Development and Test of Multifunctional Tool for Continuous Plugging and Drill-out

In recent years， despite significant advancements in drilling and completion technologies for deep and ultra-deep wells， lost circulation remains one of the most prevalent downhole complexities encountered during the development of deep and ultra-deep oil and gas reservoirs. In drilling operations， economic losses attributable to lost circulation account for approximately 25% to 40% of the total costs. This paper proposes a continuous plugging and drill-out operation method for cement slurry applications. This method can reduce the number of round trips required for cement slurry plugging and subsequent drill-out of cement plugs， thereby significantly shortening the operational cycle of cement slurry plugging operations. On this basis， a comparative analysis was conducted on the advantages and disadvantages of four technical principles， i.e. hydraulic drive， mechanical drive， mechanically controllable throttling + hydraulic drive， and hydraulically controllable throttling + hydraulic drive. The mechanically controllable throttling + hydraulic drive mode was selected as the optimal target in this study. According to the <italic>Hydraulic Calculation Manual</italic> and the <italic>Drilling Engineering Technical Manual</italic>， and through fluid simulation analysis， a theoretical formula for hydraulic thrust was established. Then， a multifunctional tool for continuous plugging and drill-out was developed by adopting the design of cutter block mis-expansion structure， 45° expansion angle cutter block， cement slurry accumulation and solidification control structure， three long centrally-connected blades， integrated bit structure， and large-diameter water hole. The results of laboratory experiments and field tests demonstrate that the theoretical formula for hydraulic thrust yields relatively accurate calculation， providing a theoretical support for the serialization of the multifunctional tool for continuous plugging and drill-out. Moreover， the multifunctional tool facilitated a successful job of cement slurry pumping and cement plug drill-out in a single trip at Well ZS-X， with the wellbore diameter achieved after drilling out the cement plug meeting the design specification. Thus， it enables a continuous plugging and drill-out process without tripping out， which features one trip less than conventional jobs. Its application is expected to significantly shorten the operational cycle of cement slurry plugging.