Frequently Asked Questions
What is an FPSO?
An FPSO is a Floating Production, Storage and Offloading unit and is just one of a range of different types of floating systems used by the offshore oil and gas industry today. It is similar in appearance to a ship but is designed quite differently and carries on board all the necessary production and processing facilities normally associated with a fixed oil and gas platform, but with the addition of storage tanks for the crude oil recovered from the wells on the seabed below. It is moored permanently on location and is connected to the wells below by flexible risers.
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What different types of floating systems are there?
As the name suggests, floating systems are not fixed permanently to the seabed but are designed to be moored to remain on station for long periods of time. There are many different variants of these systems, and the terminology and acronyms vary too, even for the same "system"!
Some common abbreviations include:
||Floating storage and offloading system, often a ship or barge-shaped floating hull incorporating tanks for storage of produced oil, and a method of loading the oil into offtake tankers. These installations do not have any production or processing facilities.
||Floating production, storage and offloading vessel which includes, in addition to its storage and offloading capability, facilities for receiving crude oil from producing wells and processing it for export by separating water and gas.
||Floating production system: a general term to describe any floating facility designed to receive crude oil from producing wells and process it. It may not have facilities for storage, in which case export would be by pipeline to shore or to a nearby FSO.
||Floating Storage Unit; a floating facility intended only for storage of oil. Export may be by pipeline to an onshore facility rather than offloaded to shuttle tankers. Sometimes used synonymously with FSO.
FPS units - which have production but usually no storage facilities - can take many forms. They range in size from converted barges installed with separation equipment for small scale production of up to 25,000 barrels of oil per day (b/d) to giant purpose-designed vessels with capacity for processing more than 200,000 b/d. Some may be converted drilling rigs or semi-submersible and tension-legged platforms.
FPSOs, which combine production, storage and offloading facilities, are usually "ship-shaped" and may be purpose built or converted from an existing hull, incorporating key modifications to increase the strength or fatigue resistance in particular areas.
Each design has its own advantages depending on the oilfield water depth, local environmental conditions and economic factors.
How many floating units are there?
There are currently 15 FPSO and FPS units operating on the UK Continental Shelf and 70 worldwide.
Why use a floating system?
Across the world, oil and gas is being found and produced in ever-deeper waters. Here, water depth, ocean currents and harsh weather conditions may all influence the decision on which type of production installation to use. A fixed installation may not be technically feasible in a particularly challenging location where a floating unit would offer the best solution.
Floating systems are also a cost-effective solution for developing smaller, satellite or marginal fields in shallower water as they can be floated off when reservoirs are depleted, and re-used elsewhere. The benefits of "recycling" such facilities are not just economic but also environmental.
How does an FPSO keep on station?
The offshore industry has developed highly sophisticated mooring and station-keeping systems which enable oil production vessels to operate safely and reliably.
In the UKCS, where weather conditions can be extreme, most vessels have a central mooring arrangement located within the hull in a "turret", that allows them to rotate freely around the point of mooring in response to shifting weather direction. This is known as "weathervaning" and allows the vessel's bow always to point into the prevailing wind and currents, minimising the impact of nature's forces. Often thruster systems are also used to supplement the station-keeping and control vessel heading.
In countries with more benign weather, such an arrangement may not be required and the vessel is kept on station by an array of moorings and anchors, known as a spread-moored system.
How does an FPSO recover oil and gas?
The hydrocarbons treated on an FPSO or FPS are produced through wells that are located on the seabed. Untreated liquids are brought to the surface via subsea equipment on the sea floor including valves at the well (a "Christmas tree"), a manifold to connect several wells together into one flowline, which is then linked to the vessel. These pipelines must pass from the seabed to the floating facility at the surface - and are called "risers". They must be flexible to accommodate the heaving motion of the vessel above, and be very resistant to fatigue.
What are the safety precautions on board an FPSO?
Safety on board any production facility has the utmost priority. Robust safety standards must be in place and rigorously enforced. In the UK, all operating companies must submit a Safety Case to the Health and Safety Executive, which:
- demonstrates that the company has in place safety management systems;
- has identified risks and reduced them to as low as reasonably practicable;
- has put management controls in place;
- has a safe refuge for personnel in the event of an emergency and
- has made provisions for safe evacuation and rescue.
Features which contribute to the safe operation of FPSOs are described below:
The hull must be designed for at least the expected life of the field - often 15 to 25 years - and constructed to standards that will permit it to remain at sea during this time without access to dry docking facilities. Of special importance is how the vessel will survive a possible collision at sea. Normal maritime criteria are used such that the vessel will be able to stay afloat with any two hull compartments flooded.
Crude oil stage tanks, an integral part of the FPSO hull, are blanketed with inert gas to maintain a safe environment for loading and discharging crude oil.
Oil and gas processing is controlled and monitored remotely. Shutdown systems are built in to close off the flow and contain hydrocarbons under pressure in an emergency and allowing depressurisation via a flare stack.
Protection against fire and explosion is provided in the form of protective coatings and blast or firewalls. Water deluge systems are installed in open areas and sprinkler systems in closed areas. The accommodation block is mechanically ventilated and pressurised, taking fresh air from a safe location remote from the process equipment, and is thus a safe refuge for personnel.
Emergency evacuation is primarily by helicopter from a helideck situated directly above the accommodation block, or by service craft. Other methods use lifeboats, life rafts and standby service craft working in the field. Personnel are trained to respond to various accident scenarios relating to the process systems, including safe shutdown of operations, de-pressurisation and eventual evacuation. All personnel are provided with personal safety equipment such as survival suits and life vests.
How is the oil taken ashore?
In the UK, crude oil is normally transported to shore using dedicated off-take or "shuttle" tankers specially designed for the weather conditions found offshore in Britain.
For example, most shuttle tankers are now equipped with a bow-loading system, usually hydraulically operated. Bow loading was first introduced in 1975 and has proved to be highly reliable over the years. The method is well suited to the harsh conditions often experienced in UK waters.
Other features include emergency shut down equipment and dynamic positioning to keep the tanker on station at a safe distance away from the FPSO or storage facility while loading.
Cargo is transferred by flexible hose or hoses which connect the installation with the tanker. The process of loading from the stern of the FPSO to the bow of the shuttle tanker is known as "tandem loading"
What floating production facilities currently operate on the UKCS?
There are currently 15 floating production facilities in operation on the UK Continental Shelf. The most recent FPSO to arrive in the North Sea is Kerr-McGee's Global Producer III which has just left Swan Hunter's Newcastle-upon-Tyne ship yard for the Leadon field in the Central North Sea. The first oil is due to flow by the end of 2001.
Other recent start-ups using FPSO technology are Amerada Hess's Chestnut field, also in the Central North Sea, which came on stream in July 2001and BG's Blake field which is linked by pipeline (known as a "tie-back" system) to Talisman's existing FPSO facility on the Ross field.
Amerada Hess used FPSO technology in the North Sea with the commissioning of the Petrojarl I in the early 1990s to produce oil from the small Angus field. Interestingly, new production technology has given Angus a fresh lease of life and after lying dormant for eight years, it has been redeveloped and oil has once again started to flow. This time, production is tied-back by pipeline to another FPSO, the Uisge Gorm, which already services the Fife, Fergus and Flora fields 18 km away to the south east.
In the remote, deep waters to the west of Shetland, two floating facilities produce oil from BPs' Schiehallion and Foinaven fields respectively, the only fields currently in production in the Atlantic Margin.
The following is a list of the FPSOs and FPS operating on the UKCS today:
||Type of floating system
||Teal, Teal South and Guillemot A
||Triton - Bittern, Guillemot West & North West