The addition of composites to the range of materials available for coiled tubing manufacture has raised a number of issues. An understanding of the advantages and limitations of this new material will serve to more clearly identify the niche for composite coiled tubing in oilfield service.

Current assumptions as to what diameter of coiled tubing is suitable for a particular application are no longer valid. The change in stiffness for any given coiled tubing diameter associated with a custom designable composite matrix requires careful modeling of all forces acting on the tubing during well interventions.

Hardware issues must also be addressed if a new tube material is to be integrated into the existing world wide coiled tubing fleet. Bend radius limitations related to product stiffness will have an impact on the suitability of existing reels and injector goosenecks. Field serviceable flush OD end and repair connections are necessary if composites are to approach the versatility of metal coiled tubing products.

Previous industry efforts have identified three principle applications for composite coiled tubing. Permanent wellbore installations such as velocity, production, and injection strings in harsh environments appear to be an obvious fit. Service strings for workovers also appear to be a good application due to the fatigue characteristics of composite materials. Composite tailpieces have also been proposed to take advantage of the best properties of both materials. The advantages and disadvantages of each application identified by modeling and hardware ultimately decide whether composites are more suitable than conventional coiled tubing materials.

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