Germany's first “hot-dry-rock drilling” was successful.
For science, the positive outcome of the geothermal research project "Zokrates" in Geretsried is of great importance.
Gelting - "The experiment was a success," says Dr.
Robert Straubinger, Managing Director of Enex Power Germany, who owns the drilling site.
In an interview with our newspaper, he leaves it open whether there will be an “economically sustainable solution”.
In the summer, the starting shot was given for the operational work of the pilot project, which is funded by the Federal Ministry of Economics.
The preparatory planning work and obtaining the various permits had been going on since the beginning of the year.
After two failed drillings - the temperatures were extremely high, but the rock did not let through enough water - the aim was to investigate how the porous layers in the subsurface can be kept permeable to water.
The project team achieved their goal with an innovative approach, even if the work was "technically extremely demanding", according to Straubinger.
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Enex managing director Dr.
Robert Straubinger
© Sabine Hermsdorf-Hiss
The underground target was the Malm layer, which lies in Geretsried-Gelting at a depth of 4400 to 4800 meters, and there the area of the borehole that is no longer cased, the so-called open hole. “We pushed steel pipes in through our drilling rig,” explains the expert. The specialty: the pipes have small closable windows that allow access to the rock. In sections, quartz sand particles and water were washed into the existing joints and cracks through these windows under high pressure - around 337 tons, of which, according to Straubinger, more than half were flushed out again.
The Enex managing director assures that the pressure that is used in so-called fracking, which can trigger seismic activities underground, was well under the pressure.
This process is mainly used in the development of natural gas reserves.
A liquid is injected at high pressure to create cracks in the rock or to widen existing cracks.
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One next to the other: the steel pipes (with window) that were installed in the open hole area at a depth of 5000 meters.
© Enex Power Germany
The drilling company also came across gas in Gelting. "That stank a lot," admits Straubinger. The gas, including highly toxic hydrogen sulfide, had accumulated over the past four years that the well was closed. A layer of oil about one meter thick had also settled on the water in the hole during this time. After the gas and oil had been removed, the tests could begin. It was shown that, thanks to the new process, more water can actually be tapped than with the earlier geothermal wells. “But that only succeeded for a short time,” regrets Straubinger. "Then there was very little." A first guess: the catchment area for thermal water around the borehole has increased significantly compared to the tests in 2017,however, it still seems to be self-contained and has no connection to a “flowing” underground thermal water reservoir. But now it is the hydrogeologists' turn first. The evaluation of the results will take about half a year.
Seismometers erected around the drilling site
A highly sensitive measuring system with five seismometers at different locations - from Münsing to Eurasburg, Bairawies and Neufahrn r.
I. up to the drilling site itself - built.
According to the Enex spokesman, they were set up to register seismic events such as tremors.
But this case did not occur.
“We focused on this when planning the work,” says Straubinger, “but we are very happy that it happened that way.” Even though the work has now been completed, the seismographs “are still running”.
Waiting for permits
The derrick is still standing on Hofgut Breitenbach.
But the technical systems are now to be gradually dismantled.
In theory, this would pave the way for the next geothermal project.
The Canadian company Eavor wants to promote geothermal energy in cooperation with Enex in Gelting.
"It is still the case that we do not have all the permits yet," admits Straubinger.
“But we are confident.” He hopes that the main operating plan will be available by the end of the year and the water law permit by spring.
"Then we can start building the drilling site at the end of winter."
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By the way: Everything from the region is now also available in our regular Wolfratshausen-Geretsried newsletter.