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Shell Australia’s giant Prelude floating LNG project likely to come on stream in 2017

20 September 2016

Royal Dutch Shell is building the world’s largest floating liquefied natural gas (FLNG) project, which has the potential to transform the way natural gas resources are developed. It is designed to recover resources offshore that would otherwise be too costly or difficult to develop without the need to lay pipelines and build processing plants on land. In this article, Hazardex takes a look at the latest developments in this ground-breaking project.

Prelude FLNG on station with LNG carrier alongside - Image: Shell
Prelude FLNG on station with LNG carrier alongside - Image: Shell

The Prelude natural gas field was discovered by Shell in the Browse Basin off north Western Australia in 2007 with an additional field, Concerto, discovered nearby in 2009. Combined, these gas fields have around 3 trillion cubic feet of liquids-rich gas. The Australian Government gave the Prelude FLNG project environmental approval on November 12, 2010, and Shell took the final investment decision (FID) on May 20, 2011.

Shell says engineers worked more than 1.6 million hours during the engineering and design phase of the project.

The oil and gas giant has not published a start-up date for the project, insisting that getting the design and operating details right on a project that would be moored offshore for 25 years was more important than meeting any arbitrary deadline. Nevertheless, the indications are that the operating phase of the project is now in sight.

Speaking at the LNG18 conference in Perth in April 2016, Northern Territory deputy Chief Minister Peter Styles said that Prelude FLNG was expected to start production in late 2017, while Shell CEO Ben van Beurden said at the same event: “We expect real material cash from Prelude in 2018.”

Prelude FLNG will be the largest offshore facility ever constructed. The vessel is being built by the Technip/Samsung Consortium (TSC) at Geoje in South Korea for a joint venture between Royal Dutch Shell (67.5%), INPEX (17.5%), KOGAS (10%) and CPC Corporation (5%).

Samsung Heavy Industries (SHI) shipyard at Geoje has one of the few dry docks in the world big enough to construct a facility of this size.

For a whole year, steel was welded together by thousands of workers at the SHI yard to create the biggest hull ever built. Once structurally complete in November 2013, and weighing approximately 200,000 tonnes, the Prelude FLNG hull was floated in the dry dock before it was towed by nine tugs through Geoje harbour to its new position on the quay, where it is secured by 32 heavy mooring ropes.

At Geoje, the topside modules, many of which weigh as much as a single typical offshore platform, are now being installed on the hull and integrated. Early commissioning has begun. As many as 5,000 people work on Prelude FLNG on any given day at Geoje.

In Dubai, the construction of the Prelude FLNG turret mooring system is progressing well. Once assembled, it will be the largest turret in the world, almost 100 metres high. The first turret module was completed in September 2013 and transported to Geoje, where it was installed into the hull before it was floated. Since August 2014, four more turret modules have been shipped to Geoje and integrated into the hull.

At completion, Prelude FLNG will be 488 metres long, 74 metres wide and contain more than 260,000 tonnes of steel. At full load, it will displace more than 600,000 tonnes, more than five times the displacement of a US Navy Nimitz-class aircraft carrier.

The Noble Clyde Boudreaux drilling rig was towed to the Prelude FLNG location off the coast of Western Australia in August 2013, and drilling of the production wells is under way. The first well was completed in late December 2014.

Malaysia has been the main location for the project’s subsea system design and the construction of subsea Christmas trees, manifolds and control equipment, with two Christmas trees already installed subsea at the Prelude location in late 2014.

The Prelude loading arms are under construction at the FMC manufacturing facility in Sens, France, and in February 2014, the first Prelude loading arm was tested. Ocean conditions and the extreme cold of the LNG were simulated and the tests were deemed a success.

In Darwin, Australia, the main onshore supply base for Prelude is complete. The site is already receiving equipment for the Prelude FLNG facility.

Subsea installations - Image: Shell
Subsea installations - Image: Shell

The Prelude FLNG development in Australia will be Shell’s first deployment of its FLNG technology. The technology allows for the production, liquefaction, storage and transfer of LNG at sea, as well as the ability to process and export liquefied petroleum gas (LPG) and condensate.

The floating facility will chill natural gas produced at the field to –162°C, shrinking its volume by 600 times so it can be shipped to customers in other parts of the world.

Once constructed, the facility will be towed to its location, some 475 kilometres north-east of Broome, Western Australia. There the facility will be moored and connected to the undersea infrastructure and the whole production system commissioned.

The FLNG facility is designed to be on the Prelude gas field for 25 years, and is expected to produce 3.6 metric tonnes per annum (mtpa) of LNG, 1.3 mtpa of condensate and 0.4 mtpa of LPG for export. It is likely to be the second such facility in operation following Petronas’ PFLNG SATU, which is expected to start production off Sarawak in the coming months.

Vessel and subsea systems

The FLNG facility will be moored near to the Prelude field location in 250 metres of water, by four groups of mooring chains. Each mooring chain will be held to the sea floor by piles. The facility has been designed to withstand severe weather, including a’10,000 year’ storm – or category five cyclone - and will remain onsite during all conditions.

A series of seven production wells will feed gas and condensate from the reservoirs via four flexible risers into the facility. All subsea connections join the facility via the turret. The turret’s swivel design enables the facility to move according to wind and sea conditions as it remains fixed to the sea floor.

Prelude FLNG will have thrusters to provide a steady heading during the offloading process, but it is a fixed facility, with no means of propulsion.

The processing of gas and condensate occurs in modules onboard that occupy an area approximately one quarter the size of a typical onshore gas plant. Shell’s Dual Mixed Refrigerant (DMR) process is used to liquefy the gas.

Prelude’s LNG and LPG will be offloaded via a side by side vessel configuration using specially designed cryogenic loading arms that load the carriers. Ships will load condensate from the rear of the facility using a floating hose arrangement. The products will then be shipped directly to customers around the world.

Important attributes of Shell’s FLNG design are:

*  it can provide high production rates of up to 6 million tonnes per annum (mtpa) of liquids (including LNG, LPG and condensate);

*  it can process a wide range of gas compositions and can export LPG and condensate;

*  it uses an efficient double mixed refrigerant liquefaction cycle;

*  it can stay on station and does not have to be moved during severe weather conditions such as cyclones, which will increase the availability of the plant.

Prelude position off NW Australia - Image: Shell
Prelude position off NW Australia - Image: Shell

New technology that has been developed for FLNG includes LNG tanks that can handle sloshing, close coupling between the producing wells and the processing facility, LNG offloading arms, cooling water intake risers, turret and mooring systems, and the marinisation of processing equipment such as absorption columns and the main cryogenic heat exchangers. 

All of these technologies have been extensively modelled and tested to ensure they can operate safely and efficiently under marine conditions.

The facility’s storage tanks will be below deck. They can store up to 220,000 m3 of LNG, 90,000 m3 of LPG, and 126,000 m3 of condensate.

Shell also came up with the idea of tapping the cold of the ocean depths by pumping water to help cool the gas, avoiding the need for extra equipment on deck. An assembly of eight one-metre diameter pipes will extend from the facility to about 150m below the ocean’s surface, delivering around 50,000 m3  of cold seawater each hour.

The management of subsea wells and manifolds is carried out via umbilicals connected through the turret to the control room onboard the facility.

Subsea equipment includes production wells, Christmas Trees, manifolds, flowlines, riser base manifold, flexible risers and umbilicals, subsea distribution hardware providing hydraulics, power, communications and chemical services to the subsea wells and subsea manifolds.

The project has one drill centre, located three kilometres south of the Prelude FLNG, centre with two six-slot manifolds, a base case seven production wells with contingency for an eighth producing well. It will be connected to the gas reservoir via 12 inch flowlines connecting the production manifolds to the riser base manifold.

Each flowpath to the Prelude FLNG, consisting of the flowlines and flexible risers, will be equipped with a Fail Close Riser Base Valve (FCRBV) at the Riser Base Manifold (RBM), located at a horizontal distance of 550 metres from the centreline of the turret, to isolate the facility from the flowlines. The Prelude FLNG will be moored using 16 mooring lines connected to piles grouped into four quadrants.

Prelude Safety

Shell says safety of the Prelude FLNG facility has been paramount during its design, and its safety is on par with modern offshore oil and gas facilities. The FLNG design includes a number of key safety features including the layout (and separation) of hydrocarbon processes from accommodation modules, enlarged safety gaps between process modules, fire-proof protective coatings and specially designed product loading arms.  In addition, Lloyds Register has conducted an independent safety review of the Design Safety Case and relevant final safety assessments.

The group says: “Safety and quality are the priority for Shell at all Prelude project locations. Together with our contractors, we are constantly working to ensure that safety comes first and that everyone goes home safely every day. We have a team of 250 inspectors deployed at project locations to check that all equipment and material is delivered in accordance with our specifications.”

Major Prelude FLNG safety features

* Safety is the primary focus in Shell’s FLNG design, with multiple formal safety assessments at various stages of the design confirming that an FLNG facility would be at least equally as safe and reliable as other modern offshore production facilities currently in operation.

* Shell’s FLNG design intentionally incorporates a number of proven and tested technologies that have been in use in existing LNG plants for many years.

Artist's impression - Image: Shell
Artist's impression - Image: Shell

* Shell has adapted some elements to ensure the facility can operate safely at sea. For example, the hull has been designed to minimise motion and rolling, reducing stress on the equipment and piping on board from the movement of the sea.

* Prelude FLNG has also been designed to withstand the weather and sea conditions experienced in the north west of Australia. Substantial studies and wave basin model testing have been carried out to prove it is safe for the crew during cyclones and the facility will not sustain major structural damage.

* The fact the facility stays on station and can operate in severe conditions has significant safety benefits. It avoids the safety risks of de-manning and disconnecting and reconnecting to the gas field.

* Its size and sheer mass (600,000 tonnes fully ballasted) is in itself an important feature for maintaining stability in extreme weather.

* The hull has a double wall design so that in the unlikely event of a collision, the cargo containment protection is maximised.

* The layout of the facility is based on risk management principles. It provides as much separation as possible between the pressurised processing equipment and the accommodation block. There are safety gaps between the processing modules so in the unlikely event there was a safety incident in one module, the impact on the surrounding modules would be minimised.

* The facility also features passive fire and cryogenic protection in the form of coatings.

* Shell’s FLNG design includes Evacuation, Escape and Rescue features. This includes multiple escape routes, the main temporary refuge aft and secondary refuge forward, freefall lifeboats and integrated chute based life-raft evacuation systems. The two infield support vessels that will be stationed alongside the FLNG facility will be available for evacuation in emergency situations. A search and rescue helicopter will also be on standby 24/7.

* Shell has also founded a dedicated search and rescue helicopter service in Broome to support drilling activity and later the Prelude FLNG facility supported by a team of pilots, paramedics, engineers and crew. The service is on standby 24-hours a day and is able to respond within 15 minutes during daylight hours and 30 minutes at night.


A number of FLNG developments have been shelved this year because of energy market conditions and other considerations. Woodside’s Browse FLNG project, due to have been a near-neighbour of Prelude, has been shelved due to the “current economic and market environment”, while Inpex’s planned Abadi FLNG has been moved onshore. Exmar’s Caribbean FLNG is set for delivery in the second quarter this year, but without immediate employment as the deal with Pacific Exploration and Production was terminated.

Nevertheless, 2016 and 2017 will be ground-breaking for the new industry as the first floating LNG production facilities hit the water.

“This is revolutionary technology developed by Shell,” says Neil Gilmour, Shell Vice President Integrated Gas Development. “It has the potential to change the way we produce natural gas.”

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