Access to Fairfield Energy's Oil and Gas Infrastructure
The infrastructure code of practice is a voluntary arrangement developed by Oil & Gas UK in consultation with DECC. Under the arrangement, operators have agreed to publish high level capacity, technical and commercial data about the pipelines and facilities that they operate on the UK Continental Shelf in order to facilitate the utilisation of such infrastructure, by prospective third party users, for the development of remaining UKCS reserves
Dunlin Area Infrastructure
The Dunlin Alpha is a fixed concrete gravity based installation, which lies within the East Shetland Basin of the Northern North Sea, serving as a manned production facility for the Dunlin and Dunlin South West fields. The installation stands in 151 metres of water, 506km North-North-east of Aberdeen in block 211/23a of the UK sector of the continental shelf (195km North East of Lerwick).
The installation is a four leg, concrete gravity base structure with a steel box girder based topsides supporting two levels of modules. The storage cell system in the GBS has been taken out of service and the platform has no storage capability.
The platform has two process trains, a single three stage separation process for Dunlin (with two 1st stage separators), and the Osprey two stage process train for the subsea satellites. Nominal capacity of the respective process trains are 165,000 blpd and 85,000 blpd respectively. Both trains have produced water separation facilities employing hydrocyclones. Associated gas from both trains is used for fuel gas, off-gas from the second and third stages being fed to a single fuel gas compressor and thence to gas turbine generator sets. The platform is now fuel gas deficient and relies on external sources for direct and indirect sources of additional power. Electrical power is imported from the Shell owned Brent Charlie platform via a 33kV subsea power cable and fuel gas is imported, following Fairfield’s installation of a 4” Dunlin Fuel Gas Import (DFGI) pipeline, which runs between Thistle and Dunlin to enable delivery of a fuel gas supply from the NLGP system.
The Brent sequence fields in the Dunlin complex employ water injection as the primary means of pressure maintenance and secondary oil recovery. At present, a number of platform wells have had ESP’s installed but there is no means of providing alternative methods of artificial lift e.g. gas lift.
A total of 5 electrically driven water injection pumps are installed on the platform (2 nominally dedicated for subsea field pressure support) with a nominal capacity of 280,000 bwpd. This is currently limited by power generation and service water system constraints.
The platform is a pipeline node on the Brent system with connections to the Thistle and Murchison platforms to the North and North East of the Dunlin location. The platform also acts as the host for the subsea tiebacks of the Osprey and Merlin fields.
The Osprey subsea field is located 7km north-north-west of Dunlin in blocks 211/23a and 211/18a in a water depth of 159m and consists of 8 production wells and 4 water injection wells. Oil is produced via a subsea production manifold (PLBM), and transported through two 8" production lines contained within a 38" bundle carrier pipe to Dunlin Alpha. Osprey water injection is supplied by a 10" flexible via a central water injection manifold (WLBM) to the four satellite wells.
As of April 2014, Osprey is produced via a single 8” flowline. The existing Osprey production pipeline will be taken out of use in the Autumn of 2015 and a replacement pipeline and riser tie-in installed in late summer 2016 or Spring 2017. This system will comprise a refurbished production manifold for the existing wells tied back to Dunlin, with two 8” production lines and a new riser system.
The Merlin subsea field is located 7km north-west of Dunlin Alpha in block 211/23a-b in a water depth of 150m. There are three production wells in a daisy-chain arrangement linked by a trenched and rock-dumped production pipeline to the Osprey production flowline risers, via a crossover manifold situated 400m from Dunlin Alpha. A single Merlin water injection well is linked to the Osprey water injection pipeline by a flexible flowline via a Y-piece connecting spool.
Both subsea fields are operated from a common Aker Kvaerner subsea control system. Controls connections to both subsea fields is done via steel tube umbilicals.
The operation of the water flood on all three fields at relatively high water cut (>90% BS&W) means that the production trains for Dunlin and Osprey are currently within their nominal capacity, however the available effective operating capacity is not considered to be significant, with the Operator’s plans to increase production levels from the existing well stock.
Exported stabilised crude from the platform process (containing NGL) is commingled with oil from Thistle for onward transmission to Sullom Voe (Shetland Islands) through the Brent System via Cormorant Alpha. Production from the CNR owned Murchison platform ceased on 18th March 2014.
The following pipelines are connected to the Dunlin Alpha:
- 16-inch oil import from Murchison – due to be decommissioning in accordance with the CNR Murchison Decommissioning Programme.
- 16-inch oil import from Thistle Alpha;
- 24-inch oil export via Cormorant Alpha into the Brent system;
- Two x 8-inch oil production from Osprey;
- 10-inch water injection to Osprey;
- 8-inch water injection to Merlin (via Y-piece connecting spool from Osprey WI line);
- 8-inch oil production from Merlin to Merlin crossover manifold;
- 4-inch fuel gas import pipeline from Thistle Alpha.
In addition there is the 33Kv power cable which is connected to Brent Charlie. Availability of power supplies via this link is dictated by the ongoing capacity of the Brent Complex to export power. This capability will be lost as the Brent decommissioning programme proceeds.
The hydrocarbon import and export risers are contained within platform Leg C. The power cable and the fuel gas riser are in Leg D. A number of 14” and 10” J tubes are available for use in Leg D. A number of low pressure rated large diameter lines (16” and 24”) are also available. The exact condition of these risers would need to be confirmed before potential use.
The operator has carried out studies on retrofit of additional riser systems not compatible with the available facilities and the most feasible means of adding riser capacity would be by means of catenary flexible risers or a riser ladder.
Export capacity in Brent system has to be applied for via the Brent system operator (TAQA). Capacity information for Brent system is available on the TAQA website.
5 Year Oil Ullage
5 Year Water Injection Ullage
5 year Gas Ullage
The Dunlin Fuel Gas Import (DFGI) Pipeline is sized to provide a potential/nominal 10mmscfd flowrate export route. Export would only occur when the facility had excess gas after meeting its power generation requirement. This system was commissioned for gas import during July 2012. Earliest date for gas export service would be dependent on third party entrant profiles.
Third Party Access Agreements
There are currently no third party agreements in place regarding access to Dunlin Area assets or infrastructure (date reference: post-2004, when ICoP came into effect).
Entry / Exit Specifications
Entry and exit specifications for access to Dunlin Area infrastructure will need to be determined on a case by case basis. However, reference should be made to the relevant equivalent specifications for access to Brent Systems and Sullom Voe Terminal infrastructure, in the first instance.
Any interested parties should contact:
General Manager, Dunlin Area
Fairfield Energy Limited, 19 Abercrombie Court, Prospect Road,
Arnhall Business Park, Westhill, Aberdeen, AB32 6FE.
Website Updated: 23/01/2015.
Before decommissioning its fields, Fairfield will consult pro-actively with a wide range of stakeholders.
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