The incident on the Songa Endurance drilling unit occurred in connection with work on a production well on the North Sea field.

This involved preparations to drill a sidetrack after permanent plugging of existing well paths in well 31/2-G-4 BY1H/BY2H.

In connecting with pulling the tubing hanger, the top drive with the completion string was suddenly raised six metres out of control. At the same time, large quantities of fluid and gas flowed out of control up through the rotary table. This blowout lifted the 2.5-tonne hydraulic slips and threw some two tonnes of bushings several metres across the drill floor. The liquid column reached the top of the derrick about 50 metres above the drill floor. Activation of a number of gas detectors led to local equipment shutdowns.

The blowout preventer was activated by drilling personnel immediately after the rising fluid column on the drill floor was observed and after the string shot up.

Stabilisation of the well was not achieved until 26 October 2016 after a long and challenging period of normalisation work.

The PSA decided to launch an investigation of the incident on 17 October 2016.


The PSA investigation has concluded that the direct cause of the incident was that large quantities of gas from the reservoir beneath the tubing hanger were released.

Underlying causes are found to be multiple and complex, but can primarily be related to planning, management of change, expertise and understanding of risk.


Nobody suffered physical injury during the incident but, under slightly different circumstances, it could have led to a major accident with the loss of several lives as well as substantial material damage and emissions/discharges to the natural environment.

The PSA regards this as one of the most serious well control incidents on the Norwegian continental shelf (NCS) since Statoil’s Snorre A incident in 2004. This view is based on the incident’s scope and potential.


The PSA investigation has identified several serious breaches of the regulations. These cover:

  • compliance with procedures
  • design of well barriers
  • risk assessment as a decision base for improving the efficiency of the operation
  • expertise
  • conduct of flow check.

The identified nonconformities largely coincide with nonconformities identified after the investigated well control incidents on Snorre A in 2004 and Gullfaks C in 2010. Following these incidents, Statoil has done extensive and long-term work and implemented many measures to comply with the orders. Important improvement measures in Statoil do not appear to have had sufficient effect in parts of the company’s business.

Based on the finding of the investigation, the PSA has issued the following order to Statoil.

Pursuant to section 69 of the framework regulations on administrative decisions, see sections 6 and 21 of the management regulations on management of health, safety and the environment and on follow-up respectively, we order Statoil to:

- identify the reasons why the improvement measures implemented in Statoil after the above-mentioned incidents and which have relevance for the conditions identified after this incident have not had the necessary effect on the Troll drilling organisation, and
- present a plan to ensure that the necessary improvement measures are implemented in and have the desired effect on the Troll drilling organisation.

The deadline for complying with this order is 28 April 2017. We must be notified when the order has been complied with.

The report describes identified nonconformities in addition to those which form the basis for the notice of an order, and we request an explanation of how these nonconformities will be dealt with. The report also contains observations where a potential for improvement exists, and we request your assessment of these.