By Gwladys Fouche
OSLO (Reuters) - Investigators for the Norwegian oil safety watchdog will fly to the BP-operated Valhall field Thursday to probe the causes of a fire that forced a total evacuation of workers on Wednesday and halted output.
A BP spokesman said it was still unclear when production would resume at the field, which produces some 31,000 barrels of oil per day according to the Norwegian Petroleum Directorate.
"We are going offshore this afternoon to investigate," Oeyvind Tuntland, director for professional competence at the Petroleum Safety Authority Norway, told Reuters. "A fire at an offshore platform is always serious."
New-York listed Hess is the majority owner in the field with a 64 percent share in the field while operator BP holds the remaining 36 percent.
The fire occurred in a vent pipe, used to evacuate gasses that could ignite, on the production and compression platform of the Valhall installations, according to a preliminary report BP sent to the watchdog, Tuntland said.
The fire occurred around 1500 GMT and was put out about an hour later, he added.
"How it was ignited, we have no idea," he said. "If any place should burn, it was one of the 'best' places for it to happen. It had no big potential to escalate. But a fire is a fire."
BP evacuated personnel and all were reported safe. Some 638 people had been working at the site, which is located about 290 km (180 miles) off southern Norway.
Asked on Thursday whether BP had any estimate as to when production at Valhall may resume, BP spokesman Jan Erik Geirmo said: "Not at this point in time."
He said there was no risk of a spill from the incident.
The production platform is one of five in a complex serving the oilfield.
Valhall's oil production is piped to the offshore Ekofisk Center and then on to Teeside, England, according to BP's website. Natural gas from the platform is transported by pipeline to Emden, Germany.
The platform also processes oil and gas from a smaller field known as Hod, located some 7 miles south of Valhall and also owned by Hess (62.5 percent) and BP (37.5 percent).
Valhall has pumped oil since the 1980s and is located in 70 meters of water.
BP said on its website that Valhall's infrastructure was being revamped this year to ensure the field can continue to operate until 2050.