Probe into North Sea rig incident ends

March 3, 2026, by Melisa Cavcic

Norway’s state-owned energy giant Equinor has wrapped up its investigation into a well control incident that occurred on a semi-submersible rig working in the Norwegian sector of the North Sea. This incident is classified as being in the company’s highest category of severity.

Deepsea Bollsta; Source: Odfjell Drilling

Equinor has completed the investigation of a well control incident on the Deepsea Bollsta rig, managed by Odfjell Drilling and owned by Northern Ocean, on September 23, 2025. The incident occurred in connection with plugging a well on the Troll field, while cutting a 13-3/8″ casing at a depth of about 510 meters. A leak of gas and fluid spread to the drill floor and the shaker room, where rocks and cuttings are removed from the drilling fluid before the fluid is returned to the well.

During the incident, one person had trouble evacuating from the room due to the differential pressure that occurred; thus, they suffered minor injuries and received first aid treatment aboard after using force to get out. The gas and fluid column from the leak also damaged the ventilation system in the ceiling of the room.

Rune Nedregaard, Equinor’s Senior Vice President for Drilling and Well, commented: “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.”

The company claims that automatic gas detection triggered the rig’s safety systems and potential ignition sources were disconnected. The crew on Deepsea Bollsta activated the rig’s blow-out preventer (BOP) and diverter system in line with relevant procedures. The diverter system routed gas, fluid and pressure from the well away from the rig before the blow-out preventer closed.

The firm elaborates that blow-out preventer closed after 71 seconds; thus, stopping the flow of gas. The situation was normalised in 30 minutes. Equinor underlines that it has initiated multiple measures following the incident. A new requirement was immediately implemented to close the BOP in the event of shallow cuts and pulling the casing, regardless of activation time.

Based on the investigation’s calculations, about 930 kilos of gas leaked out in a short period of time, which is classified as a red 1 incident, the most serious category in the Norwegian firm’s management system. There was combustible gas on the drill floor and in the shaker room for a brief period of time, but potential ignition sources were disconnected.

The company’s investigation has determined that the circumstances would have to be different for the gas to ignite. The cause of the incident was determined to be the BOP 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.

As a result, the gas was not identified in advance. However, Equinor emphasizes that 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.

Nedregaard highlighted: “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. Several measures were initiated immediately following the incident.

“Equinor will share the investigation findings and implemented measures with our suppliers. The Norwegian Ocean Industry Authority’s investigation will also be important for Equinor’s follow-up moving forward.”