Statoil has concluded its in-house commission of inquiry following the gas leak on the Visund platform in the North Sea on 19 January. The underlying cause was a design fault on a knock-out drum.
The group has had an ongoing dialogue with the Petroleum Safety Authority Norway which today, 6 March, will receive a copy of Statoil's report on the inquiry.
The investigation confirms the chain of events and the direct cause as previously described by Statoil. A metal plate positioned at the flare tank's outlet to the knock-out drum collapsed, causing the damage and the gas leak. The function of the plate is to change the gas flow in the tank, to prevent liquids in the gas from being transported further to the flare.
The metal plate was deformed when it was exposed to aerodynamic forces as the gas flowed through. This created a build-up of pressure in the knock-out drum. A portion of the plate came loose and was carried in the gas flow into the flare piping. It created a hole about 50 centimetres in diameter in the pipe, where gas streamed out.
The gas leak was substantial, with a high leakage rate and large volumes of gas released into the air. All the technical safety systems and technical barriers functioned in accordance with the technical design. Following simulations, it has been concluded that at peak about 900 kilos of gas escaped through the hole per second.
"This was a very serious gas leak, which could have had considerable negative consequences," says Lars Christian Bacher, senior vice president for Statoil's Tampen business cluster. "The most important consideration is that nobody was hurt."
The Visund organisation is now carrying out the necessary repairs before production can start, with a thorough review of the entire processing facility. Production from Visund will resume when the management considers that justifiable.
Following the gas leak, Statoil has been checking other installations which have the same technical solution as Visund. The group has changed similar knock-out drum systems on the Kvitebjørn and Heidrun platforms.
The daily loss of output from Visund is roughly 35,000 barrels of oil and about five million cubic metres of export gas. Statoil's share is 32.9 per cent.
The field has been producing oil and gas since 1999, and Statoil took over as operator from Hydro on 1 January 2003.