OIL giant BP has announced the discovery of what is believed to be a large North Sea field in a boost that could extend production by more than three decades.

The firm has made two significant oil finds, one west of Shetland and another in the central North Sea.

That should lead to production doubling to 200,000 barrels a day within two years.

BP has spent billions in recent years developing new fields while also selling off mature assets in the UK Continental Shelf due to falling oil prices.

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Now the firm is understood to be excited by the prospect of detecting the Capercaillie field and Achmelvich – close to the largest North Sea filed ever found, the Clair Field west of Shetland which began production in 2005.

Tests have been carried out to discover the volumes of gas and oil present, and the data is “under evaluation”.

Scientists will evaluate the drilling results to assess future options, but staff at BP have described the find as “exciting”.

BP North Sea regional president Mark Thomas said: “These are exciting times for BP in the North Sea as we lay the foundations of a refreshed and revitalised business that we expect to double production to 200,000 barrels a day by 2020 and keep producing beyond 2050.

“We are hopeful that Capercaillie and Achmelvich may lead to further additions to our North Sea business, sitting alongside major developments such as Quad 204, which came onstream in 2017, Clair Ridge, due to come into production this year, and the non-operated Culzean field, expected to start up in 2019.”

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Interest in the west of Shetland area is surging among oil and gas firms with exploration well numbers set to reach the highest level since the price of crude oil plunge started.

It is considered strategically important region in keeping North Sea activity afloat and has already attracted interest from giants BP, Shell and Total as well as rising oil explorers Siccar Point Energy and Hurricane Energy.

The recent discovery of the giant Lancaster field by Hurricane Energy underlines the potential to make big finds in an area in which there has been relatively little drilling so far.

Private-equity backed Siccar Point Energy will also drill a well in the area while Ineos is targeting the Lyon prospect, which is estimated to contain more than 250 million barrels oil equivalent.

Last year BP started extracting oil from one of the largest new North Sea projects in recent years.

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The development followed the firm’s £3.4 billion upgrade to the Schiehallion field west of the Shetland islands close to the new Capercaillie field.

Oil and gas output is expected to reach an eight-year high in the UK North Sea this year helped by the start of production from the giant Clair Ridge and Mariner developments off Shetland.

*The Herald has amended the opening paragraph in this story to clarify that while deemed an exciting discovery, the field may not be 'one of the largest ever found' in the North Sea.