| Sean gas field | |
| Country: | United Kingdom |
| Region: | North Sea |
| Block: | 49/25 |
| Operators: | Shell 1986-2015. ONE 2015- |
| Offonshore: | Offshore |
| Owner: | Shell 1969-2015, ONE 2015- |
| Discovery: | 1969 |
| Start Production: | 1986 |
| Production Gas Mmcuft/D: | 600 |
| Est Gas Bcm: | 16.4 |
| Producingformations: | Rotliegendes sandstone |
The Sean gas field is a small natural gas and associated condensate field located in the UK sector of the North Sea, 67miles off the Norfolk coast.
The Sean gas field is a natural gas field located in the North Sea and comprises three accumulations North Sean, South Sean and East Sean. The field 67miles north-east of Bacton Norfolk and is located to the south east of the Indefatigable gas field.[1] It is named after the four partners at the time of its discovery: Shell, Esso, Allied Chemical and National Coal Board.[2] The gas reservoir is a Rotliegendes sandstone 170–290 feet (52–88 metres) thick at a depth of 8,300 feet (2,530 m). North Sean was discovered in April 1969 and South Sean in January 1970 both are located in UK Block 49/25. The original determination of the gas in place amounted to 425 billion cubic feet (12.4 billion cubic metres).
The Sean field has been developed through a number of offshore platforms.
| Sean PP | South Sean | Production & accommodation | Steel jacket | 8 | – | May and November 1985 | October 1986 | Bacton (via 30-inch 107 km pipeline) | |
| Sean PD | Drilling and wellhead | Steel jacket | 6 | 12 | January and November 1985 | October 1986 | Sean PP (bridge link) | ||
| Sean PK | Compression | Steel jacket | Planned future, never installed | Sean PP (bridge link) | |||||
| Sean RD | North Sean | Satellite wellhead | Steel jacket | 6 | 12 | January and November 1985 | October 1986 | Sean PP (via 20-inch 4.7 km pipeline) |
Production from the field began in August 1986. Sean was operated as a peak shaving field with a maximum delivery of 600 MMSCFD (million standard cubic feet per day). Processing facilities comprise 3-phase separation and gas dehydration. Gas and associated condensate are transported via a 30-inch diameter pipeline to the Shell processing facility at the Bacton gas terminal, Norfolk.
The specification of third party gas for entry into the export gas pipeline was as follows:[3]
| Parameter | Value | |
|---|---|---|
| Gross calorific value | 37–44.5 MJ/Sm3 | |
| Oxygen | <0.2% | |
| CO2 | 2 mol % maximum | |
| H2S | <3.3 ppm | |
| Total sulfur | <15 ppm | |
| Wobbe Index | 48–51.5 MJ/Sm3 | |
| Inerts | <7% | |
| Nitrogen | <5% |