For almost two decades, coiled tubing drilling (CTD) has proved to be a successful method to reach the un-swept portions of Alaska’s North Slope reservoirs. This method of drilling has evolved over the years with new technologies and efforts from contractors and operators striving to improve performance from lessons learned. Despite these improvements in equipment and processes, operators and contractors must still deal with certain inherent deficiencies of this drilling method when compared to conventional rotary drilling – suboptimal weight transfer, sometimes troublesome hole cleaning — due mainly to lack of string rotation and low flow rate range, etc. These shortcomings have the potential to induce other drilling performance problems that affect the smoothness of coiled tubing drilling operations. Severe lateral vibration and severe stalling have become acceptable evils over the years, resulting in undesirable trips for failure and unacceptable non- productive time (NPT), both undermining one of the key benefits of coiled tubing drilling – rapid pace operations compared to rotary drilling. This paper introduces a new lower-speed downhole positive displacement motor (PDM). The technology is equipped with high-performance elastomer and was engineered to improve drilling and drill-bit performance in CTD applications. Recent field deployments in Alaska’s North Slope CTD operations proved this design by eliminating earlier performance problems for improved CTD project economics. For example, the technology’s ability to allow for about 10gal/min higher flow rates (compared to other motor designs) significantly improves hole cleaning; a key aspect in CTD operations. Up to today, this downhole mud motor design has been utilized on 13 wells, accumulating 1,303 circulating hours, 577 drilling hours and over 20,700 ft drilled. Performance improvements in depth of cut, reduced lateral vibration, reduced amount of stalls, and other benefits were achieved. There was no trip for PDM failure in all of the 34 runs, traversing different formation zones. The corresponding paper will provide additional information on application benefits by investigating two recent field deployments.
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.
Conventional drilling through lower intermediate intervals in the southern portion of the Alpine field on Alaska's North Slope (ANS) has posed significant challenges, resulting in longer than planned well delivery timing, and additional costs due to accumulated drilling complications. While unstable shale sections can be drilled without significant issues, hole collapse has caused difficulties while tripping out of hole and running casings. The need to overcome these challenges for long term economical access to develop the Alpine sands reservoir section beneath the shale layers led to numerous project initiatives and operational changes. These actions all produced incremental advances to mitigate wellbore stability issues, but never provided a guarantee that a liner would be successfully run to total depth of the open hole section after the trips required to complete this task conventionally. In 2011, a new Steerable Drilling Liner system was proposed as a possible solution for drilling these wellbores while sealing off the troublesome shales. An extensive feasibility study was conducted to ascertain the technical possibility of deploying this technology safely within the Alpine field. Candidate wells were identified and a phased implementation approach was adopted to conduct field trials in order of increasing complexity of well trajectory and open hole and liner section lengths. This paper provides insights into the new technology and the field trial program. We cover the lessons learned and further improvement opportunities applicable to future deployments in this area. Based on the success of the Steerable Drilling Liner technology in this application, further deployments are scheduled to take advantage of developing Alpine reservoir sands in an economical and safe manner.
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