Re-assessment of Reservoir Dynamic Behaviour to Assist the Fourth Drilling Campaign in Mature, Geologically Complex North Sea Field

Abstract

The Dunbar Field (UKCS, Block 3/14a), operated by Total E&P UK, is situated on an intermediate terrace between the East Shetland Platform and the Viking Graben and characterised by a series of pre-Cretaceous and structurally aligned tilted fault blocks. The principal hydrocarbon accumulations are contained in the Middle Jurassic Brent Group and younger Upper Jurassic Heather Sands. Internally, the field is compartmentalised by a number of N-S faults and a secondary alignment of NE-SW faults which cross cut and often offset the main N-S faults. The larger scale faults down throw to the east and subdivide the field into four main areas; the West Flank, Central Panel and Frontal Panel with an uplifted Horst (Triassic) Panel in the south. Each of these panels has specific reservoir and fluid characteristics. The Central and Frontal panels have a substantial production history of 15 years. The field is in steep decline with high water cut in water flooded areas, and extremely low pressure in compartments produced by natural depletion. A better understanding of recovery from the main flow units is essential for estimation of drainage volume, optimisation of water injection pattern and infill well placement/completion. The ability to better define the size of the connected volumes through improved fault identification (Seismic PSDM3D Reprocessing) along with an improved understanding of the permeability field (sedimentological, petrographic, XRD, SEM, SrRSA, DST analysis & simulation studies) has been key in assessing Dunbar’s future potential. An intensive data acquisition campaign has been integrated in a comprehensive dynamic synthesis leading to a reservoir model history match that has improved our understanding of the field. This paper describes the multidisciplinary team work leading to an improved understanding of the recovery efficiency and reservoir connectivity leading to a further drilling campaign.