Research on the Mechanism of Wellbore Destabilization and Technical Countermeasures of Drilling Fluid in Horizontal Wells of Shale Formation of Ordos Basin

In the drilling process of Ordos Basin, there are sandy mudstone strata and coal interlayer, and there are risks of well wall destabilization and blocking during drilling operation; and some of the strata have problems of expansion and reduction. The shale is characterized by high mud content and strong stratification, which is prone to swelling and falling block destabilization after encountering water. Since the target block needs to complete the drilling of 1000~1200 m horizontal section in the shale formation during the industrialization stage, it needs to systematically evaluate, study and prove the applicable technology to meet the requirements of well wall stabilization, so the research on the mechanism of shale horizontal well wall destabilization and technical countermeasures of drilling fluid applicable to the target block was carried out. Through the physicochemical property analysis and performance testing of mud shale and coal rock samples, this paper comprehensively analyzes the well wall destabilization mechanism of mud shale formation, proposes a “multi-faceted synergistic” well wall stabilization technical countermeasure, and optimizes a set of compound salt drilling fluid formulation applicable to the target formation, which provides technical support for safe and efficient drilling of horizontal wells in shale formation in the target block.