Abstract
This paper presents a case history in which a tapered-OD coiled tubing (CT) workstring and a blast nozzle were used for cleanout and stimulation work in a west Texas well. The tubing's tapered OD allowed it to pass through restricted downhole IDs while maximized flow rate was maintained. These techniques resulted in greater cleaning energy, higher annular velocities, and reduced pump times.
The workstring used was primarily 1 ¼-in. OD, but it was tapered to 1 in., and then to ¾ in. The ¾-in. portion was the only part of the string that penetrated beyond the depth of the shutoff valve in the injection string. A single injector head with a vee-block design allowed for smooth size transition as the tapered string was run in and retrieved. Three or four passes of the coiled tubing length were made with the blast nozzle.
Conventional tubing cleanouts in this field require approximately 10 to 14 days; however, by using the tapered CT string and a body-load coiled tubing unit (CTU) operators can perform such treatments in 8 to 10 hours. In addition to injection-well cleanouts, other potential applications for tapered-diameter CT are presented in this paper.
