Renewed safety concerns over Total's North Sea Elgin gas leak

The leak at the Elgin field last year was the worst in the North Sea for 20 years

Renewed safety concerns have been raised about an oil and gas field which was shut down last year due to a leak.

According to a report from Reuters news agency, the operator of the Elgin field has identified concerns about the corrosive effect of chemicals on pipes.

It is further claimed by Reuters that Total has plans to close down several Elgin wells due to the safety concerns. That could be at considerable expense.

The BBC sought clarification from Total, who said it was an "old story".

The French firm had described it as a "unique event".

The report goes on to say that the concerns about corrosion have been shared with Shell, which operates the neighbouring Shearwater field and which could face similar challenges.

Reuters said Total attributed the leak to a corrosive reaction between calcium bromide used to complete the well and grease in the pipework, which under high pressure cracked the piping.

Drilling fluids, such as calcium bromide, are commonly used in other deep sea wells across the world.

Total's G4 well in the Elgin field leaked for a month and a half from March 2012, creating a huge cloud of flammable gas above the platform about 150 miles (240km) east of Aberdeen.

An air and sea exclusion zone was imposed as personnel were evacuated from the area, with the incident being described as the worst leak in the North Sea for 20 years.

Some experts fear a recurrence as operators, under pressure to offset declining output from conventional reservoirs, turn to deeper, hotter and higher pressure fields.

John Downs, a chemical engineer who runs his own consultancy group, is quoted in the Reuters report as saying: "Bromide brines have been used in thousands of wells since their introduction in the 1980s.

"An extensive well repair programme may be needed if the stress corrosion cracking caused by bromide brine in Elgin is also happening elsewhere."

'Similar problems'

The North Sea is host to the highest number of high-pressure, high-temperature (HPHT) reservoirs of any mature oil and gas producing basin.

Total UK chairman Patrice de Vivies told Reuters he had co-operated particularly closely with Royal Dutch/Shell when sharing information on the causes of the leak.

He added: "With Shell we have shared even more as they have a neighbouring field, Shearwater, meaning they potentially have, perhaps, not identical, but similar problems."

Like Elgin, Shell's Shearwater field is fed by a HPHT reservoir where temperatures can reach 140C.

At peak output, Elgin and Shearwater account for more than a tenth of British gas production.

Total's own investigation into the causes of the leak remains incomplete, though the field resumed output in March, with the backing of the Health and Safety Executive (HSE).

"We hope that the laboratory will be in a position by the end of the year to reproduce the phenomenon," Mr de Vivies said.

A Total spokesman later told BBC Scotland: "This is an old story based on information that was made publicly available at the time we resumed production on Elgin in March this year - that based on new well integrity criteria we introduced following learnings from the G4 incident, we were not going to restart all the Elgin/Franklin wells that had previously been producing.

"At the same time, we outlined what we believed to be the cause(s) of the G4 incident and also said on numerous occasions that we were sharing lessons learned with the rest of the industry."

A Shell spokesperson said: "Shell is redeveloping the Fulmar reservoir from the Shearwater platform in line with UK regulatory requirements.

"We participate actively in industry knowledge-sharing, and are confident in the safety of our well designs and operations."

The HSE said there have been no reports of leaks attributed to similar types of corrosion.