Geothermal energy has been touted as a possible solution to the world’s dangerous dependence on fossil fuels, representing a renewable and non-polluting source of power. On the minus side, it does involve drilling thousands of meters into the Earth’s crust, leading to suggestions that it could unleash major earthquakes by destabilizing the subterranean matter. Yet a new paper in the Journal of Geophysical Research hopes to quell these fears by indicating that the practice is safe after all.
The use of geothermal energy depends on the extraction of fluids and gases from geothermal reservoirs deep underground, which are typically used to operate turbines on the surface before being re-injected back to their point of origin.
To maximize the efficiency of this technology, engineers are striving to drill down to a depth of 3,000 meters (9,840 feet), where it is thought that supercritical fluids can be found. These are substances at a pressure and temperature that is too high for distinct liquid or gas phases to exist, meaning they can dissolve matter like a liquid and diffuse through solids like a gas.
However, little is known about the stability of the Earth’s crust at such depths, and it has been speculated that drilling down to this amorphous layer could trigger dangerous seismic activity. To investigate, the study authors set up eight seismic recording stations around the Venelle 2 well at the Larderello geothermal field in northern Italy.
Daily readings were taken between June 2017 and January 2018, as drilling descended to a depth of around 2,750 meters (9,020 feet). During this time, an average of two seismic events were recorded each day, which were categorized as Type 1 and Type 2 events. According to the study authors, Type 1 events were not correlated in any way with drilling activities and were therefore declared natural occurrences.
Type 2 events, however, were found to be in sync with drilling activities, increasing to a peak of 14 events a day once the well approached a depth of 2,700 meters. While the study authors conclude that these readings were almost certainly caused by fluid flow processes resulting from drilling, they point out that none of the recordings suggested major or dangerous seismic activity.
“Drilling in search of supercritical fluids caused only minimal seismic disturbance,” explained study author Matteo Lupi in a statement.
Therefore, despite public concerns about the safety of geothermal drilling, the authors state in their write-up that “geothermal operations in critical conditions can be handled without causing moderate to large-magnitude earthquakes.”