U.K. oil and gas producer Serica Energy agreed to buy North Sea peer Tailwind Energy Investments for 644 million pounds ($782 million), including debt, it said on Dec. 20, bringing on energy trader Mercuria as its biggest investor as part of the deal.

Serica, whose production operations are centered on the U.K. North Sea, said it would issue 367 million pounds of new shares, take on Tailwind's net debt of about 277 million pounds and pay 58.7 million pounds in cash upon the deal's completion.

"Through the introduction of Mercuria as a new strategic investor, we will be differentially positioned to take advantage of the opportunities we expect to arise through industry consolidation, the North Sea transition deal and potentially overseas," Serica's CEO Mitch Flegg said.

Shares of Serica fell 4% to 266.5 pence at 9:50 GMT.

Geneva-based Mercuria, which is the largest shareholder of Tailwind, will have a 25.2% holding in Serica as part of the deal, the London-listed company said.

The deal to buy Tailwind Energy Investments from Tailwind Energy Holdings comes months after Serica rejected North Sea investment firm Kistos' 1.2 billion pound offer, and made its own proposal to buy Kistos, which the investment firm also refused.

Kistos ultimately walked away from making a bid for Serica in August.

Serica on Tuesday also reaffirmed its 2022 production, which will be within 26,000 boe/d-28,000 boe/d.