Seadrill has been slapped with an order by Norway’s safety watchdog after a probe uncovered regulatory breaches that led to unintentional disconnection of risers on the semi-submersible rig West Mira.

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The incident occurred on 14 March this year while the rig, operated by Seadrill and owned by affiliate Northern Ocean, was drilling a production well for Wintershall Dea at the German operator’s Maria field in the Norwegian Sea.

The rig’s lower marine riser package became decoupled after the rig lost position due to the impact of heavy weather, resulting in the automatic disconnection system (ADS) being activated.

“The disconnection signal was given after the ADS exceeded the five-degree activation point, which in turn automatically cut the string and shut in the well,” according to the investigation report by the Petroleum Safety Authority (PSA).

Consequently, the drill string had to be fished out of the well, with the drilling operation delayed by about three days as a result.

Drilling fluid leak

However, drilling was not being carried out in hydrocarbon-bearing layers of the reservoir when the incident occurred, which prevented any discharges from the reservoir into the natural environment, and no one was injured.

“The well was isolated by the shear ram in the blowout preventer (BOP). Since the weight of the drilling mud included a riser margin for the section, the barriers remained intact,” the report stated.

About 50 cubic metres of drilling fluid was released from the riser into the sea when the drill string was cut, it said.

“The PSA has concluded that the probability of losing well control while drilling in the reservoir section was low,” the agency said.

But it added: “The incident could have caused material damage to the facility and its equipment.”

'Cost-cutting'

The PSA determined that “a combination of sub-optimal mooring lines and extensive use of thruster capacity to maintain position meant thruster power was insufficient to withstand the dynamic forces at the time of the incident”.

The agency attributed the incident to a combination of factors including reduced situational awareness and assessment of risk, as well as cost-cutting and concentration on efficiency.

It found four regulatory non-conformities related to compliance with procedures, risk understanding, learning lessons from earlier incidents to prevent recurrence and deficiencies in meeting management responsibilities conferred by the German operator.

Seadrill has now been ordered to identify and initiate measures to prevent a recurrence of such an incident on the rig and present a plan to ensure the necessary measures are implemented on this and other drilling units, with a deadline of 15 October for compliance with the order.