The Norwegian authorities have completed an investigation into a potentially catastrophic accident that happened aboard a Statoil-run drilling rig in the North Sea in 2016.
The well control incident occurred on October 15, 2016, aboard the Songa Endurance semi-submersible drilling rig at the Troll field off Norway, prompting Statoil to evacuate non-essential personnel.
While nobody was injured, the Norwegian oil industry safety watchdog Petroleum Safety Authority Norway, on Tuesday said the event could have been fatal and could have led to a substantial material damage.
The incident 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.
According to the PSA, in connecting with pulling the tubing hanger, the top drive with the completion string was suddenly raised six meters 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 tons of bushings several meters across the drill floor. The liquid column reached the top of the derrick about 50 meters 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.
Stabilization of the well was not achieved until 26 October 2016 after a long and challenging period of normalization work, PSA said.
Speaking about the causes 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.
Could have been fatal
The safety body said that under slightly different circumstances, the incident 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,” the safety authority added.
The investigation concluded Statoil has breached several regulations covering: 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 safety body also added that the irregularities identified here largely coincide with Statoil’s previous incidents on Snorre A in 2004, and Gullfaks C in 2010. The PSA has acknowledged there have been improvements on Statoil’s side since the previous incident, however, these “do not appear to have had sufficient effect in parts of the company’s business.”
Following the investigation, the PSA has now ordered Statoil to identify the reasons why the improvement measures implemented in Statoil after the previously mentioned incidents have not had the necessary effect on the Troll drilling organisation. Statoil has also been ordered to 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.