even after exposure to 200 ℃ aging for 16 hours and saturated sodium chloride brine.The API filtrate loss and high-temperature,high-pressure filtrate loss are measured at 5.5 mL and 7.6 mL,respectively.These research findings contribute to advancing the exploration and utilization of hyperbranched polymers in drilling fluids for in deep and ultra-deep reservoirs.

Key words: water-based drilling fluid, filtrate reducer, hyperbranched polymers, high temperature reservoir, high salt, deep reservoir, ultra-deep reservoir