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08/01/18 10:46

Year 2018 will see the largest ever at sea

Royal Dutch Shell will start operating off Australia the Prelude, a colossal FLNG floating liquefied natural gas platform

This year a joint venture between Royal Dutch Shell, KOGAS, and Inpex will start operating off Australia the Prelude, a colossal FLNG floating liquefied natural gas platform that is to be the world's largest vessel at present.

The main double-hulled structure was launched in December 2013 with no superstructure (accommodation and process plant) and it is being built in the Samsung Heavy Industries Geoje shipyard in South Korea by the Technip - Samsung Consortium (TSC). Construction was officially started when the first metal was cut for the substructure in October 2012.

The Turret Mooring System has been subcontracted to SBM and has been built in Drydocks World Dubai, United Arab Emirates. Other equipment such as subsea wellheads are being constructed in other places around the world. Subsea equipment is being built by FMC Technologies, and Emerson is the main supplier of automation systems and uninterruptible power supply systems; in July 2015, all 14 gas plant modules were installed.

The 488-meter-long and 74-meter-wide floating facility left the shipyard in South Korea in late June and reached the Australian waters in late July, where it will begin its job of extracting and processing gas at sea at half 2018. Currently, the vessel sits at its first location, Shell's Prelude gas field, around 125 miles north off the Western Australian coast.

The Prelude facility weather vanes 360° around a turret, moored in 248 meters of water; 3 stern thrusters enable it to maintain an optimum heading that will facilitate offtake operations within the design limits of the facility and associated cargo transfer equipment. Despite its ship-like appearance the vessel is not in the strictest sense a boat as it needs to be towed to its destinations.

Fully operational, Shell says it will harvest at least 5.3 million tons per annum (mtpa) of liquids — 3.6 mtpa of LNG, 1.3 mtpa of condensate and 0.4 mtpa of liquefied petroleum gas that is to be pumped up from below the seabed to the floating platform, where it is then cooled. It is fitted with the necessary equipment for exporting LNG/LPG via side by side mooring and loading arms and Condensate via a tandem mooring and floating hose system. It is moored to the sea bed via 16 anchor piles and chains whilst being directly connected to wells that access the gas reservoir via flexible risers routed through the turret. All reservoir, subsea control, processing, storage and loading is operated and controlled from the FLNG.

Natural gas will be extracted from wells and liquefied by chilling it to −162 °C (−260 °F); its ability to produce and offload LNG to large LNG carriers is an important innovation, which reduces costs and removes the need for long pipelines to land-based LNG processing plants. Fitting all  equipment on a single floating facility was a significant challenge. The system is designed to withstand Category 5 cyclones although workers may be evacuated before that on an EC225 rescue helicopter

The Prelude is the world's second floating liquefied natural gas platform as well as the largest offshore facility ever constructed. Analyst estimates in 2013 for the cost of the vessel were between US$10.8 to 12.6 billion; Shell estimated that the project would cost up to US$3.5 billion per million tons of production capacity. Competitive pressures from an increase in the long-term production capabilities of North American gas fields due to hydraulic fracturing technologies and increasing Russian export capabilities may reduce the actual profitability of the venture from what was anticipated in 2011.

A.S.

TAG : Gas
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