Offshore drilling is a mechanical process where awellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extractpetroleum that lies in rock formations beneath the seabed. Most commonly, the term is used to describe drilling activities on thecontinental shelf, though the term can also be applied to drilling inlakes,inshore waters andinland seas.
Offshore drilling presents all environmental challenges, both offshore and onshore from the producedhydrocarbons and the materials used during the drilling operation. Controversies include the ongoingUS offshore drilling debate.[1]
There are many different types of facilities from which offshore drilling operations take place. These include bottom founded drilling rigs (jackup barges and swampbarges), combined drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units (MODU) includingsemi-submersibles ordrillships. These are capable of operating in water depths up to 3,000 metres (9,800 ft). In shallower waters the mobile units are anchored to the seabed; however, in water deeper than 1,500 metres (4,900 ft), the semi-submersibles and drillships are maintained at the required drilling location usingdynamic positioning.
Around 1891, the first submerged oil wells were drilled from platforms built on piles in the fresh waters of theGrand Lake St. Marys inOhio. The wells were developed by small local companies such as Bryson, Riley Oil, German-American and Banker's Oil.[2]
Around 1896, the first submerged oil wells in salt water were drilled in the portion of theSummerland field extending under theSanta Barbara Channel inCalifornia. The wells were drilled from piers extending from land out into the channel.[3][4]
Other notable early submerged drilling activities occurred on the Canadian side ofLake Erie in the 1900s andCaddo Lake inLouisiana in the 1910s. Shortly thereafter wells were drilled in tidal zones along theTexas and Louisianagulf coast. TheGoose Creek Oil Field nearBaytown, Texas is one such example. In the 1920s drilling activities occurred from concrete platforms inVenezuela'sLake Maracaibo.[5]
One of the oldest subsea wells is theBibi Eibat well, which came on stream in 1923 inAzerbaijan.[6][dubious –discuss] The well was located on an artificial island in a shallow portion of theCaspian Sea. In the early 1930s, theTexas Company developed the first mobile steel barges for drilling in thebrackish coastal areas of theGulf of Mexico.
In 1937,Pure Oil and its partnerSuperior Oil used a fixed platform to develop a field 1 mile (1.6 km) offshore ofCalcasieu Parish, Louisiana in 14 feet (4.3 m) 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.[7]
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In 1945, concern for American control of its offshore oil reserves caused PresidentHarry Truman to issue an Executive Order unilaterally extending American territory to the edge of its continental shelf, an act that effectively ended the3-mile limit "freedom of the seas" regime.[8]
In 1946,Magnolia drilled at a site 18 miles (29 km) off the coast, erecting a platform in 18 feet (5.5 m) of water offSt. Mary Parish, Louisiana.[9]
In early 1947,Superior Oil erected a drilling and production platform in 20 feet (6.1 m) of water some 18 miles (29 km) off Vermilion Parish, La. But it wasKerr-Magee, as operator for partnersPhillips Petroleum andStanolind 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.[10]
When offshore drilling moved into deeper waters of up to 30 metres (98 ft), fixed platform rigs were built, until demands for drillingequipment was needed in the 100 feet (30 m) to 120 metres (390 ft) depth of the Gulf of Mexico, the firstjack-up rigs began appearing from specialized offshore drilling contractors.[11]
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The firstsemi-submersible resulted from an unexpected observation in 1961.[12] Blue Water Drilling Company owned and operated the four-column submersible Blue Water Rig No.1 in the Gulf of Mexico forShell 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 byEdward Robert Armstrong for the purpose of operating aircraft with an invention known as the 'seadrome'. The first purpose-built drillingsemi-submersibleOcean Driller was launched in 1963 byODECO. Since then, many semi-submersibles have been purpose-designed for the drilling industry mobile offshore fleet.
The first offshoredrillship was theCUSS 1 developed for theMohole project to drill into the Earth's crust.[13]
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.[14]
One of the world's deepest hubs is currently thePerdido in the Gulf of Mexico, floating in 2,438 meters (7,999 ft) of water. It is operated byRoyal Dutch Shell and was built at a cost of $3 billion.[15] The deepest operational platform is the Petrobras America Cascade FPSO in the Walker Ridge 249 field in 2,600 meters (8,500 ft) of water.[16]
Offshore drilling is usually done from platforms generically known as mobile offshore drilling units (MODU), which can be of one of several formats, depending on the water depth:
Beyond the MODUs mentioned above, offshore developments also employ a range offixed and floatingdrilling platforms that also support drilling, production, or both. Key types include:
Notable offshore fields include:
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 theTroll A platform standing on a depth of 300 meters (980 ft).[28]
Another type of offshore platform may float with amooring 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 operationssubsea, 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 theBarents Sea. One such challenge in shallower environments isseabed 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 thepetroleum industry, at least in the western world. These efforts among others are contained in the established termintegrated 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.
Offshore oil production involves environmental risks, most notablyoil spills 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 andIxtoc I oil spill).[29]Produced water is also generated, which is water brought to the surface along with the oil and gas; it is usually highlysaline and may include dissolved or unseparated hydrocarbons.
