ALL ABOUT TECH – Test drilling and initial results

Be.SHARE is based on the use of decarbonised local energy sources: geothermal energy (recovery of energy from the earth's subsoil under our parks and streets) and riothermia (recovery of energy from the waste water in our sewers). As geothermal energy plays a major role in supplying the network with decarbonised heat, a feasibility study was scheduled to confirm the technology's potential and to enable the dimensions of the geothermal probe field to be accurately calculated.

Objectives:

• Check the structure of the subsoil and the thickness of the different geological layers, as well as the drilling time in each layer, in order to estimate the time required for the drilling work.
• Determine the thermal conductivity of the subsoil, i.e. its capacity to supply heat or cold depending on the geological layer. The Enhanced Thermal Response Test (eTRT) uses a fibre optic cable to obtain very accurate measurements of variations in ground temperature. Then we can calculate the energy supplied by each layer independently of the others, identify the most interesting layers and subsequently determine the number and depth of probes to be installed.

Main results:

• The borehole reached a depth of 150 metres and was equipped with an eTRT probe. The team drilled through six layers of soil before reaching the Paleozoic basement (present from 96 m).
• The eTRT measured an average soil temperature of 11.1°C and a thermal conductivity of 2.4 W/mK. The Kortrijk clays (3rd layer) have a thermal conductivity that is +30% higher than the values currently recorded in the BrugeoTool application, while that of the Paleozoic basement is 13% higher, confirming the potential of this final layer (3.3 instead of 2.95 W/mK). The real optimisation variable is the Paleozoic basement.

These results feed into the sizing study for the probe field, providing essential data in the search for a balance between available space, the cost of drilling and the potential power per probe.

These investigations provide an initial key lesson for the development of closed geothermal energy in Brussels. In view of the specific subsoil layers found, increasing the depth of the boreholes enables much more power to be extracted per square metre of available surface area. A borehole at a depth of 200 m delivers 30% more power than two boreholes at 100 m, while using up half as much surface area. This observation can be applied across the whole region, and is a promising lead for optimising the use of public property and maximising the energy recovered to foster decarbonisation in Brussels.