This paper describes the Underbalanced Coiled Tubing Side tracks executed with a Hybrid Drilling system.

The project was executed from August 1997 to January 1999. During this time a steep learning curve was built on Hybrid drilling Unit technology.

The project comprised three sour gas wells with increasing complexity starting with a through tubing deepening, a world first through tubing double casing exit, through 5" and 7" casing, and finally a short radius side track with a 500 mtr. horizontal section. All three wells are targeted in the Zechstein Carbonate at 3000 mtr. TVD.

The learning curve on the Hybrid Drilling unit and underbalanced surface equipment is described, along with the methods used to manage the risks involved in the introduction of new technology.

The well objectives, drilling for fractures or equivalent matrix production and underbalanced design are discussed.

The different operational stages on the three wells are discussed.

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