Turret & swivel stack
The turret anchors the FPSO in place, and allows the FPSO to rotate freely with wind and current.
The swivel transfers the oil and gas from the reservoir via the anchored part of the turret which is stationary to the ship side of the turret which rotates with the FPSO.
The turret and swivel allows deployment of the FPSO to locations with severe weather, and ensures safe operation in the most demanding conditions.
The flare tower has a key safety function to safely burn and dispose of gas from the process plant in case of process upsets or in case the gas in the process facilities must be released for other reasons.
The flare tower is connected to the FPSO flare system, which collects all relief and gas vents from the process facilities. Flaring of gas is normally limited by using the gas for fuel, gas export or reinjection.
When the gas is separated from the oil it must be compressed and processed to be used as fuel, exported or reinjected into the reservoir. The pressure of the gas is increased in the gas compressor in order to export or reinject the gas.
Normally the process includes the treatment of the gas to remove water and liquid hydrocarbons, giving a clean hydrocarbon gas that can be exported, reinjected or partly used as fuel to power the FPSO.
The main process plant on the FPSO is the separation facilities, where the raw well stream from the reservoir is split into stabilised crude oil, hydrocarbon gas and produced water.
The oil is heated to boil off excess gas and remove water, thus making the oil stable for storage. Residual oil is removed from the produced water before overboard disposal or reinjection to the reservoir.
The most common processing is done via gravity separation in large pressure vessels, taking advantage of the difference in density between oil, gas and water. The stabilised oil is then stored onboard the FPSO.
Processing of oil requires large amounts of heat to increase the temperature of the well stream sufficiently to enable processing in the process plant.
This heat is supplied via the heating medium system, normally operating with a closed loop of pressurised, heated fresh water, or in some cases steam. The heat is most commonly generated from the hot exhaust coming from gas turbines via large heat exchangers called waste heat recovery units. In some cases supplementary heat is also produced via fired boilers.
Large amounts of power is needed to operate the FPSO, and since operation is normally done in remote areas this power must be generated on board the FPSO.
There are two main forms of power generation, either by gas turbine generators or by steam driven generators. The power generation is fuelled by hydrocarbon gas from the process facilities on board the FPSO, with diesel as backup fuel.
Smaller diesel generators located in the hull supply essential and emergency power if the main power generation is not available, to ensure safe operation of the FPSO.
The switchroom serves to distribute the power from the power generation to all consumers on board the FPSO. The switchroom contains electrical switchboards and distribution boards necessary to distribute the electrical power to all consumers on the FPSO.
In addition, the switchroom also contains some control panels to control parts of the topside or subsea facilities.
BW Offshore FPSO’s accommodates its management and employees with everything that is needed for extended operations at sea.
This includes cabins, recreational areas, gym and fully staffed galley.
Landing area for helicopters, facilitates timely on-site transport and serves as an additional evacuation option.
The helideck also has facilities to enable refuelling of helicopters as needed.
The FPSO is kept in position by a mooring system consisting of several mooring lines.
The most common configurations are a turret mooring system or spread mooring system. While the spread mooring keeps the FPSO in a fixed position by having mooring lines in each corner (starboard/port forward and aft), the turret configuration allows for the FPSO to weather wane (rotate) around the stationary part of the turret where the mooring lines are connected.
The mooring lines for the FPSO are typically made up of a combination of chain and wire or polyester rope, depending on the water depth on the installation site.
Risers and umbilicals
A mixture of oil, gas and produced water is transported from the subsea installation(s) or wellhead platform(s) to the FPSO by means of large flexible pipes called risers. Other risers may transfer injection water back to the subsea facilities or wellhead platform for pressure support in the reservoir via water injection wells.
Surplus hydrocarbon gas in excess of any gas used for fuel to power the FPSO is transferred via gas export riser(s) to gas export pipelines to shore, or gas injection pipelines to gas injection wells.
Umbilicals are a collection of tubing, power and signal cables bundled together, which support subsea facilities or wellhead platforms with power, signals, hydraulics and production chemicals from the FPSO.
The hull of the FPSO contains several very large cargo tanks for storage of the processed crude oil until ready for offloading into receiving tanker.
The storage tanks have inert gas facilities to ensure a non-explosive atmosphere.
There are pumping facilities in the hull to pump the oil out of the FPSO storage tanks and into the receiving tanker for transfer to onshore refineries or other reception facilities.
When the crude oil is pumped from the FPSO storage tanks to the receiving tanker, the volume of the crude oil must be recorded as a basis for calculation the net value of the crude oil.
This measurement is done in the fiscal metering station where flow instruments of high accuracy measure the flow of oil from the FPSO to the receiving tanker. For FPSOs with gas export equivalent facilities for gas will record the volume of gas flowing from the FPSO to the export pipeline.
The crude oil is normally exported in batches, and the time between each offloading is dependent on the FPSO’s available storage and the production rate.
The offloading hose is a flexible connection between the FPSO and the receiving tanker, allowing for tandem offloading operations.
The hose is dropped in the water and taken to the receiving tanker, where it is connected to its crude receiving facilities. Once the receiving tanker is secured to the FPSO via the hawser, and the hose is securely connected to the receiving tanker, large crude oil transfer pumps on the FPSO will pump the oil from the storage tanks on the FPSO to the storage tanks on the receiving tanker. The FPSO continues with full production while the offloading operation is carried out.
The offloading hose can either be stored floating in the sea or on a very large hose reel between offloading operations.
Central Control Room
The Central Control Room (CCR) is the brain of the operations, controls the operation of most process facilities on the FPSO, and houses all normal and emergency control functions.
The CCR is continuously manned 24 hours a day to ensure efficient, safe and effective production.