What is an FPSO? Floating production, storage and offloading explained
Deskely Completions team Singapore
An FPSO (floating production, storage and offloading unit) is a ship-shaped vessel that receives oil and gas from subsea wells, processes it on board, stores the oil in its hull and offloads it to shuttle tankers. It brings a whole production facility to fields that are too deep, too remote or too small for a fixed platform and a pipeline.
This guide covers how an FPSO works, the main types and mooring systems, newbuilds and conversions, how FPSOs compare with other floating units, and how one is built, completed and commissioned.
- An FPSO produces, processes, stores and offloads oil at sea, with no pipeline to shore.
- Turret-moored FPSOs turn with the weather; spread-moored ones hold a fixed heading.
- Hulls are newbuilt or converted from tankers; topsides modules are built in parallel and integrated.
- An FPSO has tens of thousands of tags to complete and commission across several yards and the field.
What does FPSO stand for?
FPSO stands for floating production, storage and offloading. Each word is a function:
- Floating: the unit is a moored vessel, not a fixed structure, so it can work in deep water and be moved to another field at the end of a field's life.
- Production: the topsides process plant separates the well stream into oil, gas and water, treats each, and handles gas for reinjection, fuel, export or flaring.
- Storage: stabilised crude is stored in cargo tanks in the hull, often around a million barrels or more.
- Offloading: the oil is transferred to shuttle tankers, typically in tandem (bow to stern) or side by side, every few days or weeks.
Shell's Castellon, in the Spanish Mediterranean in 1977, is generally cited as the first FPSO. FPSOs are now the most common type of floating production system, used from the North Sea to Brazil, West Africa and Southeast Asia.
How an FPSO works
- 01Subsea wells
Production wells on the seabed are connected through flowlines and manifolds to the FPSO.
- 02Risers
Flexible or steel risers carry the well fluids up to the vessel, through the turret or along the side of a spread-moored hull.
- 03Separation
On the topsides, separators split the stream into oil, gas and produced water.
- 04Treatment
Oil is stabilised and dewatered; gas is compressed, dried and used for fuel, reinjected or exported; produced water is cleaned before discharge or reinjection. Water injection and gas lift systems support the reservoir.
- 05Storage
Crude goes to the cargo tanks in the hull.
- 06Offloading
A shuttle tanker connects by hawser and hose and the crude is pumped across and metered.
Around the process plant sit the utilities that make the vessel a self-contained facility: power generation, cooling, heating, nitrogen, instrument air, chemical injection, flare, fire and gas detection, firewater and accommodation.
Turret and spread mooring
| Mooring | How it works | Suits |
|---|---|---|
| Internal turret | A turret inside the hull, usually near the bow, is anchored to the seabed; the vessel weathervanes around it | Harsh environments, many risers |
| External turret | The turret is mounted outside the hull on a bow structure | Moderate environments, fewer risers, conversions |
| Disconnectable turret | The buoy can be released so the vessel sails away | Cyclones, typhoons and ice |
| Spread mooring | Mooring lines at the bow and stern hold a fixed heading | Benign, directional environments such as West Africa and parts of Brazil |
A turret has a swivel stack that passes fluids, power and signals from the fixed risers to the rotating vessel. Spread-moored FPSOs avoid the swivel and can take a very large number of risers along the side of the hull.
Newbuild and conversion
An FPSO hull is either built new for the project or converted from an existing tanker, usually a VLCC (very large crude carrier). Conversions have historically been faster and cheaper; newbuilds give a longer design life and a hull designed for the field. A growing share of hulls are standardised newbuild designs, built repeatedly so that schedule and cost are more predictable.
FPSOs are either owned by the oil company or leased from a contractor that builds, owns and often operates the unit for the field operator under a long-term charter.
FPSO vs FSO, FLNG and other floating units
| Unit | What it does |
|---|---|
| FPSO | Produces, processes, stores and offloads oil |
| FSO | Floating storage and offloading only, no processing |
| FLNG | Floating liquefied natural gas: produces and liquefies gas, stores and offloads LNG |
| FSRU | Floating storage and regasification unit: receives LNG and sends gas ashore |
| Semi-submersible, TLP, spar | Floating production platforms without large storage, exporting by pipeline |
How an FPSO is built
- 01Concept and FEED
Field development studies fix the capacities, the hull and mooring concept and the topsides process design.
- 02Hull
The hull is built in a shipyard, or the donor tanker is refurbished and converted, including the turret or mooring interfaces and the living quarters.
- 03Topsides modules
Process, utility and power modules are fabricated in parallel, often at different yards or in different countries.
- 04Integration
Modules are lifted onto the hull and connected: piping, electrical, instrument and telecom interfaces across modules and hull.
- 05Mechanical completion and commissioning at the yard
Systems are completed, tested and commissioned as far as possible in the yard, where it is far cheaper than offshore.
- 06Sail-away and hook-up
The FPSO is towed or sails to the field, connected to its moorings and risers, and the remaining systems are commissioned offshore.
- 07First oil
Wells are opened up and production starts, followed by performance testing and the ramp-up to plateau.
Completions and commissioning on an FPSO
An FPSO is one of the most demanding completions jobs in the industry. A typical unit has tens of thousands of tags across hundreds of subsystems, built by several contractors in several yards, then integrated, commissioned and partly re-commissioned offshore. Every tag needs its inspection and test records, every subsystem its certificates, and the punch and carry-over work has to follow the vessel from the yard to the field.
What goes wrong is usually the data: each yard keeps its own registers and spreadsheets, the same tag is recorded differently in two places, and the completion picture at sail-away is assembled by hand. Work that is not finished in the yard costs many times more to finish offshore, so knowing exactly what is open before sail-away matters. See mechanical completion vs commissioning and commissioning 101.
Where Deskely comes from
Deskely began as the in-house completions system on Compass Energy's own FPSO conversion and construction projects. It has run FPSO completions since 2014, on MODEC FPSO projects since 2016, holding every tag, inspection, punch item and certificate in one register from the first module yard to the field.
The Deskely products for this
Frequently asked questions
What does FPSO stand for?
Floating production, storage and offloading: a vessel that produces and processes oil and gas, stores the oil in its hull and offloads it to shuttle tankers.
How does an FPSO work?
Well fluids come up risers from subsea wells to the topsides, where they are separated into oil, gas and water. The oil is stored in the hull and offloaded to shuttle tankers; the gas is used for fuel, reinjected or exported.
What is the difference between an FPSO and an FSO?
An FSO only stores and offloads oil. An FPSO also has a process plant on board that produces and treats the well stream.
What is a turret on an FPSO?
A rotating mooring system, inside or outside the hull, that anchors the vessel while letting it turn with the wind and waves. Risers pass up through it and a swivel transfers fluids and power to the vessel.
How much oil can an FPSO store?
It depends on the hull. Many FPSOs store around one to two million barrels; a converted VLCC hull can hold about two million.
How long does it take to build an FPSO?
It varies with the design and whether the hull is new or converted, but projects commonly take several years from contract award to first oil, including integration, commissioning and offshore hook-up.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016