Floating liquefied natural gas
||This article contains wording that promotes the subject in a subjective manner without imparting real information. (May 2011)|
Floating liquefied natural gas (FLNG) refers to water-based liquefied natural gas (LNG) operations employing technologies designed to enable the development of offshore natural gas resources. While no FLNG facilities currently exist, a facility is in development by Royal Dutch Shell, and is due to be completed by around 2017. Floating above an offshore natural gas field, the FLNG facility will theoretically produce, liquefy, store and transfer LNG (and potentially LPG and condensate) at sea before carriers ship it directly to markets.
Studies into offshore LNG production have been conducted since the early 1970s, but it was only in the mid-1990s that significant research backed by experimental development began.
In 1997, Mobil developed a FLNG production concept based on a large, square structure with a moon-pool, commonly known as "The Doughnut". In 1999, a major study was commissioned as a joint project by Chevron Corporation and several other oil and gas companies. This was closely followed by the so-called 'Azure' research project, conducted by the EU and several oil and gas companies. Both projects made great progress in steel concrete hull design, topside development and LNG transfer systems.
Since the mid-1990s Royal Dutch Shell has been working on its own FLNG technology. This includes engineering and the optimization of its concept related to specific potential project developments in Namibia, Timor Leste/Australia, and Nigeria.
A number of major gas and oil companies are still researching and considering FLNG developments, with several initiatives planned for the future. However, the world's first development of FLNG is Shell's Au$12bn Prelude FLNG project, 200 kilometres (120 mi) offshore Western Australia. Royal Dutch Shell announced their investment in FLNG on 20 May 2011 and construction began in October 2012.
In April 2010 Shell's FLNG technology was selected as the Sunrise Joint Venture’s preferred option for developing the Greater Sunrise gas fields in the Timor Sea. This followed an extensive and rigorous concept-evaluation process during which the merits of the project were weighed up against alternative onshore solutions. The Woodside-operated JV is now seeking to engage regulators on the concept selection process. Following the decision by Shell to go ahead with its Prelude FLNG development, the Sunrise project would be the second deployment of Shell’s proprietary FLNG design.
In February 2011, Petronas awarded a FEED contract for an FLNG unit to a consortium of Technip and Daewoo Shipbuilding & Marine Engineering. The facility will be located in Malaysia, although the specific gas field is unknown.
Petrobras has invited three consortiums to submit proposals for engineering, procurement and construction contracts for FLNG plants in ultra-deep Santos Basin waters. A final investment decision is expected in 2011.
Meanwhile, Japan's Inpex plans to leverage FLNG to develop the Abadi gas field in the Masela block of the Timor Sea, with a final investment decision expected by the end of 2013. Late in 2010, Inpex deferred start-up by two years to 2018 and cut its 'first phase' capacity to 2.5 million tons per year (from a previously proposed capacity of 4.5 million tonnes).
According to a presentation given by their engineers at GASTECH 2011, ConocoPhillips aims to implement a facility by 2016-19, and has completed the quantitative risk analysis of a design that will undergo pre-FEED study during 2011.
GDF Suez Bonaparte – a joint venture undertaken by the Australian oil and gas exploration company Santos (40%) and the French multi-international energy company GDF Suez (60%) – has awarded a pre-FEED contract for the Bonaparte FLNG project offshore Northern Australia. The final investment decision is expected in 2014, with startup planned for 2018. The first phase of the project calls for a floating LNG production facility with a capacity of 2 million mt/year.
Chevron Corporation is currently considering an FLNG facility to develop offshore discoveries in the Exmouth Plateau of Western Australia, while ExxonMobil is waiting for an appropriate project to launch its FLNG development.
Moving LNG production to an offshore setting presents a demanding set of challenges. In terms of the design and construction of the FLNG facility, every element of a conventional LNG facility needs to fit into an area roughly one quarter the size, whilst maintaining the utmost levels of safety and giving increased flexibility to LNG production.
Once a facility is in operation, wave motion will present another major challenge. LNG containment systems need to be capable of withstanding the damage that can occur when the sea’s wave and current motions cause sloshing in the partly filled tanks. Product transfers also need to deal with the effects of winds, waves and currents in the open seas.
Many solutions to reduce the effect of motion and weather are again to be found in the design, which must be capable of withstanding – and even reducing – the impact of waves. In this area, technological development has been mainly evolutionary rather than revolutionary, leveraging and adapting technologies that are currently applied to offshore oil production or onshore liquefaction. For example, traditional LNG loading arms have been adapted to enable LNG transfers in open water, and hose-based solutions for both side-by-side transfers in calmer seas and tandem transfers in rougher conditions are nearing fruition.
|This section's factual accuracy is disputed. (June 2011)|
Natural gas is the cleanest-burning fossil fuel. It is also abundant and affordable and may be able to meet world energy needs by realising the potential of otherwise unviable gas reserves (several of which can be found offshore North West Australia). FLNG technology also provides a number of environmental and economic advantages:
- Environmental - Because all processing is done at the gas field, there is no need to lay long pipelines all the way to the shore. There is also no requirement for compression units to pump the gas to shore, dredging and jetty construction or the onshore construction of an LNG processing plant, all of which significantly reduce the project's environmental footprint. Avoiding construction also helps preserve marine and coastal environments. Additionally, environmental disturbance would be minimised during the later decommissioning of the facility, because it could be disconnected easily and removed before being refurbished and re-deployed elsewhere.
- Economic – Where pumping gas to shore can be prohibitively expensive, FLNG makes development economically viable. As a result, it will open up new business opportunities for countries to develop offshore gas fields that would otherwise remain stranded, such as those off the coast of East Africa.
The FLNG facility will be moored directly above the natural gas field. It will route gas from the field to the facility via risers. When the gas reaches the facility, it will be processed to produce natural gas, LPG, and natural gas condensate. The processed feed gas will be treated to remove impurities, and liquefied through freezing, before being stored in the hull. Ocean-going carriers will offload the LNG, as well as the other liquid by-products, for delivery to markets worldwide. The conventional alternative to this would be to pump gas through pipelines to a shore-based facility for liquefaction, before transferring the gas for delivery.
In the case of Shell’s Prelude FLNG, engineers have managed to fit every component of an LNG plant into an area roughly one quarter the size of a conventional onshore plant. Even so, Shell's facility will be the largest floating offshore facility ever built: It will measure around 488m long and 74m wide, and when fully ballasted will weigh 600,000 tonnes (roughly six times as much as the USS Nimitz aircraft carrier).
The specifications make Shell's FLNG facility particularly well-suited for fields with high production rates for reserves starting at 2 to 3 trillion cubic feet (57×109 to 85×109 m3) and beyond – less than a tenth the size of the Groningen gas field off the Netherlands.
The Shell FLNG facility will be constructed at Samsung's Geoje Island shipyard in Korea. Some modules may be constructed elsewhere and then transferred to the shipyard for assembly. The facility can remain on station for more than 25 years, and its lifetime can be further extended through overhaul and refurbishment. The hull has a design life of 50 years.
A unique feature of Shell’s FLNG design is its ability to stay safely moored in harsh weather conditions, including category five cyclones. Potentially, this could result in more uptime for the facility.
Additionally, Shell designers have optimised safety on the facility by locating storage facilities and process equipment as far from crew accommodation as possible. As a result of this, the accommodation areas of visiting LNG carriers are also at maximum distance from critical safety equipment. Safety gaps have been allowed between modules of process equipment so that gas can disperse quickly in the event of a gas leak.
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