▎ 摘　　要

NOVELTY - A fluid loss additive used for drilling fluid, comprises modified natural high molecular polymer and nanoparticle at weight ratio of 1-10:10-20. USE - The fluid loss additive is used for drilling fluid and oil extraction field (all claimed), preferably for drilling construction in high temperature and high pressure formations in environmentally sensitive areas. ADVANTAGE - The method has simple technique, low cost, high yield and mild and controllable condition. The product has high temperature resistance, salt resistance to saturation, good anti-shearing stability, low high temperature, high pressure loss, good high temperature stability and high environmental protection. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for preparing fluid loss additive comprising preparing modified natural high molecular polymer and grafting and copolymerizing with nanoparticles.