The deal comes only weeks ahead of a deadline set by the government in April for DEA owner investment firm LetterOne to dispose of the oil and gas fields it bought from German utility RWE.
The terms of the sale have not been disclosed.
In a statement, Ineos chairman Jim Ratcliffe said: “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.”
The deal comes amid a protracted slump in global oil prices that has lead to cutbacks in the North Sea and cast a shadow over the fate of commodities groups.
The sell-off of the gas fields was ordered by Ed Davey, the then-Energy Secretary, in the wake of sanctions against Russia due to the crisis in Ukraine.
There was concern further sanctions against the country could jeopardise the continued operation of the assets.
Ineos also owns a number of shale gas licences in England and Scotland and is investing over £500m bringing US shale gas to the UK and to Norway.