In the pursuit of a carbon-free economy, the focus on geothermal energy extraction is intensifying.
Energy producers worldwide are eagerly seeking safer methods to tap into the potential of deep underground geothermal energy.
At the forefront of this effort is EPFL associate professor Brice Lecampion, leading the Laboratory of Geo-energy (GEL) and holding the Gaznat Chair on Geo-Energy at the School of Architecture, Civil and Environmental Engineering (ENAC).
Lecampion’s research group is actively contributing to this endeavor, developing models to understand the behavior of the subsurface, particularly focusing on how subsurface fluid injections interact with fractures in rocks.
Understanding the Impact of Fluid Injections on Geothermal Operations
The significance of their work lies in the role of underground water injection in the extraction of renewable geothermal energy.
Recently published in the Proceedings of the Royal Society A, the scientists’ latest findings pave the way for a better comprehension of the underlying physical mechanisms that trigger seismicity during geothermal operations.
Balancing Prospects and Controversy
Geothermal wells, which lie deep underground (4–6 km below the surface), are not without controversy.
Switzerland and other regions have witnessed opposition to geothermal power plant plans due to concerns over potential seismic events and subsurface pollution.
One such case is the resistance faced in Haute-Sorne, Jura Canton.
Delicate Fractures and Hydraulic Stimulation
Geothermal wells closer to the surface remain in permeable rock layers, allowing water to circulate freely.
However, as the wells go deeper, they encounter impermeable rock formations, necessitating the creation of fractures where water can flow.
Engineers must either artificially induce these fractures or stimulate existing ones to increase permeability, achieved through hydraulic stimulation.
While this process enhances rock permeability, it also carries the risk of triggering earthquakes, as exemplified by the Basel pilot project in 2006 when fluid-injection operations led to a magnitude 3 earthquake, ultimately resulting in the project’s abandonment.
The Lingering Risk of Induced Earthquakes
The concern lies in the aftermath of fluid injection – the risk of induced earthquakes persists even after the injection has ceased.
Alexis Sáez, a co-author of the study and a Ph.D. student at GEL, explains that their research focuses on earthquakes occurring between a few days and a few months after the end of fluid injection.
They have uncovered a new physical mechanism that can lead to these delayed earthquakes.
The Development of a 3D Model
To address these risks, Lecampion and Sáez have developed a sophisticated 3D computer model and conducted comprehensive technical analyses of how fluid injection and fractures interact.
They meticulously described the ongoing deformation of fractures post-injection, shedding light on how this process may promote the triggering of earthquakes.
Engineers Gain Critical Insights
Sáez emphasizes that their model offers valuable guidance and calculation methods for engineers.
Integrating these strategies can mitigate the seismic risks associated with geothermal operations, enabling the unlocking of geothermal energy’s vast potential to facilitate the decarbonization of our energy systems.
A Step Towards a Safer Geothermal Future
As of now, predicting the occurrence of injection-induced earthquakes remains challenging, with engineers primarily relying on statistical approaches, similar to those used for natural earthquakes.
Nevertheless, this research marks a significant advancement in implementing physics-based approaches to manage the inherent seismic risk, making way for a safer and more sustainable geothermal energy future.
With continued efforts from researchers like Brice Lecampion and Alexis Sáez, the world inches closer to harnessing the power of geothermal energy without compromising on safety and environmental concerns.
FAQs
Geothermal energy is a renewable energy source derived from the Earth’s natural heat. It originates from the radioactive decay of minerals and the heat remaining from the planet’s formation. This energy can be harnessed and converted into electricity or used directly for heating and cooling purposes. Geothermal energy is renewable because the Earth’s heat is essentially inexhaustible over human timescales.
Geothermal energy is typically extracted by drilling wells into the Earth’s crust, where hot water or steam reservoirs exist. In some cases, the reservoirs are not permeable enough to allow easy fluid flow. In such instances, engineers employ fluid injection techniques to either create artificial fractures or stimulate existing ones. This process, known as hydraulic stimulation, enhances the permeability of the rocks, facilitating the extraction of geothermal energy.
Induced earthquakes are seismic events that are triggered by human activities, such as fluid injections in geothermal operations. When high-pressure fluids are injected into the Earth’s crust, they can increase pore pressure and stress on existing geological faults. This heightened stress can eventually cause the faults to slip, resulting in an earthquake.
While natural earthquakes are caused by tectonic forces and geological processes, induced earthquakes are directly related to human activities. Natural earthquakes occur due to the movement of tectonic plates, while induced earthquakes are the result of activities like hydraulic fracturing, fluid injection, or reservoir-induced seismicity.
Yes, induced earthquakes are a significant concern for geothermal energy projects, especially when fluid injections are involved. The injection of fluids can lead to increased seismicity, which poses risks to nearby communities and infrastructure. Mitigating these risks and ensuring safe geothermal operations is a crucial aspect of developing geothermal energy sustainably.
Researchers employ various methods, including computer modeling and technical analyses, to study the behavior of subsurface fluid injections and their interaction with fractures in rocks. By simulating and observing these processes, they gain insights into the mechanisms that trigger induced earthquakes and develop strategies to mitigate their impact.
To reduce the risk of induced earthquakes, engineers can carefully manage the rate and volume of fluid injections. Additionally, continuous monitoring of seismic activity during and after injection operations can help identify potential risks. Implementing physics-based approaches, like the 3D computer model developed by Brice Lecampion and Alexis Sáez, can guide engineers in creating safer geothermal projects.
Yes, geothermal energy remains a viable option for a carbon-free economy. While there are risks associated with induced earthquakes, ongoing research and the development of advanced models are enhancing our understanding of these risks. By employing proper risk management and mitigation strategies, the potential of geothermal energy to contribute to decarbonization outweighs the risks.
More information: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (2023). DOI: 10.1098/rspa.2022.0810
