Platform Name - Tern Alpha. The Tern oilfield is an oilfield situated north east of

Lerwick Lerwick (; non, Leirvik; nrn, Larvik) is the main town and port of the Shetland archipelago, Scotland. Shetland's only burgh, Lerwick had a population of about 7,000 residents in 2010. Centred off the north coast of the Scottish mainland ...

Shetland Islands Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the no ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

, in block numbers 210/25a.

History

The Tern field was discovered in April 1975 by well 210/25-1, drilled by semi-submersible rig Sedco 135G in a water depth of . It started production in 1989. Until July 2008, the oilfield was operated by

Royal Dutch Shell Shell plc is a British multinational oil and gas company headquartered in London, England. Shell is a public limited company with a primary listing on the London Stock Exchange (LSE) and secondary listings on Euronext Amsterdam and the New Yo ...

and licensed by Shell/

Esso Esso () is a trading name for ExxonMobil. Originally, the name was primarily used by its predecessor Standard Oil of New Jersey after the breakup of the original Standard Oil company in 1911. The company adopted the name "Esso" (the phonetic p ...

. On 7 July 2008, it was purchased by TAQA Bratani, a subsidiary of the Abu Dhabi National Energy Company, along with the Eider, North Cormorant, Cormorant Alpha, Kestrel and Pelican fields and related sub-sea satellite fields.

Reserves and geology

Estimated recovery of Tern oilfield is of oil. The oil has a gravity of 34°API. Structurally, it is a triangular uplifted block of the Brent Group bounded by NNW-SSE and NNE-SSW trending faults and sealed by overlying

Kimmeridge Clay The Kimmeridge Clay is a sedimentary deposit of fossiliferous marine clay which is of Late Jurassic to lowermost Cretaceous age and occurs in southern and eastern England and in the North Sea. This rock formation is the major source rock for North ...

(the dominant

source rock In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been depos ...

, with debated contributions from the much deeper

Old Red Sandstone The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also exte ...

) and Shetland Group

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

Tern oil platform

The Tern oil platform is a steel jacket production and drilling platform. It was built by RGC Offshore at Methil yard and was installed in May 1988. As well as processing the fluids from the Tern reservoir, the platform also processes fluids from the Hudson, Falcon and Kestrel fields. Once processed, the oil is co-mingled and exported to

Sullom Voe Terminal The Sullom Voe Terminal is an oil and gas terminal at Sullom Voe in the Shetland Islands of Scotland. It handles production from oilfields in the North Sea and East Shetland Basin and stores oil before it is transported by tanker. Construction ...

via the North Cormorant and Cormorant Alpha platforms by the Brent System pipeline. Well fluids from the Tern

wellhead A wellhead is the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment. The primary purpose of a wellhead is to provide the suspension point and ...

s are routed to two parallel separation trains, Train A and Train B.Hydrocarbon Facilities - Oil Process and Export System diagram (March 2000) Train A comprises a 3-phase (oil, gas and

produced water Produced water is a term used in the oil industry or geothermal industry to describe water that is produced as a byproduct during the extraction of Petroleum, oil and natural gas, or used as a medium for heat extraction. Produced water is the kind ...

) Production Separator. Separated oil is routed to a 2-phase (oil and produced water) Train A Dehydrator where further produced water is removed. Oil from the Dehydrator is cooled and pumped via a metering skid to the export pipeline. Train B comprises a 3-phase Production Separator from which oil is cooled, pumped and mixed with Train A oil prior to metering. Well fluids from the Hudson field are routed to the 3-phase Hudson Production Separator. Separated oil can be routed through the 2-phase Hudson Dehydrator and thence to coolers and segregated metering prior to mixing with the Train A and B oil prior to export. Produced water from the Production Separators and Dehydrators is treated before disposal overboard. Gas from the Separators is co-mingled and compressed in three stages of compression.

Fuel gas Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Most fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources energy that c ...

is taken from the discharge of the second stage of compression. Compressed gas is used for gas-lifting both the Tern and Hudson oil production wells. Gas is treated in a treatment packing prior to metering and export by pipeline. The Hudson Field which is located in 210/24, started producing over the platform in 1993. The peak production was 4.70 million tonnes per year. The Tern platform later added the Kestrel Field, located in 211/21a, this small subsea tieback started production in 2001. The latest addition to the Tern was Cladhan which started producing in 2017.

References

{{Shell oil ExxonMobil oil and gas fields North Sea oil fields Oil and gas industry in Shetland Oil fields of Scotland Shell plc oil and gas fields

History

Reserves and geology

Tern oil platform

See also

References