Statoil has released the findings of its investigations into last year’s well control incident that occurred on the Troll field off Norway.
The incident occurred during well plugging by the mobile rig Songa Endurance and led to a gas leak that pushed seawater more than 30 meters (98 feet) up the derrick before the well was closed by the annular preventer inside the blowout preventer (BOP) about one minute later.
Statoil’s internal investigation defined the incident as having a high degree of seriousness and concluded that at worst it could have led to loss of life if the safety equipment had failed to function as intended or if the gas had been ignited.
The BOP was quickly activated and stopped the gas leak, and five gas detectors automatically turned off equipment that could have produced sparks.
The investigation report concludes that two main findings weakened the barriers and helped gas reach the drill floor. The first was that existing downhole valves were used as barriers against the reservoir and were unintentionally opened. The second related to the annular preventer inside the BOP that should have been closed before the operation was started, because it was not possible to measure the pressure below the wellhead sealing.
After the incident, action was taken to ensure that downhole valves are not used as barriers and a deeply set plug was reintroduced as a barrier during use of vertical Christmas trees.
Statoil’s investigation report is available here.