The Tartan oil field is a significant crude oil producing field in the UK sector of the North Sea, 187 km north-east of Aberdeen. Production of oil started in 1981 and ceased in 2020, the Tartan Alpha installation is currently (2021) undergoing decommissioning.

Tartan oil field
Tartan oil field is located in North Sea
Tartan oil field
Location of Tartan oil field
CountryUnited Kingdom
RegionNorth Sea
Location/blocks15/16a and 14/20a
Offshore/onshoreOffshore
Coordinates58°22′11″N 00°04′25″E / 58.36972°N 0.07361°E / 58.36972; 0.07361
OperatorsRepsol Resources UK
OwnerRepsol Resources UK
Field history
DiscoveryFebruary 1975
Start of productionJanuary 1981
Abandonment2020
Production
Estimated oil in place14.1 million tonnes
(~ 12.8×10^6 m3 or 80.5 million bbl)
Recoverable oil62 million barrels (~1.1×10^7 t)
Producing formationsUpper Jurassic sandstone

The field

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The Tartan oil field is located in Blocks 15/16a and 14/20a of the UK North Sea continental shelf. Its name continues the Scottish theme of oil fields in the area (eg Claymore, Piper, Scott).[1] The Tartan field was discovered in February  1975 and the oil reservoir comprises an Upper Jurassic sandstone at a depth of 9,800 to 12,000 feet (2,9873 to 3,658 metres).[2] The reservoir and its fluids had the following characteristics:[2]

Tartan reservoir and fluids
Parameter Value
Porosity 8–18 %
Permeability 70–500 md %
API gravity 37–40°API
Gas Oil Ratio 900 standard cubic feet/barrel
Sulfur content 0.7 %
Pressure/temperature 4,600–5,700 psi (31,715–39,300 kPa) at 220–240 °F
Recoverable reserves 62 million barrels, 14.1 million tonnes

Owners and operators

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The initial owner of the field was Texaco North Sea Limited which also operated the field. Talisman assumed ownership in 2000. The company became Talisman Sinopec Energy, then Repsol Sinopec.[3]

Development

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The field was developed by a single integrated drilling, production and accommodation platform: Tartan Alpha (Tartan A). The principal design data of the Tartan A platform is given in the following table.[2]

Tartan A platform design data
Installation Tartan A
Coordinates 58°22’11”N 00°04’25”E
Water depth, metres 142
Fabrication substructure McDermott-Hudson, Cherbourg and Methil
Jacket weight, tonnes 14,400
Topsides design Lawrence Allison
Topsides weight, tonnes 14,100
Function Drilling, production, accommodation
Accommodation (crew) 200
Type Steel jacket
Legs 4
Piles 28
Well slots 30
Throughput oil, barrels per day (bpd) 75,000 + 14,400 Natural Gas Liquids
Water injection, bpd 105,000
Platform installed June 1979
Production started January 1981
Oil production to Claymore
Gas production to Frigg pipeline

Tartan Alpha was originally connected to the Piper Alpha platform through a 19 km 18-inch diameter gas pipeline. The failure of the riser of this pipeline at about 22:20 6 July 1988 during the Piper Alpha disaster led to a second major explosion followed by a widespread fire.[4]

Production from Tartan's faulted reservoir was 'disappointing'. Texaco therefore halted production well drilling on Tartan and focussed on the Highlander field, about 13 km north-west of Tartan, to enable the field to produce through Tartan.[2]

Tartan satellites

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In addition to its own production several other smaller fields were tied back to Tartan. The design data is summarized below.[5]

Name of field Highlander Petronella Galley Duart Tartan North Terrace
Year installed 1985 1986 1998 2007 2004
Distance from Tartan, km 13 11 14 3.4
Production pipeline, inches 12 8 10 8 6
Gas lift pipeline, inches 8 12 3
Water injection pipeline, inches 4 8
No. of Wells 1 1 1

Production from the Galley field was originally through the Northern Producer a floating production facility.[6]

Processing

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Oil from the wellheads and subsea tie-ins was routed to one of five 1st stage 3-phase (oil, gas, water) separators. Oil flowed from the 1st stage separators to the single 2nd stage separator and from there was pumped through metering streams to the 27 km 24-inch diameter oil export pipeline to Claymore.[5]

Produced water from the separators was treated in a degassing vessel and hydrocyclones to an oil-in-water concentration of less than 30 mg/litre prior to discharge overboard.[5]

Gas from the separators was compressed in the single 5 stage compression train. Gas was treated to remove hydrogen sulfide. Some gas was used to provide lift gas for the wells and the remainder was exported via a 72 km 18-inch pipeline to the Frigg MCP01 bypass line, and thence to St. Fergus.[5]

By 2017 there were 5 Tartan production wells and 1 subsea injection well.[5]

The fluid handling capability of the Tartan facilities in its latter years of operation was as follows:[5]

Treatment facility Capacity
Crude oil 30,000 bbls/day
Gas compression 40-66 MMSCFD (million standard cubic feet per day)
Dehydration 70 MMSCFD
Gas sweetening 70 MMSCFD

Decommissioning

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Repsol Sinopec were granted a Cessation of Production authorisation by the UK Oil and Gas Authority in August 2020.[7] Repsol Sinopec have submitted decommissioning plans to the Oil and Gas Authority, and are undertaking decommissioning of the Tartan installation and its associated infrastructure.[8]

References

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  1. ^ Department of Trade and Industry (1994). The Energy Report. London: HMSO. pp. 88 and map 8. ISBN 0115153802.
  2. ^ a b c d Oilfield Publications Limited (1985). The North Sea Platform Guide. Ledbury: Oilfield Publications Limited. pp. 641–46.
  3. ^ "Tartan Oil Field". abarrelfull. Retrieved 18 October 2021.
  4. ^ "Safety of offshore oil and gas operations: Lessons from past accident analysis" (PDF). publications.jrc.ec.eur. 2012. Retrieved 18 October 2021.
  5. ^ a b c d e f Repsol Sinopec. "Tartan A: Infrastructure Code of Practice" (PDF). repsolsinopecuk.com. Retrieved 18 October 2021.
  6. ^ "Galley oil field". abarrelfull. Retrieved 18 October 2020.
  7. ^ "Repsol Sinopec calls time on Tartan Alpha after 40 years". Energy Voice. 2020. Retrieved 18 October 2021.
  8. ^ Oil and Gas Authority. "Decommissioning Project summary". Retrieved 18 October 2021.