Installation of 2 7/8-in. Coiled-Tubing Tailpipes in Live Gas Wells
- J.A. Campbell (Nowsco Well Service U.K. Ltd.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 1994
- Document Type
- Journal Paper
- 442 - 447
- 1994. Society of Petroleum Engineers
- 3 Production and Well Operations, 2 Well Completion, 1.7.5 Well Control, 1.6 Drilling Operations, 4.1.2 Separation and Treating, 1.6.1 Drilling Operation Management, 4.2.4 Risers, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 3.3.1 Production Logging, 4.5 Offshore Facilities and Subsea Systems, 4.1.5 Processing Equipment, 5.6.9 Production Forecasting, 1.7 Pressure Management, 2.2.2 Perforating
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This paper describes a technique for installing 2 7/8-in. coiled tubing astailpipe extensions below existing production packers in live gas wells. Italso covers the use of coiled tubing as a way to complete wells. Large savingsin rig time and deferred production have been realized with this technique.Fluid losses to the formation do not occur, and no expensive rig time is neededto kill or clean up the wells, as required for conventional workovers belowexisting production packers. This technique is particularly applicable indepleted reservoirs that could be impaired by traditional workover methods.
The Leman gas field, discovered in the early 1960's, has been producing gasfrom the Rotleigendes sandstone since 1969 (Fig. 1). As cumulative productionhas increased, reservoir pressures have declined to the point where theformation cannot support a column of fluid, causing problems whenever workoversthat require kill fluid across the perforated interval are attempted. Theseoperations can result in large fluid losses to the formation, leading toformation damage and delayed reinstatement of production. In most cases, anytubular changes or work associated with completions is performed by settingisolation plugs in the existing tailpipes, which prevents any associatedproblems with loss of kill fluids to the producing in terval. As productionrates have declined, the ability of individual wells to lift produced fluid hasbeen reduced, so liquids accumulate in the wellbore. Liquid loadup in thewellbore has resulted in increased hydrostatic pressure on the reservoir,further reducing the energy available to produce gas.
A number of Leman wells have been worked over recently with a cantileverjack up rig to replace the original 5 1/2-in. pro duction string with a 31/2-in.-diameter string to improve production velocities and fluid removal fromthe wells. Although these operations have continued, it was recognized in 1991that the existing tailpipes would have to be extended several hundred feet downto the perforated interval to optimize production velocities in the casingsections below the production packers.
With the known problem of performing workovers across the perforatedinterval, the decision was made to use wireline to install 2 7/8-in. tailpipeextensions with the wells still live. Any technique to install tailpipes wouldbe financially beneficial only if it could be done without introducing killfluid into the producing formation. The maximum length of tailpipe that couldbe run on wireline with current techniques was about 50 ft. Post commissioningresults have shown that tailpipes of this length do not provide sub stantialbenefits. It was recognized that the tailpipe length would be crucial formaximizing the lifting capacity of the produced gas below the productionpacker.
Therefore, it was decided to initiate a program to install 27/8-in.-diameter tailpipes below the existing production packers in lengths ofup to 700 ft. The length of the tailpipes to be installed was dictated by thedistance between the existing tailpipes and the perforated intervals, which inmost cases was from 500 to >700 ft. Installation of these tailpipes wouldensure increased gas production velocities in the entire casing sec tions (Fig.2).
Workover Procedure and Implementation
Combining the installation of these tailpipe extensions with replacing theoriginal larger-diameter production string with a smaller-diameter productionstring more suited to the reduced production rates of the field appearedcost-effective. As discussed, because of well kill problems, we decided toinstall the tailpipes on coiled tubing with the wells live. Thecoiled-tubing-installed tailpipes would be left in the completions withwireline plugs in place, effectively leaving the well isolated and ready for arig to perform a conventional tubular replacement.
This technique would have the following benefits.
1. The coiled-tubing installation could be carried out on the productionplatform before the workover rig was on location, thus saving rig time.
2. The operation using coiled tubing to install the tailpipes could beperformed with the wells live.
3. The addition of wireline-retrievable plugs in the bottom of the installedtailpipes would mean that the wells could be left suspended, ready for theworkover rig to perform the tubing replacement (Fig. 3).
4. After replacing the tubing, the rig could be released immediately and thewells brought on production by use of platform- based nitrogen equipment toevacuate the workover fluid before the wireline plugs in the 2 7/8-in.tailpipes were pulled, which was the previous workover practice.
An installation procedure involving the following steps was designed.
1. From the production platform, rig up 2 7/8-in. and 1 1/2-in.coiled-tubing blowout preventer (BOP) equipment. Run the required length of 27/8-in. coiled tubing into the well; complete with wireline plugs in thebottomhole assembly (BHA) (Fig. 4).
2. Hang off the required length of 2 7/8-in. coiled tubing in the BOPsystem. Close both sets of tubing rams/slips and cold-cut the pipe on surface.Install a permanent packer on 2 7/8-in. coiled tubing ( Fig. 5).
3. Rig down the 2 7/8-in. coiled-tubing injector; rig up the 1 1/2-in.coiled-tubing equipment; and attach the 1 1/2-in. coiled tubing to packer andpacker running tool (Fig. 6).
4. Run 2 7/8-in. tailpipe to depth on 1 1/2-in. coiled tubing. Tag the no-gonipple and space out for depth correlation (Fig. 7).
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