Adds details on the deal in paragraphs 4-7

By Peter Frontini

SAO PAULO, Dec 28 (Reuters) - Engie Brasil EGIE3.SA said on Thursday it had reached a deal to sell a 15% stake in natural gas pipeline firm TAG to Canadian investment fund Caisse de Depot et Placement du Quebec (CDPQ) for 3.1 billion reais ($641 million).

After the deal's conclusion, CDPQ will raise its stake in TAG to 50%, while Engie Brasil will own 17.5% and its French parent company will hold the rest, giving it an indirect 50% stake.

In 2019, Engie and CDPQ jointly acquired a 90% stake in TAG from state-run oil firm Petrobras PETR4.SA for about $8.6 billion at the time, purchasing the remainder the following year.

TAG owns and operates a large part of Brazil's natural gas pipelines with some 4,500 km (2,800 miles) over 10 states in the country that have a firm contracted natural gas handling capacity of 74.67 million cubic meters per day.

The deal, which is expected to close by the end of January pending regulatory approvals, implies an enterprise value of 37.5 billion reais for TAG, compared with 35.1 billion reais in 2019, according to Engie.

The proceeds of the sale will be used to implement Engie Brasil's investment plan in renewable energy and transmission lines "without increasing pressure on leverage, ratings and payout," Chief Financial Officer Eduardo Takamori said in a statement.

The company will hold a conference call on Friday morning to discuss the transaction.

($1 = 4.8501 reais)

(Reporting by Peter Frontini; Editing by Chris Reese, David Alire Garcia and Jamie Freed)

((Peter.Siqueira@thomsonreuters.com; +55 11 56447727;))