RIO DE JANEIRO, Oct 21 (Reuters) - Brazilian state-run

oil company Petrobras' could start oil and gas

production in the Foz do Amazonas basin within seven years if

large reserves are confirmed, the company's Chief Executive

Magda Chambriard told Reuters on Tuesday.

Brazil's environmental agency Ibama on Monday

greenlit

Petrobras to drill an exploratory well in Foz do Amazonas,

near the mouth of the Amazon River. The drilling should last

around five months.

"We could delineate the reservoir in about two years and,

if it's good enough, we'll be producing in seven or eight

years," Chambriard said in an interview.

If this deadline is met, production should start as

Petrobras' output at Brazil's pre-salt region starts to decline,

offsetting the loss, said Chambriard.

The area to be drilled, in deep waters off the shore of the

Amazonian state of Amapa, is considered Petrobras' most

promising oil frontier, sharing geology with nearby Guyana,

where ExxonMobil ( XOM ) is developing huge fields.

The company plans to drill six additional wells in the

environmentally sensitive region, but obtaining a license for

them should be easier than for the first one, said Chambriard,

as most environmental requirements are already met.

In 2023, Ibama denied Petrobras a request to drill there,

which the company immediately appealed, stoking divisions within

Brazil's government between environmental advocates and allies

pushing for oil and gas development in the region.

To finally meet Ibama's requirements, Petrobras invested

millions of reais to improve the firm's emergency response in

case of a spill.