Traditional coiled tubing drilling (CTD) operations employ bent mud motors to create bit rotation that enable diverging wellpaths. As coil rotation is not applicable, an additional downhole orientation device is required for directional control of the motor. For more than a decade, this setup has enabled reliable and successful CTD operations worldwide. It also has been, over time, driven to its limits. Several apparent drawbacks with this platform include unfavorable drag that limits the maximum horizontal reach, suboptimal wellbore quality causing challenges in subsequent liner running operations or the increased distance of inclination measurements from the drilling bit. While some of those can be managed to a certain extent, others are intrinsic to the bent-motor steering concept. The need to further improving well construction economics requires that the CTD operational envelope be extended with new concepts and technologies.
This paper covers the introduction and utilization of a new directional steering technology that is based on the concept of closed-loop steerable drilling systems from rotary drilling applications. The new 3-in. rib-steered motor (RSM) design includes three hydraulically expandable ribs that are controlled from surface during drilling. In such setup required wellbore contact forces are generated that are necessary for drilling complex 3D well profiles. The RSM platform also offers the capability to drill tangents, which is impossible with the combination of bent motors and downhole orientation devices. Testing of this new platform commenced in 2008 in Alaska for BP, and it was further improved to become a new standard technology for horizontal or tangent sections in high-end CTD applications. Since then, 3-in. RSM bottomhole assemblies have drilled more than 23,000 feet in more than 13 wells in Alaska. Compared to bent motor drilling, RSM technology improves weight transfer and enables precise control of weight on bit to total depth (TD) for significant extension in lateral section length. It also improves hole quality to make liner running operations more reliable, and reduces non-drilling time by reducing the amount of required wiper trips for hole cleaning purposes. This paper discusses these aspects in more detail and uses available field data to show and support the technology’s benefits and its impacts on project economics.