A series of regionally correctable unconformity bounded sequences has been identified within the Paleocene interval of the West of Shetland area. These sequences contain a succession of sandstones deposited in deep-water environments within the Early to 'mid' Paleocene (Danian to early Thanetian) with a gradual shallowing upwards to shelf and deltaic deposits in the Late Paleocene.Reservoir properties of these sandstones vary widely, with porosities ranging from >30% to below 10%, and permeabilities from >2D to <0.1 mD. Although there is a severe reduction of reservoir quality with depth of burial, certain sandstone units have retained high porosities (>20%) and permeabilities (10-100mD) at below 3 km burial depth. This preservation of reservoir quality is due in part to depositional facies, but mineralogical/diagenetic variability has also allowed the preservation of porosity and permeability. In particular, the presence of grain rimming chlorite in these sandstones is fundamental in preserving porosity.Log and core analyses of these sandstones has shown that interpretation of reservoir potential and fluid saturations is not straightforward. The effect of diagenetic minerals on log responses and in particular the salinity of formation waters (both in water-and hydrocarbon-bearing zones) were poorly known at the start of the study, and had to be accurately quantified.

Introduction 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. P. 329

The Brent East reservoir of the Alwyn North Field, with few producer wells and a relatively short production life, represents a challenge for data gathering and reservoir management. Accurate reservoir description had to be obtained rapidly to adjust to unexpected events in order to maximise recovery and prepare enhanced oil recovery programmes.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Dunbar Field, lying in the East

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