Floating production facilities in the past primarily functioned as fast-track alternatives for producing marginal reservoirs or as temporary facilities to accelerate production start-up. But as discoveries moved into deeper water and more remote areas, deployment of a floating production system (FPS) many times has been the only option for exploiting the discovered resources.
Deepwater floating facilities have also taken on a role similar to that of a fixed platform and now act as regional hubs, particularly in the Gulf of Mexico, for tying in new subsea discoveries to an existing pipeline or offloading infrastructure.
As discussed in the special report on floating production systems, starting on p. 68, more than 120 FPSs are in operation in the world, and new ones are under construction or being planned. The North Sea and Offshore Brazil have about half of the existing installations, with the remainder in other active producing provinces such as the Gulf of Mexico and off Southeast Asia, West Africa, and Australia.
Most installed facilities lie in shallow-150-400 ft-water, but many of the facilities under construction are for deepwater deployment.
Facility types
The floating structure that supports the topsides production or processing equipment defines the type of FPS. These systems include the semisubmersible FPS; monohull floating production, storage, and offloading (FPSO) vessels; deep-draft caisson vessels (DDCV), or spars; and tension leg platforms (TLPs).
Most floating production hulls are made of steel, although some are made of concrete.
TLPs and spars have the advantage of being designed as dry-tree units or terminals for subsea wellheads and manifolds. Semi FPSs and FPSOs, on the other hand, require tie-in to subsea wellheads or manifolds, although future designs may allow them to handle dry trees.
These floating supporting structures come in various sizes and shapes that greatly depend on the water depth and expected sea states, as well as the topsides weight that the structures will be supporting and, in the case of FPSOs, the amount of oil that the vessel will be storing.
Except for the current FPSOs, the other FPSs have been designed to accommodate drilling or workover rigs.
Long history
Installation of production facilities on floating structures is not a new concept. These systems have been a part of the offshore production scene since the 1970s, and some barge installations in shallow water might predate this.
The site of the first deployment, in 1972, of a ship-shape storage vessel was in Ardjuna field off Indonesia, in shallow water. In 1977, the first FPSO installation site, in 377 ft of water, was in Castellon field off Spain.
The US in 1981 saw the deployment of its first floating storage and offloading (FSO) vessel, in Hondo field off California. The unit, dubbed an OST (offshore storage and treatment facility), was removed in 1990 and replaced by a pipeline and onshore processing facilities. Since that time, no other FSO or FPSO has been installed in US waters, although the industry expects the US Mineral Management Service soon to rule favorably on allowing such vessels in the Gulf of Mexico.
The North Sea Argyll field, described as a marginal and complex field, was the site for the deployment of the world's first semisubmersible FPS in 1975. The unit was converted from a drilling rig.
The North Sea also had the world's first TLP. It was deployed in Hutton field in 486 ft of water in 1984. In 1989, the Gulf of Mexico saw its first TLP, in Jolliet field, required because the 1,768 ft water depth was beyond the capability of most fixed-platform concepts.
The spar-based production facility is the most recent concept to be deployed. The Gulf of Mexico had the first such facility, which was deployed in 1996 in Neptune field in 1,930 ft of water. Some expect the spar-type designs to be the structure of choice as development extends to 10,000 ft of water and deeper. Already under construction is a spar designed for 5,400 ft of water. It will be moored in the Gulf of Mexico's Horn Mountain field.
Most FPSs primarily have been designed to handle oil production, although some also process gas and are in service as floating LPG units, such as in Ardjuna field, Takula field off Cabinda, and Escravos field off Nigeria. The N'Kossa floating development, off Congo (Brazzaville), also produces LPG.
Future prospects for floating systems include facilities for gas-to-liquids conversion or LNG facilities for monetizing stranded gas.
