Brazil's Petroleo Brasileiro SA will sell its 50 percent stake in a Nigerian oil and gas exploration venture to a consortium led by top oil trader Vitol for $1.53 billion, the latest step in the state-controlled oil company's debt reduction drive, according to a securities filing on Wednesday.

The other 50 percent stake in Petrobras Oil and Gas BV, also known as Petrobras Africa, is owned by Brazilian investment bank BTG Pactual, which in a Wednesday filing confirmed a Reuters report that it would likely hang on to its portion after previously mulling a sale.

Petrobras, one of the world's most indebted oil majors, had targeted $21 billion in asset sales for 2017 and 2018, but only succeeded in unloading $9.5 billion worth by the end of the first half.

The deal involves a stake in some of two deepwater exploration blocks that are among Nigeria's largest and lowest-cost fields. Swiss-based Vitol is expected to shoulder the largest part of the investment, spending an estimated $1 billion, according to a Reuters report in June about the oil trader's interest.

Vancouver-based Africa Oil Corp and Delonex Energy, an Africa-focused oil company, are members of the consortium.

Petrobras earlier this year sold a 25 percent stake in Roncador, one of Brazil's largest oil fields, to Norway's Equinor ASA for about $2 billion.

It is also in talks to sell its TAG gas pipeline unit, probably to a group led by France´s Engie SA, for more than $7 billion, although the process has been halted by a Brazilian Supreme Court injunction.

A source with direct knowledge of Petrobras' operations told Reuters on Tuesday that the oil company wished to obtain an additional $20 billion through asset sales through the end of next year.

(Reporting by Marcelo Rochabrun; Editing by Chris Reese and Peter Cooney)