Three-dimensional regional-scale hydrostratigraphic modeling based on sequence stratigraphic methods: a case study of the Miocene succession in Denmark

A sound hydrogeological model is the heart of every well-performing groundwater model. A sequence stratigraphic approach has been tested, which has been widely used in the petroleum industry since the 1980s for the construction of three-dimensional hydrogeological models for sedimentary basins. The sequence stratigraphic interpretation has been established for the Miocene succession in western Denmark based on seismic profiles, gamma-ray logs, sediment descriptions and palynological analysis of borehole samples. The up to 400-m-thick Miocene succession consists of deposits originating from deep marine to terrestrial depositional environments. The succession is subdivided into six sequences, corresponding system tracts and distinct lithofacies covering the period from late Oligocene to latest late Miocene. The final model is converted into a binary three-dimensional model that shows the location, geometry and thicknesses of potential deep aquifers, and is prepared for groundwater flow modeling. The model provides a qualified geological description of the connectivity between deep sand formations and the ground surface. By comparison to a traditional lithofacies model based on sediment descriptions of borehole samples, it is shown that the new method gives a more sound geological understanding, which is essential when flow paths and the vulnerability of deep aquifers are evaluated.