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In the Bakken field surrounding Williston, N.D., a typical horizontal well consists of a 10,000-ft vertical section, and a 4,000-to-5,000-ft lateral section. As drilling and completion technologies have improved, lateral sections are now reaching 9,000 to 11,000 ft in length. As a result, CT providers are now being challenged to reach these extended depths, which, in some cases, can exceed a total of 20,000 ft. Sanjel’s CT team in Williston recently exceeded this depth twice.
Working on a multi-well pad for a major operator, Sanjel’s CT team reached depths of 20,164 ft and 20,783 ft on consecutive wells. Lab technicians found a friction reducer fluid that significantly reduced the amount of friction between the CT and the well. This allowed the CT to deploy in its entirety and reach a significant depth, without experiencing friction lockup on the deepest well. Before reaching the final depth, Sanjel successfully milled out 26 plugs in a single trip within 48 hr.
In cases like this, considerations of extended-reach CT include proper support equipment sizing and string design, to ensure optimum performance.
CT injector design focuses on ease of operation, maintenance
Costly downtime can be minimized with oilfield equipment that is easy to operate and maintain. AXON Energy Products analyzed CT injector fundamentals and operating parameters to achieve maximum serviceability, while maintaining performance. The company’s new CT injector includes external location of major serviceable components, interchangeable parts, combined assemblies and optimized skates.
All operating and tensioning cylinders are interchangeable, and located externally for ease of maintenance. The drive mechanism utilized for the chains and grippers is integrated to further minimize the requirement for CT spare parts. Additionally, the drives are mounted opposite one another, allowing for counter-rotation of the chain and grippers.
The integrated chain and gripper assembly circumvents maintenance issues, such as individual inserts and damaged screws. Simply removing the chain master link enables the entire assembly to be extracted and replaced in a matter of minutes. Fabricated from high-strength aluminum for optimal durability and weight, the skates include a replaceable, hardened wear plate, and are designed for easy removal through the side of the injector.
Combined with the CT injector’s field-proven technologies, AXON’s design improvements allow for ease of operation and maintenance to reduce downtime.
Tubing grade improves fatigue life
NOV Quality Tubing has developed QT-1300, a CT grade with minimum yield strength of 130,000 psi, that has improved fatigue life over existing lower-strength grades, while providing superior load-bearing capacity for use in live-well interventions and completions. This represents an increase of 20,000 psi in minimum yield strength over the previously highest available grade. The longest string of QT-1300 manufactured, to date, is more than 35,000 continuous ft in length.
To ensure functionality, QT-1300 has been tested for compatibility with typical CT equipment, such as injectors, connectors for downhole tools, and BOPs (BOP shear and slip testing). It has also been incorporated into third-party fatigue modeling, as well as proprietary service company models.
QT-1300 has been utilized successfully by development partners, both onshore and offshore, in HPHT wells, and for extended reach applications. Onshore successes have been seen in North American shale plays, such as the Bakken and Eagle Ford. Offshore, both in the North Sea and in the Gulf of Mexico, QT-1300 has enabled operators to perform operations that were not previously feasible. 
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