The National Offshore Petroleum Safety and Environmental Management Authority confirmed to Energy News this morning a "possible hydrocarbon release" from the Prelude earlier this month.
"A sheen was observed in close proximity to the Prelude, however it dispersed quickly, and was thought to be a small quantity of petroleum fluid," a spokesperson told Energy News this morning.
"It is not considered a spill and certainly not a major incident," NOPSEMA's spokesperson told Energy News.
"NOPSEMA inspectors were on board the Prelude on 6-7 November as part of a scheduled inspection, and the hydrocarbon release formed part of the inspection scope. There have been no further releases and the source of the notified release continues to be investigated."
The incident is classed as an "uncontrolled hydrocarbon release" as it was estimated less than 100 litres of hydrocarbons have entered the waters.
However Offshore Alliance said via its Facebook page this morning the slick was caused by one of the vessel's thrusters, and accused operator Shell of trying to keep the issue under wraps.
They claim the slick was between 2km and 4km and more than 600 metres wide from the back of the vessel.
Shell has not confirmed any spill to Energy News and last week did not elect to respond to questions about the alleged thruster malfunction.
Workers however allege the spill was due to malfunctions with the thrusters.
The slick comes just a week after the massive vessel suffered maintenance issues with two of its three thrusters.
NOPSEMA hasn't publically issued a notice to Shell yet regarding the spill and did not issue one in regard to the thrusters' suggested malfunction as it was not deemed "safety critical" by the regulator.
The Rolls Royce-built thrusters allow the vessel to weathervane around its turret.
Shell said in 2017 they were a "key feature in Prelude's design" which would ensure it could "withstand wind and sea conditions including a one in a 10,000-year storm".
The huge, $5.3 billion floating LNG vessel has a nameplate capacity of 3.6 million tonnes of LNG per annum, 1.3Mmtpa of condensate and 400,000 tonnes of condensate.