3D CARTOGRAPHY AND GEOSCIENCES APPLICATIONS. THE FRENCH GEOLOGICAL SURVEY APPROACH

Geological institutes are faced to an increasing need in building accurate and complex 3D models, including even more data and constraints. This implies continuous methodological research.

In order to provide to the whole 3D models demands, BRGM is developing tools and methodologies fitted to specific needs and is also working with geomodelling technologies already used in other geoscience fields (mining and petroleum).

The geological modeller softwares, developed by BRGM, are well adapted to model the geometry in different geological settings:

- GDM MultiLayer (© BRGM) suited for data control and layer cake models;

- 3D Geomodeller (© BRGM Intrepid-Geophysics) for 3D geology based on an implicit modelling of surfaces.

This method is actually very close to the “geological thinking”. A geological model is made 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 and combines geological modelling and validation through geophysical inversion. This methodology has been successfully applied from basin contexts to complex orogenic domains.

Lately, there is an important demand for 3D modelling of the structure of underground reservoir to physical and chemical simulations.

In order to provide “ready-to-use” 3D solid models populated with facies or petrophysical properties, BRGM is using commercial geomodelling softwares, with appropriate mesh generation and geostatisticals tools. This methodology is generally used in the context of sedimentary basins.

Furthermore, a research project is currently ongoing to improve modelling methods with new capabilities for enabling tetrahedral and hexadral mesh generation exploitable by simulation softwares.

3D geomodelling process, incorporated in different geosciences applications such as geological mapping, hydrogeology, geotechnics, mineral resources, geothermal resources, CO2 storage and seismic risk, can be then defined as:

- The ability to describe the geometry of geology at depth from scattered and heterogeneous data;

- The ability to provide uncertainties concerning this geometry;

- The ability to exploit this geometry for different purposes: visualisation, geological predictions, resources evaluation and process simulation.