The use of coiled tubing (CT) drilling technology is rapidly expanding and its important to note that the technology is still in the process of testing its boundaries and limitations. However, this is a necessary phase in the learning curve. Probably the most logical approach is to consider the market or application niches best suited to coiled tubing drilling technology.
Six horizontal sidetrack wells were drilled in North Oman using CT. The objective of these trials was to evaluate the technical and economical feasibility of this drilling technique. For all the six wells, the existing completion was removed from just above the upper packer and the remaining completion abandoned, then a window was milled in the 7 inch casing, allowing the well to be sidetracked using a whipstock, and built up through the formation of interest.
This paper discusses the three main problems faced during drilling these wells, and the suggestions for improvement. The problems discussed involves the following: difficulties in setting the whipstock, problems in cleaning the hole, and difficulties in handling the tubing. Whipstock types are discussed, and the one best suited for this type of application is recommended. A proposed schematic of a rig is shown to minimize the problem of handling the tubing for this type of application.