A-Fields natural gas fields

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The A-Fields (Audrey, Ann, Alison and Annabel) are natural gas reservoirs and gas production facilities in the southern North Sea; about 123 km east of Spurn Head, Yorkshire. The fields produced natural gas from 1988 to 2016.

Contents

The A-fields

The Ann gas field was discovered as early as May 1966 and Audrey in March 1976 but there was limited local infrastructure to transport gas to shore. [1] The Lincolnshire Offshore Gas Gathering System (LOGGS) was commissioned in 1988 and designed to act as a hub and central gas processing, compression and transport facility for the area. Gas from LOGGS was routed to the Theddlethorpe gas terminal. [1]

The Audrey field is located in the UK Offshore Blocks 49/11a and 49/15a. The field was initially developed and operated by Phillips Petroleum Co. Ltd., later ConocoPhillips, then by Spirit Energy. [1] The Ann field is in Block 49/06 and 48/10a and was developed by Phillips, later ConocoPhillips, then by Spirit Energy. Alison in Block 49/11a was originally licensed to Phillips. Annabel was in Block 48/10a and was also originally licensed to Phillips, it was designed to produce gas from the Saturn gas field. [1]

The gas reservoirs in the A-Fields are Upper Leman Sandstone Formation of the Lower Permian Rotliegend Group. [2]

Phillips had assigned the letter ‘A’ to the license; all the prospects were given female names starting with ‘A’. [1]

Development

The A-Fields were developed by a number of platforms, subsea structures and pipelines.

The design parameters of the Audrey and Ann production facilities are summarised in the table. [2] [3] [4] [5] [6]

Audrey and Ann installations
InstallationAudrey A (WD)Audrey B (XW)Audrey WMAnn A4Ann (XM)
Block49/11a48/1549/11a49/0649/02
Coordinates53°32.37809'N 02°00.86304'E53°34.06775'N 01°58.16642'E53°32.42530'N 02°00.45707' E57.715556°N 2.056111°E53°42.88684'N 02°03.29081'E
Installation typeFixed steel platformFixed steel platformSubsea wellheadSubsea wellheadSubsea wellhead
Installed1987199019931993
Water depth, metres2730272929
Substructure weight, tonnes1,06386534.622 x 13.2
Topsides weight, tonnes1,2761,298
No. of legs44
No. of Wells104112
Gas export toLOGGS PPAudrey AAudrey AAnn XMLOGGS
Export pipeline length, diameter16.9 km, 20-inch4.4 km, 14-inch0.492 km, 8-inch0.128 km, 6-inch41.8 km, 12-inch
Pipeline numberPL496PL723PL575PL2164PL947


The design parameters of the Alison, Annabel and Ensign production facilities are summarised in the table. [2] [6] [5]

Alison, Annabel and Ensign installations
InstallationAlison (KX)Annabel AB1Annabel AB2Annabel templateEnsign
Block49/11a48/10a48/10a48/10a48/14a
Coordinates53.509234°N 2.169722°E53.675000°N 1.925000°E53.682500°N 1.925000°E53.681633°N 01.923609°E53°35.4322'N 1°46.3988'E
Installation typeSubsea wellheadSubsea wellheadSubsea wellheadSubsea manifoldFixed steel platform
Installed19952005200520052011
Water depth, metres2330303023
Substructure weight, tonnes582
Topsides weight, tonnes530
No. of legs4
No. of Wells1113
Gas export toAlison Tee on the Ann to LOGGS pipelineAnnabel templateAnnabel templateAudrey AAudrey A
Export pipeline length, diameter0.048 km, 8-inch0.037 km, 8-inch0.133 km, 8-inch17.8 km, 10-inch17 km, 10-inch
Pipeline numberPL947PL2066JW12PL2066JWAB2PL2066PL2838


In addition to the gas production pipelines there were also 3-inch methanol pipelines from  LOGGS to Audrey A and B and to Ensign. There were also control umbilicals to the subsea wellheads. [3]

Gas production

A summary of the key gas production data for the A-Fields is shown in the table. [7]

A-Fields gas production
FieldAudreyAnnAlisonAnnabelEnsign
Start of production19881993199520052012
Peak flow, million cubic metres/y2,41348881901150
Year of peak flow19901994199620062013
Cumulative production to end of 2014, million cubic metres19,7962,8696973,413255
Production ceasedMay 201620122010May 20162018

The gas production profile, in mcm/y, for Audrey is as shown. [7]

Decommissioning

The Alison and Ann fields had reached the end of their economic lives in 2010 and 2012 and were closed-in. Audrey was shut down in 2016. Ensign was still operating but the closure of LOGGS and Theddlethorpe gas terminal in August 2018 closed the gas export route; when no alternative export route was found the Ensign installation was decommissioned. [8]

See also

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References

  1. 1 2 3 4 5 Department of Trade and Industry (1994). The Energy Report. London: HMSO. pp. 27, 28, 121, 134. ISBN   0115153802.
  2. 1 2 3 Asset Data Sheets for Audrey, Ann, Alison, Saturn (Annabel) Centrica
  3. 1 2 "Audrey Decommissioning Programmes" (PDF). assets.publishing.service.gov.uk. Archived (PDF) from the original on 2019-07-24. Retrieved 12 December 2021.
  4. "Ann and Alison Fields Decommissioning Programmes" (PDF). assets.publishing.service.gov.uk. Archived (PDF) from the original on 2021-12-13. Retrieved 12 December 2021.
  5. 1 2 "Inventory of Offshore Installations". odims.ospar.org. Archived from the original on 2021-11-25. Retrieved 12 December 2021.
  6. 1 2 "OGA interactive Maps". ogauthority.maps.arcgis.com. Archived from the original on 2019-01-26. Retrieved 12 December 2021.
  7. 1 2 "Oil and Gas UK – Field data". www.gov.uk. Archived from the original on 2015-10-27. Retrieved 12 December 2021.
  8. "Ensign Installation Decommissioning Programme" (PDF). spirit-energy.com. Archived (PDF) from the original on 2021-12-13. Retrieved 12 December 2021.