Abstract: Biyang depression of Henan oilfield is one of the important areas of exploration and development for unconventional resources.The mudstone section of BiYe HF1 well in the area has the problems of bit balling,frequent collapse in shale section and etc.Therefore,polyamine potassium drilling fluid system has been adopted for the two-open deflecting section in BiYe HF2 well.Through the asphalt,paraffin and effective sealing without penetrating agent and proper drilling fluid density to form strong support for borehole well and this solves the problems of bit balling and shale collapse caused by dispersed formation.The white oil-base drilling fluid system has been adopted in three-open section,which effectively guarantees the construction safety of pure shale and the long horizontal section of horizontal well.There is no bit balling and safety accident for the whole well and borehole wall is stable and running smoothly.