Cygnus gas field
# Cygnus gas field

The Cygnus gas field is a natural gas reservoir and gas production facilities in the UK sector of the southern North Sea. It is about 150 km of east of the Lincolnshire coast and started gas production in 2016.

## The field

The Cygnus field extends over UK offshore Blocks 44/11a and 44/12a. The field was discovered in 1988 by Marathon Oil. The reservoirs are Permian Leman sandstone and Carboniferous sandstone formations and have recoverable reserves of 760 billion cubic feet.

In 2019 the Cygnus gas field was jointly owned by Spirit Energy (61.25 %) and Neptune Energy (38.75 %), Neptune E&P UK Ltd operates the infrastructure.

## Development

Production from the field has been developed in stages. In the first stage gas was produced by wells on the Cygnus Alpha platform and then routed by pipeline to the Bacton Gas Terminal via the Esmond Transmission System. The next stage entailed development of the north west part of the field produced from the Cygnus Bravo platform which was routed 7 km to the Cygnus Alpha installation.

Details of the Cygnus field infrastructure are as shown.

Cygnus installations :

| Platform name | Cygnus A WHP | Cygnus A PU | Cygnus A QU | Cygnus B |
| - | - | - | - | - |
| Block | 44/11a | 44/11a | 44/11a | 44/12a |
| Installation type | Fixed Steel platform | Fixed Steel platform | Fixed Steel platform | Fixed Steel platform |
| Coordinates | 54°36’36”N 02°22’29”E | 54°34’14”N 02°17’28”E | 54°34’12”N 02°17’23”E | 54°35’59”N 02°11’46”E |
| Function | Wellheads | Processing and utilities | Accommodation and utilities | Wellheads |
| Crew | 66 | 66 | 66 | Unattended |
| First gas | December 2016 | December 2016 | December 2016 | August 2017 |
| Water depth, metres | 22.5 | 22 | 21.7 | 22 |
| Design | AMEC | AMEC | AMEC | AMEC |
| Jacket fabrication | BiFab Methil | BiFab Methil | BiFab Methil | BiFab Methil |
| Jacket weight, tonnes | 1,858 | 3,146 | 1,958 | 2,194 |
| Topside fabrication | Heerema Hartlepool | Heerema Hartlepool | BiFab | Heerema Hartlepool |
| Topsides dimensions, metres | 23 x 23 x 10 | | | |
| Topsides weight, tonnes | 1,474 | 3,911 | 2,960 | 2,753 |
| No. of legs | 4 | 8 | 4 | |
| No. of well slots | 10 | – | – | 10 |
| No. of Wells | | – | – | |
| Production to | Cygnus APU across bridge | Bacton via Esmond system | – | Cygnus A PU |
| Production capacity | | $9.1×10^^6$ $m^3$ $(320×10^^6$ cu ft) per day | – | |
| Pipeline length and diameter | – | 50 km, 610 mm | – | 7.28 km, 324 mm (12.75 in) |
| Pipeline Number | – | PL3088 | – | PL3086 |

## Production

Cygnus gas has a minimum Wobbe Index of 46.6 to 46.8 $MJ/m^3.$ This is below the minimum specification for entry into the National Transmission System (47.2 $MJ/m^3).$ Cygnus gas en route to Bacton, commingles within the ETS pipeline with gas from Trent and Tors fields. The mixed gas arrives at Bacton with a minimum Wobbe index of 46.5 to 46.7 $MJ/m^3.$ If there is a reduction of gas flow from the other fields that deliver gas to Bacton then the output of Cygnus is constrained. To maintain Cygnus flow a temporary reduction of Wobbe Index from 47.2 $MJ/m^3$ to 46.5 $MJ/m^3$ at the NTS entry point at Bacton terminal was agreed in 2020.

