Coiled tubing has made great advances in recent years, increasing in size, strength and reliability. This has lead to a great increase in services that can be run on coiled tubing and in turn has lead to bigger, more complex and more expensive coil equipment being built and offered to the market.

With all this new equipment now on the market, it becomes more difficult to select the most appropriate equipment for a particular job, or indeed for a project of work that involves many different types of operations. There is a tendency to assume that "biggest is best". Both commercially and technically, the big coil unit may not always be the best choice.

This paper gives examples of the current capabilities of coiled tubing units, dispelling some of the myths associated with the smaller units such as "You cannot drill with a small coil unit" or "You always need a big coil unit in order to get higher circulation rates". The paper also lists applications where big coil units absolutely should not be used. Finally, guidelines are set out based on general technical and economic performance comparisons between varying size coil units.

Several techniques are listed which permit smaller coil sizes to be used in place of bigger units. The paper uses examples from actual field work and computer simulations.

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