In the process of going through multi-layers in drilling of Bohail Oilfield Group, it was difficult to solve the problems of wellbore collapse and falling off and wellbore instability in Dongying and Shahejie Formations. By continuously using active and soft mud shale borehole stability mechanism, an easy control treatment agent was chosen to improve the inhibitory, adhere to the concept of soft restrain in the upper strata and strong inhibition in the lower formation, a kind of polyamine

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... tor PF-HAS was used instead of PF-JMH-YJ, PF-HAS was moderately used for inhibition to the soft mudstone, and compatible with KCl, by which the problems of hard control of rheology in traditional PEC system and drilling pipe stuck in tripping were solved and complications in drilling were reduced. Because of its good compatibility with the PEM system, the PEC system can be compatible with PEM system, at the same time, a layer of intermediate casing for drilling in Ninghuazhen Formation, Guantao Formation, Dongying and Shahejie Formations is saved, it greatly improves the operation efficiency, and it provides an important guidance for the drilling operations in the other oil fields in Bohai Area.