RIO DE JANEIRO U.S. oil company Chevron discovered an oil seep in an offshore Brazilian oil field run by Petrobras near the site of a November leak that led to civil and criminal charges and sparked concerns about some of the world's most promising deep sea reserves.
No traces have been found on the surface, but droplets of oil were found leaking from the seabed of Petrobras' Roncador field, 500 meters away from Chevron's adjacent Frade field, Brazilian regulator ANP said.
Chevron said it first detected the seep on Saturday.
Leaks in November and March at Frade led to the suspension of operations there, as well as lawsuits for more than $20 billion and criminal charges against Chevron and its drilling contractor Transocean.
The latest leak adds to questions about the charges against Chevron and stokes broader concerns about the safety and speed with which Brazil can develop giant new offshore oil resources.
The Campos basin, which includes Roncador and Frade, and the neighboring Santos basin contain an estimated 100 billion barrels of oil. Brazil hopes the region will help it produce more than 7 million barrels a day of oil by 2020, passing the United States to be the world's No. 3 oil producer.
Evidence of another leak in the basin quickly caught the attention of the prosecutor pressing charges against Chevron, who has already said he is expanding his investigation to other companies and fields in the Campos basin.
"I'm going to look at this very carefully," said Eduardo Santos de Oliveira by telephone. "It's very close to Frade."
Still, some scientists have called the accusations swirling around the Campos basin hasty and exaggerated, in light of the small, naturally occurring seeps that originally attracted oil companies to the deep-sea deposits.
"We've confused things with the recent court cases," said geologist Cleveland Jones, of the State University of Rio de Janeiro, by telephone. "Seeps are common in the Campos Basin ... and oil in small amounts is not an ecological problem."
Chevron said it traced the seep with a remote submarine outside the Frade field.
"Upon further investigation with a remote operated vehicle, we determined the seep point was outside the boundary of the Frade field," Chevron said in a statement. "We have notified the operator of the concession."
State-run Petrobras confirmed in a statement it had found the source of the oil seep in the seabed of its Roncador field, 120 kilometers (75 miles) off the coast of Rio de Janeiro.
A November accident at a well in the Frade field caused a spill of about 3,000 barrels due to operational and safety violations and improper well design, according to the ANP's four-month investigation.
Chevron's November spill was less than 0.1 percent the size of BP's 2010 Deepwater Horizon disaster in the Gulf of Mexico. In the BP spill, 11 died and about 4.9 million barrels leaked over three months. In Frade, no one was hurt, no oil came near the Brazilian coast and the leak was stopped in four days, according to Chevron.
The subsequent March seep in the Frade field led Chevron and its partners there, Petrobras and a Japanese group led by Inpex and Sojitz, to shut down production at the field, which was averaging 62,000 barrels daily, in order to study the source of the leak.
Chevron said the March leak totaled about two barrels, over half of which was captured, making it less than 0.1 percent of the field's November spill.
(Writing by Brad Haynes; Editing by Daniel Magnowski and Muralikumar Anantharaman)