Combustible gas escaped onto the drill floor and shaker room on Deepsea Bollsta
Equinor has acknowledged that an incident on board a semi-submersible drilling rig working on the Troll gas field offshore Norway was the most serious category in its safety management system.
The Deepsea Bollsta was plugging a well on the Troll field when a leak of gas and fluid spread to the drill floor and the shaker room.
One person in the shaker room had trouble getting out due to the differential pressure that occurred. The person suffered minor injuries and received first aid treatment on board the rig after using force to get out of the room.
The ventilation system in the ceiling of the room was also damaged.
Automatic gas detection triggered the rig’s safety systems and potential ignition sources were disconnected.
The crew on the Deepsea Bollsta activated the rig’s blow-out preventer (BOP) and diverter system, which routed the gas, fluid and pressure from the well away from the rig before the BOP closed.
The BOP closed after 71 seconds, and this stopped the flow of gas. The situation was normalised in 30 minutes, according to Equinor.
An investigation showed that about 930 kilogrammes of gas leaked in a short period of time. This is classified as a red one incident, the most serious category in Equinor’s management system, the company said.
The cause of the incident was that the BOP was in the open position when the casing was cut, while at the same time confined gas was present behind the casing.
The annulus behind the casing was logged before the cutting, but the equipment was not calibrated correctly. This meant that the gas was not identified in advance.
Equinor said the incident did not have the potential for an uncontrolled blowout. The gas was from a limited volume confined behind the casing, and was not in contact with the reservoir. The barriers against the reservoir were intact.
“We’re taking the well control incident that led to a gas emission on Deepsea Bollsta very seriously. There were considerable forces at play and gas came aboard. This was a dramatic event for those who were at work.
“At the same time, all safety barriers functioned as intended and the crew handled the situation well, thus preventing any escalation,” said Rune Nedregaard, Equinor’s senior vice president for drilling and wells.
“We’ve received a thorough investigation report that will form the basis for lessons learned. Among other things, the investigation points to technical factors that can prevent such incidents.”
Equinor will share the investigation findings and implemented measures with its suppliers, while the Norwegian Ocean Industry Authority is also conducting an investigation.
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