Equinor Investigates Deepsea Bollsta Well Control Incident

Incident Overview

On 23 September 2025, a well control incident occurred on the Deepsea Bollsta drilling rig during operations on the Troll field. The incident involved a gas and fluid leak while cutting a 13-3/8" casing at a depth of about 510 meters.

Impact and Response

The leak spread to the drill floor and shaker room, causing minor injuries to one person who struggled to evacuate due to differential pressure. The gas and fluid column also damaged the room's ventilation system. Automatic gas detection triggered safety systems, disconnecting potential ignition sources. The crew activated the blow-out preventer (BOP) and diverter system, routing gas and pressure away from the rig.

Resolution and Measures

The BOP closed after 71 seconds, stopping the gas flow, and the situation was normalized in 30 minutes. Equinor implemented new measures, including a requirement to close the BOP during shallow cuts and casing pulls. The investigation revealed that about 930 kilos of gas leaked, classifying the incident as a red 1, the most serious category.

Investigation Findings

The incident was caused by the BOP being open during casing cutting, with confined gas present behind the casing. Incorrectly calibrated equipment failed to identify the gas in advance. The gas was from a limited volume and not in contact with the reservoir, with reservoir barriers intact. Equinor plans to share findings and measures with suppliers and considers the Norwegian Ocean Industry Authority's investigation crucial for future follow-up.