Chunhua Block of Shengli Oilfield is one block where shale caving formation, borehole instability, well click, trip sticking, drill pipe blocking and sticking during completion logging and other downhole complex issues were encountered during the drilling process. The paper was based on slow down pressure transmission, filtrate invasion and strong inhibition of cooperation anti-sloughing basic principle. Through optimization and compatibility of the major additives, a new-type drilling fluid is characterized by good rheological properties, filtration loss, lubricity, stability and strong inhibition. The new drilling fluid has been applied in 5 wells for block test. The result showed that all wells gained a satisfactory anti-sloughing effect. The enlargement ratio of well bore diameter was reduced efficiently. The drilling time was saved. And the ratio of successful logging by one time was 100%.
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