Petrobras is considering scaling down the size of the fourth floating production, storage and offloading vessel to be installed at the Mero field in Brazil's Santos basin pre-salt province.

Petrobras executive manager for Libra (Mero) Fernando Borges said the Brazilian player recently drilled a well in the Mero-4 area that yielded different results than the rest of the reservoir.

The Petrobras-led consortium, which also includes European supermajors Shell and Total, as well as China National Petroleum Corporation and China National Offshore Oil Corporation, is carrying out studies to analyse potential different scenarios regarding the oil processing capacity of the upcoming floater.

The first three FPSOs for Mero will feature topsides able to handle 180,000 barrels per day of oil and 12 million cubic meters per day of natural gas.

Borges acknowledged the Mero-4 FPSO could be slightly smaller, with capacity to produce 150,000 bpd instead, but stressed all options are still on the table.

“The well drilled in Mero-4 brought us some distinct information in that part of the reservoir that was a bit different than we anticipated, so this will require a deepening of the geological model of the area,” he told Upstream.

“Our goal remains to contract a floater with capacity for 180,000 bpd for Mero-4, but a unit able to produce 150,000 bpd is not off the radar.”

Petrobras had plans to tender for the Mero-3 and Mero-4 FPSOs this year, but results of the new well led the state-controlled company to postpone the latter until it acquires more data from the play.

“We are maturing our studies, but these will only be completed in either late 2019 or early 2020,” said Borges, confirming market talk that the tender for the Mero-4 floater will now happen next year.

“If the reservoir studies evolve well, they will be perfected with our partners as we collect new information from the area, and only then will we design the best project for Mero-4. There is a chance the 180,000-bpd FPSO may be excessive.”

He explained carbonate reservoirs such as Mero are heterogeneous by nature and complex to develop, despite all the experience garnered by the oil company in the pre-salt fairway over the last decade.

“Sometimes we have part of the oil-water contact in a section of the reservoir with more traps. The oil is all connected, but there are cases where the oil-water contact happens at different depths or does not occur at all,” Borges said.

“All these scenarios could lead to a change in the concept model. We need to understand as best as we can how all the fluids are connected so we can properly design our pairs of producer and injector wells to achieve the maximum oil recovery from that portion of the reservoir.”

Petrobras is set to collect more data from the Mero-4 area later this year, when the oil company will start a 12-month extended well test in the area with the Pioneiro de Libra FPSO.

The consortium has since December been running a new test in the region where the Mero-2 FPSO will be installed. According to Borges, the EWT is again generating spectacular results, with the field producing about 42,000 bpd from a single well. Total hydrocarbons output is above 58,000 barrels of oil equivalent per day, with all gas being re-injected into the reservoir to maximise oil production.

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Petrobras ponders Mero-4 FPSO size call