A typical offshore Oil/Gas platform.
An
offshore platform, often referred to as an
oil platform or an
oil rig, is a lаrge structure used to house workers and machinery needed to drill wells in the ocean bed, extract
oil and/or
natural gas, process the produced fluids, and ship or pipe them to shore. Depending on the circumstances, the platform may be
fixed to the ocean floor, may consist of an
artificial island, or may
float.
Most offshore platforms are located on the
continental shelf, though with advances in technology and increasing crude oil prices, drilling and production in deeper waters has become both feasible and economically viable. 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 kilometers) from the platform.
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 centre for multiple wells.
Types
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 distinct types
[3] of platforms and rigs:
[edit] Fixed platforms
Main article:
Fixed PlatformA fixed platform base under construction on a Louisiana river
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 ft (520 m).
[edit] Compliant towers
These platforms consist of slender flexible towers and a pile 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 to 3,000 feet (460 to 910 m).
[edit] Semi-submersible platform
Platform P-51 off the Brazilian coast is a semi-submersible platform These platforms have hulls (columns and pontoons) 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 and/or polyester rope during drilling and/or production 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 3,000 m).
[edit] Jack-up platforms
Jack-up platforms (or jack-ups), as the name suggests, are platforms that can be jacked up above the sea using legs that can be lowered, much like
jacks. These platforms are typically used in water depths up to 400 feet (120 m), although some designs can go to 550 ft (170 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.
[edit] Drillships
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 ft (3,700 m).
[edit] Floating production systems
The main types of floating production systems are
FPSO (floating production, storage, and offloading system). FPSOs consist of large monohull structures, generally (but not always) shipshaped, equipped with processing facilities. 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.
[edit] Tension-leg platform
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 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 (180 and 1,300 m). Mini TLPs can also be used as utility, satellite or early production platforms for larger deepwater discoveries.
[edit] Spar platforms
Spars are moored to the seabed like TLPs, but whereas a TLP has vertical tension tethers, a spar has more conventional catenary mooring lines. Spars have to-date 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 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 adjusting the mooring line tensions (using chain-jacks attached to the mooring lines), to move horizontally and to position itself over wells at some distance from the main platform location. The first production spar was
Kerr-McGee's Neptune, anchored in 1,930 ft (590 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 ft (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 (expected mid-2009), it will be the deepest ever, at almost 8,000 ft (2,400 m). The first Truss spars were Kerr-McGee's Boomvang and Nansen. The first (and only) cell spar is Kerr-McGee's Red Hawk.
[edit] Normally Unmanned Installations (or NUI)
These installations (sometimes called toadstools), are small platforms, consisting of little more than a
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.
[edit] Conductor Support Systems
These installations, also known as
satellite platforms, are small unmanned platforms consisting of little more than a
well bay, and a small
process plant. They are designed to operate in conjunction with a static production platform which is connected to the platform by flow lines and/or by
Umbilical cable.
[edit] Particularly large examples
The
Petronius Platform is a compliant tower in the
Gulf of Mexico, which stands 2,000 feet (610 m) above the ocean floor. It is one of the
world's tallest structures.
The
Hibernia platform is the world's largest (in terms of weight) offshore platform, located on the Jeanne D'Arc basin, in the
Atlantic Ocean off the coast of
Newfoundland. This
Gravity base Structure (GBS), which sits on the ocean floor, is 364 feet (111 m) high and has storage capacity for 1.3 million barrels (210,000 m
3) of crude oil in its 278.8-foot (85.0 m) high caisson. 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.
[edit] 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 platform and/or tanker loading facility. Elements in the oil/gas production process include
wellhead,
production manifold,
production separator,
glycol process to dry gas,
gas compressors,
water injection pumps,
oil/gas export metering and
main oil line pumps.
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.
[edit] Essential personnel
Not all of the following personnel are present on every platform. On smaller platforms, one worker can perform a number of different jobs. The following also are not names officially recognized in the industry.
- OIM (offshore installation manager) who 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) who 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;
- second mate to meet manning requirements of flag state, operates Fast Rescue craft, cargo ops, fire team leader;
- third mate to meet manning requirements of flag state, operates Fast Rescue craft, cargo ops, fire team leader;
- ballast control operator to operate fire and gas systems;
- 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 to maintain the lifeboats and manning them if necessary;
- control room operators, especially FPSO or production platforms;
- catering crew, including people tasked with performing essential functions such as cooking, laundry and cleaning the accommodation;
- production techs to run the production plant;
- helicopter pilot(s) living on some platforms that have a helicopter based offshore and transporting workers to other platforms or to shore on crew changes;
- maintenance technicians (instrument, electrical, mechanical).
[edit] Incidental personnel
- 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
[edit] Drawbacks
The nature of their operation — extraction of volatile substances sometimes under extreme pressure in a hostile environment — means risk, 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 UK sector of the
North Sea, exploded after a gas leak. The resulting investigation conducted by Lord Cullen, and was called the 'Cullen Report', was highly critical of a number of areas, including, but not limited to, management within the company, the design of the structure, and the Permit to Work System. The report was commissioned in 1988, and was delivered November 1990.
[4] The accident greatly accelerated the practice of providing living accommodations on separate platforms, away from those used for extraction.
However, this was in itself a hazardous environment. In March 1980, the '
flotel' (floating hotel) platform
Alexander Kjelland capsized in a storm in the
North Sea with the loss of 123 lives.
[5]
In 2001, the
Petrobras 36 Oil Platform exploded and killed 11 people in
Brazil. The platform sank five days after the explosions.
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.
[edit] Ecological effects
NOAA map of the 3,858 oil and gas platforms extant in the Gulf of Mexico in 2006
In British waters, the cost of removing all platform rig structures entirely was estimated in 1995 at £1.5 billion, and the cost of removing all structures including pipelines—called a "clean sea" approach—at £3 billion.
[citation needed]
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
[who?] expressed at the practice of partially demolishing offshore rigs to the point that ships can traverse across their site; there have been instances
[who?] of
fishery vessels snagging nets on the remaining structures. Proposals for the disposal at sea of the
Brent Spar, a 449 ft (137 m) 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.
[citation needed]
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.
[6] 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.
[7] In the
Gulf of Mexico, more than 200 platforms have been similarly converted.
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