Cygnus Gas Field, North Sea, United Kingdom

Key Data

The Cygnus gas field is situated over UK Continental Shelf blocks 44/12a and 44/11a. The field is operated by GDF Suez, which also owns a 38.75% stake. Centrica has a 48.75% interest and Bayerngas holds the remaining 12.5%. Bayerngas acquired its interest from Endeavour in August 2010.

The field was discovered in 1988 and lies at water depth of 76ft. The preliminary estimates showed that it may have reserves of two trillion cubic feet of gas, with around 500bcf of gas in the eastern region alone. The discovery is one of the largest in the Southern North Sea.

Cygnus gas field development

"The Cygnus gas field has reserves of two trillion cubic feet of gas."

The field development plan for the first phase of Cygnus was sanctioned by the UK's Department of Energy and Climate Change (DECC) in August 2009. Phase I is targeted at developing the eastern part of the field, which comprises 16 production wells tied back to six platforms. Production is expected to start in 2013. The produced gas will be exported to the Murdoch field centre by a 27km, 12in-diameter pipeline.

Two appraisal wells were successfully drilled in 2009. Another two appraisal wells were drilled during the first half of 2010 to appraise the western part of the field. The development plan for the second phase will be drawn based on these appraisal drilling results.
Sword CTSpace software was opted for document control and collaboration for the initial design phase of the project.

In October 2011, AMEC was awarded the front end engineering and design (FEED) contract of the Cygnus field. The FEED study will be completed in 2012. The final investment decision on developing the field will be taken after the study.

Cygnus discovery and drilling

The Cygnus gas field was discovered in 1988 while drilling the 44/12-1 exploration well, which identified a gas-bearing Leman reservoir. The following year, the field was appraised by well 44/11-2, which insured the presence of Leman and Carboniferous reservoirs in a different fault block.

"The Cygnus gas field may have reserves of two trillion cubic feet of gas."

The drilling of yet another appraisal well, 44/12-2, over the original discovery fault block confirmed the presence of gas.

The appraisal well drilling continued in February 2009 to evaluate the reservoir quality and fluid content of the primary Leman reservoir in the eastern part of the field. Drilling was also carried out to test the deeper Carboniferous reservoir as a secondary target.

Well 44/12a-3 confirmed the presence of gas in the Leman and Carboniferous intervals of the reservoirs. It was drilled by a Noble Ronald Hoope jack-up rig. The successful drilling of the 44/12a-3 appraisal well enables further extension of southern part of North sea. It was drilled to total depth of 3,790m and around 905,600m³ of natural gas was extracted on daily basis during the testing period.

Further, to identify the size of the field, a fourth well, 44/12/a-4, was drilled to a depth of 3,744m. The test flow rate was 32 million cubic feet per day. An additional appraisal drilling was also carried during the first quarter of 2010 over the western area of the field. Well 44/11a-4 indicated higher reserves and resource estimates, and extended the boundary of the field further to the north and to the west. It was drilled by an ENSCO 100 jack-up rig.

The well was drilled up to 12,207ft and found a good quality, gas-saturated Leman sand reservoir of 54ft, with a sand thickness of 130ft gross and 85ft of net pay.

The well tested at a rate of 28 million cubic feet per day. A sixth appraisal well - 44/12a-5, drilled in July 2010, confirmed the Southern North Sea to be one of the largest reserves in the UK. The reserves are estimated to range from 500 billion cubic feet to an upside of 1.2 trillion cubic feet. The DECC also extended the field licence to P1731 with additional blocks 44/11b and 44/12b.

Cygnus rigs

"The Noble Ronald Hoope rig is owned by Noble Drilling."

The Noble Ronald Hoope rig is owned by Noble Drilling and was built by CNIM at La Seine sur Mer, France, in 1982. The rig was used for drilling the 44/12a-3 well.

The rig can drill up to 250ft underwater. The maximum drilling capacity of the rig is 25,000ft and it can accommodate 80 people. The ENSCO 100 jack-up rig is owned by ENSCO. The rig was built in 1987 at Clydebank, Scotland. It can drill up to 328ft underwater and has a maximum drilling capacity of 30,000ft.

The Cygnus gas field was discovered in 1988 and lies at a water depth of 76ft.

The Cygnus gas field is one of the largest discoveries in the southern North Sea.

The Noble Ronald Hoope rig was used to drill the 44/12a-3 well.