Drilling deep for geothermal energy: Little seismic disturbance recorded

According to a new study, geothermal drilling in deep layers is a technological challenge but it is not related to strong seismic events.

Geothermal energy is the thermal energy produced and stored in the sub-surface of the Earth. It is a renewable energy source that could assist humanity in tackling the climate change phenomenon. Geothermal energy is characterized by many advantages; it does not depend on weather conditions, it has a high energy performance and it can be utilized for heating, cooling and for production of electricity. 

One major drawback of geothermal energy is that the resources associated with it, are located in tectonically active regions. Therefore, a main question arises on whether drilling of a well could influence the tectonic setting resulting in strong earthquakes.

A study, published in JGR: Solid Earth, focuses on seismic activity associated with geothermal drilling in search of supercritical fluids, substances subjected to a pressure and a temperature higher than their critical point. Supercritical fluids are in a fuzzy physical phase as they cannot be considered fluids or gases and have a large power content.

Those substances are found in great depths where drilling is challenging. According to Matteo Lupi, co-author of the study and Professor in the Department of Earth Sciences in the University of Geneva (UNIGE) Faculty of Science, drilling up to 1500 meters is relatively safe, but "...we have to drill deeper (in order to generate more power), which is both a technological and a scientific challenge. Below these depths, the stability of the drilling site is more and more difficult and poor decisions could trigger an earthquake.”

Researchers studied a geothermal field in Italy where engineers have been trying for years to drill a 3,000-meter well but their efforts have been unsuccessful. The scientific team attempted to drill a bore to reach the desired depth and installed 8 seismic stations around it capable of measuring the seismic shocks linked to the drilling. The team did not manage to reach the 3000-meter threshold due to high temperatures presented at a depth of 2750 meters. 

Nevertheless, they collected significant data regarding earthquake incidents induced by drilling. “The good news is that for the very first time, drilling in search of supercritical fluids caused only minimal seismic disturbance, which was a feat in such conditions and a strong sign of the technological progress that has been made”, Prof. Lupi mentioned.

The authors of the study are optimistic about developing the necessary technology to drill in deeper layers in search of supercritical fluids in the future.

Reaching these depths would also reveal significant geologic data that still remain unknown. “What’s more, we still don’t know exactly what this bed is made up of: is it a transition between molten and solid rocks? Or does it consist of cooled granites releasing fluids trapped at this level?,” Riccardo Minetto, lead author of the study and a researcher in UNIGE’s Department of Earth Sciences, stated.