Once oil moves from the reservoir into the FPSO and has been processed, the oil will be stored within the vessel's 14 storage tanks. These tanks have a capacity ranging from over 50,000 barrels to nearly 78,000 barrels. The biggest tanks are 27m x 17m x 26m high. The Terra Nova FPSO is double hulled - providing double containment. The oil cargo tanks are located within the inside hull, and are surrounded by a series of ballast tanks, which contain seawater. The FPSO's storage tanks can store up to 960,000 barrels and have a heating system to help prevent any build up of wax in the tanks. To move oil to market from the Terra Nova field, oil is transported by a shuttle-tanker capable of storing 850,000 barrels of oil. However, oil must first be moved from the FPSO into the shuttle tanker via the vessel's offloading system - designed for wave 'significant' heights of up to about five metres (16.5 feet). When it is time to transfer oil, the shuttle tanker positions itself about 70 metres behind the FPSO. The FPSO then sends a messenger line toward the tanker. Attached to this line is a mooring line known as the Mooring Hawser and an Offloading Hose - a hose 20 inches in diameter that transports the oil from the FPSO to the tanker.
Once the offloading hose is securely connected to the tanker, and the vessels meet a series of safety checks and balances, the transfer of oil can begin. Fuel is pumped from the FPSO's storage tanks into two export pipes, through the export line to the Offloading Hose. Crude flows through the Offloading Hose at a rate of up to 50,000 barrels per hour. During the transfer, the oil passes through what is known as the Export Oil Fiscal Metering Package. This allows the Terra Nova owners to calculate the amount of crude offloaded and available for sale in the market. It will take about 24 hours to transfer a full load of crude from the FPSO to the tanker.
The Terra Nova FPSO is a sophisticated ocean-going oil production installation. From dynamic positioning to fresh water generators, numerous state-of-the-art systems and features have been designed into the vessel to make it as safe and efficient as possible.
Staying on station A redundant Dynamic Positioning (DP) system is used to help the FPSO maintain position, monitoring the heading of the vessel, its side-to-side and fore and aft movements. The vessel's location is constantly monitored by two independent global positioning satellite systems, and a Hydro-Acoustic Position Reference (HPR) system, which receives location signals from six transponders on the seabed. The vessel is equipped with five powerful thrusters (five megawatts each), which can be used to keep the FPSO within two to three metres of a given set point. This is especially important during operations to connect the FPSO with the spider buoy, and when offloading oil to a shuttle tanker. Maintaining balance The FPSO's ballast system works in conjunction with its oil cargo system. The more oil that is stored in the inner storage tanks, the less ballast water is kept in the outer hull, and viceversa. Vessel Control Systems operators keep a close eye on the amount of oil and water being stored and where it is located. Terra Nova plans to keep the FPSO at an operating draught of between 12.5 and 18.5 metres providing optimum stability to the vessel, as well as keeping the deck high out of the water. When the FPSO is carrying a full load of crude, it will weigh approximately 200,000 tonnes. Closely related to the oil cargo system is the Inert Gas system. This system burns diesel fuel to produce an oxygen deficient air which can be stored on top of oil in the cargo tanks, providing an extra measure of safety by preventing the build up of combustible fumes in the tanks. Generating power The turbine generators are the main source of power for the FPSO. Each of these generators can produce 40 megawatts of power, which is enough power for 50,000 homes. Shortly after first oil, the generators will be fueled by gas from the Terra Nova field. The generators are also capable of running on any combination of field gas and diesel. Converting salt water into fresh water The FPSO uses between 20 to 30 cubic metres of water a day, mainly in the accommodations complex for showers and for operations in the galley. While some of this water will be loaded from supply vessels, the FPSO can provide its own water, through two fresh water generators that convert salt water into fresh water. The combined efforts of these generators can provide 50 cubic metres of water - about twice the daily amount needed for the FPSO. Heating the vessel The FPSO also has a specialized Heating Ventilation and Air Conditioning (HVAC) system that provides temperature control and air circulation. In an emergency, the HVAC system will provide for internal circulation of air to the Temporary Safe Refuge (TSR) area for two hours.
The Terra Nova project is pioneering subsea technology on the Grand Banks. Advances include the use of 'glory holes' - depressions in the seabed to protect subsea equipment from scouring icebergs. It also has the world's largest disconnectable turret that will allow the FPSO to halt production and leave the area if threatened by ice or icebergs. Offshore interfaces When the Terra Nova FPSO arrives at its offshore site, it will connect to the spider buoy, which is approximately 20 metres in diameter and weighs over 1 300 tonnes. The spider buoy is connected to a series of flexible pipelines, called risers, which will deliver oil, gas and water to and from the FPSO.
A complex subsea network Terra Nova's riser / flowline system consists of nearly 40 kilometres of flexible flowlines, risers and control umbilicals. It has been designed to withstand a 100-year storm that could bring waves up to 30 metres high. Fifteen risers will emerge from the spider buoy - eleven for production/injection and four umbilicals. These umbilicals are essentially 'extension cords' filled with small lines that send electrical power, fluids and commands to control the wells and manifolds in the glory holes. Some of Terra Nova's flowlines have been placed into trenches in the seabed, while others are buried under tonnes of crushed rock and sand. This not only offers protection from icebergs, it provides added insulation for production lines in the chilly North Atlantic. From reservoir to FPSO Oil from the Terra Nova reservoir must go through a series of mechanisms before it reaches the FPSO. Fluid travels from the reservoir through the production wells, enters the wellhead and flows into a series of production valves and piping known as the 'Christmas Tree'. The fluids are then routed through the manifolds - a series of valves and piping that provides the connection between the Christmas Trees and the flowlines. Valves within the production manifold determine which flowline will transport fluids to the FPSO. Terra Nova will have six wells ready for operation when the FPSO goes offshore - four oil producers, one gas injector, and one water injector.
The Terra Nova FPSO has four main topsides modules - the M02 water injection module, the M03 separation and high pressure compression module, the M04 produced water/glycol module, and the M05 separation and low pressure/ medium pressure compression module. In addition to containing modules that process and separate the oil, gas and water produced from the wells, the topsides structures also include the turret assembly, the flare tower, the power generation module, the offloading reel, and the platform cranes. Once reservoir fluids enter the FPSO, it moves up through the turret and into the topsides modules. In the separation and compression modules, the fluids are separated into oil, water and gas streams. The processed oil is then routed to the vessel's storage tanks, from where it will eventually be loaded onto tankers and shipped to market. The separated water and gas streams will undergo further treatment. The produced water will be cleaned and routed to the ocean. The gas may go back through the turret to be reinjected into the well or reservoir to aid in oil recovery. Additionally, some of the gas will be used to run machinery on the FPSO, such as the boilers and power generation modules. In
the event of a process upset or shutdown when the gas compressors are not running, a small portion of the gas could be burned off through a flare tower located at the rear of the vessel. Modules M02, M04, the flare tower and miscellaneous deck assemblies were built at the Bull Arm Fabrication Site, where the power generation module was also assembled. The M03 and M05 modules were constructed in Scotland. The modules, which weigh up to 2 200 tonnes each, were lifted onto the FPSO at Bull Arm in late May and early June by the heavy lift crane Asian Hercules II. Terra Nova's flare tower is among the largest ever built, rising 100 metres from the rear deck of the vessel. In fact, a counterbalance was required to keep the flare structure upright when it was being lifted onto the FPSO.
The turret is the mooring point for the FPSO as well as the interface between the subsea systems and the topsides modules. It serves as a connecting point between the FPSO and the subsea systems, and is the pathway for getting oil from the reservoir into the vessel. Water and gas, used for injection into the reservoir, will also leave the vessel through pipes in the turret.
Weighing more than 4 000 tonnes with an overall height of 70 metres, the Terra Nova turret is the largest disconnectable turret mooring system ever built. Constructed to operate in the harsh North Atlantic environment to cope with hazards such as icebergs, it is composed of the upper turret, lower turret and spider buoy. The spider buoy - approximately 20 metres in diameter and weighing over 1 300 tonnes, supports nine anchor chains and up to 19 risers. When connected to the spider buoy, the Terra Nova turret is stationary. Specialized bearings allow the FPSO to rotate, or 'weathervane', around the turret, so that the front of the vessel is always facing into the wind. In an emergency situation, the FPSO can disconnect in about 15 minutes. If the FPSO must disconnect, the spider buoy settles into a mid-water depth - ready to reconnect when the FPSO returns. The lower turret provides the connection with the spider buoy and includes winches and other equipment needed to maintain the connection between the FPSO and the spider buoy. The upper turret houses a collection of manifolds, hydraulic and electrical control equipment, as well as the swivel stack. The swivel stack serves as the interface between the subsea production system and the topsides processing and storage system. The swivels form a series of fluid flow paths which connect to piping on the FPSO itself. These swivels allow fluids or electrical signals to move back and forth from the subsea to the topsides while permitting the vessel to rotate around the turret. Mooring Systems A significant proportion of UKCS hydrocarbon reserves are produced by turret moored FPSOs which will remain permanently on location for periods between five and 25 years. Over the years, mooring line quality control has improved significantly and designs have evolved to minimise the consequences of possible failure. However, many different types of mooring system are used in UK waters today, and approaches to their inspection, repair and replacement can vary from company to company. UKOOA is keen to identify which management procedures are the most effective, so that the highest standards of safety and operation may be promoted across the whole of the industry. In April 2001, UKOOA commissioned Noble Denton Europe Ltd to look into the design, construction and operation of mooring systems over the last five years, including seabed anchors, mooring lines, the turret interface and associated systems such as winches and thrusters. The work includes recommendations for improving mooring system integrity.
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. Click on the picture below to view it in full:
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: FSO 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. FPSO 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. FPS 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. FSU 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 Newcastleupon-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: Operator
Field
AGIP Conoco Texaco Amerada Hess Shell BP Kerr-McGee Kerr-McGee Kerr-McGee Conoco Enterprise Talisman BP Shell
Balmoral Banff Captain Chestnut
Amerada Hess
Curlew Foinaven Gryphon Janice Leadon MacCulloch Pierce Ross Schiehallion Teal, Teal South and Guillemot A Triton - Bittern, Guillemot West & North West
Type of floating system FPS FPS FPSO FPS
Installation Date
FPSO FPSO FPSO FPS FPSO FPSO FPS FPSO FPSO FPSO
September 1997 November 1996 September 1993 February 1999 September 2001 April 1997 February 1999 March 1999 July 1998 August 1996
FPSO
March 2000
June 1986 January 1999 December 1996 July 2001
GIRASSOL LUANDA, ANGOLA Girassol is located about 210km NNW of Luanda, Angola. It lies in 1350m of water. It will be developed using a subsea facility tied back to an FPSO. Girassol base-case reserves are estimated at around 700 millions of barrels (bbls). Production is expected to start by the end of 2000. SUBSEA The subsea production system will initially provide for 40 wells: 23 production wells, 14 water-injection wells and three gas-injection wells.
FPSO - HULL The bare hull was built in Hyundai Heavy Industries (HHI) shipyard in Korea and moved out of dry dock in July 1999. It will be able to store two million barrels of crude oil and support processes with a capacity of 200,000b/d. It has an overall length of 300m, a moulded breadth of 59.5m, a moulded depth of 30.5m and a design draught of 22.77m. The design life of the hull is 20 years without dry docking. Current deadweight is 343,000t which includes 98% of cargo capacity and 50% of slop tanks. The hull features a double-sided construction with 12 ballast wing tanks measuring 7m wide, as well as two fore-peak and two aft-peak ballast tanks. In total, it has 12 cargo tanks. TOPSIDES The main contractor, MAR Profundo Girassol - a joint venture between ETPM and Buoygues - originally subcontracted to build the integrated deck at Fos-sur-Mer in France. It has since re-awarded the contract to Hyundai. This deck is 180m long by 60m wide. It weighs approximately 20,000t. It contains living quarters, oil treatment, storage, metering and offloading, gas treatment and reinjection facilities. The process deck is located 7m above the deck of the hull. It contains facilities for produced water treatment at a flow rate of 180,000BPD as well as facilities for 3 million m3/day gas lift, 8 million m3/d gas compression at 285 bars, and gas dehydration. ACCOMODATION The living quarters unit is located at the aft end of the hull and is designed to accommodate 140 people in 80 cabins. HOOK-UP The integrated deck will be transferred to the hull, and the hook-up of the hull/topsides as well as the pre-commissioning will be complete. MOORING The FPSO will be towed from Korea to the Girassol Field, offshore Angola, where the risers and umbilicals will be installed and connected ready for commissioning and for first oil. The FPSO will be spread-moored with 16 lines, four at each corner. The anchor lines will be a composite assembly of chains and cables connected to 16 suction anchors. RISERS AND UMBILICALS
The east side of the FPSO will be designed to receive the umbilicals and risers from three riser towers. Each of the riser towers will be connected to the FPSO by a riser. In addition, ten umbilicals will be connected to the base of the riser towers. The west side of the FPSO is designed to receive further risers and umbilicals if needed. OFFLOADING The FPSO is designed for two offloading systems, one for normal operation with a buoy, one as back-up offloading, in tandem. Both systems are located at the bow of the FPSO. The main offloading system includes a loading buoy, located approximately one mile away from the bow of the FPSO. This can accommodate tankers from 80,000 to 400,000DWT, with a nominal offloading rate of 6,000m3/h through two rigid steel catenary 16in lines. The tandem offloading is a conventional system with a mooring hawser assembly and handling system, and an offloading hose and its handling system. It is designed to accommodate tankers up to 200,000DWT at a nominal offloading rate of 8000m3/hour. The field will come on-stream in 2001.
The Girassol FPSO hull being completed at the Hyundai yard.
The Seaway Eagle will carry out most of the installation work on the Girassol field.
The Girasoll field layout diagram.
The riser towers and flowline bundles as they will be installed.
A CAD detail of the top of the riser towers.
A CAD detail of the top of the riser tower (left) and the riser tower on the seabed (right).
