French oil major TotalEnergies has announced diversification of key stake in a prolific oil producing asset to Shell.

The company said on Thursday it agreed to sell its 12.5 per cent stake in the Bonga oilfield offshore Nigeria to Shell the field's operator, for $510 million.

The deal will bring Shell's stake in Bonga to 67.5 per cent and shows its continued interest in producing oil offshore Nigeria after selling its spill-plagued Nigerian onshore assets to Renaissance, a consortium of four local companies and an international energy group.

Last year, the owners of Bonga decided on an extension of the field to add 110,000 barrels of oil equivalent per day with the first oil expected to flow by the end of the decade. Bonga's floating production vessel has a capacity of 225,000 bpd.

"This acquisition brings another significant investment in Nigeria deep-water that contributes to sustained liquids production and growth in our Upstream portfolio," said Shell's upstream Chief Peter Costello.

Exxon subsidiary Esso Exploration and Production Nigeria holds 20 per cent and Oando's Agip 12.5 per cent of Bonga.

The deal, subject to approvals, is expected to close by the end of the year.