Georesources: Exploring the subsurface for geothermal energy

Geothermal energy has the potential to meet a significant proportion of our future heating needs. But what exactly is geothermal energy and how does the subsurface function as a heat reservoir?

The diagram illustrates the principle of hydrothermal geothermal energy, which can be used for heating or power generation. Underneath a large city, water from deep underground is extracted via deep boreholes and brought to the surface. For heating purposes, thermal energy is extracted via a heat exchanger at this point. The cooled water is then pumped back into the formation. This thermal water cycle can be implemented using two boreholes (a doublet), or as a multi-doublet system, as shown in the diagram. The output achieved in this way is suitable for grid-connected heat supply to larger structures, such as neighbourhoods.

In order to explore the subsurface and determine the conditions for the use of geothermal energy, test drillings are carried out.

What is measured in the borehole? 

• Volume flow, temperature and chemical and physical parameters.
• Borehole integrity (i.e. the integrity of the deep drilling engineering structure).
• Changes in fluids
• Precipitation due to changes in solution equilibria.

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