Turning ground heat into energy: geothermal drilling

As decarbonising buildings becomes a priority, geothermal drilling offers a sustainable way to tap the natural heat of the ground. This precise, well-controlled technique efficiently supplies heating and cooling systems while reducing dependence on fossil fuels.

Geothermal drilling means boring into the ground to capture the Earth's natural heat. It allows geothermal probes to be installed, which then recover that heat to supply heating or cooling systems.

Drilling advances using a string of steel rods about three metres long each, connected one after another as the hole deepens. Thanks to the chuck, our drillers can quickly screw and unscrew the rods while drilling or pulling out, ensuring optimal productivity on site.

Once the target depth is reached, the hole is fully flushed to remove sediment and particles that could affect the quality of the borehole. The drill string is then withdrawn so the geothermal probe can be lowered. It is pulled to the bottom of the hole by a weight of about 42 kg.

The drill bit is fitted with carbide inserts that scrape the ground. Water is injected inside the rods and comes out through small openings. This flow cools the bit and also carries the cuttings to the surface as mud. The mud is then sent to a settling container where the water is separated from the solids so it can be reused in the circuit.

Drilling water therefore plays a double role: it controls the temperature of the bit, which can get very hot in rocky ground, and it carries sediment to the surface. In the Brussels and Walloon Brabant regions, for example, clay soils produce particularly fine mud, typical of those formations.

Once the casing has been partly removed, we inject a geothermal grout. It has an excellent thermal conductivity, which improves heat exchange between the ground and the probe. It also secures the borehole by sealing off the different geological layers and groundwater aquifers.

Geothermal drilling is precision work that combines advanced engineering, in-depth knowledge of the subsurface and rigorous management of fluids. It is a key step in deploying sustainable heating and cooling based on renewable energy from the ground.

Watch the full drilling video here: https://www.youtube.com/watch?v=9lDoSbhm3uo