NORWAY – Equinor completes investigation into Deepsea Bollsta well control incident
Equinor has completed its investigation into a well control incident that occurred on 23 September 2025 on the Deepsea Bollsta drilling rig during well-plugging operations at the Troll field. The event resulted in a brief release of gas and fluids that spread to the drill floor and the shaker room.
Automatic gas detection systems immediately activated the rig’s safety mechanisms, disconnecting potential ignition sources. The crew responded according to procedures by activating the blowout preventer (BOP) and the diverter system. The diverter redirected gas, fluids, and pressure away from the rig before the BOP closed. The BOP sealed the well after 71 seconds, stopping the gas flow, and the situation was brought under control within approximately 30 minutes.
During the incident, one worker in the shaker room encountered difficulty evacuating due to pressure differences caused by the gas release. The individual forced their way out of the room, sustaining minor injuries, and later received first-aid treatment on board. The gas and fluid column also damaged the ventilation system in the ceiling of the shaker room.
According to Equinor’s calculations, around 930 kilograms of gas escaped in a short period. Because of the scale of the release, the event was classified as a Red 1 incident, the most serious category in the company’s internal management system. Although combustible gas briefly reached the drill floor and shaker room, ignition risks were minimized as safety systems had already disconnected potential ignition sources. Investigators concluded that the circumstances would have needed to be different for ignition to occur.
The investigation found that the incident happened because the BOP remained open when the casing was cut while gas was trapped behind the casing. Although the annulus behind the casing had been logged before the cutting operation, the monitoring equipment had not been properly calibrated, meaning the presence of gas was not detected in advance. Equinor stated that the situation did not have the potential to develop into an uncontrolled blowout since the gas came from a limited volume confined behind the casing and was not connected to the reservoir. Barriers protecting the reservoir remained intact.
Rune Nedregaard, Equinor’s Senior Vice President for Drilling and Well, said the company takes the incident very seriously. He noted that the event was dramatic for those involved, but emphasized that safety barriers worked as intended and the crew handled the situation effectively, preventing escalation.
Following the investigation, Equinor has introduced several measures aimed at reducing the risk of similar incidents. One immediate change requires the BOP to be closed whenever shallow cuts and casing pulling take place, regardless of the originally planned activation timing. The company also plans to share lessons learned and implemented improvements with its suppliers.
Equinor added that findings from the investigation will contribute to ongoing safety improvements, alongside the separate review being conducted by the Norwegian Ocean Industry Authority.
Photo credit: Odfjell Drilling. All rights reserved.