Large deposits of hot water under Vienna – wien.ORF.at

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The heat supply is an essential key to climate protection in the city, as shown by a study commissioned by Wien Energie. Wien Energie is therefore researching the utilization of renewable heat sources. The focus is on deep geothermal energy.

Decarbonise heat supply by 2040

Since 2016, the energy service provider has been researching the geological subsurface in the greater Vienna area together with partners from science and industry in the GeoTief Vienna project. Now concrete results are available in the form of a comprehensive geological 3D model: The so-called Aderklaa conglomerate, a promising hot water deposit for deep geothermal energy, is located at a depth of around 3,000 meters.

Wien Energie / FOTObyHOFER

Geothermal energy is crucial for the heating transition

District heating is crucial for the heating transition, i.e. the switch to renewable heat supply. In 2040, around 56 percent of the city’s heating requirements are to be covered by district heating, the rest mainly by heat pumps. The district heating should then be completely climate-neutral.

In addition to waste incineration and waste heat recovery, geothermal energy also plays an important role. “There is a huge amount of heat slumbering under Vienna. We want to use this for the heat supply in the future. With the 3D model, we now have a detailed picture of the Vienna underground and can start planning specific projects. By 2030, we want to be able to supply up to 125,000 households with heat from the depths, ”says Michael Strebl, Chairman of the Wien Energie management board.

The potential area extends above ground from Donaustadt to Simmering. In these areas, Wien Energie sees opportunities to use the hot water three kilometers below ground for renewable district heating. The research estimates a potential of up to 120 megawatts of thermal output.

Geotief is entering the decisive phase

Wien Energie / FOTObyHOFER / Christian Hofer

The GeoTief Vienna research team is working on an accurate mapping of the deep underground of Vienna

16,000 measuring points for illustration

Since 2016, the GeoTief Vienna research team has been working on the most accurate mapping of Vienna’s deep underground to date. In a first step, inventory data from the hydrocarbon industry was analyzed and evaluated. Then 3D seismic measurements were carried out. For this purpose, 16,000 wireless sensors were laid out in an area of ​​around 175 square kilometers in 2017, which recorded seismic reflections from the underground.

For this purpose, special vehicles were used to send vibrations – similar to ultrasound – into the ground. 50 terabytes of data were then analyzed and merged with the existing data.

Deposits formed 20 million years ago

In the course of the analysis and interpretation of the data by the research team, the Aderklaa conglomerate came into focus. It can be defined and classified particularly well using the data collected. This rock layer is geologically the Miocene filling of the Vienna basin.

The deposits formed around 20 million years ago. Based on the models, the location / expansion, geometry, depth, thickness and possible geological fault systems in the Aderklaa conglomerate in the study area could be determined.

Up to 100 degrees water temperature

The geometry and previously known hydraulic properties of the thermal water reservoir are promising. At a depth of around 3,000 meters, the water temperature in the Aderklaa conglomerate should be up to 100 degrees Celsius and could therefore be suitable for use for district heating in Vienna. However, there is always only one exploratory drilling that can be absolutely certain. Before the decision to implement a geothermal system is made, further research work will be carried out in parallel to the first planning steps until spring 2022.

“GeoTief Vienna is the most comprehensive geology research project that has ever taken place in Austria. Now that we have identified a potential area, we will take a closer look at its properties by examining an old borehole. When these results are available, we have done all the preparatory work that is possible to minimize geological risk, ”explains Wien Energie Managing Director Karl Gruber.

Research test in Essling

With a practical test in Essling, the GeoTief Vienna research project is currently in its final phase. From October to the end of 2021, investigations have been carried out at the former exploratory drilling site of Wien Energie, which are intended to provide further information on the rock properties in the Aderklaa conglomerate.

The focus is on the permeability of the rock and the chemical composition of the thermal water. A mobile crane and three large water basins have been erected for the test. In the course of the test, water is pumped and fed into the basin. After the work has been completed, the research facility will be completely dismantled and the borehole will be closed again.

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