The gas escape on Gullfaks B occurred in connection with leak testing after maintenance work on a production well. The gas derived from a volume trapped between the downhole safety valve and the Xmas tree. It proved impossible to operate the emergency shutdown valves on the well.
The leak lasted about an hour, with an initial rate of 1.3 kilograms of gas per second. Some 800 kilograms of gas were released. No people were injured in the incident, but the leak created a serious position on the installation. Personnel present in the area could have been subject to serious or fatal injury if the gas had ignited.
Under slightly different circumstances, a leak to the air could have occurred at a significantly higher rate. Generally speaking, both size and ignition potential of a gas cloud rise with an increasing leak rate. A significantly higher leak rate than the one which actually occurred could very probably have caused the build-up of a large explosive gas cloud in the area and thereby represented an explosion risk with a substantial potential for becoming a major accident.
The PSA’s investigation team carried out investigations and conversations on Gullfaks B, followed by interviews with personnel in the land organisation and a review of documents.
The investigation concludes that serious deficiencies have been revealed in Statoil’s planning, approval and implementation of activities related to the maintenance of choke valves on Gullfaks B.
That includes deficiencies in management work on supervising that this activity was pursued in an acceptable manner.
The PSA sees that a number of the deficiencies identified by its investigation have features in common with shortcomings found when following up earlier incidents, including:
The PSA is concerned that improvement processes pursued after these and other incidents in Statoil appear to be failing to have an effect.
It has accordingly asked Mr Michelsen to submit a written explanation by 29 April 2011 covering the following conditions, among others.
On the basis of the response it receives from Mr Michelsen, the PSA will decide what action might be needed.