High-Risk Coiled-Tubing Intervention Results in Substantial Savings
- Finlay Neil Thom (BJ Services Co. UK Ltd.) | Michael John Taggart (BJ Services Company) | James D. Murdoch | Brian Ewing (Welltonic Limited)
- Document ID
- Society of Petroleum Engineers
- SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, 23-24 March, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 4.3.4 Scale, 1.7 Pressure Management, 2.2.2 Perforating, 1.6 Drilling Operations, 1.6.11 Plugging and Abandonment, 1.14 Casing and Cementing, 2 Well Completion, 1.6.1 Drilling Operation Management, 4.5.3 Floating Production Systems, 1.6.9 Coring, Fishing, 1.11 Drilling Fluids and Materials, 4.1.5 Processing Equipment, 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing), 4.1.2 Separation and Treating, 3 Production and Well Operations, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.10 Drilling Equipment
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Shell U.K. Limited Teal P1 subsea well was completed in July 1996 with a peak flow rate of 40,000 bopd. During the completion phase there were a number of problems and failed attempts in setting the production packer, which subsequently resulted in debris in the wellbore. To prevent this debris damaging the turret assembly in the FPSO, a debris barrier, consisting of a perforated tail pipe and a 3 ½?? bridge plug, was installed in the production tubing 50 ft below the TRSSSV. Problems with the TRSSSV and the subsea tree valves resulted in a completion workover being scheduled. Prior to pulling the production tubing, the A-annulus was pressurised to 3500 psi to reduce the differential pressure across the tubing. At 2850 psi there was a sudden loss in pressure indicating a leak in the outer casing string. The workover was suspended and the well left in a safe condition. Planning for a full abandonment was then implemented.
Two abandonment options were possible: remove the debris barrier and abandon the well using coiled tubing, or drill a secondary well which would intercept the reservoir section of Teal P1 allowing it to be isolated. The coiled tubing option was only given a 30% chance of success, but due to the potentially large cost saving if successful, this became the primary option. The main hazard in the coiled tubing intervention would be removing the 3 ½?? bridge plug from the debris barrier which had been in place for over 12 years. To address this a number of onshore trials were carried out to determine if the plug could be milled if fishing was not achievable.
After a total of 52 coiled tubing runs with a variety of customised BHA's, the requirements of the coiled tubing intervention were met allowing full abandonment of the reservoir. This paper discusses the well history, requirements of the coiled tubing intervention, the onshore trials and the offshore operation.
The process of mature well abandonment should always be kept in mind during every stage of the wells operating life. Relatively simple additions to the well design, which may seem the most appropriate for that particular time, may create substantial problems during the abandonment process.
Teal P1 is a subsea well operated by Shell U.K. Limited located in the central North Sea. It was completed in July 1996 and had a peak production rate of 40,000 bopd. During the completion stage, operational difficulties in setting the production packer in the wellbore resulted in several failed setting attempts. This resulted in a larger than expected volume of debris in the well. The completion schematic is shown in figure 1. As this debris had the potential to damage the turret seals in the FPSO that the well produced into, a debris barrier assembly was designed and installed in a short time period. This debris barrier assembly consisted of a pre-perforated tail pipe with a 3 ½?? bridge plug installed in the base, all hung off with a packer in the 5 ½?? production tubing at 945.5 ft md, as shown in figure 2.
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