Drilling through shallow gas zones can be a major hazard, especially in offshore operations. An innovative technique using tender-assisted coiled tubing (CT) drilling is presented, which allows the determination of hazardous shallow gas presence with minimum risk, prior to mobilization of a large drilling barge. One advantage of the use of CT drilling is in increased safety because there are no personnel on the platform while drilling as the barge is kept 1 50 ft. away from the platform. Should a shallow gas flow occur, the gas is diverted with only minimal equipment exposed to damage and no danger to personnel.

The technique of tender-assisted coiled tubing drilling has been used to drill five 3-7/8 in. slim hole wells in Lake Maracaibo, Venezuela. Equipment, techniques, and safety merit to perform the drilling operation are described. The successful multiwell campaign has provided

References and illustrations at end of paper a drastic improvement in safety while significantly reducing top-hole drilling costs. With the learning curve progress allowed by a multiwell program, it is demonstrated that drilling rates with CT can exceed those of conventional rotary drilling.


This technique is applicable to many shallow gas problems both on land and offshore.

Technical Contributions
  1. A unique, safe solution to the long-standing problem of drilling in a shallow gas environment.

  2. The first coiled tubing drilling in South America is described.

  3. Results of the multiwell campaign show that the learning curve requires several wells to obtain a realistic estimate of the efficiency of drilling with CT as compared to conventional rotary drilling.

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