Composite bridge plug drilling and milling technology by tubing in horizontal well and its application

In view of high cost and easy pipe sticking when drilling and milling composite bridge plug using coiled tubing and in conjunction with the characteristics of low formation pressure of Changqing tight reservoirs, this paper presents a technique of drilling and milling composite bridge plug with tubing-conveyed tool in horizontal wells. A flat milling shoe was improved; long-life screw with stable performance was optimized while considering both RPM and torque; a drilling and milling tool assembly with localization was made by the principle of realizing functions and simplicity. The miminum construction displacement was designed as per annular slip velocity model. The maximum drilling pump pressure was obtained by calculating eccentric annular pressure loss. In order to accurately calculate bit pressure in horizontal wells, the technique of adding bit pressure was proposed as per the maximum allowable bit pressure of screw to control suspension weight while controlling the pump pressure drop. This technology was field tested in 8 wells in Changqing oilfield, and a maximum of 13 composite bridge plugs were drilled out in one run; the milling time for single bridge plug was less than 120 min and the fastest time for drilling and milling one plug was 40 min, so its performace-price ratio is no less than that of coiled tubing.