RIASSUNTO
Abstract
Well 2/4-14 in the Norwegian Sector encountered well control problems inJanuary 1989 at a depth of 4734 m. After some days effort to reestablish normalpressure control the well blew out on surface of the floater and had to beclosed in using the shear ram. This left the subsea BOP closed and with a shutin wellhead pressure of 10000 psi. In addition a full string of drillpipe withapproximately 4500 m of coiled tubing was left in the well. After an attempt toregain control by bullheading heavy mud, in which a flexible kill line bursted,the well was left for a period. Preparations were made to reenter the well withhigh pressure snubbing equipment to fish out the drillpipe and coiled tubing,so that the well could be circulated dead. In parallel to this effort a reliefwell was started immediately.
After the well was reopened it was discovered that the casing had burstedand that the well was blowing out underground.
On December 12, 1989, 295 days after the shear ram was closed, the well waskilled.
Another four months were required to finish cleanup and final abandonment ofthe blowout well.
The paper presents the case history and indicates some of the tools andtechnology that was developed to regain control of this well.
Introduction
On January 20 and 21, 1989 well 2/4-14 blew out twice before finally beingclosed in with the shear ram/fail safe valves on the BOP (See Fig. 1, 2). onlya minor amount of oil/gas was released to the environment but the shut inwellhead pressure was left at approximately 10.000 psi (690 bar).
PLANNING OF CONTROL OPERATION PLANNING OF CONTROL OPERATION An evaluation ofthe operations on and responses of the well prior to closing in, - and thecomplex tubular strings left in the well, resulted in a conclusion that a majorwell control operation had to be initiated.
The objective of this activity was identified as:
""To regain control of 2/4-14 as soon as possible in a manner whichpermits the well to be securely plugged and abandoned according to theobjectives in the NPD drilling regulations. During this operation safety shallbe a primary consideration"".
Further, a safety philosophy was established which stated:
""The operation shall if possible be performed with normal level ofsafety for personnel and environment.""
""Two risky operations will not be performed at the same time, and as faras possible the operation will be performed so that a reasonable fallback ismaintained at all times"".
Through evaluations it was concluded that in order to satisfy the objectiveplugging of the well, a significant amount of the tubulars (drill pipe/coiledtubing) had to be removed from the well. Otherwise the deep parts of the wellcould not be satisfactory plugged.
A parallel approach was chosen:
- To start drilling of a kill well (2/4-15S)
- To start mobilizing for a high pressure snubbing operation in 2/4-14
This parallel approach was considered to give the best probability forreaching the objective as it was identified.
MOBILIZATION AND START OF OPERATION
Drilling of the kill well 2/4-15S started January 31, 1989 using the semi-submersible drilling rig ""Treasure Saga"" (TS), immediately afterinstalling a back up plug in the annular preventer of the BOP stack on the2/4-14 wellhead. The kill well was spudded 1182 m south of the 2/4-14 well (SeeFig. 3).
For the reentry operation it was decided to contract the jack-up drillingrig ""Neddrill Trigon"" (NT) and use this as a base for a surfacesnubbing operation into the subsea well.
P. 775