Underbalanced Drilling



During managed pressure drilling (MPD) with a conventional drilling rig into a gas bearing formation severe losses were encountered. Surface pressures up to 180 Bar were recorded. The well was temporarily killed by pumping 250 mT of LCM material and a viscous seal pill and the drilling rig was demobilized. In total 5300 m³ of mud was lost. A HWO/Snubbing operation was required to complete the well.


Underbalanced well conditions had to be expected during all activities.
  • Mill and retrieve bridge plug.
  • Drill further into the gas bearing formation.
  • Install 4-1/2” liner.
  • Install production completion.

Planned Execution

  • HWO/Snubbing unit was required in order to deal with pressurized well conditions.
  • 21m high BOP stack was assembled to lubricate BHAs in and out of the well.
  • Well deepening was conducted utilizing a MWD assembly with a 5-7/8” PDC bit powered by a 4-3/4" GT Motor. The HWO unit rotary table provided additional rotating performance.
  • 4-1/2" Liner needed to be deployed under pressure.


  • Successfully retrieved bridge plug.
  • Sufficient depth was reached to ensure a good producing well. Drilling conditions were harsh as the continuous lost circulation had a negative impact on the total drilling performance.
  • 4-1/2” Liner was snubbed in the well under pressure and was successfully installed.
  • Successfully installed production completion under dead well conditions.
  • Zero incidents and accidents.
  • Entire operation was completed in 58 Days.
  • Operation was conducted to full customer satisfaction.