The outage affected Sverdrup's so-called Phase 2 development, although it was not immediately clear how big the output reduction was.

Sverdrup Phase 2, which began producing last month, had not yet ramped up to its full capacity of 185,000 barrels per day, the company said, without elaborating.

The field's power supply is now expected to be restored at midnight local time (2300 GMT), according to a regulatory statement on the Nord Pool electricity exchange.

Sverdrup, with an overall capacity of some 720,000 barrels of oil per day from its Phase 1 and 2 developments, gets its electricity via power cables from land.

(Reporting by Nerijus Adomaitis, editing by Terje Solsvik and Gwladys Fouche)