2023-07-20 13:42:27
As we go deeper into the Earth, the temperature increases. It is calculated that this increase, known as the geothermal gradient, varies on average between 25ºC and 30ºC for each kilometer of depth. As is logical, the subsoil temperature can vary according to the geographical location and the geological characteristics of each area. Volcanic and tectonically active regions, such as Iceland or certain parts of the Pacific Rings of Fire, tend to have higher groundwater temperatures. In Iceland, for example, geothermal installations only need to go down 1,000 or 2,000 meters to obtain water at a temperature of 150ºC or more, a temperature that allows energy to be obtained for dual use, generating electricity and heating.
By harnessing the heat stored deep within the Earth, this form of energy offers undeniable benefits, but also poses significant challenges.
One of the main advantages of geothermal energy is its renewable nature and, most importantly, it is inexhaustible. Unlike solar or wind energy sources, which are dependent on weather conditions, geothermal energy is constant, making it a stable option for electricity and heating generation. Now, how can we use that energy for our benefit? Victor Vilarrasa, our guest on Talking to Scientists, explains that the subsoil, depending on the composition of its rocks, tends to store large amounts of water in pores and cracks.
One of the most common technologies is the so-called EGS (acronym in English for Enhanced Geothermal System). The method consists of drilling one or several wells to the working depth, which usually reaches 4 or 5 kilometers deep. Cold water is injected from the surface into a well under high pressure. The high pressure of the injected water makes it possible to open the natural cracks in the rock, allowing the water to pass to another well where it is collected at a high temperature and brought to the surface. At temperatures of 150ºC or higher, the water is liquid in the depths due to the high pressures to which it is subjected, but it becomes steam at the atmospheric pressure of the surface, a steam that is used to move the turbines that generate electricity. When the temperature drops, the steam liquefies and becomes a source of hot water that can be incorporated into the heating circuits of homes. In the final process, the water is reinjected into the first well to restart the cycle.
However, geothermal energy also presents challenges. An example of the challenges is the case of the Basel Deep Geothermal Project, in Switzerland, in the years 2006 and 2007. The objective of the project was to take advantage of the heat stored in the subsoil to generate electricity and heating. However, during the phase of high-pressure water injection into the geothermal well, a series of earthquakes occurred. As Víctor Vilarrasa recounted during the interview, the activity was initially very low, but when a magnitude 2 earthquake was detected, those responsible for the project decided to stop the injection of high-pressure water. It was then that an earthquake of magnitude 3.4 on the Richter scale occurred. Subsequently, more than 10,000 additional earthquakes were recorded in the following months, with magnitudes ranging from 2.0 to 3.4. These seismic events were noticeable to the local population and caused minor damage to some buildings, which is why the project was cancelled.
Now, a team of scientists, including Víctor Vilarraasa, has developed a numerical tool that makes it possible to reproduce the reactivation of the faults that occurred in the Basel EGS. The study paves the way for the development of methodologies that allow geothermal energy to be used safely and cleanly to produce electricity continuously 24 hours a day, seven days a week and with zero CO2 emissions. The work, published in the journal Communications Earth & Environment, has been carried out in collaboration with the Institute for Environmental Diagnosis and Water Studies (IDAEA-CSIC) and the University of Colorado.
We invite you to listen to Víctor Vilarrasa, a researcher at the Mediterranean Institute for Advanced Studies, a joint Institute of the Higher Council for Scientific Research and the University of the Balearic Islands.
REFERENCES:
Boyet, A., De Simone, S., Ge, S. and Vilarrasa, V., 2023. Poroelastic stress relaxation, slip stress transfer and friction weakening controlled post-injection seismicity at the Basel Enhanced Geothermal System. Communications Earth & Environment. DOI: 10.1038/s43247-023-00764-y
#Cienciaes.com #Advantages #challenges #geothermal #energy #spoke #Víctor #Vilarrasa