Once again, hot dry rocks can be not only small things causing the foot-pain, but HDR is also the synonym for geothermal energy utilization. Enhanced geothermal systems - this is the whole approach telling about the possibility to established closed water loop bringing geothermal heat from Earth‘s depth under the surface.
In previous part we wrote about the first three most famous HDR research projects in Europe (Rosemanowes Quarry in Britain, European HDR Project Soultz in France and Le Mayet in France). From the group of six, let‘s have a look at the other three ones:
- Fjällbacka in Sweden,
- Falkenberg in Germany,
- Bad Urach in Germany.
HDR project in Fjällbacka
What has project on the west coast of Sweden common with Geothermania? The date of birth with one member of your team (1984) :-) Now serious. This one is primarily focused on addressing geological and hydro-geological questions. At the same time, the big research issue there was the set of questions regarding the reservoir development. The project started with drilling three wells - drilled to depths of 70, 200 and 500 meters. Then the next step followed: creating the reservoir 450 meters deep. In 1998, the 4th well had been drilled and in 1989 the permanent 40-day circulations was established. All that on tectonic shield composed of granite. The lessons learned in Fjällbacka refer mainly to hydro-mechanical behavior of the Hot dry rock reservoir. A series of experiments provided also the valuable knowledge about the state of stress in wells as well as in reservoir. The project finished in 1990.
HDR project in Falkenberg
All started in 1978. Falkenberg project can be described as the proof that hydraulic pressure alone could keep reservoir‘s joints open. The first well was drilled to the depth of 450 meters. Once it was finished, the reservoir stimulation through the borehole started. Subsequently, seven additional wells were drilled in order to enable established water loop through the artificial reservoir. On the other hand, those wells had only limited capacity or flow rate.
The projects was localized in north-east of Bavaria in Germany on granite ground, somewhere extending to the surface. This was the ideal place for hydro-mechanical testing at small depths. Being not deep under the surface was also meant as an opportunity to have each detail under control and almost direct observation. Therefore the project greatly helped understanding HDR issue itself.
The main borehole (HB4a) was drilled into depth of a little bit more than 250 meters. The closed loop was established with the flow rate of 3,5 liters per second, under the pressure of 18 MPa. For the testing purposes, seven other geothermal wells were drilled - reaching the reservoir in depths from 300 to 500 meters (on area 100 x 100 meters). The water circulated in various periods with different set of properties - all were compared. The results from Falkenberg teach us much about the impacts of hydro-fracture stress. This was an example of relatively short-term project, which finished in 1983.
HDR project in Bad Urach
Bad Urach is the area characterized by numerous geothermal anomalies around. The research started in 1997 and took till 1990. Project located some 50 km south from Stuttgart was focused on one hand on studying natural anomalies, but at the same time on assessing the possibility if hot aquifers could be used for heating. In addition, there were plenty of tests linked to basement rocks - and the geothermal researchers collected information about HDR concept itself.
In 1970 and 1974 two basic geothermal wells had been drilled - Urach I, respectively Urach II. Both were 800 meters deep. After those two, the third one began to be drilled in 1977 - after 231 days of work it reached the depth of 3334 meter (it penetrated 1700 meters into the crystalline basement). Six years later, Urach III had been prolonged into the depth of almost 3500 meters. The tests were focusing on hydro fracture stress measurements as well as on analyzing a series of small scale stimulations with subsequent fluid circulation.
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