Investigation finds breaches of regulations following ‘West Hercules’ incident

Norwegian Petroleum Safety Authority Norway (PSA) has completed its investigation of the incident on West Hercules rig on January 16, 2019, when the lower marine riser package (LMRP) was unintentionally disconnected. Several breaches of the regulations have been identified.

West Hercules drilling rig / Image source: Seadrill

The West Hercules rig was drilling the 7132/2-1 wildcat in the Barents Sea offshore Norway when the incident occurred. The well 7132/2-1 lies in production license 857, where Equinor Energy is the operator.

This sixth-generation GVA 7500 semi-submersible drilling rig is owned and operated by Seadrill Management.

The rig received an acknowledgement of compliance (AoC) from the PSA in 2012.

The incident

According to the PSA’s report on Wednesday, the LMRP became unintentionally disconnected at 22.46 on January 16 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 meters.

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

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 January 18 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.


The PSA said that 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.

However, the PSA noted that, had the same incident occurred at a later time, with hydrocarbons present, 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 signaled disconnection of the LMRP from the BOP.

Breaches of 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, and see-to-it duty.

Seadrill has been asked by the PSA to explain how the first five nonconformities 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 May 29, 2019, to respond to the PSA’s requests.

In related news, the PSA recently gave a notice of order to Seadrill regarding its management of emergency preparedness, logistics, maintenance and the working environment on the West Hercules drilling rig following an audit conducted last February.

End of April has been particularly turbulent for the rig as Greenpeace activists climbed the West Hercules on Monday, April 29, during its stay near Rypefjord village, Norway, to protest against Equinor’s Arctic drilling plans.

After spending 16 hours on the rig, the Greenpeace activists ended the protest due to bad weather.

Come early May and Equinor was cleared to use West Hercules rig for Sputnik well, which is located in the Barents Sea offshore Norway. Drilling is scheduled to begin this month and is estimated to last for 33 days.

Offshore Energy Today Staff

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