Indefatigable gas field explained

The Indefatigable gas field is a large natural gas and associated condensate field located under the North Sea 60 miles (98 km) off the Norfolk coast.

The field

The Indefatigable gas field is a natural gas field located in the North Sea. The field is 67 miles (107 km) north-east of Great Yarmouth and is named after the Indefatigable Banks, a shallow sand bank beneath which it is situated.^[1] The gas reservoir is a Rotliegendes sandstone 200–300 feet (61–91 m) thick at a depth of 8000–9000 feet (2440–2740 m).^{[2] [3]} It was discovered in June 1966 and extends over several blocks: 49/18, 49/19, 49/23 and 49/24. The original determination of the gas in place amounted to 126 billion cubic metres. Blocks 49/18 and 49/23 were originally licensed to Amoco (since 2003 to Perenco UK Limited) and Block 49/19 and 49/24 to Shell. Production from the field began in September and October 1971. Gas and associated condensate are produced via the Leman gas field to the Bacton Gas terminal, Norfolk.

The Indefatigable gas composition and properties are as follows.^[4]

Composition	%
Methane	91.8
Ethane	3.39
Propane	0.85
i-butane	0.16
n-butane	0.20
i-pentane	0.07
Hexanes	0.06
Heptanes plus	0.16
Nitrogen	2.73
Carbon dioxide	0.52
Hydrogen sulfide	Nil
Gas gravity	0.61 %
Mean condensate content	3.0 bbl/million cubic foot
Btu rating	1015 Btu/cubic foot

Baird gas field

The Baird gas field is located in Block 49/23 and is licensed to Perenco (originally Amoco). It was discovered in September 1993 and has recoverable reserves of 1.82 billion cubic metres. Gas is produced via a seabed well assembly and a pipeline to Inde 49/23 D. The peak production was 0.66 billion cubic metres per year.

Development

The Indefatigable field has been developed through a number of offshore installations.

The Inde installations developed by Amoco, now owned by Perenco, were:

Perenco (former Amoco) Inde installations!Installation!Location Block!Platforms!Function!Type!Legs!Well slots!Installed!Production start!Production to

Inde A Complex	49/18	Inde AD	Drilling	Steel jacket	8	12	July 1970	September 1971	Inde AT
		Inde AP	Production	Steel jacket	8	–	1970	September 1971
Inde B Complex	49/18	Inde BD	Drilling	Steel jacket	8	12	1973	June 1974	Inde AT
		Inde BP	Production	Jackup	4	–	1973	June 1974
Inde C Complex	49/23	Inde CD	Drilling	Steel jacket	8	12	August 1976	July 1977	Inde AT
		Inde CP	Production	Steel jacket	8	–	1976	July 1977
Inde Compression	49/23	Inde AT	Pipeline terminal	Steel jacket	6	–	May 1971	September 1971	Leman 49/27B
		Inde AC	Compression	Steel jacket	12	–	Jacket June 1979, topsides Summer 1980	November 1980	–
		Inde AQ	Accommodation	Steel jacket	4	–	June 1979	–	–
Inde D	29/23	Inde D	Wellheads and production	Steel jacket	4	4	1990	1990	Inde C

The Perenco Indefatigable 49/23A complex also receives gas from other fields and third parties:

• Bessemer (49/23E) installation and its satellite N.W. Bell (49/23-9) via a 14.5 km 16-inch pipeline.
• Wenlock (49/12A) installation owned by Alpha Petroleum via a 36.231 km 8-inch pipeline. A three well-slot installation was installed in the Wenlock field in 2006 with wells commissioned in 2007, 2008 and 2009. Production declined quickly and make the installation uneconomic and a Decommissioning Programme  application was submitted to the Oil & Gas Authority in 2021.^[5]
• Davy (49/30A) installation and its satellites Davy North (49/30A-7A) and Davy East (53/5B-7) via a 43 km 16-inch pipeline.

The Inde installations developed by Shell were:

Shell Inde installations!Installation!Location Block!Platforms!Function!Type!Legs!Well slots!Installed!Production start!Production to

Inde J Complex	49/24	Inde JD	Drilling/production	Steel jacket	8	6	June 1970, April 1971	September 1971	Inde AT
		Inde JP	Satellite (accommodation)	Steel jacket	4	–	April 1972	–	–
Inde K Platform	49/24	Inde K	Drilling/production/ accommodation	Steel jacket	10	6	July 1971, June 1972	March 1973	Inde AT
Inde L Platform	49/24	Inde L	Drilling/production	Steel jacket	6	6	February 1977	October 1978	Inde K
Inde M Platform	49/19	Inde M	Drilling/production	Steel jacket	4	4	Spring 1985	October 1985	Inde J
Inde N Platform		Inde N	Drilling/production	Steel jacket	4	4	1980's		Inde K

Production from the Shell Inde field ceased in 2005, Inde J, K, L, M, and N were subsequently decommissioned and removed.^[6]

Production

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

See also

• Leman gas field
• Hewett gas field
• West Sole gas field
• Viking gas field
• Sean gas field
• Davy, Bessemer, Beaufort, Brown and Boyle gas fields

Notes and References

1. Book: Department of Trade and Industry. The Energy Report. HMSO. 1994. 0115153802. London. 29, 60, 61.
2. Book: Tiratsoo, E. N.. Natural Gas. Scientific Pres. 1972. Beaconsfield.
3. Web site: Geological Society London. 2003. The Indefatigable Field, Blocks 49/18, 49/19, 49/23, 49/24, UK North Sea. 23 September 2021. lyell.
4. Book: Oilfield Publications. The North Sea Platform Guide. Oilfield Publications Limited. 1985. Ledbury. 339–359.
5. Web site: Wenlock Decommissioning Programmes. 9 December 2021. assets.publishing.service.gov.uk.
6. Web site: Shell. 2014. Indefatigable Field Platforms and Pipelines Decommissioning Programme Close Out Report. 25 September 2012. gov.uk.