Prelude floating liquefied natural gas (FLNG) facility is being developed by Shell for its Prelude and Concerto fields in the Browse Basin, offshore of Western Australia. It is the first FLNG development in the world.

The FLNG complex enables placement of the liquefaction facilities directly on the offshore fields. It is based on Shell’s own technology.

Prelude’s front-end engineering and design (FEED) was undertaken by the Technip Samsung Consortium (TSC), a joint venture of Technip and Samsung Heavy Industries. The same consortium is also responsible for the construction of the facility. Inpex, Korea Gas and CPC also respectively hold 17.5%, 10% and 5% stake in the project.

Prelude is being constructed at Samsung’s shipyard in Geoje Island in South Korea. Once built, the facility will be towed to its location, 475km offshore of Broome. It will be moored at the location for 25 years, when it will need an overhaul.

Purpose of the world’s first FLNG development

The FLNG facility will process gas at the field itself. It can prove economical to the fields where reserves are low and development of separate processing facilities may not be profitable.

The facility will provide for development of various small and remote offshore fields, which have not been tapped so far for their uneconomical propositions. Australia has about 140tcf (trillion cubic feet) of stranded gas.

Shell will initially utilise the facility to process gas extracted from the Prelude and Concerto fields, which have gas reserves of about 3tcf. The fields are small and remote, thus making them suitable for the use of FLNG.

Design of the floating liquefied natural gas facility

"Shell will initially utilise the facility to process gas extracted from the Prelude and Concerto fields, which have gas reserves of about 3tcf."

Prelude is expected to be the largest floating facility in the world. It will be 488m long, 74m wide and the topsides will weigh more than 50,000t each. A fully-loaded FLNG will weigh about 600,000t, six times more than an aircraft carrier.

The constructed facility will be towed to the site and moored at a water depth of 250m, by four groups of mooring chains. The mooring chains will be held by suction piles in the seabed.

The FLNG has been designed to overcome category five cyclones and will be suitable to be used under severe metocean conditions in distant offshore fields.

The hull of the FLNG will have tanks to store gas. More than 260,000t of steel will be used in the construction of the facility.

Seven boiler units will be installed on the topside for power generation and the LNG production processes. The facility will comprise of about 3,000km of electrical and instrumentation cables.

Development of Prelude, the largest floating facility in the world

Shell awarded the FEED contract to TSC in July 2009. It has simultaneously signed another contract with the consortium to design, construct and install multiple FLNG facilities over a period of 15 years.

The decision to develop Prelude and Concerto fields using the FLNG technology was announced in October 2009.

The board of Royal Dutch Shell took the final investment decision on the project in May 2011 and TSC was asked, in the same month, to proceed with the construction. The first steel for the facility was cut in October 2012.

The first production of gas is expected in 2017.

Processes and economic benefits of Shell’s FLNG facility

The facility freezes the produced natural gas to -162°C and reduces the volume of the produce by 600 times. The gas is stored in tanks. The frozen gas is loaded to ocean-going carriers. The carriers also carry the by-products, such as condensate and LPG.

"The FLNG complex enables placement of the liquefaction facilities directly on the offshore fields."

Prelude is estimated to produce 3.6mtpa of LNG, 1.3mtpa of condensate (equivalent to 35,000 bbl/d) and 0.4 mtpa of LPG, totalling 5.3mtpa of liquids.

The FLNG will enable liquefaction of gas at the field itself, avoiding the need for land-based infrastructure such as pipelines, compression platforms, jetties and processing plants. This will be economical while producing stranded offshore fields.

The facility requires less material, land and seabed areas than conventional onshore facilities.

The project is expected to create 350 direct jobs in Australia and also bring-in tax revenues to the government. It is also expected to benefit the local businesses as Shell plans to make huge capital and operational investments in the facility. Construction of the facility will employ approximately 5,000 people while an additional 1,000 people will be involved in the construction of the various equipment worldwide.

Suppliers linked to the Prelude FLNG facility

GE Oil & Gas will supply two steam turbine-driven compressor trains which will be used to cool the natural gas.

Kawasaki Heavy Industries (KHI) will provide seven boiler units, which will produce 220t each hour of high-temperature and high-pressure steam.

Norsafe will deliver free fall lifeboats which have a capacity of 70 people and are certified for a drop height of 40m. SBM Offshore will supply the mooring systems.