The inherent advantages and limitations of drilling with coiled tubing have been the subject of many presentations in the last several years. The potential benefits that coiled tubing drilling systems offer have prompted development of several competing systems that are now being brought to the market. Although each of these approaches share some similarities, unique features have been introduced that enhance the value of the available systems.

Full exploitation of coiled tubing drilling systems dictate that a practical approach be taken. Specifically, the most attractive approach is the one most highly leveraged to deriving the benefits offered by using coiled tubing. Because the coiled tubing drilling system is subject to limitations with respect to force delivery and the inability to rotate, the application of this emerging technology needs to be directed to a niche where it provides the operator best value.

Coincident with the developments in coiled tubing drilling, industry's acceptance of underbalanced drilling techniques has been growing. It is now widely understood that the advantages of coiled tubing drilling are most evident in underbalanced operations. These advantages of technology will be applied to a wide range of well-finishing and re-entry operations to increase both the productivity and recovery of hydrocarbons from existing fields.

This paper presents the latest technology being applied in underbalanced coiled tubing drilling operations and highlights the additional advantages of using a pressure deployment system. Operations conducted in the first ten months of 1996 using these tools are reviewed.

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