French oil giant Total announced on Monday that it had sold 20 percent of its stake in OML 138 block oilfield to Sinopec, a subsidiary of China Petrochemical Corporation.

Total said the transaction, which would bring the largest hydrocarbon producer in France 2.5 billion U.S. dollars, remained subject to the approval of Nigerian authorities.

The OLM 138 block contains the Usan field which started production in February 2012 and accounts for less than 10 percent of the company's equity production in Nigeria, Total added in a statement.

"The transaction is aligned with Total's active portfolio management... This sale of an asset operated from a minority position will allow us to focus our resources on the material growth opportunities in Total's portfolio," said Yves-Louis Darricarrere, the group's president upstream.

Celebrating fifty years of presence in Nigeria this year, Total's production in the West African country was at 287,000 barrels of oil equivalent per day in 2011.

Total, which operates in more than 130 countries all over the world, announced a 20-percent rise in its adjusted net income to 3.34 billion euros (4.27 billion U.S. dollars) in the third quarter thanks to a rebound of refining and chemical activities.