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 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. 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.
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. 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.
The gas reservoirs in the A-Fields are Upper Leman Sandstone Formation of the Lower Permian Rotliegend Group.Asset Data Sheets for Audrey, Ann, Alison, Saturn (Annabel) Centrica
Phillips had assigned the letter 'A' to the license; all the prospects were given female names starting with 'A'.
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. +Audrey and Ann installationsInstallationAudrey A (WD)Audrey B (XW)Audrey WMAnn A4Ann (XM)Block49/11a48/1549/11a49/0649/02Coordinates53°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′EInstallation typeFixed steel platformFixed steel platformSubsea wellheadSubsea wellheadSubsea wellheadInstalled1987199019931993Water depth, metres2730272929Substructure weight, tonnes1,06386534.622 x 13.2Topsides weight, tonnes1,2761,298–––No. of legs44–––No. of Wells104112Gas export toLOGGS PPAudrey AAudrey AAnn XMLOGGSExport pipeline length, diameter16.9 km, 20-inch4.4 km, 14-inch0.492 km, 8-inch0.128 km, 6-inch41.8 km, 12-inchPipeline numberPL496PL723PL575PL2164PL947
The design parameters of the Alison, Annabel and Ensign production facilities are summarised in the table. +Alison, Annabel and Ensign installationsInstallationAlison (KX)Annabel AB1Annabel AB2Annabel templateEnsignBlock49/11a48/10a48/10a48/10a48/14aCoordinates53.509234°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′EInstallation typeSubsea wellheadSubsea wellheadSubsea wellheadSubsea manifoldFixed steel platformInstalled19952005200520052011Water depth, metres2330303023Substructure weight, tonnes582Topsides weight, tonnes––––530No. of legs––––4No. of Wells111–3Gas export toAlison Tee on the Ann to LOGGS pipelineAnnabel templateAnnabel templateAudrey AAudrey AExport pipeline length, diameter0.048 km, 8-inch0.037 km, 8-inch0.133 km, 8-inch17.8 km, 10-inch17 km, 10-inchPipeline 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.
Gas production A summary of the key gas production data for the A-Fields is shown in the table. +A-Fields gas productionFieldAudreyAnnAlisonAnnabelEnsignStart of production19881993199520052012Peak flow, million cubic metres/y2,41348881901150Year of peak flow19901994199620062013Cumulative production to end of 2014, million cubic metres19,7962,8696973,413255Production ceasedMay 201620122010May 20162018
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.
See also
List of oil and gas fields of the North Sea Theddlethorpe Gas Terminal Lincolnshire Offshore Gas Gathering System Easington Catchment Area Planets gas fields
References