North Sea oil

Learn more about North Sea oil

Jump to: navigation, search
Image:North Sea Oil Platforms.jpg
North Sea Oil Platforms

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


[edit] History

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" was 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 drilled 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.

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).

[edit] Licensing

There are five countries with North Sea Production. All operate a tax and Royalty licencing regime. The respective sectors are divided by median lines agreed in the late 1960s:

  • United Kingdom - licences are administered by the DTI (Department of Trade and Industry- Website). The UKCS is divided into quadrants of 1 degree latitude and one degree longitude. Each quadrant is divided into 30 blocks measuring 10 minutes of latitude and 12 minutes of longitude. Some blocks are divided further into part blocks where some areas are relinquished by previous licensees. For example block 13/24a is located in quad 13 and is the 24th block and is the a part block of this block. The UK government has traditionally issued licences via periodic (now annual) licensing rounds. Blocks are awarded on the basis of the work programme bid by the participants. The UK DTI has been very active in attracting new entrants to the UKCS via Promote licencing rounds (less demanding terms) and the fallow acarage initiative where non-active licences have had to be relinquished.
  • Norway - licences are administered by the NPD (Norwegian Petroleum Directorate Website in English ). The NCS is also divided into quads of 1 degree by 1 degree. Norwegian licence blocks are larger than British blocks, being 15 minutes of latitude by 20 minutes of longitude (12 blocks in a quad). Like Britain there are numerous part blocks formed by relicensing relinquished acreage.
  • Denmark - The Danish sector is administered by the Danish Energy Authority (website in English). The Danes also divide their sector of the North Sea into 1 degree by 1 degree quadrants, their blocks however are 10 minutes latitude by 15 minutes longitude. Part blocks exist where partial relinquishments have taken place.
  • Germany - Germany and the Netherlands share a quadrant and block grid - quadrants are given letters rather than numbers. The blocks are 10 minutes latitude by 20 minutes longitude. Germany has the smallest sector in the North Sea.
  • Netherlands - The Dutch sector is located in the Southern Gas Basin and shares a grid pattern with Germany.

[edit] Reserves and production

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. [1]. The production is expected to fall to one-third of its peak by 2020.

[edit] 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 stratigraphic order:

[edit] Devonian

[edit] Carboniferous and Permian

[edit] Triassic

The Triassic play is located in the Central North Sea. The reservoir is composed of fluvial and lacustrine sandstones of the Skaggerak formation. Fields with Triassic reservoirs include J-Block (Judy, Jade, Joshephine) and Marnock

Triassic reservoirs are also important in the East Irish Sea (Morecambe gas field, Sherwood Sandtsone) and Southern North Sea (Hewett gasfield complex - Bunter sandstone)

[edit] Middle Jurassic

Northern North Sea tilted fault blocks; Brent Series deltaic sands of Bathonian age. 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.

[edit] Upper Jurassic

  • Upper Jurassic Central North Sea, Fulmar Play - The Oxfordian Age Fulmar sandstone is a shallow marine unit present in the southern part of the Central Graben. It is also present in the Norwegian sector where it is called the Ula formation. This reservoir is very good quality with high porosities which can be preserved under deep (6000m) burial in high pressure high temperature (HPHT) fields such as Elgin, Franklin and Shearwater.
  • Upper Jurassic Turbidites - These Kimmeridgian/Volgian sandstone reservoirs are found in the Outer Moray Firth. The Buzzard Field, the largest discovery in recent years has an Ettrick formation turbidite reservoir.
  • Fanglomerates 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 developments being developed along-strike since as sub-sea tie-back technology develops

[edit] Lower Cretaceous

The Lower Cretacous play developed in the 1980s and 1990s. The reservoir rocks are Aptian / Albian turbidites. Most discoveries are stratigraphic traps . Examples include the Britania gas field and the Blake oil field

[edit] Upper Cretaceous

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 cored either by salt diapirs or Pre-Cretaceous Horsts.

[edit] Palaeocene

Central North Sea Tertiary turbidite sand fans - the Forties field (57°45'N 01°E) targeted 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.

  • 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.)

[edit] List of fields

South to north.

[edit] Netherlands

    • Onshore
    • Offshore (serviced from The Hague
      • Zuidwal
      • Ameland - (whether this will be developed onshore of offshore is an open question)
      • Many fields in Quadrantrs P, Q, K, L, some in blocks E, F

[edit] United Kingdom

Reference DTI Brown book

[edit] Germany

    • Onshore
      • Wietze "near Hanover", discovered in 1859!
      • The Schoenebeek field of the Netherlands extends across the border.
    • No commercial developments offshore

[edit] Denmark

[edit] Norway

Reference - Norwegian Petroleum Directorate fact pages on oil fields

[edit] 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
    • Offshore
      • Various blocks licensed for exploration, several discoveries not yet developed.
  • Iceland
    • 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; February 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

[edit] See also

[edit] External links

North Sea oil

Personal tools
what is world wizzy?
  • World Wizzy is a static snapshot taken of Wikipedia in early 2007. It cannot be edited and is online for historic & educational purposes only.