Incident probe on Statoil’s Visund finds well barrier breaches

Visund

Norway’s offshore security watchdog, the Petroleum Safety Authority (PSA), has identified multiple regulation breaches during its investigation of the well-control incident at Statoil’s Visund A platform in the Norwegian North Sea.

Statoil, who is the operator of the Visund field, shut down production on March 16 this year after experiencing problems with the well. The incident occurred due to a buildup of well pressure in connection with the completion of a drilling operation.

Days after the incident, the PSA launched its investigation in order to clarify the events and identify the underlying cause of the incident.

According to the agency’s incident report from Thursday, Statoil tried to kill the well and discovered that both kelly cock valves below the top drive had jammed, one in the closed position, which prevented the use of normal kill procedures. Alternative kill methods were assessed, while attempts were made to operate the valves.

The well was shut in using a valve on the BOP. The pressure was observed in the well, which finally stabilized at 84 bar.

Actual consequences

The safety agency’s investigation showed that the installation was depressurized and production at Visund had to be shut down. No injuries to persons, material damage or emissions to the external environment were registered as a result of the inflow into the well.

Potential consequences

The report stated that this incident differs from others due to the fact that well killing was prevented by a jammed valve and due to the assumption that the barrier in the well was verified in the form of a confirmed inflow test.

PSA assessed that in very slightly different circumstances, the well kick might have led to a complicated and long-lasting kill operation with the potential for escalation of risk.

Non-conformities

The investigation report has shown several non-conformities including the design of well barriers, verification of well barriers, classification of safety-critical equipment, the maintenance program for kelly cock valves, and the configuration of the seabed BOP.

Furthermore, PSA identified improvement points concerning well barriers, the risk register in DOP documents, and training and drills.

Statoil must report on how the non-conformities and improvement points will be dealt with by August 18, at the latest.

The Visund oil and gas field is 22 kilometers northeast of the Gullfaks field in the Tampen area. Oil production began in 1999 and gas production in 2005.

The field has been developed using the Visund FPDU, a semi-submersible drilling, processing and accommodation platform. Statoil is the operator of the field and its partners are Petoro, ConocoPhillips, and Total E&P Norge.

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