Abstract: Based on the molecular design of high temperature treatment agent，with the humic acid and acryloyloxyethylbutyl acid(AOBS),acrylamide (AM),acrylic(AA) graft copolymerization,by orthogonal experiments,in consideration of the solution viscosity of the product,the impact of the product on drilling fluid viscosity and fluid loss results,further studies of the humic acid dosage is made and the synthesis formula is determined:non ionic monomer and ionic monomer ratio is 1.5:1.0,the ionic monomers neutralization degree is 100%,the reaction mixture mass fraction is 50%,humic acid dosage is 34%.The low molecular weight AOBS AM AA / humic acid graft copolymer is synthesized,and by the using of infrared spectroscopy and thermal analysis,the structural and thermal stability of products is analyzed.Experimental results show that the graft copolymer has good thermal stability,resistant temperature reaching 240℃.It has a good fluid loss control effect both in fresh water,salt water and saturated salt water drilling fluid.Besides,it has little effect on drilling fluid viscosity.Graft copolymer has a certain viscosity reduction effect in drilling fluid which has a high content of bentonite,so it can control the high temperature thickening of drilling fluid effectively.It has good compatibility with the SMC,SMP.It can effectively control the high temperature and high pressure filtration loss volume and rheological property of drilling fluid when used in KCl drilling fluid which has a density of 2.57g/cm³.

Key words: drilling fluid, drilling fluid additive, ultrahigh temperature, fluid loss additive, graft copolymer, humic acid