Detection and prediction of Lower Cretaceous sandstone distribution in the Scapa Field, North Sea

Abstract

Abstract The Scapa Field is a combination structural/stratigraphic trap located in UK North Sea Block 14/19, 112 miles northeast of Aberdeen. The productive intervals consist of turbidite sandstones in the lower part of the early Cretaceous Valhall Formation. Three discrete sandstone bodies have been identified during the development of the Scapa Field, ranging in age from early Valanginian to late Hauterivian. The sandstones are interbedded with marls, limestones and conglomerates that filled the early Cretaceous northwest-southeast trending syncline between the Halibut Shelf and Claymore tilt block, on the southwest flank of the Witch Ground Graben. The combination of lithofacies, wireline log correlation, palaeontological, reservoir production and pressure studies led to the recognition of a five-fold subdivision (‘SA’ to ‘SF’) of the Scapa Sandstone Member. Detailed seismic studies, in particular amplitude extraction mapping using the 3D data set, have enhanced the interpretation of the distribution of the sandstone bodies. Tight conglomerate facies dominate the Lower Valhall sequence to the south in a narrow fringe bordering the Halibut Shelf. Reservoir sandstones interfinger with these conglomerates and thin to the north, changing facies to sandy marls onto the Claymore tilt block. Within the main Scapa syncline, sandstone distribution was controlled by clastic input associated with subtle structural control. The gravity-driven turbidite system concentrated deposition in the bathymetric lows. Lime muds were deposited in a constant hemipelagic rain, both over the intervening highs and interbedded with the sands.