Abstract: Polymer-sulfonate oil-mixed drilling fluid was used in ultra-deep directional wells in Tahe Oilfield.Although this drilling fluid can meet the requirement of ultra-deep directional drilling,it is unable to satisfy the requirements of environment and reservoir protection.Therefore,on the basis of cationic emulsion polymer drilling fluid,KCl-cationic emulsion polymer-sulfonate drilling fluid was selected by introducing sulfonated material to improve the temperature resistance,adding KCl to improve its inhibitory properties.Laboratory performance evaluation showed that KCl-cationic emulsion polymer-sulfonate drilling fluid was similar with polymer-sulfonate oil-mixed drilling fluid in high temperature lubricity,inhibition and stability.Practical application showed KCl-cationic emulsion polymer-sulfonate drilling fluid could satisfy the requirements of cutting carrying,anti-sloughing,lubrication,and environmental protection of ultra-deep directional wells in Tahe Oilfield,replaced polymer-sulfonate oil-mixed drilling fluid,and was suitable for ultra-deep directional wells in similar geological conditions with Tahe Oilfield.