Traditionally, completion engineers have faced a dilemma when deciding whether to run a large-bore, hydraulically set, permanent or retrievable packer completion. Thanks to advances in cutting technology, this decision is no longer an either/or proposition. The innovative alternative which has been enabled by through-tubing cutting technology is the removable packer completion.
Combining a through-tubing-conveyed hydromechanical cutter with a "cut-to-retrieve" packer had never previously been attempted. In addition to providing an innovative solution for difficult service environments, the new capabilities gained by combining these technologies has led to the development of a work-string-conveyed method of cutting and retrieving the packer, thus enlarging the scope of viable applications for the removable packer completion.
This paper will review the removable packer completion and the coiled-tubing-conveyed hydromechanical pipe cutting system and describe in detail how the technology was proven, both in the laboratory and at the rig, and how it is being used to design and complete wells in Alaska and Kazakhstan.
The increased use of coiled tubing in the last twenty years has led to many technological advances in through-tubing workover operations such as fishing, impact services, milling, underreaming and hydromechanical pipe cutting systems.
Because these operations are often performed to solve unforeseen problems, traditionally they have not been planned for during the completion design phase. As a result, challenges and restrictions placed on through-tubing tools and equipment can complicate through-tubing workover operations and add to their cost.
Although the "cut-to-retrieve" feature of the removable packer may still be considered a contingency application, the due consideration and planning afforded the hydromechanical pipe cutting system at the completion design stage has effectively repositioned this through-tubing workover application from an "afterthought" to an extremely reliable and effective enabling technology.
The removable packer was developed to offer large inside diameter, high performance and design simplicity missing from retrievable packers.
The removable packer is retrieved by cutting the packer mandrel and picking up on the tubing. The packer and its tailpipe can then be removed from the well without the need to mill over the packer. (It should be noted, however, that since the mandrel is cut, redressing and re-running the packer will, in all likelihood, be uneconomical.)
The cut-to-remove concept is based on the premise that the cross-section of the packer's cut zone is similar to that of the production tubing. Thus, existing through-tubing cutting technology can be used to cut the mandrel of the removable packer.
The primary challenges were to establish a method of locating the cut region and optimizing the original hydromechanical pipe cutter design for this application. Existing location methods were established and are described in this paper. Optimizing the cutter design included controlling the depth of the cut, which was deemed a critical issue. If the cutter severs the mandrel and the outer housing, the removable packer will not be capable of removing the lower half of the packer and the tailpipe. (Figure 1)
For the removable packer concept to be viable, operators requested multiple retrieving scenarios. Four were developed:
Coiled-tubing conveyed hydromechanical cutter
Workstring-conveyed hydromechanical cutter
Standard milling method
Chemical cut method
All four systems were designed and validated for use. (Figure 2)