Rocks under water pressure

New experiment at the geothermal laboratory Gro Sch nebeck

Geothermal pilot plant in Groß-Schönebeck © A. Saadat, GFZ Potsdam
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A new series of experiments at the Geothermal Research Center Groß Schönebeck has now started the GeoForschungsZentrum Potsdam (GFZ). In the so-called hydraulic stimulation experiments, large amounts of water are pressed under high pressure in a bore 4.4 kilometers deep into the ground. Naturally existing fissures and cracks in the rock should be widened by the water pressure and additional flow paths should be created.

The experiments will take about six weeks, according to the Potsdam researchers. As early as 2003, this concept was followed by successful tests in a second borehole at the site. At that time, around twelve million liters of water were pumped into the subsoil.

The geothermal project in Groß Schönebeck aims to use geothermal energy not just for heating, but for power generation. To do this, the geoscientists want to extract the natural deep water contained in the rock from a borehole, use it in the future geothermal power plant and then pump it down again in the second borehole - a closed water cycle.

Minimum temperature only reached at four kilometers depth

"Only at a depth of more than four kilometers, under local geological conditions, do you meet the minimum temperatures of 150 ° C required for power generation. In order to be able to successfully operate a power generation plant under these conditions, as much deepwater as possible from the hot rock must be extracted, "explains project leader Dr. Ing. Ernst Huenges from the GFZ Potsdam. "The more permeable the rock, the more water flows through the reservoir to the production well."

The stimulation is carried out in three injection phases in different rock layers. Huenges holds that this kind of earthquake is a weak earthquake: "We had already carried out such an experiment in 2003 at this site with its typical sedimentary rocks for the North German Basin - without noticeable seismic activity." The routine of the Hydrofracture is routinely determined. Monitored experiments with highly sensitive seismic gauges. A month-long long-term experiment between the two holes will then review the success of the stimulation and document the increased water flow. display

Experiments since 2001

At the Geothermal Laboratory in Groß Schönebeck, scientific experiments and investigations have been carried out since 2001 on the use of geothermal energy for the power supply. To this end, a former natural gas well from the 1990s was first reopened by GFZ Potsdam and extended to a depth of 4.3 kilometers. In January 2007, the scientists then completed a second 4.4 km deep hole, where the stimulation work is now taking place.

(idw - GeoForschungsZentrum Potsdam, 15.08.2007 - DLO)