RIO DE JANEIRO, Sept 29 (Reuters) - Studies by Brazilian state-run oil company Petrobras show that a single oil block of Amapa's equatorial margin could total more than 5.6 billion barrels of oil, the country's mines and energy minister said on Friday.

Alexandre Silveira's remarks come as the oil giant bids to drill a well at the mouth of the Amazon river on the coast of northern Amapa state, a controversial topic that has divided President Luiz Inacio Lula da Silva's own coalition.

Silveira and other cabinet ministers support Petrobras' attempt to drill the well, while environmentalists have spoken against it as the area is seen as environmentally sensitive.

The reserve estimates, Silveira told reporters, come from "geological and geophysical studies" carried out in the region which is near Guyana, where Exxon Mobil has made important discoveries.

"Guyana and Suriname have an enormous potential, and Petrobras has internal studies showing that this block in the Brazilian side has the potential of having 5.6 billion barrels of oil," Silveira said.

Brazil's environmental protection agency Ibama has

previously rejected

Petrobras' request to drill the well, citing discrepancies in environmental studies. The oil giant, however, has appealed the decision.

Some of Lula's ministers and Petrobras CEO Jean Paul Prates defend that oil coming from the region would help both the company and government make money to pay for their energy transition goals.

Lula has staked his international reputation on reversing environmental back-sliding under his far-right predecessor Jair Bolsonaro, when Amazon deforestation soared.

Yet he is under pressure to deliver much-needed growth to poor, underdeveloped regions in the north and northeast, and wants

Petrobras to be an engine

of that growth. (Reporting by Rodrigo Viga Gaier; Editing by Steven Grattan)