Andrew
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The Andrew reservoir lies at a depth of some 2,430 metres below sea level and is contained within the Palaeocene. In addition there is an underlying lower Cretaceous gas reservoir, which has not been fully appraised. Twelve horizontal production wells and one gas re-injection well were originally drilled to tap the reservoir.
Estimated recoverable reserves of:
This compares with Annex B estimates of:
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After the discovery, commercial innovations allowed Andrew to be developed into a viable field. Andrew was eventually developed by an Alliance of BP and seven contractors, which tied financial rewards firmly to the final cost of the project.
The final project cost around #290 million and the savings were shared among the Alliance partners. The total project costs including drilling and pre-operations were around #432 million. The Andrew Alliance consisted of BP, Brown & Root, Santa Fe, Saipem, Highlands Fabricators, Allseas, Emtunga, and Trafalgar House.
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Production began in 1996 and field life is expected to be around 18 years.
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At peak production Andrew produced around 80,000 barrels of oil per day.
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In 2002 production had declined to 33,000 barrels per day and 40 million standard cubic feet of gas per day, remaining gas is re-injected to maintain reservoir pressure.
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The oil is exported through a 10-inch diameter, 16-kilometre long pipeline to the Brae-Forties system.
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The gas is exported through an 8-inch diameter, 44 kilometre long pipeline to the Central Transmission System (CATS).
The Development
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The Andrew development consists of:
The steel structure consists of:
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Three template wells and two Cyrus wells were drilled prior to the installation of the jacket to enable early production. The alliance contract was adopted for the drilling and completion phase of the project and involved: Baker Hughes Inteq, Schlumberger, Santa Fe and Transocean.
Oil Processes
Fluids from the various producing wells combine at a production manifold and from there they are carried to the process plant. A two-stage separation system separates water and gas from the oil. The stabilised crude is then expected via the Brae-Forties system.
Gas Processes
After separation from the oil and water, the gas is dehydrated, compressed, metered and exported to the CATS system and then onwards to Teesside. Dry fuel gas from the gas process is used as fuel for the platform's three, 6-megawatt gas turbine driven generators.
Produced Water
Produced water from the separators is routed to hydrocyclones, which separate residual hydrocarbons from the water. Processed, clean water is then discharged to the sea with an average oil in water concentration of less than 20 parts per million.
EMAS (Eco Management Audit Scheme)
In August 1998 the Andrew facilities received ISO 14001 and EMAS accreditation. As a result, Andrew became the first offshore oil or gas installation to receive EMAS accreditation.
Harvesting the maturing field
Production from the Andrew field began to decline in the first quarter of 2000 as the gas plant reached full capacity. In order to maintain production rates, a program of infill drilling began at the end of 2001. A four-dimensional seismic survey has shown very clearly the areas of the reservoir in which significant quantities of oil remain. Three additional wells have already been drilled to access these areas and a plan is in place to drill another new well from the platform early in 2004.
During 2002/2003, a, program of well work was performed to add extra perforations to two of the wells and access more oil.
Despite the increasing age of the processing facilities, the operations team has been very successful in increasing both the efficiency and reliability of the platform. Late 2002 saw the longest sustained run of production from the platform since start-up, with production efficiency well above 90%. Fibre-optic cables are planned for 2004 to improve communications between the platform and the shore. This will reduce operating costs and enable constant monitoring of process equipment in order to identify deterioration in performance, allowing early maintenance and reduce plant downtime.
Future drilling will focus on low cost options, which will save both time and money. This is likely to be sidetracks or through tubing rotary drilling (TTRD). These techniques involved drilling from an existing well into another section of the reservoir in which oil still remains, instead of drilling from the seabed to the reservoir.
When most of the oil has been recovered the gas cap will be produced. This blow down of the reservoir is likely to begin around 2012 and final production from Andrew is likely to be during 2015.
