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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.

The A-fields

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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

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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
Installation Audrey A (WD) Audrey B (XW) Audrey WM Ann A4 Ann (XM)
Block 49/11a 48/15 49/11a 49/06 49/02
Coordinates 53°32.37809'N 02°00.86304'E 53°34.06775'N 01°58.16642'E 53°32.42530'N 02°00.45707' E 57.715556°N 2.056111°E 53°42.88684'N 02°03.29081'E
Installation type Fixed steel platform Fixed steel platform Subsea wellhead Subsea wellhead Subsea wellhead
Installed 1987 1990 1993 1993
Water depth, metres 27 30 27 29 29
Substructure weight, tonnes 1,063 865 34.62 2 x 13.2
Topsides weight, tonnes 1,276 1,298
No. of legs 4 4
No. of Wells 10 4 1 1 2
Gas export to LOGGS PP Audrey A Audrey A Ann XM LOGGS
Export pipeline length, diameter 16.9 km, 20-inch 4.4 km, 14-inch 0.492 km, 8-inch 0.128 km, 6-inch 41.8 km, 12-inch
Pipeline number PL496 PL723 PL575 PL2164 PL947


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

Alison, Annabel and Ensign installations
Installation Alison (KX) Annabel AB1 Annabel AB2 Annabel template Ensign
Block 49/11a 48/10a 48/10a 48/10a 48/14a
Coordinates 53.509234°N 2.169722°E 53.675000°N 1.925000°E 53.682500°N 1.925000°E 53.681633°N 01.923609°E 53°35.4322'N 1°46.3988'E
Installation type Subsea wellhead Subsea wellhead Subsea wellhead Subsea manifold Fixed steel platform
Installed 1995 2005 2005 2005 2011
Water depth, metres 23 30 30 30 23
Substructure weight, tonnes 582
Topsides weight, tonnes 530
No. of legs 4
No. of Wells 1 1 1 3
Gas export to Alison Tee on the Ann to LOGGS pipeline Annabel template Annabel template Audrey A Audrey A
Export pipeline length, diameter 0.048 km, 8-inch 0.037 km, 8-inch 0.133 km, 8-inch 17.8 km, 10-inch 17 km, 10-inch
Pipeline number PL947 PL2066JW12 PL2066JWAB2 PL2066 PL2838


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

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

A-Fields gas production
Field Audrey Ann Alison Annabel Ensign
Start of production 1988 1993 1995 2005 2012
Peak flow, million cubic metres/y 2,413 488 81 901 150
Year of peak flow 1990 1994 1996 2006 2013
Cumulative production to end of 2014, million cubic metres 19,796 2,869 697 3,413 255
Production ceased May 2016 2012 2010 May 2016 2018

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

Decommissioning

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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

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  1. ^ a b c d e Department of Trade and Industry (1994). The Energy Report. London: HMSO. pp. 27, 28, 121, 134. ISBN 0115153802.
  2. ^ a b c Asset Data Sheets for Audrey, Ann, Alison, Saturn (Annabel) Centrica
  3. ^ a b "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. ^ a b "Inventory of Offshore Installations". odims.ospar.org. Archived from the original on 2021-11-25. Retrieved 12 December 2021.
  6. ^ a b "OGA interactive Maps". ogauthority.maps.arcgis.com. Archived from the original on 2019-01-26. Retrieved 12 December 2021.
  7. ^ a b "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.