Coiled tubing drilling uses a continuous length of steel or composite pipe wound on a large reel, eliminating traditional pipe connections during tripping operations. CT typically ranges from 1 to 3.5 inches in diameter and can extend to depths exceeding 15,000 feet, enabling rapid deployment and retrieval compared to conventional jointed drill pipe.
Operational Advantages
The primary advantage is elimination of pipe connections, dramatically reducing tripping time and associated NPT. The CT injector continuously feeds pipe into the wellbore while maintaining well control, enabling drilling and circulation without stopping for connections. This proves especially valuable for underbalanced drilling, well interventions, and re-entry operations.
Depth and Performance Records
Extended reach operations have demonstrated CT capabilities:
- Sakhalin-1 project (SPE-92783, 2005): Record CT runs supporting completions at 11,680m MD
- Modern systems achieve depths of 25,000+ feet with appropriate pipe specifications
Limitations
CT drilling is constrained by fatigue cycles (pipe life decreases with repeated bending over the reel), tensile limits in deep wells, and inability to rotate the string (requiring downhole motors for all rotation). Weight-on-bit delivery becomes challenging in extended reach sections due to pipe flexibility and friction.
Automation Synergy
Downhole force control systems address CT's inherent WOB limitations by generating thrust locally, enabling effective drilling in wellbore geometries where CT flexibility would otherwise prevent adequate bit loading.