Norwegian authorities are to probe a well control incident involving a Seadrill semi-submersible last week as it was drilling a wildcat for Equinor, with operations now halted by the state-backed operator.

The incident on 16 January caused work to be stopped on the West Hercules as it drilled the 7132/2-2 well on the Gjokaasen prospect in Equinor-operated production licence 857.

The lower marine riser package on the rig’s blowout preventer became “unintentionally disconnected” during drilling operations, leading to the halt in work, the Petroleum Safety Authority (PSA) said on Monday.

There were no injuries or environmental damage as a result of the incident, which the PSA said it will now investigate.

The safety body has informed Norwegian police of the incident, the cause of which is unknown.

A spokesperson for Equinor told Upstream that operations on the well were halted as of late Thursday last week "and will remain so until we know the cause of the disconnect".

Seadrill has initiated an investigation into the incident, the spokesperson continued.

The West Hercules mobilised to the Gjokassen well earlier this month after drilling the 7122/7/7S appraisal well at Goliat West on the Goliat field in the Barents Sea for operator Vaar Energi.

That well hit hydrocarbon-bearing sandstones in a Lower and Upper Jurassic reservoir after being drilled to a vertical depth of 1240 metres into the Tubaaen and Fruholmen formations in Vaar-operated production licence 229.

It uncovered an oil and gas column of 18 metres thickness in the targeted Tubaaen formation that was said to have what Vaar said were “excellent” reservoir properties, while a 35-metre oil column was found in a lower reservoir in the Fruholmen structure.

(This article has been amended from the original. The original stated that the rig was drilling the 7132/2-1 well at the time of the incident. However, it had already moved on to the 7132/2-2 well - Gjokassen Deep - at the time of the incident.)

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Equinor halts drilling after ‘well control incident’ on rig