Statoil outlines plans for Mariner, Bressay fields in UK North Sea

Sept. 12, 2011
Statoil and its partners Eni and Nautical Petroleum have selected a development concept for the Mariner heavy oil field project in the northern UK North Sea.

Offshore staff

ABERDEEN, UK – Statoil and its partners Eni and Nautical Petroleum have selected a development concept for the Mariner heavy oil field project in the northern UK North Sea. They plan to install a 25,000-metric ton (27,558-ton) production, drilling, and quarters (PDQ) platform based on a steel jacket in 110 m (361 ft) water depth.

Oil will be sent to a ship-shaped floating storage unit (FSU) with storage capacity of 850,000 bbl moored 2.5 km (1.55 mi) away from the platform. The platform will import fuel gas via a connection to an existing gas pipeline

In addition to a conventional drilling rig, there will be a well completion and workover unit below the platform’s rig floor, with a cantilever jackup providing further well construction capability during the first few years of development.

Statoil estimates Mariner’s recoverable reserves at 300-500 MMbbl. However, the oil is ultra-heavy and viscous, with API gravities of 12.1°-14.6° and viscosities ranging from 67 cp in the field’s Maureen reservoir to 508 cp in the Heimdal reservoir.

Due to the low well flow rates and likelihood of early water breakthrough, Statoil says many wells are needed. The platform will have 50 integrated well slots – Statoil has drawn up 145 reservoir targets for production or injection, but this figure should be achieved through use of multi-branch wells, side tracks, and reuse of slots.

All the wells will be equipped with electric submersible pumps (ESPs).

The topsides process equipment will be designed to handle large liquid rates and oil/water emulsions. Additionally, the oil will be diluted with a lighter crude upstream of the ESPs to ease flow and oil/water separation.

FEED studies are under way, and Statoil aims for sanction of the development project and major contract awards toward the end of next year. If all goes to the current plan, the topsides and jacket would be installed by 2Q 2016, with first oil in the last quarter of that year.

At a briefing last week at Offshore Europe in Aberdeen, Peter Mellbye, executive VP for Development and Production International, said the company aimed to start development of the nearby Bressay heavy oil field a year after Mariner gets under way.

He estimated Bressay’s recoverable reserves at 200-300 MMbbl. Currently Statoil and partner Shell are examining two concepts, he added. One is a replica of the scheme for Mariner, while the other, involving an FPSO and wellhead platform, could be a lookalike to Statoil’s Peregrino heavy oil development offshore Brazil.

Here the gravity of the crude is 12° API, reservoir pressure is low, and there remains uncertainty at this stage over the subsurface and the number of wells that would be required.

The two projects, he added, would incur a probable gross investment of $9.5 billion, and annual operating costs of $238 million when the fields are in production. Statoil plans to establish a new operations center in Aberdeen for this program, with 700 personnel, some brought from Norway.