Oil giant Petrobras last week announced it had identified the presence of hydrocarbons off the coast of northern Amapa state, nearly a year after it began drilling.
The majority state-owned firm began exploration after a five-year process to obtain an environmental permit.
The discovery is "a passport to this country's future and in saying this, I'm not denying my fight to one day be free of fossil fuels," Lula declared on a visit to Petrobras's operations base, dressed in one of the company's orange jumpsuits.
Brandishing a vial containing a sample of the crude, he joked: "I'm going to keep it in a chest, it's so good, it smells so good."
The veteran leftist supports the gradual phasing out of fossil fuels to curb climate change.
However, he believes Brazil needs oil revenues to fund the transition to clean energy and achieve energy sovereignty.
The oil was found in a maritime region known as the Equatorial Margin, about 175 kilometers (110 miles) off the Amazon coast.
Petrobras President Magda Chambriard said that another 15 to 20 days of drilling were needed to determine the size of the field.
Experts have warned for years that burning fossil fuels is the main cause of global warming.
Environmentalists also argue that drilling threatens a region rich in biodiversity, situated off the coast of the world's largest rainforest.
Lula, 80, is seeking a fourth non-consecutive term in October elections.