Development of Coiled Tubing Downhole Electric Motor Drilling System

Coiled tubing sidetracking technology is globally recognized as a cornerstone engineering approach for efficient hydrocarbon recovery in mature well stock revitalization projects. However, conventional hydraulically-driven power drilling tools exhibit critical limitations including low rock-breaking efficiency and limited lateral reach in horizontal sections, which severely restrict the application scope of coiled tubing sidetracking technology in brownfield redevelopment. To address these challenges, aligning with the industrial trend toward downhole tool electrification and intelligentization, we innovatively propose a full electric direct-drive coiled tubing downhole motor drilling system. This breakthrough includes: Development of an electric downhole motor drilling system specifically engineered for 7″ casing window-cutting operations；Implementation of high-torque-density permanent magnet synchronous direct-drive downhole electric drilling tools with advanced control system; Breakthroughs in long-distance downhole power transmission & communication technologies; Integration of downhole measurement-while-drilling (MWD) and well trajectory control systems. These technological advancements have been rigorously validated through laboratory drilling condition simulation tests, establishing critical technical foundations for full electrification and intelligent transformation of coiled tubing sidetracking downhole tools. The first generation of coiled tubing drilling technology featured fully hydraulically-driven cable-less systems. Its typical bottom-hole assembly (BHA) configuration was: “Coiled Tubing + Connector + Safety Release + Hydraulic Orienter + Mud Pulse MWD (Measurement While Drilling) Tool + Mud Motor + Bit.“ This system was widely used in shallow surface drilling and well-deepening operations. The second generation introduced cabled coiled tubing drilling technology, with a BHA configuration of: “Coiled Tubing (with internal cable) + Connector + Safety Release + Wired MWD Tool + Electrically/Hydraulically Controlled Orienter + Mud Motor + Electrically Steered Tool + Bit.” This technology has been extensively applied in through-tubing (casing) sidetracking of horizontal wells, achieving maximum horizontal section lengths exceeding 1,200 m [1–4]. Currently, China has commercialized cable-less coiled tubing drilling technology, while the development of cabled coiled tubing drilling systems remains in its early stages. Although cabled technology significantly expands the operational scope of CT drilling, the inherent limitations of traditional hydraulically-driven downhole tools—such as low hydraulic efficiency and insufficient power output in small-diameter CT systems—restrict drilling efficiency. Globally, research efforts are actively exploring cabled coiled tubing drilling systems with downhole electric motors based on 3–1/2″ coiled tubing. In recent years, CNPC Engineering Technology Research Institute has integrated its advanced downhole electric motor drilling system with CT technology, developing a 3–1/2″ coiled tubing electric motor drilling system for window sidetracking in 7″ casing. Key technologies have undergone successful laboratory verification.