Basel to reopen geothermal well – but not the EGS project
View of Basel, Switzerland (source: flickr/ taintfair, creative commons)
Alexander Richter
15 Jun 2017
The well drilled for the Basel EGS project is to be opened again to release pressure to prevent seismic events. This does not mean though a restart of the project itself.
The Basel geothermal project made headlines several years ago. As one of the key EGS projects worldwide (Enhanced/ Engineered Geothermal System), it was to be a milestone and case for further EGS development worldwide.
With a well drilled in 2006, the team of Geopower Basel pumped water into the well with the goal to retract heated water back from the reservoir to be created. But with smaller earthquakes tied to these efforts, the project was halted in 2009, as we reported back then.
Now, the geothermal well that has been closed since 2009 is going to be opened again, with work to start in the beginning of July. The goal is to prevent further earthquakes, through slowly draining ground pressure over several weeks. The city authorities of Basel have approved of the technical concept.
The reason for the opening is an increase in the not noticeable micro-seismic events over the past few months – due to the increase in pressure under the cover of the closed geothermal borehole in small hinges. The Basel-Stadt Health Department (GD) had opened the hole at the end of March. This is intended to reduce the likelihood of a noticeable quake.
The now approved scheme provides for a step-by-step opening and a controlled release of pressure over ten weeks, as the Health Department and the Industrielle Werke Basel (IWB) announced in a joint communication yesterday. Between each release, it is waited for a week and the development of earthquake activities and the pressure curve evaluated.
The well should remain open
The work is only continued when a small or no earthquake activity is detected. The pressure drain is to be increased in stages as a result. In addition to routine monitoring, the Swiss Earth Service (SED) conducts daily a “highly detailed” search for earthquakes near the borehole. The well could be closed at any time.
For the opening of the borehole by the authorities, the IWB’s costs amount to CHF 250,000 ($260,000), according to a spokesman on request. In order to prevent a new pressure buildup, the drill hole should remain open for several years after the work.
In a next step, a further concept is to be developed in order to secure the borehole in the long term. The findings of the opening phase are to be taken into account.
According to the report, however, the experts do not rule out the possibility of an earthquake that can be felt by the population even after opening up in the coming years. According to today’s assessment, however, a damage quake remains “unlikely”.
«Deep Heat Mining» project failed
The borehole had been constructed as part of a Basler geothermal energy experiment. The drilling began in 2006 after several years of preparation. The “Deep Heat Mining” project wanted to heat cold water in the deep rock and use the heat above, for which purpose the rock below should be made permeable by means of water pressure.
This process, however, called “shearing” triggered earth jolts. On December 8, 2006, a strong 3.4 earthquake hit the region, which was the end of the CHF100 million project. Experts were surprised by the strength of the bumps, and the population saw itself too little prepared for this possibility.
At the end of 2009, the Basle Government definitely buried the project. In 2011 the well was closed. Since 2012, the Swiss Earth Service has been monitoring the locality on behalf of the city canton.
Source: Baseler Zeitung
