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.
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).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). rack and pinion gear system on each leg. dynamic positioning system to maintain position over the well. They can drill in water depths up to 12,000 feet (3,660 m). 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. 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. well bay, helipad and emergency shelter. They are designed to operate remotely under normal conditions, only to be visited occasionally for routine maintenance or well work.
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).
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 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.
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.
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