The Balder and Jotun fields are located on the western flank of the Utsira High, close to the eastern pinch-out of a Tertiary submarine fan system. Although similar in many aspects, the fields display important depositional, structural and stratigraphic differences which influence the choice of development strategy. The subsurface development strategy for the fields has been designed to optimize oil capture and minimize risk based on the interpreted reservoir geology. Therefore, differences between the exploration histories and reservoir geology are reflected in the development strategy of the two fields.
Both fields comprise Tertiary reservoir sands shed from the East Shetland Platform and transported across the Viking Graben area onto the Utsira High by sandy debris flows and turbidites. These distal gravity flow deposits display both thin-bedded sands and thicker more massive sandstones (>100 m). In the Balder Field, an intricate interaction between deposition and soft sediment deformation processes generated a complex network of reservoir compartments with common fluid contacts. In the Jotun Field, the oil–water contact is also common between all three structures, but a gas cap is restricted to one of the structures.