Summary

In 1974 North Cormorant field accumulations were discovered by Shell U.K. The field was initially owned by Shell U.K and Esso until 2008 when TAQA Britani purchased it, along with several other North Sea assets. The purchase included all equity, associated infrastructure and production licenses.

The North Cormorant platform was installed in 1981 and production commenced the following year . It is a single fixed platform with steel jacket. The platform has two production trains for separation of oil, gas and water. It has the design capacity to process around 180,000 barrels of crude a day. The processed oil from North Cormorant platform is sent to TAQA's Cormorant Alpha platform located in the South Cormorant field. The oil is transported via the Brent System Oil Pipeline to the Sullom Voe terminal for sale.

North Cormorant production rate was highest in its early years, rapidly increasing from 1982 up until 1984 where production rates peaked. Productions rates then started to decline sharply until 1991 when they reached a plateau. The decline was caused by the reservoir pressure dropping off quickly, due to weak aquifer support.

Up until the exchange of operator in 2008 Shell U.K and Esso carried out a number of developments in order to maintain reservoir production. Shell and Esso had more profitable projects to concentrate on, so subsequently sold a number of their North Sea assets to the smaller company TAQA. This included the whole Cormorant field.

Since ownership TAQA has been carrying out a number of development strategies aimed at increasing production. Simultaneously upgrading platform facilities.

Introduction

The Cormorant field is located 95 miles northeast of the Shetland Islands at a depth of about 500 ft in the U.K. North Sea. It was discovered by exploration well 211/26-1 in 1972; the fifth field to be discovered in the Northern North Sea. It straddles blocks 211/21a and 211/26a and is made up of four discrete accumulations spread along a major N-S trending fault terrace. Oil is produced from the sandstones belonging to the Brent Group. The sedimentary rocks comprising the Brent Group were deposited in a fluvial-wave dominated delta system during the Middle Jurassic. The reservoir has a typical gross thickness of 250-300 ft, locally increasing to 550 ft over faults active during sedimentation. Reservoir porosity varies from 16-28%, with average permeability ranging from tens of md to 1300md. The accumulation contains highly under-saturated crude (34-36 API ) oil which was initially over pressurised by some 1000-1270 psi. (Gluyas, J.G, 2003)

Exploration and Appraisal

Initially Cormorant South (Block1) was discovered by a Shell exploration well in 1972. Four intervals within the Brent sandstone were tested at flow rates of up to 7,800 barrels/day of 36 API oil. Between 1973 and 1977 a total of eight exploration and appraisal wells were drilled on the Cormorant field proving the remaining accumulations in blocks 2, 3 and 4. In 1974 exploration well 211/21a-2 discovered the Cormorant North accumulation. Oil reserves estimated in place for the North Cormorant field was just over 1,000 million barrels. (Wood Mackenzie 2003)

Development

The North Cormorant platform is located between the north and central accumulations. The installation can cater for a maximum of up to 214 personnel. It consists of an eight-legged steel jacket sub-structure, anchored by piles to the seabed. The Module Support Frame, which is attached to the jacket, acts as a base support for two levels of modules. The platform also has separation, compression, injection and generation facilities. There is a single drilling rig. The platform has J-tubes for flowlines from up to 18 subsea satellites

Development began in 1978 with installation of the South Cormorant platform, followed by the North Cormorant platform in 1981. The area between the two platforms was developed with subsea technology.. A single-satellite well P-1 began production in 1981, and an underwater manifold center was installed in 1982.When the North Cormorant platform was installed the size and shape of the hydrocarbon accumulations were not clear and it was decided to use a conventional platform along with an under water passive distribution manifold in order to provide injection support in south of block 4. Once the PDM was installed it proved poor injection indexes when it was tested. This was due to the reservoir properties. The PDM was no longer considered a practical project. As an alternative highly deviated injection wells were drilled from the platform. The platform has pre-curved conductors to allow for the earlier well deviation, increasing reservoir coverage by up to 20%. Initially the production wells saw a rapid drop in pressure confirming a lack of aquifer support. In 1985, three appraisal wells were drilled which were retained as possible recompletion candidates for water injection. (Wood Mackenzie 2003).The North Cormorant platform has 40 slots on the deck, the last of which was used in 1995. Since then, as per the revised development plan, the only economic option has been to sidetrack wells, with a high water cut to other targets within the field, in order to recover bypassed oil. Developing additional reserves. By 2001 a total of 42 oil producers and 20 water injectors had been drilled and completed from the platform. In addition there have been 11 geological sidetracks, mostly required due to the proposed well not penetrating a sufficient reservoir section as a result of a fault cut out.

For development purposes the whole Cormorant field was split in half; north and south. The northern part is developed by the North Cormorant platform and the southern part the south platform.On 7 July 2008 TAQA Britani Ltd purchased several North Sea assets. The purchase included all equity, associated infrastructure and production licenses relating to the Tern, Eider, Cormorant North, South Cormorant, Kestrel and Pelican fields. The 420-million investment allowed for a number of projects designed to revive production from these facilities and extend economic field life into 2020 and beyond. (Taqa)Within two years of taking over, oil production from the fields including Cormorant North, increased from below 25,000 bbl/d in 2008 to 40,000 bbl/d, Some of this was due to the re-establishment of the dormant drilling rigs on the North Cormorant platform which led to five infill wells being drilled last year on the North Cormorant field. (Gluyas, J.G, 2003)In 2011 North Cormorant underwent a integrated control system replacement along with water injection upgrades. This year, TAQA gained FDP approval and announced that they aim to drill 2 new platform production wells into the North Cormorant Block 4 field. During the same drilling campaign 1 appraisal well will be performed on the Cormorant East field, also drilled from the North Cormorant platform. The second North Cormorant production well will be dependent upon the results from the Cormorant East appraisal well. Should the appraisal well into Cormorant East demonstrate a deep contact and well developed Brent sequence and if the FDP is approved, then the appraisal well will be completed and a further injection well into Cormorant East will be drilled. These activities will be performed at the expense of the second North Cormorant production well. (Offshore Technology 2014)The processed oil from North Cormorant platform is sent to TAQA's Cormorant Alpha platform located in the South Cormorant field. The oil is then transported via the Brent System Oil Pipeline to the Sullom Voe terminal for sale

Summary of the main events in the development of North Cormorant fieldYearEvent

1972Blocks 211/21 and 211/26 awarded to shell and Esso. 211/21-21 discovery well drilled into block 1.

1974 Cormorant North field accumulations discovered. (Block 4) discovered by well 211/21-2

1975 Block 3 discovered by well 211/213s1

1979First 3D seismic survey required

1981North Cormorant platform installed

1982 Oil production started

1983 Water injection started

1984Second 3D seismic survey acquired

1984Peak production at 122655 BBL/D

1991New year storm caused structural damage to the platform. (lost part of the passive fire protection). Production shut down for around 6 weeks in April and May. Third 3D seismic survey required.

1995Secondary development based on drilling sidetracks from existing wells in order to recover bypassed oil. Developing additional reserves.

2008On 7 July TAQA Britani Ltd purchased several North Sea The purchase included all equity, associated infrastructure and production licenses relating to the Tern, Eider, Cormorant North, South Cormorant, Kestrel and Pelican fields and related sub-sea satellite fields assets from Shell U.K. and Esso

2010Reinstatement of the dormant drilling rig leading to five infill wells being drilled

2011North Cormorant underwent a Integrated control system replacement along with water injection upgrades.

2014North Cormorant latest project started. (See development above)

2018Production licence expires

(Gluyas, J.G, 2003)

ProductionNorth Cormorant commenced production in February 1982. Liquids production has been disappointing. Although flow and production rate was initially good the reservoir pressure rapidly dropped. To counter this the drilling programme was altered to include more water injection wells at an earlier stage. This had a consequence of lowering North Cormorants production peak production from 122,655 barrels/day 1984 to 106,000 barrels/day in 1985. There after production continued to decline until it reached at plateau of 30,000 barrels/day in 1991.North Cormorant produces gas volumes in association with its oil. It started gas production in 1982. It produced around 40mmcfd at peak. After fuel requirements sales volumes are much less than this and peak sales production of 29mmcfd occurred in 1986. (Wood Mackenzie 2003)Oil and gas production from the Cormorant area was severely limited on 8th April 1989. This was due to a gas leak on the Alpha platform. The accident occurred during the time an emergency shut down valve was being installed on the gas export line that leaves Cormorant Alpha. Gas production from Cormorant had been cut and a plug fitted to the severed line during installation of the ESV. The plug became dislodged resulting in the gas leak at the top of the C4 leg of the platform. An explosion took place but no fire occurred along with no casualties. The Brent pipeline system which pass through the C4 leg, before leaving for St Fergus were immediately shut down. Production from all Cormorant fields recommenced 6 weeks later. (Offshore technology 2011)During 1991 a new year storm caused structural damage to the Cormorant North platform. Causing it to lose a part of the passive fire protection. Production shut down for around 6 weeks in April and May. (Gluyas, J.G, 2003)As shown in the graph below. Oil production slipped steadily from a peak of 6,258.499 bbls/yr of oil in 1986 to below 522,488 bbls/yr in 2008. When TAQA Britani took charge they initially broke the decline slightly increasing production to 641,758 in 2010. During 2011 and 2012 production dropped again to 463, 419bbls/yr. In 2013 there was a slight increase in production to 509,516 bbls/yr. (Decca 2014) Due to the current development by TAQA production is estimated to increase.

North Cormorant Key Facts LocationNorth Sea, East Shetland Basin

Producing HorizonMiddle Jurassic, Bajocian

Water Depth161m

Blocks211/21a 211/26a

OperatorTAQA

ParticipantsTAQA

Platform TypeFixed Jacket

Discovery DateAugust 1974

Production Started1982

Peak Oil Production1984

Peak Gas Production1986

Hydrocarbon QualityGravity (API) 33.8-36GOR (sct/bbl) = 224-770Viscosity (cp) = 0.6-1.2

(Taqa 2014)

Map

References Cormorant East - Offshore Technology. 2014. Cormorant East - Offshore Technology. [ONLINE] Available at: http://www.offshore-technology.com/projects/cormorant-east/Cormorant oilfield - Wikipedia, the free encyclopedia. 2014. Cormorant oilfield - Wikipedia, the free encyclopedia. [ONLINE] Available at: http://en.wikipedia.org/wiki/Cormorant_oilfield. [Accessed 21 October 2014].Decca. 2014 Department of Energy and Climate Change.Gluyas, J.G, 2003. United Kingdom Oil and Gas Fields. 1st ed. USA: The Geological Society of LondonHome - OnePetro. 2014. Home - OnePetro. [ONLINE] Available at: https://www.onepetro.org/Mackenzie, Wood Mackenzie, 2003. Cormorant. UK Upstream ServiceTAQA . 2014. TAQA . [ONLINE] Available at: http://www.taqaglobal.com. [Accessed 21 October 2014].

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