Gas flow while setting tubing hanger in wellhead

A gas producer well was being prepared for temporary abandonment. Prior to setting a temporary abandonment plug no flow from the tubing and annulus was confirmed. The X-mas tree was nippled down and the tubing hanger lifted to replace the tubing hanger. Then the flange type tubing hanger was replaced with a mandrel tubing hanger to allow BOP installation. When lowering the tubing hanger into the wellhead, the tubing hangers stopped 2ft above the wellhead. A rig site decision was made to unset the completion packer to enable landing of the tubing hanger. Gas flow occurred while attempting to set the tubing hanger. Flow was diverted through the casing valve while they continued to set the tubing hanger followed by nippling up the BOP. The well was then successfully shut-in on a pipe ram preventer for kill operations. The well was killed by bullheading the tubing and annulus.

Observation prior to execution of a temporary plug abandonment job confirmed no flow from the tubing & annulus. The activity continued with nippling down the X-mas tree and lifting the tubing to replace the flange type tubing hanger with a mandrel one to allow BOP installation. When lowering the mandrel tubing hanger into the wellhead, the tubing hanger stopped at 2 ft above the wellhead. The decision was made at the rig site to unset completion packer in the well to be able to lower the tubing and set the tubing hanger. Gas flow was observed while attempting to set tubing hanger in the wellhead. Flow was diverted through the casing valve while continuing to set the tubing hanger followed by nippling up the blow out preventer. The well was successfully shut-in on the pipe ram preventer for the killing operation.

The well was killed by bullheading formation fluid down the tubing and annulus.

What Went Wrong?:

Inconsistency of approved well program execution:

• Hydrostatic barrier prior to x-mas tree removal was not established – decision was based on accepted practice from previous well execution.
• The risk of unsetting packer was not communicated and addressed.
• Well control risks of well program deviation (i.e. unsetting completion packer and not establishing hydrostatic pressure barrier) were not recognized nor followed with Risk Assessment (RA) and Management Of Change (MOC) process.

Corrective Actions and Recommendations:

• Displace Kill Fluid prior to beginning a single barrier operation and ensure all well programs for special operations require a hydrostatic barrier to be in place at all times.
• Install flow control to pump and bleed prior to commencing operation.
• Retrain rig personnel on hazard recognition and the MOC process.

safety alert number: 330
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