West Hercules was drilling the 7132/2-1 wildcat in the Barents Sea when the incident occurred.

This sixth-generation GVA 7500 semi-submersible drilling facility is owned and operated by Seadrill Management. It received an acknowledgement of compliance (AoC) from the PSA in 2012.

Well 7132/2-1 lies in production licence 857, where Equinor Energy is the operator.

The incident

The LMRP became unintentionally disconnected at 22.46 on 16 January as the bottom hole assembly (BHA) was passing through the blowout preventer (BOP).

The incident occurred during preparations for drilling the 12 ¼-inch section in the well after completion of the 42- and 17 ½-inch top hole sections. This work covered drilling, cementing and pressure-testing  of the most recently set casing string – 20-inch x 13 3/8-inch – at a measured depth of 595 metres.

When the incident occurred, the sea was calm with a heave of 0.4 metres and good weather conditions. The water depth at the location is 293 metres.

The blind shear ram (BSR) in the BOP activated automatically when the LMRP was disconnected, and seawater in the riser drained to the sea. Subsequent observations showed that the BSR had failed to cut the drill string, which was stuck fast in the BOP.

A decision was taken by the PSA on 18 January to investigate the incident. The investigation team’s mandate included clarifying the course of events, and assessing direct and underlying causes with the emphasis on human, technical and organisational (HTO) as well as operational conditions from a barrier perspective. This mandate covered conditions up to the time of the incident.


No personal injuries or harmful discharges to the environment were caused by the incident.

The incident occurred while the well was secured with casing and a cement plug at the bottom. No risk accordingly existed of discharges from the reservoir to the environment.

Had the same incident occurred at a later time, with hydrocarbons present, however, the position could have been more demanding with environmentally harmful discharges from formations in the 12 ¼- or 8 ½-inch sections.


The direct cause of the incident was a fault in the automatic disconnect system (ADS), which signalled disconnection of the LMRP from the BOP.

Breaches of the regulations

Six nonconformities have been identified by the investigation. These relate primarily to

  • risk management
  • competence and capacity
  • procedures and compliance
  • maintenance
  • management of change
  • see-to-it duty

What happens now?

Seadrill has been asked by the PSA to explain how the nonconformities covered by the first five bullet points above will be dealt with.

The sixth nonconformity relates to the see-to-it duty, and is directed at the responsible operator. Equinor has been asked by the PSA to explain how this nonconformity will be dealt with.

Both companies have been given a deadline of 29 May 2019 to respond to the PSA’s requests.