During an early February earnings call Shell boss Ben van Beurden called the ongoing problems "teething troubles" but confirmed the $20 billion-plus vessel would be offline through the first quarter of 2022.
The company was ordered by the offshore regulator, NOPSEMA, to shut down the facility in December, following a small fire caused by an electrical fault which tripped the facility's main power, forcing the company to use backup diesel generators and evacuate staff.
A report from the regulator suggested a power outage could have led to ‘catastrophic failure' on the vessel.
The root cause of the fire, that saw personnel suffer heat exhaustion, work 30 hour shifts, go without toilets and running water and eventually be evacuated via ships and helicopters, isn't yet known.
However, the National Offshore Petroleum Safety and Environmental Management Authority says the possibility of further electrical issues is "foreseeable and credible".
Until reliability can be established NOPSEMA will not let the 3.6 million tonne per annum vessel restart.
It said the brevity of its initial investigation didn't allow its inspectors to decide if Shell had broken the Offshore Petroleum and Greenhouse Gas Storage Act 2006, which governs oil and gas operations, but it may investigate this later.
"The inspectors conclude that until power to safety critical equipment is made reliable and robust, the operator should not proceed to restart the facility beyond essential operations," it said.
The offshore watchdog said a draft offered by Shell for its internal investigation to determine the power system issues doesn't "plan to assess all of the issues associated with the incident to ensure the immediate risks (such as the multiple cases of heat exhaustion, failure of critical hotel services and safety critical systems (e.g. communications) or the potential to exceed the flare system design limits) during a future similar incident are identified and recommendations are made to mitigate them".
One other damning finding among cases of heat stroke, total loss of power and refrigeration in the kitchens and air conditioning in staff areas was that ‘black start procedures', or those used to restart power systems internally such as the distributed control system, only came back online because vendor experts "happened to be on board" at the time, according to NOPSEMA's report.
Seven workers were treated for heat stress with four needing IV transfusions.
The NOPSEMA investigation suggested this could have been because workers were in "turn-out fire fighting suits in the hot substructure areas for extended periods before and after the room entry".
It said anecdotal evidence from those interviewed stated temperatures in the living areas hit between 40C-45C as air conditioning shutdown and humidity worsened, causing a difficult surface to walk on as water pooled.
Some onboard worked 30 hour shifts and there were suggestions to NOPSEMA that those in charge were more concerned with restarting the vessel than the safety of the 250 onboard, the report noted.
After the initial fire it found the "cumulative risk" on Prelude was significantly higher than normal thanks to disabled safety systems, communication systems and much higher heat and humidity.
Most of all cooling of the substructure near the LNG storage tanks could have led to "catastrophic failure" if not fixed, as was previously reported by WA Today and Energy News.
NOPSEMA received a tip off December 14 that Shell was "not acting on the results of fatigue assessments" but after discussions with Shell, decided not to pursue that matter.
Overall it found Shell managed immediate risks and by the time inspectors arrived aboard a week later the incident was under control but although some threats were mitigated they were not ‘ALARP', or as low as reasonably possible.
Handheld radio communication on the vessel was limited and the only way to communicate with shore was via radio relay, one of the reasons helicopter lifts had to be delayed and some staff were transported to shore via ship.
It suggests during any future power failures life-sustainment systems are available from air conditioning to sewerage and ensuring adequate drinking water and food refrigeration, must be mitigated.
Shell has advised NOPSEMA it will conduct more reviews.
At the earnings Q&A, Van Beurden said the Prelude, which started up years late after huge cost overruns, is "quite a unique challenge as you can imagine".
He said Western Australia's tight border control was making it "difficult to get people in", due to the 14-day quarantine requirements.
"To get a vendor specialist in means that person will have to quarantine for weeks before they can go on board, so these problems compound the issue a little bit but also we want to make sure when we restart that we have resolved the problem."
The NOPSEMA report made no mention of this.
"On 2 December 2021 at approximately 11.00PM AWST, smoke detected in an electrical utility area triggered the automatic fire detection and management systems on board the Prelude FLNG facility," a Shell spokesperson told Energy News.
"The room was made safe by the systems in place and it did not spread further. All workers on the facility are safe and accounted for.
"Production on Prelude has been suspended temporarily, and an investigation into the cause of the incident is underway. We will continue to work methodically through the stages in the process to prepare for hydrocarbon restart with safety and stability foremost in mind."