“GeoTief Wien” locates hot water 3,000 meters below the city

Geothermal energy has been one of the hopes of the energy transition not only since the Ukraine war and the debate about a possible Russian gas boycott. In Vienna, too, it was assumed that there were large energy reserves in the form of hot water under the city area. In 2012, however, drilling became an expensive failure. Before a new attempt, an extensive exploratory project was started in 2016, which has recently been given the green light. The located reservoir is at a depth of 3,000 meters.

Research project created first accurate 3D model

Research project created first accurate 3D model

Finding such energy reserves is “as much a technical as it is a scientific challenge,” says geophysicist Maria-Theresia Apoloner. “You now have more options than in 2011. The research team took measurements at over 16,000 measuring points and collected several terabytes of data. This enabled us to create a detailed 3D model of Vienna’s underground for the first time.” They found what they were looking for in a porous layer of rock called the “Aderklaa conglomerate” below an area that stretches from Donaustadt to Simmering. “Our target horizon was actually four kilometers deep.” It will now be necessary to drill far less deeply to get to the layers containing hot water, which, according to an initial estimate by Wien Energie, could supply up to 125,000 households with heat by 2030.

Investments are substantial

In contrast to “near-surface geothermal energy”, which is used for heat pumps, for example, “deep geothermal energy” is the extraction of thermal energy from a depth of 300 meters or more. “Deep geothermal energy makes sense where many people live and there is a district heating network,” explains the seismologist who works at the Central Institute for Meteorology and Geodynamics (ZAMG), who started the “GeoTief Vienna” energy research project on Tuesday (May 24, 6 p.m , also as a live stream) at the start of the General Assembly of the European Geoscientific Union (EGU) in a public lecture in the ballroom of the Austrian Academy of Sciences. In addition to ZAMG, the AIT, the Geological Federal Institute, Montanuni Leoben, OMV and RAG Austria AG are also involved in the project, which is managed by Wien Energie. The investments required for development are not inconsiderable. The pressure on the scientists as well as on the technicians, who should land their borehole exactly in the target area, is therefore great.

However, in addition to the geological risk, there can also be a seismological risk in geothermal projects: if you drill into a fault zone, there is a risk of tremors being triggered when the water is injected. Science then speaks of “induced seismicity”. In the case of hydrothermal use, it was mostly imperceptible micro-tremors, Apoloner assured in the APA interview, that there are of course also extreme examples of petrothermal use (which does not use naturally occurring water vapor or thermal water, but the heat stored in the rock), for example in 2017 in Pohang in South Korea with a magnitude of 5.5 and over 2,000 damaged buildings or in 2006 in Basel with a magnitude of 3.4.

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faults under close observation

The last case in particular has been “excellently researched” and provides instructions for future geothermal projects. Above all, it is important to keep the faults in question under precise seismological observation in advance, in order to know later whether minor earth movements are within the usual range or whether they were actually caused by geothermal use. Furthermore, you have to try not to hit a fault directly with the borehole and to control the water pressure.

Overall, however, deep geothermal energy is safe and will also become an important building block for the future energy mix in Austria, says the scientist. The Geothermie Österreich association estimates that this could increase the share of renewable energy in district heating generation from 46 percent (in 2016) to up to 86 percent in 2050. According to the association, only five percent of the potential of deep geothermal energy in Austria is being used, and the possible share of this energy source in the necessary CO2 savings is enormous.

Service: Link to the lecture at the OeAW:; Project homepages:;

(APA/red, photo: APA/Wien Energie/APA order graphic)