Updated calculations now show a resource estimate of between 40 million and 90 million barrels of recoverable oil equivalents of gas and condensate, while the previous projection was for 23 million to 94 million barrels.

"This drilling has considerably lifted the floor of the resource estimate, thus reducing the risk and yielding a more robust project," Dag Omre, head of Spirit Energy's Norwegian subsidiary, said.

"We aim to submit a plan for development and operation to the authorities in 2019, which will allow for production to start in 2022," he added.

The company said it planned to develop the Fogelberg discovery by using a seabed installation tied into Equinor Aasgard B platform some 18 kilometres away.

Spirit, an oil and gas joint venture created last year between Centrica and Bayerngas Norge, holds a 51.7 percent stake in the licence, while PGNiG holds 20 percent, Faroe Petroleum 15 percent and Dyas Norge 13.3 percent.

Dyas' deal to acquire its 13.3 percent stake from Faroe is still pending approval from Norwegian authorities, Spirit added.

Spirit is also developing the North Sea's Oda discovery, which holds about 47 million boe and is expected to start producing in 2019.

($1 = 0.7598 pounds)

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