A new detailed Bouguer anomaly for the exploration of the deep geothermal reservoir in SW-Belgium

Located next to the Variscan front, the center of the Hainaut (SW-Belgium) is known for its deep geothermal potential. Indeed, the geothermal reservoir of the Carboniferous limestones, located in the Brabant Parautochton, currently supplies water at a temperature of between 65°C and 72°C from three deep wells in the Mons area. Although the use of geothermal energy is one of the main solutions to decrease or abandoning fossil energies, it is still very limited in this area. This situation is partly due to major uncertainties in the structure and the geometry of the reservoir which are holding back public and private investments and delay geothermal projects.

 

For these reasons, we have conducted new geophysical surveys in the center of the Hainaut region for the last fifteen years. Among these, two gravimetric surveys in relation to the More-Geo project (ERDF funding) were carried out in 2019 and in 2022. As the production levels in the geothermal reservoir of the Carboniferous limestones are karstified, replacing massive anhydrites, the study of gravimetry disturbance is appropriate. The main goal is to provide information about deep geological structures and precisely on the geothermal reservoir by refining the localisation and the extent of karstified and anhydrite levels.

 

The result of the 2019 and 2022 surveys is a new dataset of 13,000 measurements spread over 3,400 stations located in an area of 820 km². The classical Bouguer anomaly has been obtained after a full processing of the instrumental gravimetric measurements, using exclusively open-source Python libraries.

 

Special attention is given to the terrain correction which in our case is based on the modelisation of the topographic surface by rectangular prisms and on the evaluation of the gravitational influence of these prisms. The method used combines a “large-scale” terrain correction modelling the topography up to 167 km in extent with prisms of 25 m resolution and a “local” terrain correction correcting the inaccuracies of the first grid with prisms of 1 m resolution over a more limited area.

 

Results are the mapping of the Bouguer anomaly, the upward continuation, upward derivative and horizontal derivative obtained with the interpolation method of equivalent sources. The two last maps are at the base of structural interpretations of the Paleozoic basement. These results and specifically the processing will be a key to refine the localisation and the extent of deep geothermal targets within the Paleozoic basement. This will require specific processing taking into account the thick and highly heterogeneous Meso-Cenozoic cover of the Mons Basin.