Well Plugging Operations in West of Shetland Horizontal Wells Using Coiled Tubing Techniques
Authors: Munro C. , Ferguson S.E. , Engel S.P. 
Published: December 2007

Foinaven is the first field to be developed in the West of Shetland province. The paper describes how deep set plugs were successfully deployed, tested and retrieved from extended reach wells using coiled tubing techniques.

A sub-sea development, in 500 metres of water, Foinaven will have 14 production wells. Most, if not all of these wells will have extended reach horizontal sections, with tangent angles of over 80 degrees.

The wells are completed, in some cases tested, and left suspected with hydrocarbons to surface and plugged accordingly. The sub-sea Christmas trees are installed when the weather conditions are favourable.

Results, Observations and Conclusions. The first 4 well completions are described in the paper. Severe weather conditions combined with the challenges of working from a semi-submersible drilling rig in high angle wells caused several problems. These included:extreme coiled tubing weight indicator fluctuations.control of impact hammer during jarring operations.lack of confidence in shear values of setting pins while in the horizontal sections, and resulting effects on deep set plug integrity.impact and consequences of debris accumulation within the completion tubing and the effect on plug setting and retrieval.

The paper describes how these difficulties have been resolved or minimised.

Applications. The paper will be applicable to any coiled tubing operations that involve either sub-sea completions or extended reach wells.

Technical Contributions.The Foinaven producer completion is described with suspension philosophy.The plug design and applications are described, including the onshore testing requirements.Accelerated age testing of elastomeric barriers is described.The coiled tubing equipment rig up and operational procedures are described.

Background

The Foinaven oilfield is located 180 km West of Shetland in the Atlantic Ocean. Discovered in 1992 by BP Exploration the field is located across Block Nos 204/19 and 204/24a in 500 metres water depth with a shallow reservoir of Palaeocene sands separated by shales at 2,000-3,000 metres TVD. A phased sub-sea development was sanctioned in late 1994 and is the first of BP's Atlantic Frontier projects to be developed on a "fast track" basis. There is no present infrastructure in the area to support oilfield developments and the area is exposed to challenging weather conditions and unpredictable current regimes.

The sub-sea architecture is designed around 2 drill centres with a manifold on each feeding to a floating production, storage and off-loading vessel (FPSO) designed for 85,000 barrels per day annual average oil production, with full water injection, gas compression and produced water handling facilities.

A total of 22 reservoir penetrations are planned for the development of which 14 are oil producers, 7 water injectors and 1 gas injector disposal well. Many of these wells are at deviations greater than 80 degrees, which require coiled tubing for deep well plugging operations.

Foinaven represents a very high cost operating environment during the well installation phase, owing to the requirement for fourth generation semi-submersible drilling units for drilling and completion operations.

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