Abstract: A hydrophobically associating polymer, JD, has been synthesized with long chain alkyl dimethyl allyl ammonium chloride, acrylamide, N-vinyl pyrrolidone and acrylic acid in a certain ratio of initiators and a certain polymerization condition. JD was developed to deal with the difficulties in plugging highly heterogeneous permeable formations with conventional lost circulation materials (LCMs). IR characterization showed that JD was a copolymer of the four monomers. Analyses of a 0.3% JD solution, a 0.6% JD solution and a 4% bentonite slurry containing 0.3% JD with transmission electron microscope (TEM) demonstrated that a micelle-like hydrophobically associating structure, with sizes between 0.1-0.2 μm, was formed among the polymer molecules. Meanwhile, a dynamic network was formed between the molecules of JD and bentonite particles, a reason for JD to have superior plugging performance. Using FEI's Quanta200F (a field emission environmental scanning electron microscope) to examine the mud cake formed by a JD treated drilling fluid, it was found that a network structure was generated on the surface of the mud cake by the polymer molecules. In static plugging experiment with a drilling fluid treated with 0.3% JD, it was found that mud losses through a 0.45 mm-0.90 mm sand bed was reduced by 82%, and sand beds of 0.22 mm-0.45 mm and 0.12 mm-0.22 mm were completely plugged, with almost no mud loss. This meant that JD can be used to plug heterogeneous permeable formations to prevent mud losses of different rates. In laboratory experiments, JD showed good compatibility with SMP-II, SPNH and poly glycols. When mixed with Redu1, NH₄-HPAN and emulsified asphaltene, the viscosity and the gel strengths of the mixtures were increased to some extent, making JD more suitable for use in drilling fluids with moderate viscosity and gel strengths.