CT laid pipelines will soon move up to 6.625-in. diameter

SCS has achieved lay rates of around 1,000 meters per hour when installing coiled tubing pipelines.

• The coiled tubing is installed using a powered reel drive unit which deploys the pipe to a lay ramp normally mounted at the stern of the vessel. [60,852 bytes]

The use of coiled tubing for pipeline applications is now available as an alternative to conventional rigid and flexible flowlines. Currently available in diameters up to 4.5 in., coiled tubing can prove extremely cost-effective for flowline applications.

The low production costs of the pipe together with fast, efficient installation from modern dynamically positioned (DP) vessels can produce cost savings of 45% compared to a conventional rigid flowline, and 55% compared with flexible pipe.

Although not widely used in the North Sea, coiled tubing has been utilized very successfully in various oil and gas fields around the world. This is the case in Egypt, where the Gulf of Suez Petroleum Company (GUPCO) has over the past few years installed many miles of coiled tubing pipelines for chemical injection, gas lift, water injection, and gas production lines.

Laying operations

The cost of installing a coiled tubing pipeline is a significant proportion of the overall cost of the pipeline; consequently, fast and efficient installation procedures are critical factors to the overall success of the project. Stolt Comex Seaway (SCS), with a fleet of DP construction vessels, has been a pioneer in the development of coiled tubing pipeline installation techniques, and has successfully installed many miles of coiled tubing pipelines for GUPCO in the Gulf of Suez.

The coiled tubing is installed using a powered reel drive unit which deploys the pipe to a lay ramp normally mounted at the stern of the vessel. Once on the lay ramp, the pipe is passed through hydraulic straightening rollers, and then paid out using a tensioner to control the lay stresses in the pipe.

The angle of the lay ramp can be adjusted to suit the water depth in question. The pipe is paid out through the lay system continuously as the vessel moves along the pre-determined pipeline route. SCS has achieved lay rates of around 1,000 meters per hour when installing coiled tubing pipelines. Once the reel is empty, a full reel is moved into the power reel drive unit, and the two pipeline sections welded on the lay ramp using a full bore socket connection.

The size of the coil tubing lay system is relatively compact. As a result, SCS has been able to perform additional activities such as diving support and flowline tie-ins from the lay vessel, which can prove extremely cost effective for small field developments.

Manufacturing

The manufacturing process for coiled tubing produces pipe with a much smoother internal surface than conventional seamless pipe. This results in a reduced pressure drop along coiled tubing flowlines, which is provides the potential of selecting a smaller pipeline diameter thereby creating further cost-saving potential.

Currently coiled tubing is available in dia meters up to 4.5 in.; however, development work is in progress to increase the capacity to 6.625 in., which greatly increases the potential of coiled tubing for production flowline applications.

As the need for cost-effective field development solutions increases, the use of coiled tubing for pipeline applications can make a significant contribution towards achieving these aims.

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