The comprehensive understanding of the deep subsurface is the imperative prerequisite for the assessment of subsurface potentials geared towards sustainable management and efficient use of geopotentials avoiding usage conflicts and areas at risk. The evaluation of the subsurface, thus, must be based on a sound and holistic 3-dimensional assessment of the fundamentals and demands cross-border coherent information on the structures and features of the subsurface. A major challenge in 3D geological modelling down to great depths is the availability of data with an adequate distribution and resolution.

GeoMol’s 3D geological models are based on seismic data, scattered and clustered borehole evidence and the conceptual models of the basin evolution. By far the largest data pool are seismic sections and, lately, 3D seismic surveys. More than 28,000 km seismic lines have been selected as the basis for 3D modelling. Originating from multiple sources and various dates of origin these data are subject to heterogeneous interpretations which have gone through several paradigm shifts over the last decades. Thus, it is essential to standardise the data with regards to technical parameters and content prior to further analysis, exploiting the technical advances in seismic processing: An effort has been made to adjust all lines to the same reference level, amplitude and step of signal processing to avoid mismatching at intersections and at the country borders. After applying the whole sequence of processing steps from scanned paper plots to filtered post-stack migrated SEG-Y files structural features can be identified more precisely and certain seismic pattern can be used in the interpretation of the sedimentary buildup (facies), which is crucial for defining areas with an adequate hydraulic conductivity of aquifers, e.g. for geothermal use. To improve the accuracy and reach of correlating rock characteristics and their seismic signature, several synthetic seismograms based on borehole measurements have been generated and parallelized with the bore logs.

GeoMol’s 3D modelling procedure consists of several workflows customized to the specific needs of each partner, depending on the 3D modelling software used, and if modelled in time or depth domain. If modelling in time-domain, calibration of layer surfaces is done by borehole data re-converted into time-domain based on check shot data available for many drillings. Regionalized velocity models for time-depth conversion are applied at a late stage of modelling only, to facilitate later model refinement by additional seismic sections where needed.

The stratigraphic subdivision of the Alpine foreland basins has evolved from regional approaches and reflects the complex basin evolution. Thus, working cross-border requires also a semantic harmonization of the different – as historically grown – nomenclatures and the alignment of stratigraphic peculiarities to allow the correlation of a uniform stratigraphic column with the prominent seismic reflectors trace­able over the entire basins. Core of the project GeoMol is a structural 3D subsurface model of the principal units for the entire Northern Molasse, providing the framework to fit in all existing and emerging models in their true spatial setting. Five detailed models in pilot areas have been built to cover specific questions of the subsurface use and/or seismic risk which might inhibit the utilisation of geopotentials. These models consist of up to 13 litho-stratigraphic units ranging from the Cenozoic basin fill down to Mesozoic and late Paleozoic sedimentary rocks and the crystalline basement.

Links to GeoMol publications on the subject: