Nigeria's oil output fell close to a 22-year low this month due to attacks on oil pipelines in the southern Niger Delta, home to much of the country's oil and gas wealth, compounding the impact of low oil prices on Africa's largest economy.
On Wednesday, Shell Petroleum Development Co (SPDC) said it declared force majeure on Bonny Light crude exports on Tuesday after closing the Nembe Creek Trunk line (NCTL) for repairs after a leak.
NCTL carries all the country's Bonny Light. A Shell spokesman blamed technical issues, without giving further details. However, a community leader in the Delta said an explosion had shut down the pipeline.
The outage pushed oil futures higher, with benchmark Brent crude trading up 5 cents at $45.57 per barrel by 1321 GMT, after being slightly lower before the announcement.
Nigeria was due to export around 217,000 barrels per day of Bonny Light crude in June, out of a total of 1.7 million bpd. If all Bonny Light production is cut, it would bring output to below 1.5 million bpd for the first time since September 1994, according to Energy Information Administration data.
Nigeria exports almost all its production. Nigerian oil production was above 2 million bpd as recently as 2013, the EIA data shows.
Shell and Chevron have evacuated oil workers in the past few days due to a surge in attacks on oil facilities, according to Nigerian labour unions.
Recent violence has raised concern that militants might resume an insurgency that has been quiet for the past several years.
A labour union on Tuesday called for the evacuation of oil workers from the region.
Last week, a group known as Niger Delta Avengers attacked a Chevron facility in the Delta after claiming a strike in February against a Shell pipeline, which shut down the 250,000 bpd Forcados export terminal.