Mariner back on track

Statoil’s two UKCS heavy oil developments – Mariner in block 9/11a and Bressay in blocks 3/27b, 3/28a, 3/28b, 9/2a and 3/a – are back on track having been halted by the operator in March following the UK Chancellor’s decision to increase the supplementary charge on oil and gas production from 20% to 32%. Meg Chesshyre reports.

Together, the Mariner and Bressay fields represent a gross investment of roughly £6 billion with annual operating costs of around £150 million. According to Peter Mellbye, the Norwegian operator’s EVP for international development & production, fact-based discussions with the UK Treasury had provided a good basis for going forward. The approach they took was that they wanted to do something to incentivise new investment, and at the same time they had obviously to weigh that up against the revenue consequences, noted Mellbye. ‘The time effect made a big difference when it came to this type of project.

‘After a period of uncertainty, we are back on track with the landmark Mariner and Bressay developments,’ said Mellbye, pointing out that Statoil’s heavy oil experience includes the Grane field development off Norway and the Peregrino field offshore Brazil.

Mariner, first discovered 30 years ago and the subject of a number of development studies by different operators since, will be developed using a PDQ platform based on a steel jacket, with a floating storage unit.

Mariner PDQ and FSO.

Low well flow rates and early water breakthrough necessitate a large number of wells, artificial lift, and a process designed to handle large liquid rates and oil-water emulsions. A total of 145 reservoir targets for production or injection are planned for Mariner, requiring multi-branch technology, sidetracks and reuse of slots.

Statoil expects a final investment decision in late 2012 and first oil in late 2016. Invitations to tender are expected late 2012/early 2013. Aker Solutions was awarded a FEED earlier this year. The PDQ platform will have topsides of about 25,000t, 50 integrated well slots (28 production, 20 water injection, one make up water, one waste) with an eight-leg steel jacket weighing about 18,000t. Water depth at location is 110m. The living quarters will accommodate 150 personnel. The FSO – 2.5km from the platform – will be a traditional ship shape and offer storage for 850,000 barrels (crude and diluent combined). The PDQ will connect to an existing gas pipeline for the import of fuel gas.

In addition to the conventional drilling rig, a separate well completion and workover unit will be included below the rig floor. To add further well capacity, initially a cantilever jackup rig will be employed in addition to platform drilling. All wells will be equipped with electrical submersible pumps and in addition the oil will be diluted with a lighter crude upstream of the ESPs to ease the flow and oil/water separation. Recoverable reserves are put at 300-500 million barrels.

For the smaller Bressay field development, scheduled one year behind Mariner to benefit from its learnings, two concepts are under consideration: a replica Mariner, or the same FPSO/wellhead platform combination Statoil employed in Brazil for its Peregrino development. OE

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