Offshore drilling is a mechanical process where a wellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extract petroleum that lies in rock formations beneath the seabed. Most commonly, the term is used to describe drilling activities on the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

, though the term can also be applied to drilling in

lakes A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

, inshore waters and inland seas. Offshore drilling presents environmental challenges, both offshore and onshore from the produced hydrocarbons and the materials used during the drilling operation. Controversies include the ongoing US offshore drilling debate. There are many different types of facilities from which offshore drilling operations take place. These include bottom founded drilling rigs ( jackup barges and swamp barges), combined drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units (MODU) including semi-submersibles or drillships. These are capable of operating in water depths up to . In shallower waters the mobile units are anchored to the seabed, however in water deeper than the semi-submersibles and drillships are maintained at the required drilling location using dynamic positioning.

History

Around 1891, the first submerged oil wells were drilled from platforms built on piles in the fresh waters of the Grand Lake St. Marys in Ohio. The wells were developed by small local companies such as Bryson, Riley Oil, German-American and Banker's Oil. Around 1896, the first submerged oil wells in salt water were drilled in the portion of the Summerland field extending under the Santa Barbara Channel in California. The wells were drilled from piers extending from land out into the channel. Other notable early submerged drilling activities occurred on the Canadian side of Lake Erie in the 1900s and Caddo Lake in Louisiana in the 1910s. Shortly thereafter wells were drilled in tidal zones along the Texas and Louisiana gulf coast. The Goose Creek Oil Field near

Baytown, Texas Baytown is a city in the U.S. state of Texas, within Harris and Chambers counties. Located in the Houston–The Woodlands–Sugar Land metropolitan statistical area, it lies on the northern side of the Galveston Bay complex near the outlets of t ...

is one such example. In the 1920s drilling activities occurred from concrete platforms in Venezuela's

Lake Maracaibo Lake Maracaibo (Spanish: Lago de Maracaibo; Anu: Coquivacoa) is a lagoon in northwestern Venezuela, the largest lake in South America and one of the oldest on Earth, formed 36 million years ago in the Andes Mountains. The fault in the northern se ...

. One of the oldest subsea wells is the Bibi Eibat well, which came on stream in 1923 in Azerbaijan. The well was located on an artificial island in a shallow portion of the Caspian Sea. In the early 1930s, the

Texas Company Texaco, Inc. ("The Texas Company") is an American oil brand owned and operated by Chevron Corporation. Its flagship product is its fuel "Texaco with Techron". It also owned the Havoline motor oil brand. Texaco was an independent company unt ...

developed the first mobile steel barges for drilling in the brackish coastal areas of the Gulf of Mexico. In 1937, Pure Oil and its partner

Superior Oil Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places *Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lake ...

used a fixed platform to develop a field offshore of Calcasieu Parish, Louisiana in of water. In 1938, Humble Oil built a mile-long wooden trestle with railway tracks into the sea at McFadden Beach on the Gulf of Mexico, placing a derrick at its end - this was later destroyed by a hurricane. In 1945, concern for American control of its offshore oil reserves caused President Harry Truman to issue an Executive Order unilaterally extending American territory to the edge of its continental shelf, an act that effectively ended the 3-mile limit " freedom of the seas" regime. In 1946, Magnolia drilled at a site off the coast, erecting a platform in of water off St. Mary Parish, Louisiana. In early 1947,

erected a drilling and production platform in of water some off Vermilion Parish, La. But it was Kerr-Magee, as operator for partners

Phillips Petroleum Phillips Petroleum Company was an American oil company incorporated in 1917 that expanded into petroleum refining, marketing and transportation, natural gas gathering and the chemicals sectors. It was Phillips Petroleum that first found oil in the ...

and Stanolind Oil & Gas that completed its historic Ship Shoal Block 32 well in October 1947, months before Superior actually drilled a discovery from their Vermilion platform farther offshore. In any case, that made Kerr-McGee's well the first oil discovery drilled out of sight of land. When offshore drilling moved into deeper waters of up to , fixed platform rigs were built, until demands for drilling equipment was needed in the to depth of the Gulf of Mexico, the first jack-up rigs began appearing from specialized offshore drilling contractors. The first semi-submersible resulted from an unexpected observation in 1961. Blue Water Drilling Company owned and operated the four-column submersible Blue Water Rig No.1 in the Gulf of Mexico for Shell Oil Company. As the pontoons were not sufficiently buoyant to support the weight of the rig and its consumables, it was towed between locations at a draught midway between the top of the pontoons and the underside of the deck. It was noticed that the motions at this draught were very small, and Blue Water Drilling and Shell jointly decided to try operating the rig in the floating mode. The concept of an anchored, stable floating deep-sea platform had been designed and tested back in the 1920s by Edward Robert Armstrong for the purpose of operating aircraft with an invention known as the 'seadrome'. The first purpose-built drilling semi-submersible ''Ocean Driller'' was launched in 1963 by ODECO.. Since then, many semi-submersibles have been purpose-designed for the drilling industry mobile offshore fleet. The first offshore drillship was the ''CUSS 1'' developed for the

Mohole Project Mohole was an attempt in the early 1960s to drill through the Earth's crust to obtain samples of the Mohorovičić discontinuity, or Moho, the boundary between the Earth's crust and mantle. The project was intended to provide an ear ...

project to drill into the Earth's crust. As of June 2010, there were over 620 mobile offshore drilling rigs (jackups, semisubs, drillships, barges, etc.) available for service in the worldwide offshore rig fleet. One of the world's deepest hubs is currently the Perdido in the Gulf of Mexico, floating in of water. It is operated by Royal Dutch Shell and was built at a cost of $3 billion. The deepest operational platform is the Petrobras America Cascade FPSO in the Walker Ridge 249 field in of water.

Main offshore fields

Notable offshore fields include: * the North Sea * the Gulf of Mexico (offshore Texas, Louisiana, Mississippi, and Alabama) * California (in the Los Angeles Basin and Santa Barbara Channel, part of the Ventura Basin) * the Caspian Sea (notably some major fields offshore Azerbaijan) * the Campos and Santos Basins off the coasts of Brazil *

Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

and Nova Scotia (

Atlantic Canada Atlantic Canada, also called the Atlantic provinces (french: provinces de l'Atlantique), is the region of Eastern Canada comprising the provinces located on the Atlantic coast, excluding Quebec. The four provinces are New Brunswick, Newfoundlan ...

) * several fields off West Africa most notably west of Nigeria and Angola * offshore fields in South East Asia and Sakhalin, Russia * major offshore oil fields are located in the Persian Gulf such as Safaniya, Manifa and Marjan which belong to Saudi Arabia and are developed by

Saudi Aramco Saudi Aramco ( ar, أرامكو السعودية '), officially the Saudi Arabian Oil Company (formerly Arabian-American Oil Company) or simply Aramco, is a Saudi Arabian public petroleum and natural gas company based in Dhahran. , it is one of ...

. * fields in India (Mumbai High, K G Basin-East Coast Of India, Tapti Field, Gujarat, India) * the Taranaki Basin in New Zealand * the Kara Sea north of Siberia * the Arctic Ocean off the coasts of Alaska and Canada's

Northwest Territories The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...

Challenges

Offshore oil and gas production is more challenging than land-based installations due to the remote and harsher environment. Much of the innovation in the offshore petroleum sector concerns overcoming these challenges, including the need to provide very large production facilities. Production and drilling facilities may be very large and a large investment, such as the Troll A platform standing on a depth of . Another type of offshore platform may float with a mooring system to maintain it on location. While a floating system may be lower cost in deeper waters than a fixed platform, the dynamic nature of the platforms introduces many challenges for the drilling and production facilities. The ocean can add several thousand meters or more to the fluid column. The addition increases the equivalent circulating density and downhole pressures in drilling wells, as well as the energy needed to lift produced fluids for separation on the platform. The trend today is to conduct more of the production operations subsea, by separating water from oil and re-injecting it rather than pumping it up to a platform, or by flowing to onshore, with no installations visible above the sea. Subsea installations help to exploit resources at progressively deeper waters—locations which had been inaccessible—and overcome challenges posed by sea ice such as in the Barents Sea. One such challenge in shallower environments is seabed gouging by drifting ice features (means of protecting offshore installations against ice action includes burial in the seabed). Offshore manned facilities also present logistics and human resources challenges. An offshore oil platform is a small community in itself with cafeteria, sleeping quarters, management and other support functions. In the North Sea, staff members are transported by helicopter for a two-week shift. They usually receive higher salary than onshore workers do. Supplies and waste are transported by ship, and the supply deliveries need to be carefully planned because storage space on the platform is limited. Today, much effort goes into relocating as many of the personnel as possible onshore, where management and technical experts are in touch with the platform by video conferencing. An onshore job is also more attractive for the aging workforce in the petroleum industry, at least in the western world. These efforts among others are contained in the established term integrated operations. The increased use of subsea facilities helps achieve the objective of keeping more workers onshore. Subsea facilities are also easier to expand, with new separators or different modules for different oil types, and are not limited by the fixed floor space of an above-water installation.

Effects on the environment

Offshore oil production involves environmental risks, most notably

oil spill An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into th ...

s from oil tankers or pipelines transporting oil from the platform to onshore facilities, and from leaks and accidents on the platform (e.g. Deepwater Horizon oil spill and Ixtoc I oil spill). Produced water is also generated, which is water brought to the surface along with the oil and gas; it is usually highly

saline Saline may refer to: * Saline (medicine), a liquid with salt content to match the human body * Saline water, non-medicinal salt water * Saline, a historical term (especially US) for a salt works or saltern Places * Saline, Calvados, a commune in ...

and may include dissolved or unseparated hydrocarbons.

References

External links