North Sea oil is a mixture of hydrocarbons, comprising liquid oil and natural gas, produced from oil reservoirs beneath the North Sea.
In the oil industry, the term "North Sea" often includes areas such as the Norwegian Sea and the area known as "West of Shetland", "the Atlantic Frontier" or "the Atlantic Margin" that is not geographically part of the North Sea.
Brent crude is still used today as a standard benchmark for pricing oil, although the contract now refers to a blend of oils from fields in the northern North Sea.
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Commercial extraction of oil on the shores of the North Sea dates back to 1851, when James Young retorted oil from torbanite (boghead coal, or oil shale) mined in the Midland Valley of Scotland.[1] Across the sea in Germany, oil was found in the Wietze field near Hanover in 1859, leading to the discovery of 70 more fields, mostly in Lower Cretaceous and Jurassic reservoirs, producing a combined total of around 1340 m³ (8,400 barrels) per day.[1]
Gas was found by chance in a water well near Hamburg in 1910, leading to minor gas discoveries in Zechstein dolomites elsewhere in Germany.[1] In England, BP discovered gas in similar reservoirs in the Eskdale anticline in 1938, and in 1939 they found commercial oil in Carboniferous rocks at Eakring in Nottinghamshire.[1] Discoveries elsewhere in the East Midlands lifted production to 400 m³ (2,500 barrels) per day, and a second wave of exploration from 1953 to 1961 found the Gainsborough field and 10 smaller fields.[1]
The Netherlands' first oil shows were seen in a drilling demonstration at De Mient during the 1938 World Petroleum Congress at The Hague.[1] Subsequent exploration led to the 1943 discovery by Exploratie Nederland, part of the Royal Dutch/Shell company Bataafsche Petroleum Maatschappij, of oil under the Dutch village of Schoonebeek, near the German border.[2] NAM found the Netherlands' first gas in Zechstein carbonates at Coevorden in 1948.[2] 1952 saw the first exploration well in the province of Groningen, Haren-1, which was the first to penetrate the Lower Permian Rotliegendes sandstone that is the main reservoir for the gas fields of the southern North Sea, although in Haren-1 it contained only water.[3] The Ten Boer well failed to reach target depth for technical reasons, but was completed as a minor gas producer from the Zechstein carbonates.[3] The Slochteren-1 well found gas in the Rotliegendes in 1959,[3] although the full extent of what became known as the Groningen field was not appreciated until 1963 - it is currently estimated at ~96×1012 cu ft (2,700 km3) recoverable gas reserves.[2] Smaller discoveries to the west of Groningen followed.
The UK Continental Shelf Act came into force in May 1964. Seismic exploration and the first well followed later that year. It and a second well on the Mid North Sea High were dry, as the Rotliegendes was absent, but BP's Sea Gem rig struck gas in the West Sole field in September 1965.[4] The celebrations were short-lived because the Sea Gem sank with the loss of 13 lives after part of the rig collapsed as it was moved away from the discovery well.[4] Larger gas finds followed in 1966 - Leman Bank, Indefatigable and Hewett, but by 1968 companies had lost interest in further exploration of the British sector, a result of a ban on gas exports and low prices offered by the only buyer, British Gas.[4] West Sole came onstream in May 1967.[4] Licensing regulations for Dutch waters were not finalised until 1967.
The situation was transformed in December 1969, when Phillips Petroleum discovered oil in Chalk of Danian age at Ekofisk, in Norwegian waters in the central North Sea.[4] The same month, Amoco discovered the Montrose field about 217 km (135 mi) east of Aberdeen.[4] BP had been awarded several licences in the area in the second licensing round late in 1965, but had been reluctant to work on them.[4] The discovery of Ekofisk prompted them to drill what turned out to be a dry hole in May 1970, followed by the discovery of the giant Forties oilfield in October 1970.[4] The following year, Shell Expro discovered the giant Brent oilfield in the northern North Sea east of Shetland in Scotland. Oil production started from the Argyll field (now Ardmore) in June 1975[5] followed by Forties in November of that year.[6]
Volatile weather conditions in Europe's North Sea have made drilling particularly hazardous, claiming many lives. The conditions also make extraction a costly process; by the 1980s, costs for developing new methods and technologies to make the process both efficient and safe, far exceeded NASA's budget to land a man on the moon.[7] The exploration of the North Sea has been a story of continually pushing the edges of the technology of exploitation (in terms of what can be produced) and later the technologies of discovery and evaluation (2-D seismic, followed by 3-D and 4-D seismic; sub-salt seismic; immersive display and analysis suites and supercomputing to handle the flood of computation required).
The largest field discovered in the past 25 years is Buzzard also located off Scotland , found in June 2001 with producible reserves of almost 64×106 m³ (400m bbl) and an average output of 28 600 m³ to 30 200 m³ (180,000-190,000 bbl) per day.[8] Most if not all of the UK oil fields are located in or just beside Scottish waters.
Following the 1958 Continental shelf convention and after some disputes on the rights to natural resource exploitation [9] the national limits of the exclusive economic zones were ratified. Five countries are involved in oil production in North Sea. All operate a tax and royalty licensing regime. The respective sectors are divided by median lines agreed in the late 1960s:
The British and Norwegian sections hold most of the remainder of the large oil reserves. It is estimated that the Norwegian section alone contains 54% of the sea's oil reserves and 45% of its gas reserves.[10] More than half of the North Sea oil reserves have been extracted, according to official sources in both Norway and the UK. For Norway, the Norwegian Petroleum Directorate [11] gives a figure of 4,601 million cubic metres of oil(corresponding to 29 billion barrels) for the Norwegian North Sea alone (excluding smaller reserves in Norwegian Sea and Barents Sea) ultimate of which 2,778 cubic metres (60%) has already been produced prior to January 2007. UK sources give a range of estimates of reserve, but even using the most optimistic "maximum" estimate of ultimate recovery, 76% had been recovered at end 2010.[12] Note the UK figure includes fields which are not in the North Sea (onshore, West of Shetland).
United Kingdom Continental Shelf production was 137 million tonnes of oil and 105 billion m³ of gas in 1999.[13] (1 tonne of crude oil converts to 7.5 barrels.[13][14][15] The Danish explorations of Cenozoic stratigraphy, undertaken in the 1990s, showed petroleum rich reserves in the northern Danish sector, especially the Central Graben area.[16] The Dutch area of the North Sea followed through with onshore and offshore gas exploration, and well creation.[17][18]
Exact figures are debatable, because methods of estimating reserves vary and it is often difficult to forecast future discoveries.
Peaking in 1999, production of North Sea oil was nearly 950 000 m³ (6 million barrels) per day. Natural gas production was nearly 280×109 m³ (10 trillion cubic feet) in 2001 and continues to increase, although British gas production is in sharp decline.[19]
UK oil production has seen two peaks, in the mid 1980s and late 1990s, with a decline to around 300×103 m³ (1.9 million barrels) per day in the early 1990s.[20] Monthly oil production peaked at 13.5×106 m³ (84.9 million barrels) in January 1985[20] although the highest annual production was seen in 1999, with offshore oil production in that year of 407×106 m³ (2559 million barrels)[21] and had declined to 231×106 m³ (1452 million barrels) in 2007.[21] This was the largest decrease of any other oil exporting nation in the world, and has led to Britain becoming a net importer of crude for the first time in decades, as recognized by the energy policy of the United Kingdom.[22] The production is expected to fall to one-third of its peak by 2020.
In the North Sea, Norway's Statoil natural-gas platform Sleipner strips carbon dioxide out of the natural gas with amine solvents and disposes of this carbon dioxide by geological sequestration. Sleipner reduces emissions of carbon dioxide by approximately one million tonnes a year. The cost of geological sequestration is minor relative to the overall running costs. As of April 2005, BP is considering a trial of large-scale sequestration of carbon dioxide stripped from power plant emissions in the Miller oilfield as its reserves are depleted.
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