“We decided to proactively shut down production on a temporary basis because it provides the most efficient way to resolve the issue,” Scott Sandlin, president of the Hibernia Management and Development Company, said in a statement released by ExxonMobil.

Hibernia – which opened for production in 1997 and is located about 196 miles (315 kilometers) east of St. John's, Newfoundland – is jointly owned by Chevron, Suncor and Equinor (formerly Statoil) in addition to ExxonMobil, which holds the majority share.

The oil deposit below Hibernia – accessed via underwater drilling – is estimated to contain more than 1.2 billion barrels of oil.

The discharge occurred during “routine activities related to removing water” from the storage cell, the statement said. HDMC has not specified how much oil was discharged, but it estimated the initial sheen was approximately 66 feet by 2,953 feet (20 meters by 900 meters) and said that it was dissipating.

An earlier statement released by Exxon said that sheen monitoring was ongoing and more information would be released when it became available, adding that all platform personnel were safe.

HDMC's initial response included “mechanical dispersion” – spraying the sheen with a water jet to disperse the oil particles – and deploying absorbent barriers to contain it.

A buoy was also sent out to track the sheen's movement in the Atlantic, and a surveillance flight took place.

ExxonMobil declined to comment about which direction the sheen appeared to be flowing and if it posed a risk for aquatic life in the area, which is a popular breeding ground for whales. But the later statement said that wildlife observers had been sent to the area, both in the supply vessel used to deploy the absorbent barriers and a separate vessel. One observer also participated in the surveillance flight.

No wildlife had been spotted in the affected area, the statement said.