Exhibitors & Products
Events

Storing heat underground can make an important contribution to the heating transition. One option for this is to store heat in aquifers, i.e. permeable rock layers that carry groundwater (Aquifer Thermal Energy Storage or ATES for short). At the Berlin-Adlershof site, the Berliner Blockheizkraftwerks-Träger- und Betreibergesellschaft (BTB) is currently planning the largest heat storage facility in the German capital as part of the “Reallabor GeoSpeicher Berlin” project – in cooperation with the GFZ German Research Centre for Geosciences and the TU Dresden.

Around 85 percent of the heat fed in is to be recovered

The aquifers targeted for storage are located at a depth of around 400 meters, where temperatures are around 23 degrees Celsius. If the research drilling, led by Dipl.-Ing. Stefan Kranz and Dr. Katrin Kieling from Section 4.3 “Geoenergy” of the GFZ German Research Centre for Geosciences, and the results obtained turn out to be promising, the plan is to feed 90-degree water into the system during the summer months. This water will come from the excess heat of a wood-fired power plant that uses waste wood for energy generation. In winter, the hot water would then be pumped back up and fed into the existing district heating network. Models show that around 85 percent of the heat fed in can be recovered.

Potential savings: around 10,000 tons of CO2 per year

The planned aquifer storage facility is intended to contribute to the decarbonization of district heating in southeast Berlin, because it could replace a quarter of the heat that currently still comes from the Berlin-Schöneweide hard-coal-fired heating plant in winter with renewable energy. This would save around 10,000 tons of CO2 per year.

So they started drilling

The actual drilling work took place from July 29 to August 2, 2024 as part of the EU-funded PUSH-IT project. Using a so-called directional drilling method, a sidetrack was drilled from an existing well, i.e., a branch that leads away from the original well at a slight incline. For this purpose, employees of the contracted drilling company Anger's Söhne Bohr- und Brunnenbaugesellschaft mbH worked together with GFZ researchers in 24-hour shifts. In order to obtain continuous information on the grain size distribution in the rock and the chemical and mineralogical composition from the drilling section between 211 and 410 meters, a sample of the drill cuttings was taken and examined for each meter drilled. In some cases, the samples could be characterized directly on site by the geoscientist M.Sc. Lioba Virchow, who is doing her doctorate at the GFZ, using a mobile X-ray fluorescence analysis.

Analyses of the deep rock

After the successful completion of the drilling work, various geophysical borehole measurements were carried out to further characterize the reservoir rock. Subsequently, the well was completed: it was cased, with the casing in the area of the potential storage layer – between 371 and 389 meters depth – designed as a filter to the rock. In addition, fiber optic cables were laid along the entire length of the casing and the filter area. The GFZ spin-off FOMON GmbH and GFZ Section 2.2 “Geophysical Imaging of the Subsurface” were significantly involved in this. The fiber optic cables enable continuous monitoring of the temperature along the borehole at half-meter intervals, as well as the measurement of acoustic signals and strain measurements, which can provide information about mechanical changes in the casing and cementation. This work was successfully completed in September 2024. In the current phase, tests are being carried out, among other things, to determine how water can be pumped from the storage layer, and later also how it can be fed in. To do this, the drilling mud produced during drilling was first removed by pumping clear water, and the first formation water was pumped out of the storage layer and sampled. The gradual increase in the pumping rate and the subsequent rest period provide information about the productivity and hydraulic behavior of the well.

Interim conclusion

Dr. Guido Blöcher, hydrogeologist and head of the working group “Sustainable Production Technologies” in the GFZ section Geoenergy, sums up: “We have determined a promising productivity index of over one liter per bar and second, which suggests that good production rates can be achieved with the connected sandstone. This is particularly important for large-scale heat storage.” And Dipl.-Ing. Stefan Kranz, head of the working group ‘Geothermal Process Engineering and System Integration’ in the GFZ section ‘Geoenergy’, emphasizes: ”The completion of the research well now enables further tests to characterize the storage behavior of the Hettang Sandstone. As part of the PUSH-IT project, we will now conduct investigations into the thermal and hydraulic behavior of the storage rock and also look at the influence of temperature on geochemical and microbiological processes.” The results will then be incorporated into the implementation of the heat storage system of the Berliner Blockheizkraftwerks-Träger- und Betreibergesellschaft (BTB).

Video