An oil platform (oil rig) is a large structure with facilities to drill wells, to 
extract and process oil and natural gas, and to temporarily store product until it 
can be brought to shore. In many cases, the platform contains facilities to house 
the workforce as well.
Тhe platform may be fixed to the ocean floor, may consist of an artificial 
island, or may float.
Remote subsea wells may also be connected to a platform by flow lines and 
by umbilical connections; these subsea solutions may consist of single wells or 
of a manifold center for multiple wells. Larger lake- and sea-based offshore platforms and drilling rigs are some of 
the largest moveable man-made structures in the world. There are several types 
of oil platforms and rigs.
Fixed platforms are built on concrete or steel legs, or both, anchored direct-
ly onto the seabed, supporting a deck with space for drilling rigs, production 
facilities and crew quarters. Such platforms are, by virtue of their immobility, 
designed for very long term use. Various types of structure are used, steel jack-
et, concrete caisson, floating steel and even floating concrete. Steel jackets are 
vertical sections made of tubular steel members, and are usually piled into the 
seabed. Concrete caisson structures often have in-built oil storage in tanks be-
low the sea surface and these tanks were often used as a flotation capability, 
allowing them to be built close to shore and then floated to their final position 
where they are sunk to the seabed. Fixed platforms are economically feasible 
for installation in water depths up to about 520 m.
Compliant towers consist of slender flexible towers and a pile foundation 
supporting a conventional deck for drilling and production operations. Compli-
ant towers are designed to sustain significant lateral deflections and forces, and 
are typically used in water depths ranging from 460 to 910 m.
Semi-submersible platforms have hulls of sufficient buoyancy to cause the 
structure to float, but of weight sufficient to keep the structure upright. Semi-
submersible platforms can be moved from place to place; can be ballasted up or 
down by altering the amount of flooding in buoyancy tanks; they are generally 
anchored by combinations of chain, wire rope or polyester rope, or both, during 
drilling or production operations, or both, though they can also be kept in place 
by the use of dynamic positioning. Semi-submersibles can be used in water 
depths from 60 to 3,000 m.
Jack-up Mobile Drilling Units (or jack-ups) are rigs that can be jacked up 
above the sea using legs that can be lowered, much like jacks. These MODUs 
(Mobile Offshore Drilling Units) are typically used in water depths up to 120 m, 
although some designs can go to170 m depth. They are designed to move from 
place to place, and then anchor themselves by deploying the legs to the ocean 
bottom using a rack and pinion gear system on each leg.
A drillship is a maritime vessel that has been fitted with drilling apparatus. 
It is most often used for exploratory drilling of new oil or gas wells in deep wa-
ter but can also be used for scientific drilling. Early versions were built on 
a modified tanker hull, but purpose-built designs are used today. Most drillships 
are outfitted with a dynamic positioning system to maintain position over the 
well. They can drill in water depths up to 3,700 m.
The main types of floating production systems are FPSO (floating produc-
tion, storage, and offloading system). FPSOs consist of large monohull struc-
tures, generally (but not always) shipshaped, equipped with processing facili-
ties. These platforms are moored to a location for extended periods, and do not 
actually drill for oil or gas. Some variants of these applications, called FSO 
(floating storage and offloading system) or FSU (floating storage unit), are used exclusively for storage purposes, and host very little process equipment. This is 
one of the best sources for having floating production.
The world's first Floating Liquefied Natural Gas (FLNG) facility is current-
ly under development.
Tension-leg platforms (TLPs) are floating platforms tethered to the seabed 
in a manner that eliminates most vertical movement of the structure. TLPs are 
used in water depths up to about 2,000 m. The «conventional» TLP is a 4-
column design which looks similar to a semisubmersible. Proprietary versions 
include the Seastar and MOSES mini TLPs; they are relatively low cost, used in 
water depths between 180 and 1,300 m. Mini TLPs can also be used as utility, 
satellite or early production platforms for larger deepwater discoveries.
Gravity-based structure (GBS) can either be steel or concrete and is usually 
anchored directly onto the seabed. Steel GBS are predominantly used when 
there is no or limited availability of crane barges to install a conventional fixed 
offshore platform. Steel GBS do not usually provide hydrocarbon storage capa-
bility. It is mainly installed by pulling it off the yard, by either wet-tow or/and 
dry-tow, and self-installing by controlled ballasting of the compartments with 
sea water. The GBS may be connected to either a transportation barge or any 
other barge using strand jacks. The jacks shall be released gradually whilst the 
GBS is ballasted to ensure that the GBS does not sway too much from target 
location.
Spar platforms are moored to the seabed like TLPs, but whereas a TLP has 
vertical tension tethers, a spar has more conventional mooring lines. Spars have 
to-date been designed in three configurations: the «conventional» one-piece cy-
lindrical hull, the «truss spar» where the midsection is composed of truss ele-
ments connecting the upper buoyant hull with the bottom soft tank containing 
permanent ballast, and the «cell spar» which is built from multiple vertical cyl-
inders. The spar has more inherent stability than a TLP since it has a large coun-
terweight at the bottom and does not depend on the mooring to hold it upright. 
It also has the ability, by adjusting the mooring line tensions to move horizon-
tally and to position itself over wells at some distance from the main platform 
location.
Normally unmanned installations (NUI), sometimes called toadstools, are 
small platforms, consisting of little more than a well bay, helipad and emergen-
cy shelter. They are designed to be operated remotely under normal conditions, 
only to be visited occasionally for routine maintenance or well work.
Conductor support systems, also known as satellite platforms, are small 
unmanned platforms consisting of little more than a well bay and a small pro-
cess plant. They are designed to operate in conjunction with a static production 
platform which is connected to the platform by flow lines or by umbilical cable, 
or both.
A typical oil production platform is self-sufficient in energy and water 
needs, housing electrical generation, water desalinators and all of the equipment 
necessary to process oil and gas such that it can be either delivered directly on shore by pipeline or to a floating platform or tanker loading facility, or both. 
Elements in the oil/gas production process include wellhead, production mani-
fold, production separator, glycol process to dry gas, gas compressors, water 
injection pumps, oil/gas export metering and main oil line pumps.
Larger platforms assisted by smaller ESVs (emergency support vessels) 
like the British Iolair that are summoned when something has gone wrong, e.g. 
when a search and rescue operation is required. During normal operations, 
PSVs (platform supply vessels) keep the platforms provisioned and supplied, 
and AHTS vessels can also supply them, as well as tow them to location and 
serve as standby rescue and firefighting vessels.
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