Research and Application of Drilling, Milling-Grinding Techniques for Drilling out Composite Bridge Plugs in Coiled Tubing in Horizontal Wells

Due to the selection of improper parameters, the operational efficiency is low in the application of tubing drilling and grinding technology to drill and mill the bridge plug. Through the analysis of the characteristics of coiled tubing drilling and milling/grinding process, the working performance of drilling tools and the carrying regularity of cuttings at different sections of wellbore hole drilling, combined with the mode of drilling bridge plug:"cleaning cuttings by pulling up making circulationling at a fixed point", the operations were improved, technology was optimized, the working parameters were optimized, and a technical scheme of drilling and milling the bridge plug in the working mode of the horizontal wells was implemented. The PDC mill shoe bit with 5 blades and PDM screw drilling tools featured as medium torques and rotation speeds have been selected. It is recommended that the flow rate displacement should be maintained no lower than 420 L/min, and the weight on bit should be controlled within 14.7-19.6 kN. These technology processes have been carried out in several wells in the field. The average drilling time of a single bridge plug is shortened by 46.5 min compared with the performances before optimization and adjustment, and the consumption of drilling fluid is reduced by 49.4%. Twelve composite bridge plugs can be removed by running drilling strings once. The application results showed that the techniques of coiled tubing drilling and milling and grinding can quickly restore wellbore flow after fracturing and increase drilling efficiency. Consequently, it is worth promoting and applying widely.