Unlocking the Earth's heat: Safe and sustainable geothermal solutions for climate change

Geothermal resources exist everywhere at sufficient depth (e.g. 4km+ in Switzerland). However, large fluid fluxes must be brought to the surface to produce electricity (and use the remaining heat). This requires the presence of sufficiently permeable rocks at depth. This last requirement is at odd with the fact that deeper (often crystalline) rocks are very tight.

For decades, the geothermal community has aimed at “stimulating” the pre-existing fractures of these deep rock masses via hydraulic stimulation performed at pressures sufficiently large to shear them but lower than the pressure required to propagate new fractures. This has resulted in mixed results: many projects ended inducing large earthquakes. 

In the past few years, hydraulic fracturing technologies (adapted from the oil and gas industry) have achieved exceptional results in several projects in the US. Here, a set of new fractures is created (in a robust and reproducible way). I will discuss why this is the only technique that can systematically unlock geothermal resources and highlight a number of remaining issues to make it economically viable & sustainably acceptable.

Enhanced Geothermal Systems (EGS), unlike conventional hydrothermal geothermal systems, exploit geothermal resources through hydraulic stimulation that improves the permeability of the reservoir to create a heat exchanger. Induced seismicity is in EGS projects, not an undesired by-product but a necessary tool.

The art of successful EGS stimulation lies in creating an economically viable heat exchanger in the deep underground while avoiding larger and potentially damaging earthquakes. Especially in urbanised areas, deep geothermal resources can only be exploited using EGS technology if induced seismicity is adequately managed and controlled.

This talk will review the progress made in induced seismicity monitoring, forecasting, and mitigation strategies, showcasing the results of the EC GEOTHERMICA project DEEP.