RIO DE JANEIRO--Karoon Energy Ltd. aims to boost production by more than 60% at an oilfield it is purchasing from Petrobras, as the independent Australian firm dramatically expands its operations in Brazil, an executive said on July 25.

Petrobras on Wednesday announced the sale of the Bauna cluster in Brazil's Santos Basin for $665 million to Karoon, as well as the sale of the Pampo and Enchova shallow-water clusters to UK-based Trident Energy for $1.051 billion including future payments.

While still subject to regulatory approvals, the deals represent a significant step forward in Petrobras' aggressive drive to divest non-core assets and re-focus on exploration and production in Brazil's deepwater, 'pre-salt' area.

It was also a coup for Karoon. Shares in the firm closed up some 12.4% higher on Wednesday, its biggest intraday gain in over five years.

In a Thursday phone interview, Tim Hosking, Karoon's general manager for South America, said the firm aimed to increase production at Bauna to 33,000 barrels per day (bbl/d) by 2022, up from around 20,000 bpd currently. He said he expected the purchase to be formalized within 10 months.

To complete the acquisition, according to a corporate presentation, Karoon will use $228 million of its own cash and the firm has access to a $250 million credit line from ING. The firm also intends to raise capital via new and existing shareholders, the presentation said.

In January, Reuters reported that Karoon and Rio de Janeiro-based oil firm Petro Rio SA had placed binding offers for Bauna. Brazil-listed common shares in Petro Rio were off 3.5% on Thursday.

Hosking said Karoon will take advantage of operational synergies between Bauna and the company's nearby Neon and Goiá discoveries, formerly known as Kangaroo and Echidna.

Karoon aims to present a development plan for Neon to Brazil's ANP oil regulator by the end of August, Hosking said. The field should produce 25,000 bbl/d to 28,000 bbl/d by 2023, he added.

Petrobras, by far Brazil's largest oil producer, is selling off hundreds of relatively mature onshore and offshore oilfields, attracting a number of independent oil firms and private equity firms eager to snap up assets. Karoon will continue examining the assets that come up for sale, Hosking told Reuters.

"Certainly, Brazil is a key country for growth," he said. "If we find interesting opportunities for the company, we'll go for them.