Equinor has concluded its investigation into a well control incident on the Deepsea Bollsta drilling rig at the Troll field, about 65km west of Kollsnes near Bergen, which involved a release of around 930kg of gas.
The incident occurred while plugging a well, when crews were cutting a casing at roughly 510m depth and gas and fluid leaked, spreading to the drill floor and the shaker room.
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Automatic gas detection activated the rig’s safety systems, which led to the disconnection of potential ignition sources. The crew onboard engaged both the blow-out preventer (BOP) and diverter system according to established procedures.
The diverter system redirected gas, fluid and pressure away from the rig prior to closure of the BOP. The BOP sealed after 71 seconds, halting the flow of gas, and operations returned to normal within half an hour.
One individual encountered difficulties evacuating from the shaker room due to differential pressure during the incident. This person sustained minor injuries and received first aid on board after forcing their way out.
The gas and fluid leak also damaged the room’s ceiling ventilation system.
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By GlobalDataInvestigation findings show the brief gas release was classified as a Red 1 incident, the highest severity level in Equinor’s management system.
Gas was present on the drill floor and in the shaker room for a short time, but no ignition occurred as sources were disconnected. The investigation concluded that ignition would have required different conditions.
The analysis identified that the BOP was left open while cutting the casing, despite confined gas being present behind it. Although annulus logging took place before cutting began, incorrect calibration of equipment meant this gas was not detected in advance.
Investigators determined that there was no risk of an uncontrolled blowout because the leaked gas originated from a limited space behind the casing with no contact to the reservoir. All barriers to the reservoir remained intact.
Equinor responded by introducing an immediate requirement to close the BOP during shallow cuts and when removing casing, regardless of activation duration.
Equinor drilling and well senior vice-president Rune Nedregaard said: “We are 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. We have 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.”
The Troll field is among the largest oilfields on the Norwegian Continental Shelf and recorded daily oil production exceeding 400,000 barrels in 2002.
Prior to this, Equinor announced a commercial oil discovery in the Norwegian North Sea’s Snorre area, with estimates indicating between 25 and 89 million barrels of recoverable oil equivalent.
