Snub Drilling

Snub Drilling Overview

If very high formation pressures and uncontrollable loss of circulation are expected during underbalanced drilling, use of a snubbing or a coiled tubing (CT) unit may be necessary. This type of underbalanced drilling is known as snub drilling.

Snub drilling should be considered for wells with:

  • Very high annular surface pressure
  • Vertical fractures
  • Severe loss of circulation
  • Surface equipment limitations
  • Personnel and rig safety considerations

Communication between rig-site personnel may become a problem when drilling with extreme surface pressures in snub drilling. Hearing protection is necessary for everyone on the rig floor and close to the choke manifolds.

Coiled tubing equipment isolates the wellbore during the entire drilling operation and avoids killing wells before tripping. Coiled tubing, however, is also limited by higher cost compared to conventional rigs, and cannot run jointed pipe for casing and tubing completion operations.

Snubbing offers a versatile and safe solution in underbalanced drilling operations. The advantages of using snubbing units are as follows:

  • Pressure control is handled with the snubbing unit’s BOPs, with its annular preventer as a primary system and its rams as secondary preventers.
  • In the event of “pipe light” conditions, the snubbing unit can provide the necessary control to inject or pull pipe and tools under pressure.

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