Buzzard Field North Sea Central, United Kingdom

The Buzzard field is located in the Outer Moray Firth, central North Sea, 100km north-east of Aberdeen, and about 55km from the coast at Peterhead.

The field straddles two licences – P.986 (blocks 19/10 and 20/6) and P.928(S) (blocks 19/5a and 20/1S) – the water depth in the area is about 100m. It is operated by Nexen with 43.21254% (Nexen acquired Encana in 2004) on behalf of PetroCanada (29.89122%), BG (21.73307%) and Edinburgh (5.16317%).

The field's total recoverable reserves are estimated at more than 550 million barrels of oil, and gross production is expected to reach a plateau of 180,000 to 190,000 barrels of oil a day between 2007 and 2008. However, at the end of April 2008, production was almost halved due to the closure of the Forties pipeline in the Central North Sea – the result of a 48-hour refinery strike. The development required an investment of £1.491bn.

The field was discovered in June 2001 using the semi-submersible Ocean Nomad, which initially encountered a 400ft gross oil column which tested at 6,547bpd and 1mcf/d of gas. A subsequent sidetrack extended the oil bearing sands 4,400ft to the east and increased the gross oil column to 750ft. The high-quality Upper Jurassic turbidite reservoir lies within a stratigraphic trap at 7,800ft to 9,175ft below mean sea level.

The reservoir has a low gas / oil ratio and will require pressure maintenance through water injection from the onset of production. The reservoir also features excellent rock quality with up to 360ft of high porosity, high permeability sands with an oil saturation of up to 94%. The oil consists of medium sour crude (32.6° API, 1.4% sulphur) with minor wax and asphaltenes.

OFFSHORE PLATFORMS

The field was developed by three bridge-linked steel platforms supporting the wellhead facilities (W), production facilities (P) and a third platform supporting living quarters and utilities (UQ).

Burntisland Fabrications Limited won the contract for the management, fabrication and provision of assistance with commissioning of the 3,650t wellhead deck, to be constructed at the company's facilities at Burnt Island and Methil.

Heerema was awarded the contract for the management, fabrication and provision of assistance with commissioning of the 9,500t utilities deck. Dragados carried out the management, fabrication and provision of assistance with commissioning of the 10,000t production deck at Cadiz, Spain.

PRODUCTION WELLS

The development may well include up to 27 production wells, However eight well were pre-drilled and available for production start-up in December 2006. This drilling will be undertaken by a skid mounted jack-up rig located adjacent to the wellhead platform.

The remainder will be drilled after start-up and are anticipated to allow production to increase to reach its plateau level of between 180,000bpd and 190,000bpd by 2007-2008.

Reservoir pressure is maintained by an active water flood programme using produced water supplemented by treated sea water when necessary. Under the base case, 16 water injection wells will be drilled through two subsea manifolds located about 1km from the platforms.

Four were be pre-drilled and available at the time of production start-up. It is anticipated that infill wells will be drilled to improve production in late field life.

When it is necessary to utilise oil-based drilling muds, the cuttings will either be shipped to shore for cleaning and disposal or reinjected into a cuttings disposal well.

OIL AND GAS TRANSPORTATION

An oil transportation agreement was signed with BP to export oil from Buzzard via the nearby Forties Pipeline System to Cruden Bay and then onto Hound Point. An 18in pipeline will be laid from the Buzzard processing platform to the nearest point in the Forties System, some 28km away.

An agreement was signed with Total and Elf to export surplus gas via the Frigg system. A 10in pipeline was laid from the Buzzard location to the Captain 'T' point on the UK Frigg pipeline, some 29km away. From there the gas is transported to the St Fergus Gas Terminal.

START OF PRODUCTION

In the first quarter of 2007, the field produced 85,000 barrels of oil equivalent a day. Forties Blend crude oil changed in quality during January 2007 when crude oil from the Buzzard field began production through the FPS system.

Although there are over 50 other fields making up Forties Blend, Buzzard is now the largest component field and it has altered the hydrocarbon characteristics of the blend. The latest BP assay sampled in April 2007 shows Forties Blend to have an API of 41.8° and a sulphur level of 0.49%. This is with a Buzzard composition in the Blend of approximately 22%.

GAS IMPORT

On the basis of the reservoir as it is known now, it is likely that the platform will become gas deficient for power generation in the next five to seven years and will then need to import gas. The agreement with the Frigg UK Pipeline owners provides for the supply of fuel gas at that time as required, as well as for commissioning and start-up.