An investigation of a well control incident at Visund A that halted production at the field and evacuated workers in March has been completed by Norway’s Petroleum Safety Authority (PSA), revealing several regulation breaches at the Statoil-operated North Sea platform.
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Visund, from Statoil. |
“On 16 March 2016, in connection with a well wash during completion of a drilling operation at Visund, a well-control incident occurred involving inflow from the reservoir (a well kick). In advance of the incident, Statoil had assumed that barriers, notably in the form of a cemented 7in liner, had been verified. Shortly after the washing process was completed and the well was filled with seawater, the drill string was raised and a volume increase was observed. The well was shut in using a valve on the BOP. Pressure was observed in the well, which finally stabilized at 84 bar,” the PSA reported.
The investigation discovered that while trying to kill the well, 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.
At the time of the incident, theinstallation was depressurized and production at Visund was 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, the PSA confirmed.
What made this incident special, the PSA said, is that normal well-control methods for killing the well were prevented by a jammed valve below the top drive, and that there was originally assumed to be a verified barrier in the well in the form of a confirmed inflow test.
“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,” the PSA said.
The agency’s investigation identified non-conformities relating to 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 sea-bed BOP. In addition, improvement points were identified in respect of well barriers, the risk register in DOP documents, and training and drills.
The PSA has given Statoil a deadline of 18 August 2016 to report on how the non-conformities and improvement points will be dealt with.
The Visund oil and gas field is located in Blocks 34/8 and 34/7, about 22km northeast of the Gullfaks field in the Tampen area of the Norwegian North Sea.
The development comprises a semisubmersible steel production, drilling and quarters platform (Visund A). Water depth in the area is around 335m. The northern part of Visund has been developed using a subsea template, around 10km north of Visund A.
The subsea-completed wells on the field are tied back to the floater with flexible risers. Oil is piped to Gullfaks for storage and export. The Visund field began producing gas and exporting it to continental Europe on 7 October 2005. Visund came onstream in spring 1999.
Statoil is the operator of Visund with 53.2% stake. Partners include Petoro (30%), ConocoPhillips (9.1%), and Total (7.7%).
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