Pilot area activities – #13 Geophysical survey and groundwater monitoring in Brussels, Belgium

Resource analysis and investigation of interactions between open loop systems

The Brussels Capital Region (BCR), with an area about 161 km², has a Cenozoic soft cover where sandy formations and relatively more impermeable clayey layers alternate. This cover rests in the Eastern part of Brussels on the aquifer chalks of Cretaceous and then on the faulted and folded Paleozoic basement of the Brabant Massif composed of coherent rocks. The basement is relatively close to the surface in the SW of the pilot area (in the Senne Valley), whereas it can deepen to 200 m in the North. Only few direct observations of it are available; the top, the lithology of the Brabant Massif demonstrated a lot of uncertainties, but a very promising geothermal potential is suspected.

In the scope of MUSE, TNO and GSB combined a dense surface based high resolution seismic survey with a Fiber Optic (FO) – DAS survey (Figure 1) on a potential ATES site at Anderlecht (https://geoera.eu/blog/geophysical-survey-in-anderlecht/). The objective was to test and demonstrate the possibility to acquire a high-resolution image of the shallow subsurface to de-risk ATES systems in an urban environment in a cost-effective, low environmental impact way. Despite the difficult urban and operational conditions, the preliminary results of the DAS VSP survey showed a partial success. High (urban) noise levels, small offsets, limited source strength proved challenges to good signal.

Most of the geothermal installations in BCR are closed loops systems (85%), however a higher interest for open systems in the last two years was observed. From the five open systems currently operating in the area, three are in an 0.5 km² area in Tour & Taxis site (Figure 2). The importance to characterize the interaction between installations appears essential for a sustainable development of the SGE market at Brussels. A hydrogeological study was launched in January 2020 in collaboration with the Liege University (ULg) and Artesia to understand the potential influences between the first open system in the basement (Gare Maritime) and the two others in shallower Cenozoic aquifers (Figure 2).

Finally, experimental well temperature monitoring is currently tested in the fractured Cambrian bedrock with a high precision Niphargus device (see implementation in the Anderlecht borehole in April 2019, Figure 3).

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Figure 1: Well schematic of the Anderlecht ATES well, equipped with a multimode FO cable. The total cased depth of the well is 120 meters and the cemented section reaches down to 67 meters. The FO cable was run to and from the bottom of the well in duplex.
Figure 2: Location of three ATES at  the Tour & Taxis area where a MUSE study was launched in collaboration with ULG and Artesia to understand the potential interaction between them.
Figure 3: Implementation of the temperature measurement device Niphargus in the Anderlecht exploration well for high-precision temperature monitoring at 100m depth.


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