The Dunbar Field is situated in the south-central part of the East Shetland Basin, about 135 kms east of the northernmost Shetland islands and 25 kms south of the Alwyn North field (figure 1). The basin, an intermediate terrace region between the East Shetland Platform and the deep North Viking Graben, is characterised by a series of pre-Cretaceous structurally aligned tilted fault-blocks whose relief are clearly seen on the base Cretaceous seismic reflector.

The Dunbar area is 55 km2 (17 km long × 2 to 5 km wide). Dunbar is limited to the north and east by a major NNW SSE fault, down-throwing to the east. Internally, the field is compartmentalised by a number of N - S faults and by a secondary alignment of NE - SW faults which cross-cut and often offset the main N - S faults. The larger-scale faults downthrow to the east and subdivide the field into three main areas, namely the Westflank, the Central Panel and the Frontal Panel. In general, the flanks of the resultant fault-blocks dip gently in a westerly direction.

Sedimentary thicknesses were controlled by major synsedimentary faults. The Brent Group/Upper Massive Sands thickness in the Westflank/Central Panel 'footwall', where perhaps only partial sequences are preserved, is around 90 metres, whereas in the Frontal Panel 'hanging wall' more complete sequences were accommodated with thicknesses in the order of 280 metres.

Hydrocarbon accumulations are present at several stratigraphic levels in the Dunbar area.

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