The concept of a tapered outside diameter coiled tubing system (TODCTS) was first presented in 2004.1 This paper laid out the basic requirements for a TODCT system and the advantages of the TODCTS in ultra-deep wells (30,000-ft range). The TODCT system includes:
A modified injector that can handle more than one diameter of tubing and maintain a constant grip on the tubing throughout the length of the TODCT string.
A "transition tube" that allows sections of tubing with different ODs to be joined together.
Well-pressure control equipment (i.e., blowout preventer and stripper) that has the capability to grip and seal more than one diameter of tubing and can also grip and seal the transition tube.
An operator control house that allows remote control of the stripper elements and injector gripper elements to open or close to different diameters of tubing while still maintaining control of well pressures inside the wellbore and grip on the tubing.
This paper continues the work that was started previously. A review of the yard testing completed on the equipment is included along with a subsequent field trial done onshore in south Texas. The end result is a tested and qualified TODCT system capable of safely running tubing strings into ultra-deep wells.