Successful Campaign to Install Multi-Sectional Large Diameter Chrome CT Velocity Strings in High CO2 Wells in Bolivia

Abstract

Abstract Well intervention projects performed in remote and difficult-to-access areas using coiled tubing (CT) equipment and strings with long lengths and large diameters sometimes represent high investment projects. The use of heavy CT strings can lead to complications during lifting and transport operations. One alternative to address these issues is to transport short sections of CT to the wellsite, then connect two or more CT strings onsite. This paper provides an alternative for offshore operations where crane load capabilities are limited and for land operations in remote locations where heavy loads can compromise transportation. Conventional methods of joining CT strings are available, such as orbital welding and the use of mechanical connectors (Ehtesham 2008). These methods can be applied under controlled conditions or when the CT strings are of small diameters or lengths that enable them to fit on a single spool and the resulting weight can be accommodated. However, these methods present some shortfalls. Orbital welding requires access to qualified technicians and additional verification of the weld on site, adding time and cost to operations. Welding may also be prohibited based on wellsite conditions. Additionally, welds create de-rated sections on the tubing, reducing the potential run life of the string. Spoolable connectors are a viable option where the two strings may be joined off critical path and when the work reel is capable of holding the combined strings. Some operations must be performed using smaller work reels to accommodate the work area, or involve strings being joined during the operation, which are not ideal situations for spoolable unions. The option presented in this paper provides a new method for joining strings on the fly. The study was performed to explore the technical feasibility of mechanically joining two CT strings for velocity string (VS) projects. Challenges include making the union of these strings above the wellhead under live well conditions and the load capacity limit of the reels. The study includes design of mechanical joining tools, design of the CT strings, selection of CT hanger tools, and surface equipment. These points also include testing, mechanical stress simulations of the CT, and the procedure used to join the strings. This paper shows the best operational practices, lessons learned, and field considerations when joining multiple CT string sections of the same or different diameters and wall thickness. Performing those jobs with CT equipment provides a low-cost alternative solution to the use of workover equipment and threaded pipe. This study demonstrates the collaboration performed with an operator to develop a campaign solution for five velocity string jobs in Bolivia.