Controls on facies architecture in the Brent Group, Strathspey Field, UK North Sea: implications for reservoir characterization

The Brent Group reservoir in the Strathspey Field, UK North Sea comprises shallow marine, marginal marine and non-marine strata of variable reservoir character. Controls on the distribution, geometry, connectivity and orientation of sandbodies within the reservoir have been assessed via the application of high-resolution sequence stratigraphic methods to an integrated dataset comprising core, wireline log, 3D seismic and reservoir production data. The base of the Brent Group is a major sequence boundary overlain by weakly wave-influenced, shallow marine sandstones of the lowstand-to-transgressive Broom Formation. The overlying Rannoch Formation represents highstand progradation of a wave-dominated shoreface, which is truncated across a sequence boundary by a near-field-wide fluvio-estuarine complex (Etive Formation). Marginal-marine strata of the overlying Ness Formation are divided into field-wide units bounded by mudstones that form vertical pressure barriers. Major, oil-bearing fluvial sandbodies overlie sequence boundaries and the widths and orientations of two such sandbodiesare controlled by syn-depositional, intra-reservoir faults. The distribution of these sandbodies is therefore predictable. The Ness Formation is truncated by a major sequence boundary overlain by stacked, tidally influenced, shallow marine sandstones of the Tarbert Formation. The resulting facies architecture has been successfully used to refine reservoir models, identify bypassed oil and target infill wells.