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North Sea oil

North Sea oil:North Sea Oil Platforms
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North Sea Oil Platforms

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


Contents

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).

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:

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.

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:

Devonian

Carboniferous and Permian

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)

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.

Upper Jurassic

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

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.

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.

List of fields

South to north.

Netherlands

United Kingdom

Reference DTI Brown book

Germany

Denmark

Norway

Reference - Norwegian Petroleum Directorate fact pages on oil fields

Associated, but not strictly North Sea

See also

Categories


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

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