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North Sea oil refers to oil and natural gas (hydrocarbons) produced from oil reservoirs beneath the North Sea.

North Sea oil was discovered in the early 1960s, with the first North Sea oil coming on line in 1971 and being piped ashore at Teesside, England, from 1975, but the fields were not intensively exploited until rising oil prices in the 1980s made exploitation economically feasible. Inaccessibility and dangerous conditions offshore require complex and expensive production methods.

In reality, oil seeps had been known from coal beds on either side of the North Sea, but only a limited amount of development had occurred (Eakring oil field, Nottinghamshire, England; Edinburgh Oil Shales (which seem unrelated to later discoveries); and small discoveries in the Netherlands and Northern Germany). A "demonstration well" sunk in 1938 in association with the "World Petroleum Congress" at The Hague. After the Second World War a small number of onshore gas and oil fields were found in In 1959, an academic well sunk at Ten Boer near Groningen, Netherlands was deepened and discovered a significant gas deposit. Appraisal and development wells over the next few years brought the realisation in 1963 that the Groningen field was not just "economic", nor even "big", or "large", or "giant", but was an "elephant" field of huge potential. Given that, extending exploration into adjacent areas was a "no-brain" decision.

In large degree, 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; through-salt seismic; immersive display and analysis suites; supercomputing to handle the flood of computation required).

The North Sea contains the majority of Europe's oil reserves and is one of the largest non-OPEC producing regions in the world. While most reserves lie beneath waters belonging to the United Kingdom and Norway, some fields belong to Denmark, the Netherlands, and Germany.

Most oil companies have investments in the North Sea. Peaking in 1999, production of North Sea oil was nearly 6 million barrels (950,000 m³) per day. Natural gas production was nearly 10 trillion cubic feet (280,000,000 m³) in 2001 and continues to increase.

Brent crude (one of the earliest crude oils produced in the North Sea) is still used today as a standard reference for pricing oil.

North Sea oil production fell ten percent (230,000 barrels) in 2004, and fell an additional 12.8% in 2005. 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. *. The production is expected to fall to one-third from its peak by 2020.

List of Areas/ Plays

A play is a collection of fields or structures with common features of source rock, thermal history, trap style and structure that make lessons from the discovery and development of one field on a play closely applicable to other similar structures. In approximate historical order:
  • Sub-Zechstein Gas - Gas fields sourced from the Carboniferous Coal Measures and hosted in the Permian Rotliegend sandstone. Seals are from Zechstein (also of Permian age) halite beds. Structures are mostly due to the shape of base-salt structures. Example field - the discovery for the entire province at Groningen, Netherlands.
  • Chalk oil - The first major oil discovery was in 1969 by Phillips in the Ekofisk field of the Central North Sea (56°30'N 3°10'E). Source is Kimmeridge Clay Formation. Oil and gas generated early after deposition invaded the Cretaceous Chalk sediments and displaced the water necessary for compactional diagenesis (with later consequences). Structures are broad anticlines and blocks over faulted horsts.
  • Central North Sea Tertiary turbidite sand fans - the Forties field (57°45'N 01°E) targetted a series of sand fans in mudstone surrounds and capped by Palaeocene Basalts. Source was Kimmeridge Clay Formation again. The Forties was discovered the year after Ekofisk, following several years of frustration in failing to adequately resolve these structures and find a major field.
  • Northern North Sea tilted fault blocks ; Brent Series deltaic sands. In 1971 the Shell/ Esso joint venture drilled a poorly resolved structure in block 211 and found a classical prograding delta sand sequence (the Brent Sands overlain by a good source rock (the Kimmeridge Clay Formation, broke up into tilted fault blocks due to crustal extension, and the whole sealed by the lateral equivalent of the Chalk, the muddy Shetland Group. Several billion barrels of oil later, the Brent Field is being depressurised in the mid 2000s with shutdown looming on the horizon. Economically, this is the major play in the North Sea.
  • Fnaglomerates against faults. In the late 1980s seismic along some of the major "bounding faults" of the main basins of the North Sea revealed wedges of sediment which evidently piled up while the faults were still moving (syndepositional faulting). Magnus, Tiffany, Toni and Thelma follow this play, with many smaller developemnts being developed along-strike since as sub-sea tie-back technology develops.
  • Over-salt Sands. In the Central North Sea a large number of salt domes could early be seen to penetrate from the Zechstein up into the Tertiary cover rocks, but without adequate seismic they weren't considered good targets for development. Better seismic allows the development of numerous small fields around or above these structures. Individual fields are mostly small, but can be accommodated by tie-ing the fields back to existing facilities. Tie-in pipelines and control umbilicals of over 10 km are not unknown, despite serious technical difficulties (such as plugging of lines with methane hydrates or the rock stresses associated with piercement diapirs.)

List of Fields

(Mainly from the frontispiece map of Glennie, Petroleum Geology of The North Sea, 1998. Better criteria for inclusion could be chosen.) South to North.

Associated, but not strictly North Sea

  • Ireland (includes Northern Ireland)
    • Onshore
      • Larne Tiny prospect under the basalts.
      • Other small prospects, and significant coal-bed methane.
    • Offshore
  • Faroes
    • Onshore
      • No prospects published.
    • Offshore
      • Various blocks licensed for exploration, but no public results at the time of writing.
  • Iceland
    • Onshore
    • Offshore
      • Nothing published, but the idea is not inconceivable on the ridges extending towards Iceland from the Faroes and the East Greenland Coast.
  • East Greenland
    • Onshore
      • No prospects reported, though sediments analogous to the Mesozoic and Caenozoic deposits of the North Sea are known, so there is appreciable interest. Development would be formidably difficult, technically, logistically and politically.
    • Offshore
      • A recent conference on hydrocarbon prospects in arctic Russia (Geological Society, London ; Feburary 2006) had several speakers mention major gas prospectivity on the East Greenland coast, but they cited no sources. A conference volume is due towards the end of 2006, which may elaborate.
  • Barents Sea
    • Onshore
      • No significant prospects or potential.
    • Offshore
      • Significant exploration, appraisal and development. Insignificant commentary.

See also

External links

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North Sea | Economy of Scotland | Economy of Norway | Economy of the United Kingdom | Energy in the United Kingdom

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This article is licensed under the GNU Free Documentation License. It uses material from the "North Sea oil".

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