Coiled tubing

Engineering Approach Uses Underbalanced Coiled-Tubing Drilling

The authors of this paper describe an underbalanced coiled-tubing drilling campaign in the operator’s onshore fields using a closed-loop system design.

CT drilling tower.
Fig. 1—CT drilling tower.

Because of declining reservoir pressures in some of its onshore gas carbonate fields, the operator initiated a three-well underbalanced coiled-tubing drilling (UBCTD) campaign in its onshore Asab and Bab fields, with two wells to be drilled in Asab and one in Bab. Because of the high hydrogen sulfide (H2S) content, a closed-loop system—the first one successfully implemented in the Middle East, according to the authors—was implemented. The complete paper discusses the design and planning involved in the drilling of these three wells, the operational challenges encountered, and mitigations used.


One of the operator’s main objectives was to increase production while safely maintaining or minimizing operating costs. One method of achieving these goals is the use of coiled tubing (CT) to drill formations in underbalanced mode.

The Asab and Bab fields are southwest of Abu Dhabi.

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