| Sean gas field | |
|---|---|
| Country | United Kingdom |
| Region | North Sea |
| Block | 49/25 |
| Offshore/onshore | Offshore |
| Operators | Shell 1986-2015. ONE 2015- |
| Owner | Shell 1969-2015, ONE 2015- |
| Field history | |
| Discovery | 1969 |
| Start of production | 1986 |
| Production | |
| Current production of gas | 600×10 |
| Estimated gas in place | 16.4×10 |
| Producing formations | Rotliegendes sandstone |
The Sean gas field is a small natural gas and associated condensate field located in the UK sector of the North Sea, 67 miles (108 km) 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 67 miles (108 km) 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).[1]
The Sean field has been developed through a number of offshore platforms.[1]
| Platform | Field | Function | Type | Legs | Well slots | Installed | Production start | Production to |
|---|---|---|---|---|---|---|---|---|
| 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) |
The East Sean field has not been developed.
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.[2]
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% |
In June 2015 Oranje-Nassau Energie (ONE) acquired a 50% interest in the Sean field from Shell. SSE E&P UK holds the remaining 50% interest. ONE became the operator of Sean.[4]
