An oil platform or oil rig is a large structure used to house workers and machinery needed to drill and/or extract oil and natural gas through wells in the ocean bed. Depending on the circumstances, the platform may be attached to the ocean floor, consist of an artificial island, or be floating.
Generally, oil platforms are located on the continental shelf, though as technology improves and crude oil prices increase, drilling and production in deeper waters becomes both feasible and profitable. A typical platform may have around thirty wellheads located on the platform and directional drilling allows reservoirs to be accessed at both different depths and at remote positions up to 5 miles (8 kilometres) from the platform.
Many platforms also have remote wellheads attached by umbilical connections; these may be single wells or a manifold centre for multiple wells.
The Thames Sea Forts
of World War II are considered the direct predecessors of modern offshore oil platforms, having been pre-constructed in a very short time, they were then floated to their location and placed on the shallow bottom of the Thames
In 1938, the Superior Oil
company constructed the first offshore oil platform off the Gulf Coast of Louisiana
One such platform is currently drilling for oil near Blackfriar's Bridge. Work started in June 2008 and is expected to finish in October/November 2009.
Larger lake- and sea-based oil platforms and oil rigs are some of the largest moveable man-made structures in the world. There are several distinct types of platforms and rigs:
These platforms are built on concrete and/or steel legs anchored directly 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 (for instance the Hibernia platform). Various types of structure are used, steel jacket, 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, pioneered by the Condeep concept, often have in-built oil storage in tanks below the sea surface and these tanks were often used as a flotation capability, allowing them to be built close to shore (Norwegian fjords and Scottish firths are popular because they are sheltered and deep enough) 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 1,700 feet (520 m).
These platforms consist of narrow, flexible towers and a piled foundation supporting a conventional deck for drilling and production operations. Compliant towers are designed to sustain significant lateral deflections and forces, and are typically used in water depths ranging from 1,500 and 3,000 feet (450 and 900 m).
These platforms have legs of sufficient buoyancy
to cause the structure to float, but of weight sufficient to keep the structure upright. Semi-submersible rigs 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 with chain, wire rope and/or polyester rope during drilling operations, though they can also be kept in place by the use of dynamic positioning
. Semi-submersibles can be used in water depths from 200 to 10,000 feet (60 to 3,050 m).
Jackups, as the name suggests, are platforms that can be jacked up above the sea using legs which can be lowered like jacks. These platforms are typically used in water depths up to , although some designs can go to 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 water 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 12,000 feet (3,660 m).
FPSOs are large ships equipped with processing facilities and moored to a location for a long period. The main types of floating production systems are FPSO (floating production, storage, and offloading system)
, FSO (floating storage and offloading system)
, and FSU (floating storage unit). These ships do not actually drill for oil or gas.
TLPs consist of floating rigs tethered to the seabed in a manner that eliminates most vertical movement of the structure. TLPs are used in water depths up to about 6,000 feet (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 600 and 4,300 feet (200 and 1,300 m). Mini TLPs can also be used as utility, satellite or early production platforms for larger deepwater discoveries.
Spars are moored to the seabed like the TLP, but whereas the TLP has vertical tension tethers, the Spar has more conventional mooring lines. Spars have been designed in three configurations: the "conventional" one-piece cylindrical hull, the "truss spar" where the midsection is composed of truss elements connecting the upper buoyant hull (called a hard tank) with the bottom soft tank containing permanent ballast, and the "cell spar" which is built from multiple vertical cylinders. The Spar may be more economical to build for small and medium sized rigs than the TLP, and has more inherent stability than a TLP since it has a large counterweight at the bottom and does not depend on the mooring to hold it upright. It also has the ability, by use of chain-jacks attached to the mooring lines, to move horizontally over the oil field. The first production spar was Kerr-McGee's Neptune, which is a floating production facility anchored in 1,930 feet (588 m) in the Gulf of Mexico, however spars (such as Brent Spar
) were previously used as FSOs. Eni
's Devil's Tower
is located in 5,610 feet (1,710 m) of water, in the Gulf of Mexico, and is currently the world's deepest spar; however, when Shell
's Perdido Spar
is installed, it will be the deepest at 8,000 feet (2,438 m). The first Truss spars were Kerr-McGee's Boomvang and Nansen. The first (and only) cell spar is Kerr-McGee's Red Hawk.
These installations (sometimes called toadstools), are small platforms, consisting of little more than a well bay
and emergency shelter. They are designed to operate remotely under normal conditions, only to be visited occasionally for routine maintenance or well work
Especially large examples
The Petronius Platform
is an oil platform in the Gulf of Mexico
, which stands above the ocean floor. Depending on the criteria it may be one of the world's tallest structures
The Hibernia platform is the world's largest oil and gas platform, located on the Jeanne D'Arc basin, in the Atlantic Ocean off the coast of Newfoundland. The Gravity Base Structure (GBS), which sits on the ocean floor, is high and has storage capacity for of crude oil in its high caisson (Dorel Iosif). The platform acts as a small concrete island with serrated outer edges designed to withstand the impact of an iceberg. The GBS contains production storage tanks and the remainder of the void space is filled with ballast with the entire structure weighing in at 1.2 million tons. The platform stands high, which is half the height of New York's Empire State Building (1473) and taller than the Calgary Tower (626.6 ft).
Maintenance and supply
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 onshore by pipeline or to a Floating Storage Unit
and/or tanker loading facility. Elements in the oil/gas production process include wellhead
, production manifold
, production separator
process to dry gas, gas compressors
, water injection pumps
, oil/gas export metering
and main oil line
pumps. All production facilities are designed to have minimal environmental impact.
Larger platforms are 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.
The size and composition of the crew of an offshore installation will vary greatly from platform to platform. Because of the cost intensive nature of operating an offshore platform, it is important to maximise productivity by ensuring work continues 24 hours a day. This means that there are essentially two complete crews on board at a time, one for day shift and the other for night shift. Crews will also change out at regular intervals, nominally two weeks.
Not all of these personnel are present on every platform, on smaller platforms workers will be responsible for several areas. The names shown are not industry-wide.
- OIM (offshore installation manager) is the ultimate authority during his/her shift and makes the essential decisions regarding the operation of the platform.
- Operations Team Leader (OTL)
- Offshore Operations Engineer (OOE) is the senior technical authority on the platform
- PSTL or Operations coordinator for managing crew changes
- Dynamic Positioning Operator, navigation, ship or vessel maneuvering (MODU), station keeping, fire and gas systems operations in the event of incident
- 2nd Mate - Meets manning requirements of flag state, operates Fast Rescue craft, cargo ops, fire team leader.
- 3rd Mate - Meets manning requirements of flag state, operates Fast Rescue craft, cargo ops, fire team leader
- Ballast Control Operator _ also fire and gas systems operator
- Crane operators to operate the cranes for lifting cargo around the platform and between boats.
- Scaffolders to rig up scaffolding for when it is required for workers to work at height.
- Coxwains for maintaining the lifeboats and manning them if necessary.
- Control room operators - Especially FPSO or Production platforms.
- Catering crew will include people tasked with performing essential functions such as cooking, laundry and cleaning the accommodation.
- Production techs for running the production plant
- Helicopter Pilot(s) live on some platforms that have a helicopter based offshore. The helicopter flight crew transports workers to other platforms or to shore on crew changes.
- maintenance technicians (instrument, electrical, mechanical)
- Drill crew will be on board if the installation is performing drilling operations. A drill crew will normally comprise:
- Well services crew will be on board for well work. The crew will normally comprise:
- Well services supervisor
- Wireline or coiled tubing operators
- Pump operator
The nature of their operation — extraction of volatile substances sometimes under extreme pressure in a hostile environment — has risk and accidents and tragedies occasionally occur. In July 1988, 167 people died when Occidental Petroleum's Piper Alpha offshore production platform, on the Piper field in the North Sea, exploded after a gas leak. The accident greatly accelerated the practice of providing living accommodations on separate rigs, away from those used for extraction.
However, this was in itself a hazardous environment. In March 1980, the 'flotel' (floating hotel) platform Alexander Kielland capsized in a storm in the North Sea with the loss of 123 lives.
In 2002, an oil rig exploded just offshore near New Orleans.
Given the number of grievances and conspiracy theories that involve the oil business, and the importance of gas/oil platforms to the economy, platforms in the United States are believed to be potential terrorist targets. Agencies and military units responsible for maritime counterterrorism in the US (Coast Guard, Navy SEALs, Marine Recon) often train for platform raids.
In British waters, the cost of removing all platform rig structures entirely was estimated in 1995 at $345 billion, and the cost of removing all structures including pipelines — a so-called "clean sea" approach — at $621 billion.
Further effects are the leaching of heavy metals that accumulate in buoyancy tanks into water; and risks associated with their disposal. There has been concern expressed at the practice of partially demolishing offshore rigs to the point that ships can traverse across their site; there have been instances of fishery vessels snagging nets on the remaining structures. Proposals for the disposal at sea of the Brent Spar, a tall storage buoy (another true function of that which is termed an oil rig), was for a time in 1996 an environmental cause célèbre in the UK after Greenpeace occupied the floating structure. The event led to a reconsideration of disposal policy in the UK and Europe.
In the United States, Marine Biologist Milton Love has proposed that oil platforms off the California coast be retained as artificial reefs, instead of being dismantled (at great cost), because he has found them to be havens for many of the species of fish which are otherwise declining in the region, in the course of 11 years of research. Love is funded mainly by government agencies, but also in small part by the California Artificial Reef Enhancement Program. NOAA has said it is considering this course of action, but wants money to study the effects of the rigs in detail. Divers have been used to assess the fish populations surrounding the platforms. In the Gulf of Mexico, more than 200 platforms have been similarly converted.
Tallest oil platforms
Depth records have been published. The tallest rigid structure oil platform is the floating Magnolia ETLP
which is about . Non-floating platforms are: