(Adds details of partnership, oil field, refinery)
SAO PAULO, July 4 (Reuters) - Brazil's state-run oil company Petroleo Brasileiro SA and China National Petroleum Corp (CNPC) took another step on Wednesday in negotiations that could give the Chinese their first refining capacity in the Americas.
The companies announced in a Brazilian securities filing that they had signed a letter of intent advancing talks for a partnership to finish the Comperj refinery near Rio de Janeiro and a "participation" of CNPC in the offshore Marlim oil field.
The joint announcement confirms an April report by Reuters that said the companies were working out a deal involving a CNPC investment at Comperj in exchange for a stake in the offshore Campos Basin and rights to use the refinery.
The talks highlight rising Chinese interest in the Brazilian energy sector, which has attracted billions of dollars from oil majors over the past year for rights to new exploration blocks as the government lowers barriers to foreigners.
The companies did not offer further details and said the implementation of the partnership will depend on the success of final negotiations.
"This strategic partnership will strengthen ties between the companies and will contribute to deepen the global strategic partnership between Brazil and China," the filing said.
In November, Pedro Parente, then chief executive of the Brazilian oil firm known as Petrobras, touted a 196 meter oil column discovered in the Marlim field, which he described as the best in the Campos basin.
Petrobras and CNPC have already partnered in the giant Libra oil field off the Brazilian coast since 2013.
Last year, they also partnered to win exploration rights for the Peroba field, another promising deposit in the area known as the pre-salt, where billions of barrels of oil are trapped under a thick layer of salt beneath the ocean floor.
Petrobras has already invested some $13 billion in the Comperj complex, which needs about $3 billion in additional investment to reach an initial capacity of 165,000 barrels per day, people familiar with the matter told Reuters in April. (Reporting by Gram Slattery and Marcelo Teixeira Additional reporting by Rodrigo Viga Gaier Editing by Brad Haynes, Chizu Nomiyama and Frances Kerry)