One of BRGM's major ambitions is to understand what is happening beneath our feet, to explain it and share it with everyone. 3D modelling of the subsurface and its properties is a key part of the French Geological Survey's scientific strategy.
Films to illustrate the applications of 3D subsurface modelling
Produced with the help of l’Esprit Sorcier, this series of videos showcases the expertise of BRGM and its researchers, who harness a range of software to respond to concrete problems.
The subjects covered include understanding the subsurface using digital tools, risk management for sustainable regional development, groundwater resources, the energy transition and mineral resources, among others. Each film shows how BRGM transforms complex subsurface data into visual and interactive representations that are useful for research, public policy-making and industrial innovation.
Revealing the subsurface in 3D
Transcription
REVEALING THE SUBSURFACE IN 3D
MARC SALTEL
HYDROGEOLOGIST AT BRGM
In the 1990s, BRGM developed the Nord-Aquitaine model, MONA, which represents groundwater flows in the Nord-Aquitaine basin.
The objective is to better manage groundwater as a resource, and advise the department and the region for the exploitation of this resource.
GROUNDWATER:
LOCATING RESERVES IN AQUITAINE
VERTICAL SCALE X22.5
Aquitaine has the luxury of having groundwater of very high quality, a precious resource. It must be said that its subsurface contains many aquifers, that is, permeable rocks where water circulates slowly, sometimes taking several thousand years to reach certain geological strata. Today, nearly half of the water needs of the Gironde are withdrawn from it, including almost all drinking water needs.
MARC SALTEL
Historically, Bordeaux recovered its water from springs that existed on the outskirts of the city, and the drilling technology arrived. This made it possible to fetch water from deeper down.
The multiplication of boreholes has led to an overexploitation of this resource. Over the years, over the decades, we have seen levels fall, and this drop has alerted scientists. And that's what led to the creation of the first hydrodynamic models in the South-West.
These first models were born in the 60s. With the advent of digital technology, they are becoming more complex to represent as faithfully as possible groundwater flows. Today's MONA model is the result of 30 years of research and data compilation.
MARC SALTEL
The MONA is a tool for understanding. It allowed us to understand how deep aquifers functioned, aquifers which are unknown and are just approached by different boreholes.
So having a 3D representation like that allows you to better understand how it works, where they get their water from, and the exchanges that take place with the higher and lower horizons, etc. So it's really a tool for understanding.
It is also a prospective tool that will allow us to project ourselves into the future, to try to see a little bit the possible trajectories depending on how we use them, with the different withdrawals, the different pumping, and also according to the climate.
To do all this, you have to compile a lot of information. First of all, geological data that made it possible to know the rocks of the subsurface and their structure. In Aquitaine, there is a millefeuille of aquifers and more impermeable layers, known as the épontes. Then we add the data provided by the drilling. They allow us to know the water pressure at different locations and therefore to deduce the direction of water circulation inside the water table. We can also better understand the permeability, that is, how water flows here and there. With all this information, the model can simulate how water moves within the layers.
If we add to that the quantities of water withdrawn, forecasts of future withdrawals, but also climatic conditions, then we better understand how aquifers are recharged. We can make predictions and test scenarios to sustainably exploit groundwater.
MARC SALTEL
It's really a notion of balance that we try to recover with the recharge and withdrawals. Is the way we exploit sustainable or not? Are we still going down? Or do we finally see that on the horizon—20 years, 30 years, 50 years—we will still achieve a balance that remains acceptable?
We are also building more local models to answer more specific questions. So that's what we did south of Bordeaux to represent a set of boreholes, specifically 18 boreholes, for which we have done optimisation—that is to say, we have tried to determine, in a spatialised 3D model, the best way to operate each of these boreholes.
In addition to working at different scales, scientists can adapt their methods to other regions which also exploit their groundwater. There are already models outside Aquitaine, in France of course, but also internationally.
REVEALING THE SUBSURFACE IN 3D
A SERIES OF VIDEOS PROVIDED BY BRGM
GEOSCIENCES FOR A SUSTAINABLE EARTH
