New strategy for Kristin recovery

May 5, 2004, 09:35 CEST

A new strategy for drilling the complex Kristin reservoir in the Norwegian Sea has been proposed by operator Statoil in order to maintain the field’s recovery factor.

“This project presents special reservoir challenges, and nobody has drilled such a formation with subsea wells,” says Nina Udnes Tronstad, operations vice president for Kristin.

She explains that the extremely high reservoir pressure and temperature, of 910 bar and 170°C respectively, make big demands on subsea equipment and drilling procedures.

The high pressure also means that all the wells must be completed before the field comes on stream.

Uncertainties prevail about the flow properties of the main Garn reservoir. As a result, plans now call for five of the 12 wells to be drilled horizontally.

These would take longer to drill, and cost more than the wells in the original drilling programme. But they will allow for the possibility that flow properties are not as good as expected.

Estimated investment in the project is NOK 18.9 billion, an increase of NOK 1.7 billion from the development budget set in 2001.

This rise primarily reflects the new drilling strategy, but also includes higher costs for the platform and subsea installations. It falls within the NOK 1-2 billion range published in February.

The economics of Kristin remain satisfactory. Plans call for this gas and condensate field to begin production on 1 October 2005.

“Kristin is so demanding because drilling horizontal wells in such a reservoir represents a pioneering approach and will be technologically very challenging,” says Ms Tronstad.

“Each well will be assessed in isolation to ensure an optimal strategy and profitability for the subsequent wells.”

Together with its contractors, Statoil has led the way for technology to develop complex fields with high pressure and temperature, such as Huldra and Kvitebjørn in the North Sea.

Similarly, much experience gained by the group from the development of seabed installations on its Åsgard field in the Norwegian Sea can now benefit Kristin.

The latter stands out because it is the first field in the world with such high pressure and temperature to be developed with a subsea solution.