A failed gas seal has forced Shell to stop flowing gas to its Prelude floating LNG vessel just days after it opened subsea wells for the first time in seven months.

Shell was in the initial stages of restarting LNG production when a seal leaked in the turret that connects the 488m-long facility to equipment on the seabed.

Boiling Cold understands that the failed primary seal in a production swivel did not cause gas to escape as a secondary seal continued to work as designed. However, Shell stopped the gas flow as a precaution.

It is understood the turret has two swivels for gas produced from the reservoir to flow to the Prelude, but before this leak, the other production swivel was already out of action due to technical problems.

Prelude’s 96m high turret is secured to the seabed 250m below with 16 massive chains and allows the giant vessel to rotate freely around it according to weather conditions.

The turret designed and built by SBM Offshore has nine swivels that connect the flexible pipelines rising from the seabed to the rotating vessel.

“Designed in Monaco, built in Dubai, shipped to South Korea and for use off Australia, the turret is an example of the truly global nature of this project,” Shell projects director Matthias Bichsel said in 2014.

The turret is the largest ever built and designed to withstand the most severe storm expected in 10,000 years in the Browse basin of the Kimberley coast.

Swivels are large precision-engineered components that some industry insiders have said could take months to fix.

The failed seal is the latest of many technical problems on what is probably the most complex offshore facility ever built.

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The lack of gas will force the Prelude to use expensive diesel to generate power.

Shell declined to answer questions.


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Main image: Schematic of Prelude turret. Source: SBM Offshore.