The deal was first announced by both firms in October this year.
Under the deal, Ineos new oil and gas subsidiary Ineos Upstream has acquired gas fields, including the Breagh and Clipper South fields, in the Southern North Sea.
Near to Ineos’ assets in the North East and Scotland, the acquired fields are expected to generate 8% of the UK’s total gas.
Russian billionaire Mikhail Fridman-led investment vehicle, LetterOne acquired these fields from RWE Dea earlier this year through €5bn deal.
Ineos Breagh CEO Geir Tuft said: "We are pleased to have completed the deal to acquire this strong portfolio of natural gas assets and bring on board a highly successful and experienced North Sea industry team."
Ineos chairman Jim Ratcliffe said: "We are pleased to acquire a strong portfolio of natural gas assets and bring on board a highly successful and experienced North Sea industry team.
"Ineos has been very open about its intention to make strategic investments in the North Sea and this acquisition is our first step in fulfilling this goal. It will also help our UK petrochemical assets to have ongoing access to competitive energy."
Ineos runs Scotland’s largest manufacturing complex at Grangemouth, which is claimed to be the only refining or petrochemicals complex directly linked to the North Sea.
The company, which also has multiple Shale gas licences in England and Scotland, intends to invest further $1bn on project that will bring US Shale gas to the UK and Norway.
Image: Ineos has acquired UK North Sea gas fields from DEA Group. Photo: courtesy of INEOS.
