Abstract: The mudstone formation of Anding, Zhiluo, Shiqianfeng, and Shihezi in Sulige gas field are subject to severe wellbore collapse when drilling horizontal wells. And due to the great horizontal deviation, long horizontal section, and small borehole, it is subject to the trouble of wellbore cleaning and lubrication. The reason affecting wellbore stability was obtained by studying the geological structure, formation properties and well structure characteristics of horizontal wells in Sulige gas field, focusing on the analysis of the whole-rock and clay mineral taken from Shihezi mudstone formation. Meanwhile, the difficulties of drilling fluid technology for horizontal wells in Sulige area were analyzed systematically. According to the geological characteristics, wellbore structure and reservoir protection requirements, the drilling technical measure of using different drilling fluid systems in different formations was put forward, and the drilling fluid treatment methods and drilling operation techniques were illustrated. The safe drilling operations for the 4 high difficult horizontal wells prove that the drilling fluid techniques for extended reach horizontal wells in Sulige gas field can meet the needs of drilling large displacement horizontal wells, and provide drilling operation experience for efficiently developing Sulige gas field.