# Hewett gas field

The Hewett gas field is a large natural gas and associated condensate field located under the North Sea 19 miles (30 km) off the Norfolk coast.

## The field

The Hewett gas field is a natural gas field located in the UK North Sea. The field is named after the Hewett Ledges a sand bank feature beneath which the field is situated. The gas reservoir is a Lower Triassic (Middle and Lower Bunter) sandstone and a Permian Zechstein carbonate bed at a relatively shallow depth of 3,000–4,200 feet (914–1,280 m). The Hewett structure runs north-west to south-east and is about 18 miles long and 3 miles wide (29 km by 4.8 km). It was discovered in October 1966 and extends over blocks: 48/28, 48/29, 48/30, 52/4 and 52/5. To the north are the Big Dottie, Little Dottie and Deborah accumulations, which are separate from Hewett, but are produced through the Hewett topsides facilities. The original determination of the gas in place amounted to 115 billion cubic metres. The field was originally licensed to Phillips Petroleum Exploration UK Ltd (then from 2001 Tullow Oil UK Ltd and from 2008 Eni UK Ltd). Production from the field began in July 1969. Gas and associated condensate are exported from the field via two 30 inch diameter pipelines to the Bacton gas terminal, Norfolk. Eni submitted plans in 2019 to decommission the Hewett field and to remove all installations. The end of production is scheduled for late 2021.
The Hewett gas compositions and properties are as follows.
Hewett gas properties :
| Composition | Middle Bunter % | Lower Bunter % |
| Methane | 86.57 | 92.13 |
| Ethane | 4.87 | 3.56 |
| Propane | 1.40 | 0.85 |
| Butane and Pentane | 0.32 | 0.56 |
| Nitrogen | 6.57 | 2.36 |
| Carbon dioxide | 0.09 | 0.02 |
| Hydrogen sulfide | 500 ppm | Nil |
| Gas gravity | 0.655% | 0.607% |
| Mean condensate content | 3.2 bbl/million cu ft | 4.8 bbl/million cu ft |
| Btu rating | 1011 Btu/cu ft | 1047 Btu/cu ft |

## Development

The Hewett field has been developed through a number of offshore installations.
Hewett gas field installations :
| Installation | Location Block | Facility | Function | Type | Legs | Well slots | Installed | Production start | Production to |
| Hewett 52/5 A | 52/5 | Platform | Drilling & production | Steel jacket | 8 | 8 | September 1967 | September 1969 | FTP |
| Hewett 48/29 A | 48/29 | Platform, bridge linked to FTP | Drilling & production | Steel jacket | 12 | 8 | May 1968 | July 1969 | FTP |
| Hewett 48/29 B | 48/29 | Platform | Drilling & production | Steel jacket | 8 | 8 | August 1972 | 1973 | FTP |
| Hewett 48/29 C | 48/29 | Platform | Drilling & production | Steel jacket | 8 | 8 | 1976 | 1976 | FTP |
| Hewett FTP | 48/29 | Platform, bridge linked to 48/29 A | Field terminal platform | Steel jacket | 8 | – | 1968 | July 1969 | Bacton |
| Hewett 48/29 Q | 48/29 | Platform, bridge linked to 48/29 A | Accommodation | Steel jacket | 4 | – | | – | – |
| Other fields producing via Hewett ||||||||||
| Deborah | 48/30 | Subsea | Production | Subsea wellhead | – | 1 | 1979 | 1979 | 48/29 C |
| Little Dotty | 48/30 | Subsea | Production | Subsea wellhead | – | 1 | 1979 | 1979 | 48/29 A |
| Della | 48/30 | Subsea | Production | Subsea wellhead | – | 1 | 1988 | November 1988 | 48/29 A |
| Delilah | 48/30 | Subsea | Production | Subsea wellhead | – | 1 | | | 48/29 A |
| Area B | 48/30 | Subsea | Production | Subsea wellhead | – | 1 | | | FTP |
| Dawn | 48/29 | Subsea | Production | Subsea wellhead | – | 1 | | | 48/29 C |
| – | 48/30 & 30/10 | Subsea | Production | Subsea wellhead | – | 2 | | | 48/29 C |

## Production

The annual gas production from the Hewett field (in million standard cubic feet) was:

## Decommissioning

In 2020 Eni submitted to the UK Government a proposal for the decommissioning of the Hewett field and its installations. Production from Hewett ceased in 2021.