This case history outlines a recent coiled tubing (CT) drilling project in the Dutch Sector of the North Sea. Operations were conducted from a jackup drilling unit. The drilling unit conducted preliminary operations, commenced the sidetrack and recompleted the well. CT was used to drill the reservoir section of the new hole.
For CT, the objective was to exit through the 5-in. liner shoetrack and drill 230 ft of a 3 3/4-in. directional hole. The surface equipment had been designed to allow for the CT to be stripped out of the hole if substantial drilling fluid losses occurred. In this case, the well would be cleaned up and tested and the 3 3/4-in. section left barefoot. In the event that drilling fluid losses did not occur, then the section would be drilled overbalance with a low toxicity oil-based mud (LTOBM) and a 2 7/8-in. slotted liner deployed.
The 5-in. shoe track was cleaned out successfully with a mill and a positive displacement motor. The 3/4-in. hole section was drilled from 12,276 ft to the required total depth at 12,486 ft in 33.5 hours with one bottomhole assembly (BHA) and bit.
This case shows that with the proper planning, detailed design and execution, CT drilling can provide a cost effective alternative for drilling sidetracks.