Statoil has indicated that it will drill the 50 wells, plus another 92 sidetracks to tap the Mariner heavy oil field. Of these, 76 will be producers, 64 will be produced water re-injectors. There will also be a “make-up water well” and a waste disposal well.
Another four production wells are planned to access the Mariner East field, which lies 5 kilometres (3.1 miles) to the south-east.
Mariner wells are to be drilled from the PDQ, using a jackup located alongside the facility for between four and five years. Mariner East wells will require a semi-submersible rig.
This high well count is due to the fact that each well will only be capable of draining a small section of a reservoir before excessive water breakthrough occurs, an environmental impact statement on the project discloses.
There will be a major demand for facilities, comprising a substantial production, drilling and quarters (PDQ) platform supported on a steel jacket and fixed to the seabed with 24 piles - as well as a floating storage and offloading unit. There will also be a subsea drilling template, pipeline end manifolds, six pipeline end terminations (PLETs) as well as infield, import and export pipelines.
The PDQ design is closely based on Statoil's Norwegian Grane facility which was designed to produce heavy 18º API oil. gThe Grane facility produces a moderately heavy oil c.and was therefore seen as providing a good basis for initial design of the Mariner PDQ,h Statoil explains.
Oil production will be separated out on the PDQ, and exported to the FSU for shuttle tanker offloading. Produced water will be re-injected. Gas will be used to fuel gas turbines on the PDQ, and additional gas is to be imported via the 32-inch Norway-UK Vesterled pipeline. Downhole pumps will be used in the production wells, as well as diluent for the crude.
Offshore work is due to start in the third quarter 2015, and first oil is slated for the first quarter 2017, and from Mariner East in 2019. Altogether, the field is forecast for a production life of 40 years.
Mariner lies in UK block 9/11a and Mariner East in block 9/11b, in the UK's Northern North Sea sector, 130 kilometres (81 miles) offshore from the UK coast, and 40 km north-west from the UK-Norway median line.
In addition to gas and oil pipelines, there will be another pipeline carrying diluent to dilute the heavy Mariner crude oil – running from the FSU to the Mariner PDQ.
A power umbilical will link the Mariner East drilling template to the main PDQ, and fibre-optic cable is planned, stretching 73 km (45 miles) to link the Mariner PDQ with Statoil's operated Heimdal field in the Norwegian sector of the North Sea.
Mariner comprises two reservoirs, one in Maureen sands, and an overlaying Heimdal Sands reservoir. Statoil and its partners, Nautical Petroleum and Eni, plan to drill and exploit the Maureen reservoir first, with single production wells, and single water injectors. Heimdal is due to be produced later, with dual and single production wells and produced water injection wells.
Both are classed as shallow reservoirs, between 1,400 and 1,500 metres (4,592 – 4,920 feet) below sea level at Maureen and around 1,200 metres (3,936 ft) below sea level for the Heimdal section.
Both reservoirs feature dense, highly viscous oil: the Maureen reservoir is rated at 14.2º API and the Heimdal reservoir is heavier still, at 12.1º API.
Mariner was discovered in 1981, and four further exploration wells and 10 appraisal wells were later drilled on block 9/11 and a total of 19 reservoir penetrations have been made.
Statoil predicts Mariner will produce at a combined rate of 76,000 b/d of oil, and Mariner East at up to 22,00 b/d – once the main Mariner field is off plateau.
Production systems will therefore be designed for a maximum oil production rate of 76,000 b/d, and 80,000 b/d of crude and diluent, and a total of 320,000 b/d of oil, diluent and water combined.
The Mariner Area Development project will be operated by Statoil under UK licence P335, where it holds 65% equity, Eni has 29%, and Nautical Petroleum's subsidiary Alba Resources holds 6% Mariner East lies in P726, owned 92% by Statoil and Eni with 8%.
Project costs are put at £7.8 billion for both Mariner and the the UK Bressay heavy oil development, which is expected to follow Mariner by a couple of years.
For Mariner alone, Statoil indicates projected capital expenditure of £2.4 billion for facilities, £1.8 bn for drilling, and £102m a year of operational expenditure. At Bressay, the facilities capital expenditure is put at £2.5 bn, drilling at £1.1 bn, and operational expenditure of £108m a year.
Furthermore Statoil says the project will require a new operations base to be established in Aberdeen, with a staff of between 200 and 300, plus a long-term offshore work force in the region of 500 personnel.