The Petrobras-owned P-70 floating production, storage and offloading vessel broke its anchorage in storm conditions in Rio de Janeiro on Thursday evening.
Although the situation is now under control, the Brazilian state oil company has not yet said whether the FPSO suffered damage or will face fresh delays to ongoing work.
The P-70, which is undergoing final commissioning before moving to the Petrobras-operated Atapu pre-salt field, was in the relatively sheltered waters of Guanabara Bay, Rio de Janeiro state, when strong winds interrupted mooring operations.
The P-70 arrived in Rio de Janeiro recently after completing its journey from the shipyard of China's Offshore Oil Engineering Company (COOEC). It was transported in a dry-tow operation conducted by Dutch company Boskalis.
The incident occurred close to the port city of Niteroi, where several shipyards and fabrication yards are located.
The FPSO was unloaded from the Boka Vanguard semi-submersible heavy-lift vessel safely on Thursday morning, but unexpected strong winds hit the bay later that day, when only three of the four mooring lines had been connected, an informed source told Upstream.
Two of the mooring lines reportedly broke.
Port tugs involved in the operation could not prevent the vessel drifting about 100 metres toward the shore near Niteroi, one informed source told Upstream.
Social media footage showed the stern of the vessel towering dramatically over a roadside in a Niteroi neighbourhood.
The port tugs managed to move the FPSO to a safe position when weather conditions improved, and mooring operations are ongoing.
Petrobras has not yet replied to requests for further information about whether damage occurred.
This was the second incident to occur during the P-70 transport operation.
One person died and several others were hospitalised following a recent intoxication incident on board the Vanguard as it was transporting the FPSO to Brazil.
Six workers — all Brazilian nationals — illegally consumed a cleaning liquid found on board the FPSO, Boskalis reported.
During the journey, final works were taking place on board of the FPSO, part of the commissioning push to put the unit in production.
The Vanguard changed course towards the coast of South Africa and a medical evacuation by helicopter was organised, but too late to save the life of one of those involved.
The P-70 FPSO arrived in Brazil on 24 January and, as routinely occurs in such cases, was being moored inside the Guanabara bay during final customs clearance and commissioning work.
The FPSO was scheduled to start production for Petrobras in the first quarter of 2020, but sources were already pointing to a possible delay into the second quarter.
In a statement, Petrobras acknowledged that strong wings and storm conditions had caused the P-71 FPSO to break adrift of its mooring near the coast of Niteroi.
"Petrobras has already steered the unit back to the anchorage area in the Bay of Guanabara. There were no victims. Petrobras is investigating the causes of the accident," the statement said
The P-70 is one of a series of highly standardised — or “replicant” — FPSOs that Petrobras ordered from Brazilian shipyards in order to ramp up production on pre-salt fields. Much of the work was later transferred to China following construction bottlenecks in the Brazilian yards.
The floater is designed to produce 150,000 barrels of oil per day and 6 million cubic metres per day of natural gas, with holding capacity for 1.67 million barrels. It is able to accommodate 160 people and has a lifespan of 25 years.
The Atapu field is located in a prime area of the pre-salt province where Petrobras is developing oil production under a transfer or rights agreements signed in 2010.