Statoil has completed investigations of a well control incident on the offshore Troll field and a hydrogen leak at Mongstad, and revealed that the Troll incident could have been fatal.
On October 15, 2016, a serious well control incident occurred off Norway on a drilling rig Songa Endurance, while it was working at Troll field, prompting the company to evacuate non-essential personnel.
The well was secured with a blowout preventer around the drill string on the seabed and with a valve on the rig itself.
Ten days later, during surface maintenance, a hydrogen leak occurred due to external corrosion of a pipe socket at the Mongstad processing complex. Nobody was injured in either incident.
Statoil said on Friday that it conducted a thorough internal investigation in addition to the investigation being conducted by the PSA.
The company also held a press conference to address the findings from the internal investigation.
Margareth Øvrum, executive vice president for Technology, Projects, and Drilling in Statoil, said: “We are taking both these incidents seriously. Openness is vital to our safety work, and the investigation reports are important contributions for us to learn from the incidents. If we are to make the right decisions and carry out the right measures we need to get everything on the table.”
Songa Endurance well control incident
According to Statoil, the well control incident led to a gas leak that pushed seawater more than 30 meters 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 defines the incident as having a high degree of seriousness and concludes that at worst it could have led to a 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 factors have weakened the barriers and helped gas reach the drill floor. Namely, the existing downhole valves which were used as barriers against the reservoir were unintentionally opened, and the annular preventer inside the BOP 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, some immediate actions were taken to ensure that the downhole valves are not used as barriers, and a deeply set plug was reintroduced as a barrier during use of vertical Christmas trees.
“This is a very serious well control incident. The actions taken will improve our ability to assess risk, both before and during operations. We will share our experience from this incident with the rest of the industry,” says Øvrum.
Mongstad hydrogen leak
During pipe inspection in connection with surface maintenance in the isomerization plant at Mongstad, a portable gas detector was triggered close to a valve. When an attempt was made to close the valve, the pipe socket broke, and high-pressure hydrogen-rich gas was released.
The investigation points to external corrosion as the triggering cause. Wrong prioritization of maintenance as a result of insufficient risk understanding was identified as the root cause.
Statoil decided to intensify surface maintenance over the next two years. Safety management will be improved further by increased management presence at the plant. New detection technology will also be considered to improve the company’s ability to detect leaks.
Other incidents in October 2016
Apart from the incidents which were the focus of this investigation, three more incidents occurred in October 2016. Namely, a fire broke out aboard Statoil’s Statfjord A platform on October 16 prompting a production shutdown.
Later on the same day, Statoil also had to shut down production at its Gullfaks A platform in the North Sea after a gas alarm was triggered.
A few days before the Statfjord and Gullfaks incidents, five people were exposed to poisonous H2S gas at the Statoil-operated Sture Terminal in Hordaland, Norway.
Statoil completed its investigations of the Statfjord A and Sture Terminal incidents in December last year. The investigations showed that the risk of escalation in the Statfjord incident was small while the Sture incident had the highest degree of seriousness and, in other slightly different circumstances, it could have resulted in fatalities.