BP said on Friday it would shut its Plutonio oilfield in Angola for maintenance work in April and expected the stream to return to production in May.

A BP spokesman said the oilfield was now pumping around 90,000 barrels per day (bpd), close to half its average output since it came on stream in 2007.

We have had various problems in recent weeks with the water injection system, BP spokesman Robert Wine said. In April we are going to shut it down to fix the problem with the injection system and it will come back up in May ... if all goes well.

He said he was unable to give an exact duration for the shutdown or to comment on the fate of the crude oil cargoes that had been due to load in April.

Loading programmes from Angolan state oil producer Sonangol last week showed four Plutonio cargoes of around 1 million barrels each scheduled to load in April: two by BP and two by an independent trading company.

Angola is now scheduled to export around 1.5 million bpd in April, down from 1.73 million bpd in March. If all the Plutonio cargoes are delayed or cancelled in April, that would reduce the country's total crude oil exports for that month to around 1.37 million bpd.