APPLICATION OF HIGH-RESOLUTION 2D LANDSTREAMER VIBROSEIS IN MAPPING OF SAND-RICH MIOCENE DEPOSITS FOR GROUNDWATER PURPOSES

The Miocene succession in central and southern Jylland, Denmark was formed during four phases of shoreline progradation into the basin that covers present-day Denmark. The deposits comprise several aquifers with potential drinking water resources and have been investigated as part of a major hydrogeological programme carried out during the last 15 years. An exclusively large dataset of 1200 km high-resolution 2D onshore seismic data and 150 boreholes, 100-400 m deep and a multi-disciplinary approach including sedimentology and biostratigraphy in a sequence-stratigraphic framework, has formed the basis for an extensive mapping of the Miocene succession. One of the cornerstones has been the generally very high data quality of the seismic data acquired in the past 10 years using the landstreamer vibroseis method.

The sand-rich units of the Miocene in Denmark were deposited in wave-dominated deltas, as spit complexes and barrier islands in the down-drift areas of delta lobes and in incised valleys representing first braided river systems and later meandering rivers. A detailed interpretation of the seismic data has been performed, by identifying top and base of individual delta lobes and fluvial deposits. The thickness of individual delta lobes generally varies between 20-50 m, but can be up to more than 100 m, and the thickness of fluvial channels range from 10-60 m.

The result of the investigations is a dynamic 3D geological model that reflects the basin development and the depositional processes as well as the palaeogeographical development during the Miocene. The model is intended to serve as a geological database of lithological and stratigraphical information and provides a better understanding of the geological architecture of the aquifers than traditional lithofacies models.

We will outline the geological setting and show examples of the detailed interpretation of seismic data and geophysical logs as well as the modeling of the Miocene succession in 3D.