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Source-to-Sink Analysis of Reservoir Distribution: Lower Eocene Dornoch Delta-Hermod Fan Sediment Routing System, East Shetland Platform, Northern North Sea, UK

Abstract

Reservoir presence and quality are key exploration risks. We combine conventional analysis of stratigraphic architecture with sediment mass balance to develop a predictive approach to characterising sediment volumes and grain-size distributions, in order to reduce these key risks. Our approach is being tested using a data-rich Eocene sediment routing system comprising deltaic (Dornoch Formation) and coeval slope to basin-floor deposits (Hermod Sandstone Member) in the East Shetland Platform and Viking Graben, northern North Sea, offshore UK and Norway. Ongoing mapping using 3D seismic data and 55 key wells shows that there are at least four distinct sediment routing systems in the study area, each with a separate erosional catchment. Clinoforms in the Dornoch Formation define a near linear deltaic shoreline in plan view, implying strong sediment transport along the shoreline. Thus, the Dornoch-Hermod sediment routing systems were not closed, but there was sediment transfer between them. The basin-floor fan deposits of the Hermod Sandstone Member represent the sinks of the routing systems and are spatially distinct from each other. Ongoing work is using these mapped seismic data to calculate the sediment volumes in each Dornoch-Hermod routing system and its component parts. Grain-size distributions in the volumes are characterised using core and wireline-log data, to capture down-system fining of grain size. When combined with accurate geochronological data, the sediment volumes give estimates of sediment supply rates that can be compared with independent sediment flux estimates derived from paleohydrologic and paleogeomorphic methods. Integration of grain-size data into this volumetric framework allows a sediment mass balance approach to be implemented, which allows the position of grain-size “fronts” (e.g. down-system limit of sandstone) to be constrained. Such down-system trends in grain size can be normalised relative to accommodation space to give generic, predictive trends that can potentially be applied to exploration in data-poor frontier regions.