A Significant Satellite - the Nevis South Field, 9/13a

The Nevis South Field is operated by Mobil North Sea Ltd (ExxonMobil) in partnership with Amerada Hess Ltd, Shell UK Ltd and OMV (UK) Ltd. It is a sub-sea development tied back to the Beryl Alpha platform that lies 7 km to the east-north-east. First oil was produced in 1996 but the field is still actively being drilled to bring on new reservoirs or maximise recovery from those reservoirs already developed. Structurally the field is relatively simple, being a rotated fault block with beds dipping to the south-west. The Base Cretaceous Unconformity cuts down into the crest of the fault block such that strata are progressively eroded towards the north-east. This has led to the core of the field being Triassic reservoirs with Jurassic reservoirs on the flank. The oldest reservoir in the field is the Triassic Lewis I sequence of fluviolacustrine origin. The core illustrates a prograding lacustrine delta sequence and overlying aggradational fluvial sandstones. The Lewis I contains an unusual heavy oil which is currently being produced via a single, high-angle well. Above this unit lies the Lewis III/IV reservoir which contains the bulk of the hydrocarbons in the field. The Lewis III comprises aggradational fluvial braidplain deposits. The Lewis IV comprises an association of floodplain facies. The Lewis III/IV reservoir is exploited via three crestal producers and two water injectors. The Middle Jurassic Beryl reservoir is a high net/gross tidal channel/tidal bar succession of multi-Darcy permeability. Evacuation of the Beryl oil rim is by three horizontal wells with pressure support supplied by an extensive aquifer. The youngest reservoir comprises mass-flow sandstones of the Middle-Upper Jurassic Heather Formation. These are as yet undeveloped and are not illustrated by the selected cores.