HPHT Underbalanced Drilling



The platform was an HPHT gas producer in the Central UKCS. A well had been previously suspended with a shallow cement plug and was to be abandoned. Below the cement plug was the possibility of 800 Bar, if this pressure was found it would not be possible to contain it with mud weight hence the requirement for a snubbing unit.


The objective was to rig up a snubbing unit within the derrick of a jack-up, then drill through the shallow cement plug and clean out down to the top of the bottom cement plug. The well was then to be displaced to kill weight mud.


Over a year of planning went in to this operation, with a BPC desk engineer working in the client office.
Significant engineering and modifications to the unit had to be completed prior to operation.
Very challenging rig up with the basket level 22 m into the derrick.
Numerous different parties involved meaning good communication was paramount.
Drills were performed to ensure communication channels were clear.
First half of plug drilled open hole.
Second half of plug drilled while holding 100 bar back pressure in order to provide cushion should pressure be encountered.
No pressure encountered so continued to wash down to the top of the bottom plug.
Stopped just short of top of the bottom plug as pump pressures were getting too high.
ISS assisted client with expertise and program writing.


Completely new rig up was completed without significant issues.
Significant amount of equipment to pressure test at high pressures and all tested successfully.
Communication between all the parties worked very well.
Operation was completed on time with minimal delays.
Great team work displayed by all parties on board.
Zero incidents and accidents.