Equinor (EQNR) said Monday the Johan Castberg oil field, which it operates with a 46.3% ownership stake, has started production.

With 12 of the field's 30 wells ready to come online, the Barents Sea field is expected to reach plateau production in Q2, the energy company said. At its peak, the field will be able to produce 220,000 barrels per day, with recoverable volume estimated at between 450 million and 650 million barrels.

Johan Castberg will produce for at least 30 years, and the investment of 86 billion Norwegian krone ($8.2 billion) into developing the asset "will be repaid in less than two years," according to Equinor executive Geir Tungesvik.

"We've identified options to add 250-550 million new recoverable barrels that can be developed and produced over Johan Castberg," Equinor executive Kjetil Hove said.

The other licensees on Johan Castberg are Var Energi with a 30% stake, and Petoro with 23.7%.

EQNR shares were 0.5% higher in recent premarket activity.