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German city exploring reactivating geothermal wells drilled in the 1970s

Bad Urach old market place, Germany (source: flickr/ derfussi, creative commons)
Alexander Richter 2 Dec 2019

The municipality of Bad Urach in Southern Germany is looking at repurposing two wells drilled for a hot dry rock geothermal project in the 1970s and utilise them for a potential heating project.

As reported by our partner website in Germany, TiefeGeothermie, two wells drilled with a depth of 2,800 to 4,400 meters drilled as part of the Hot Dry Rock project in Bad Urach/ Germany in the 1970s are now to be reactivated for heat utilization. The goal is to open up water carrying layers with a sidetrack.

Bad Urach is a geothermal hotspot. Due to its location in a former volcanic area – on 200 square kilometers there were more than 300 volcanoes 17 million years ago – the ground is very hot. Among other things, this is demonstrated by the many years of balneological use. The hottest spring, which was tapped in the 1970s, supplies hot water at a temperature of 61 degrees Celsius from a depth of 770 meters.

This heat anomaly was the approach for federal, state and city at the end of the 1970s to push a hot-dry-rock project. The wells Urach 3 and 4 were drilled to depths of 2,800 and 4,400 meters. The maximum temperature that was measured then was 170 degrees Celsius.

Despite several attempts, the heat from the drilling could not be used due to technical and economic problems as well as national and political dissonances. Until then, about EUR 20 million were spent. The holes were though not filled.

Sidetrack is to open up the Muschelkalk

Now the municipality is faced with the decision to secure the holes or to use the heat. After an appraisal of an engineering firm, it has opted for the second possibility, as reported by the Südwest Presse. For about EUR 2 million, the two holes are to be filled up to a depth of 900 or 1,300 meters.

A sidetrack at a depth of 630 to 710 meters will then open up shell limestone. Here, the planners expect a temperature of about 57 degrees Celsius and a flow rate of 20 liters per second. Another well (Urach V), which should reach 800 to 1,000 meters deep, would bring the cooled thermal water back into the shell limestone.

In addition to the use in the spa, a geothermal use of heat would also be possible. According to the engineering firm that explored the opportunities, 5 to 6.7 GWh of heating energy could be obtained per year. This would provide 500 to 1,000 residential units with sustainable heating. The CO2 savings would be around 1,100 tons compared to gas heating.

Further work in the summer of 2020 would entail drilling activities on the existing wells. The following tests should give information about the economics of the project. According to information from the Südwest-Presse, the heat could already be used in 2021, provided that all work goes smoothly.

Source: SWP, via our German partner website TiefeGeothermie