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Gabriel Courrioux, BRGM (France)
Bernard Bourgine, BRGM (France)
Philippe Calcagno, BRGM (France)
Antonio Guillen, Intrepid Geophysics (Australia)
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A possible definition of 3D cartography/modelling can be sketched as:
(1) The ability to describe the geometry of geology at depth from scattered and heterogeneous data: the issue is to find the adequate interpolation methods and to find the adequate representation of geology;
(2) The ability to provide uncertainties concerning this geometry.This is generally done through geostatistics or simulation methods which lead to probability maps; (3) The ability to exploit this geometry for different purposes:
- visualisation - communication; - geological predictions; - resources evaluation; - process simulation.
The increasing demand for more and more accurate and complex modelling including even more data and constraints implies continuous methodological research. For this reason, BRGM developed tools adapted to model the geometry in different geological settings: (1) GDM MultiLayer, specially suited for data control and for layer cake models where traditional geostatistics is particularly efficient; and (2) 3D Geomodeller ( BRGM-Intrepid) for more full 3D geology based on an implicit modelling of surfaces.
In the latter, each horizon is built thanks to a 3D interpolation function (potential field cokriging) which simultaneously takes into account:
- data points on horizons locations (isopotential values);
- general orientations and polarities of structures (gradients);
- the existence of discontinuities (faults).
This method is actually very close to the "geological thinking". A geological model is made-up of a set of different horizons which are assembled with respect to their chronology and relations. A full tensor inversion gravity and magnetic modelling is integrant part of the software, which makes it an original environment to combine geological modelling and validation through geophysical inversion. This methodology has been successfully applied from basin contexts to complex orogenic domains, in polymetamorphic and magmatic terrains such as Alpine, Hercynian or Precambrian belts.
In this paper we first describe the principles of the modelling methods which are currently used. Then we illustrate how 3D geological modelling is incorporated in different geosciences applications such as geological mapping, tunnelling, geothermal resources, hydrogeology and seismic risk. Through these case studies we point out the main issues were development efforts have to be carried out.
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