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Giants of the sea

Ben Sampson

Coming together: Petronas' FLNG Satu is a gigantic 380m in length
Coming together: Petronas' FLNG Satu is a gigantic 380m in length

Enormous floating liquid natural gas vessels promise to tap into hard-to-reach reserves deep beneath the ocean floor. Ben Sampson looks at how they are being built

Coming together: Petronas' FLNG Satu is a gigantic 380m in length

The oil sector might be in the throes of readjusting to plummeting prices, but the gas market is still in rude health.

Enthusiasm for liquid natural gas (LNG) is at a high as the sector enters a new period of innovation.  The leading companies in LNG, such as Petronas, Shell, ExxonMobil, Woodside and Inpex, are developing Floating Liquid Natural Gas vessels (FLNG) to unlock smaller, more remote gas fields. Industry experts believe that the use of FLNG vessels will open up significant new oil and gas reserves around the world and predict that, if the first are successful, many more of the ships will be commissioned.

These massive ships are packed tight with all the plant, equipment and storage tanks that would normally be housed on land to clean, compress and distribute LNG while floating over a gas field. 

The two forerunners of this new type of floating gas plant are Shell’s Prelude, a 488m long behemoth that will be used in the North Sea and Petronas’ FLNG Satu, which will be used off the coast of Malaysia. Outside of south east Asia, Prelude is widely expected to become the first operational FLNG vessel. But Shell is vague about when exactly Prelude will be finished, saying it will be ready “in the next few years”. 

Meanwhile, FLNG Satu nears completion in the Daewoo dockyard in South Korea. According to the cautiously optimistic Adnan Zainal Abidin, vice-president of global LNG projects for Petronas, Satu will start work by April next year. 

FLNG Satu is 380m long, 60m wide and weighs 125,000 tonnes. The challenge of putting all of the onshore LNG processes onboard a ship is more than considerable. The reward though is the exploitation of gas fields that would otherwise go undeveloped because they are too small or too far from shore. Abidin says: “FLNG provides an avenue for us to monetise stranded gas fields, and fields that are not big enough to lay a pipeline to shore for. It’s a new way for us to develop these fields, or they wouldn’t see the light of day.

“But being the trailblazer is not easy. Everybody is watching. At the end of the day we want a product that we can rely on.”

Sky high: Satu is being constructed from a total of 20 modules
Sky high: Satu is being constructed from a total of 20 modules

In terms of functionality an FLNG vessel is most similar to an FPSO (Floating Production Storage Offloading unit). The plant and equipment topside and throughout the vessel is arranged into 20 modules. There are seven on top, from a pretreatment module through to a liquefaction module. Each module is built offsite, craned onto the vessel at the dockyard and installed. Six of FLNG Satu’s topside modules have so far been lifted on to the deck and the last topside module is currently being fitted.

FLNG Satu will produce gas at a “stranded” field 180km off the coast of the state of Sarawak in eastern Malaysia before April next year. It will produce 1.2 million tonnes of LNG a year for at least 20 years. Petronas is also building a second FLNG, which will have a larger capacity of 1.5 million tonnes per year and work another field further offshore of the Malaysian state of Sabah. FLNG Dua will be ready by 2018 and be able to operate in deeper water – up to 1,200m compared to FLNG Satu’s 200m.

After Petronas’ upstream team drills the Sarawak field and performs the subsea operations, the FLNG will be towed to the site – the vessel has no propulsion system because it will hardly ever move. It will then be moored and the riser connected to its turret. Gas will travel up to be treated in the modular plant, where contaminants such as water, CO2 and sulphur, which would freeze later in the process, are removed. The gas is then chilled and liquefied at temperatures as cold as –162ºC. The LNG is then stored and transferred directly to tankers from the vessel itself, instead of being loaded at a jetty onshore.

The equipment on board the ship differs in size and weight to what would be used onshore because on top of a ship space, access and weight is limited. Abidin says: “Building a plant on a boat has different aspects to consider than onshore. The rolling motion and pitch of the vessel has to be taken into account. It also determines the choice of processing equipment. It’s a technical challenge in itself because you want to minimise the weight in a compact area. So you have to select equipment that serves in terms of size, but also in terms of reliability and robustness in operation and maintainability.

“We made a decision early on that most of our drivers are aero-derivative gas turbine not steam, which offers a smaller footprint. How you facilitate maintenance work is also an important aspect, to access equipment and move it on and off the ship,” he adds.

Another of the major design decisions was which refrigerant to use. A variety of different permutations are available and were considered. Onshore a mix of propane is normally used, but the engineering team decided to use nitrogen for the FLNG. “We wanted to make it simple to operate. With nitrogen there is no need to import the refrigerant because it is taken from the air, which saves us a headache,” says Abidin.

“We hope that we have made the right decision with nitrogen cycle. One of its attributes is that you are dealing mainly in the gaseous phase. Being an offshore installation, dealing with gas is a lot easier than dealing with liquids, especially from a process point of view.”

Other influences on the design include the weather. There are some limitations around wave heights. Loading and unloading of LNG can only be performed up to a certain wave height. Another influence is the gas field itself. The composition of natural gas and the contaminants it contains differ from field to field. 

FLNG Satu’s process equipment has been tailored specifically for the Sarawak field, which it will operate in for 20 years, until the field is depleted. Moving costs money – towing to a new site and tethering the FLNG to the sea bed, for example, are costly operations. “Where it is economical to tie back from other fields it will be done that way. The motivation is never to move,” says Abidin. “You can’t design for all sorts of gases. You have to make a judgement call.”

The final barriers have been regulatory. Onshore plants are covered by codes and standards, but offshore is driven by marine class requirements and has to be class certified. There has therefore been a period where offshore regulatory bodies and Petronas have had to “acclimatise to each other’s requirements”, Abidin says.

The difference between onshore and offshore is also reflected in the engineering team, says Wan Badrul Hisham, head of LNG projects for Petronas’ upstream projects. He says: “In our management team there are people that have worked in plants and LNG tankers. They have different ways of thinking. When you integrate them into the project you have to harmonise their thinking to get the technical specifications.”

The project is more than 80% complete. FLNG Satu will be proof of Petronas’ engineering expertise in the global LNG market. It will also demonstrate the company’s position in the market. FLNG had been discussed as a concept for a long time, but it has taken a company that has control of the entire value chain, from exploration and production to distribution to consumers, to make it a reality. Hisham and Abidin agree that it’s for this reason that FLNG’s adoption may not be as widespread as many industry commentators have predicted. Hisham says: “There are very few people able to do this. We own the field and have the market. We can take the risk. If you are a new company and build a FLNG, they are capital intensive. You want to sell to an established buyer, but they will want security of supply and ask how reliable is the FLNG.”

However, both Hisham and Abidin believe there is a strong future for FLNG. Petronas has already assessed other opportunities around the world. Abidin says: “Other sites will be possible as well. Once the concept is proven I think we will see a lot more.”

The kudos of developing the first FLNG is considerable, but the wider implication is that to become the central part of the LNG market as the industry moves into the next decade, the first FLNG projects, such as Satu, must succeed. n

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