Thistle Alpha

Location

The Thistle Alpha installation is located 125 miles north east of Sumburgh in the Shetland Isles and 275 miles north east of Aberdeen, mainland Scotland, in block 211/ 18.  The platform coordinates are 61˚ 21’46.93”N and 01˚ 34’47.14” E and the installation stands in a water depth of 161.5m

Thistle installation

The Thistle platform is a fixed, 60 slot drilling and production installation, comprising of a conventional steel jacket with four main legs, supporting 36 modules arranged on 3 deck levels. 28 of these modules contain the equipment and machinery, which constitute the production, utilities, drilling systems and facilities. The remaining 8 modules situated on the southeast end of the installation contain living quarters (LQ), offices, the central control room (CCR), the helideck and workshops. The platform was installed on the jacket in 1978.

Installation systems

Fluids from the Thistle and Deveron reservoirs are recovered through platform drilled wells. The produced oil flows is processed through a two stage production separation system. Stabilised oil is metered and exported using the direct oil export pumps to the Brent Pipeline System. The original gas compression system has been decommissioned hence a small volume of gas separated from the oil is flared. Produced water is cleaned and discharged to the sea.

Oil evacuation system

Oil is imported from the Dons field via an 8” pipeline, and combined with the oil produced by the Thistle platform. The combined oil production is exported from the Thistle platform within a 16” oil export pipeline through the Brent Pipeline System via the Dunlin and Cormorant platforms to the Sullom Voe Oil Terminal.

Gas import

Gas is imported from the Northern Leg Gas Pipeline (NLGP) system. A portion of the import gas is used for as fuel gas to provide the Thistle installation power, with the remainder exported to the Dunlin installation.

See pdf for full details.

Heather

The Heather installation is designed to accept production fluids from Heather field and Broom field via subsea tieback. The production fluids are processed and separated into oil, gas and water. The processed oil is exported to the Sullom Voe Terminal via Ninian Central platform, while the gas is routed through compression trains for lift gas purpose.

Produced water is separated, treated and discharged overboard and sea-water is injected into both Broom and Heather fields to optimise production. Import gas is provided via the Western Leg gas pipeline to meet the fuel gas deficiencies on the platform.

See pdf for full details.

Northern Producer

The Northern Producer is located between the West and South West Don fields in the UK sector of the North Sea in Block 211/18b. The West Don, Don South West and Conrie fields are licensed to EnQuest and are pumped to Thistle Alpha via Northern Producer.

The Greater Kittiwake Area

The Kittiwake platform is located 160km East of Aberdeen, in Licence block 21/18. The platform coordinates are; latitude 57°28ˈ6"N, longitude 00°30ˈ43"E. The platform stands in a water depth of 85m.

Kittiwake Installation

The Kittiwake platform was installed in 1990 and is a fixed steel platform on the Kittiwake field with other fields being developed as subsea satellite tie‐backs to the Kittiwake platform. The subsea satellites consist of; Goosander (block 21/12), Grouse (block 21/19), Gadwall (block 21/19) and Mallard (block 21/19). These fields are collectively known as the Greater Kittiwake Area. Petrofac are the current duty‐holders, operating the installation on behalf of Enquest. Enquest and Dana Petroleum are 50/50 partners in the Greater Kittiwake Area.

The living quarters has a maximum POB of 77, and normal POB is around 70. The platform no longer has drilling facilities which were decommissioned in 2009.

Installation systems

Fluids from the Kittiwake reservoir are recovered through platform drilled wells and the Goosander, Grouse, Gadwall and Mallard reservoirs are recovered through subsea tiebacks. Originally designed for tanker export, the produced oil flows through a 4 stage crude stabilisation system. Mallard and Gadwall have their own dedicated first stage separator in parallel, before the oil is co‐mingled upstream of the second stage separator.

Stabilised oil is metered then exported using the oil export pumps to the Forties Pipeline System via a 10" oil export line to Forties Unity. Produced gas is compressed and used for fuel and gas lift. The surplus gas is exported via a 4" export line to the near‐by SEGAL gas pipeline. Produced water is cleaned and discharged overboard to the sea.

Oil evacuation system

Oil is exported via a 33km, 10" pipeline (installed in 2007) from the platform to the BP operated Forties Unity platform. Oil used to be exported onto a shuttle tanker using a single point mooring system, which was removed in 2008.

See pdf for full details.

EnQuest Producer - Alma and Galia

The Alma field was originally developed as the Argyll field by Hamilton Brothers Oil Company (HBOC). It was the first oil field placed on production in the UK sector and was in production from July 1975 until November 1992, during which time it produced 73MMstb.

The Alma field was originally developed as the Argyll field by Hamilton Brothers Oil Company (HBOC). It was the first oil field placed on production in the UK sector and was in production from July 1975 until November 1992, during which time it produced 73MMstb. It was redeveloped as the Ardmore field by Tuscan from October 2003 until June 2005 and produced a further 5MMstb.  The estimated Stock Tank Oil Initially in Place (STOIIP) is 265MMstb.  The field was abandoned at a water cut of 70%.  The Galia field was originally called the Duncan field and was produced from February 1982 until October 1992 and produced a total of 18.7MMstb from a STOIIP of 47.7MMstb.  The Alma and Galia fields have been being re-developed as a single joint development and are tied back to the FPSO EnQuest Producer via one central hub for all wells.  The Alma concept is to produce the field from the historical 70% water cut at the previous cessation of production to 95% water cut (on average). The redevelopment comprises six Electric Submersible Pump (ESP) lifted development wells drilled by a semi-submersible and produced via Floating Production, Storage and Offload (FPSO) facility. 

See pdf for full details