An application of heavy-mineral analysis to lithostratigraphy and reservoir modelling in the Oseberg Field northern North Sea

Three distinctive detrital garnet associations have been recognized in Brent Group sandstones of the Oseberg area (northern North Sea) by means of electron microprobe analysis. These have lithostratigraphical significance, with one association occurring in the Etive and Oseberg Formations, one in the Ness Formation and one in the Tarbert Formation. The stratigraphic variation in garnet population reflects changes in provenance and in the pattern of distribution of clastic detritus, although a detailed reconstruction of source areas is not possible on the basis of the available information. Differentiation of Ness and Etive/Oseberg Formations by means of detrital garnet geochemistry has enabled the recognition of fluvial chanbel sandstones belonging to the Ness Formation which have cut down into the Etive Formation shoreline complex. This provides direct evidence of communication between Ness and Etive/Oseberg, adding an extra degree of sophistication to the geological input for reservoir simulation. A strong permeability anisotropy can be modelled around the fluvial channels, and a net sand volume can be modelled in agreement with channel orientation.