Workpackage 2: 3D Geological Models
Workpackage leader: TNO
3D geological models will be developed by transforming a layer model that defines stratigraphic unit boundaries into a so-called voxel model (a voxel model consists of ‘tiles’ or volume blocks with predefined lateral and vertical dimensions) and assigning lithological or other characteristics to each voxel. Voxel modelling is relatively new, with TNO pioneering in developing those models based commonly on abundant, closely spaced borehole data (Van der Meulen et al. 2005, 2007; Vernes & Van Doorn 2005; Stafleu et al. 2011). Most experience is being built on land (e.g. Mathers & Kessler 2010). Offshore, borehole data are relatively scarce; instead, seismic networks of various densities form the main data type. This is the case for the BPNS, where UG-RCMG has acquired more than 17,300 km of high-resolution seismics. Additional seismic data are available within TNO for the southern Netherlands part of the North Sea (NPNS). Recently, the Belgian seismic data were integrated into a geological layer model to study the Quaternary evolution of the Belgian shelf (Mathys 2009). Before this unique model can be used as the basis for a voxel model, the seismically defined units need to be further ground-truthed for lithological and lithostratigraphical interpretation in a transnational context. Through interpolation in a series of simulations, all voxels will be assigned values (and associated uncertainties) for lithological and grain-size parameters. Beyond the scope of the project, any relevant parameter (e.g. porosity, permeability, erodibility) can be added to the model. The attributed geological model provides a platform supporting integrated monitoring strategies (to detect ‘true’ change), as required by a number of European Directives (e.g. MSFD). It needs emphasis that geological modelling is a learning process. Several iterations of data verification, development of property models, and automated identification of appropriate layer boundaries will be necessary.
Through flexible multi-criteria evaluation, voxel-property information can be extracted at any depth; resource calculations and maps can be made, and input parameters can be generated for process models and/or decision support systems. A first targeted output is a series of sediment maps with confidence intervals. These are required for the evaluation of MSFD indicators on Seafloor Integrity: for Belgium and the Netherlands a main requirement is that ‘The areal extent and distribution of EUNIS level 3 Habitats (sandy mud to mud; muddy sand to sand and coarse sediments), as well as of the gravel beds, remain within the margin of uncertainty of the sediment distribution, with reference to the Initial Assessment’ (Belgische Staat 2012a; Ministerie van Infrastructuur et al. 2012). Van Lancker & Van Heteren (2013a), in a review on state-of-the-art sediment parameterization in habitat mapping, stipulated that uncertainty assessments necessitate the availability of flexible sediment parameter databases with appropriate metadata on sampling and analyses. Cooper (2012) provided an example of sediment assessments related to aggregate extraction. A second targeted output relates to the 3D visualization of the voxel model. Major technological developments have made it possible that users are no longer limited by the representation of geology as static 2D printed maps, but can benefit from 3D digital representations of the geology and of related resources. It allows easy interaction (also with policy makers), and has proven invaluable for outreach and educational purposes (Kessler et al. 2009).