Important milestone towards sustainable geothermal energy
The recent creation of a permeable geothermal reservoir in granite rock has led to a breakthrough in the field of geothermal energy. Although geothermal energy has great potential as a renewable energy source, the inability to date to reliably develop it beyond geothermal hotspots has prevented it from being used on a large scale. The geothermal reservoir built with support from the two EU-funded projects GEOTHERMICA and DESTRESS could open the way to the sustainable, large-scale use of geothermal heat. Created by DESTRESS project partner Geo-Energie Suisse, the reservoir has provided technical proof that the company’s patented multi-stage geothermal stimulation concept is feasible in granite rocks. The demonstration took place at the Bedretto underground laboratory operated by research university ETH Zurich, another DESTRESS project partner. Located in a former ventilation tunnel in the Saint-Gotthard Massif of the Swiss Alps approximately 1.1 km below ground, the Bedretto site is being used to see how geothermal heat could be tapped without triggering dangerous earthquakes.
First failure, then success
Geo-Energie Suisse developed its multi-stage stimulation concept following the unsuccessful 2006 attempt to create a geothermal reservoir in a single step with a vertical, open borehole. This attempt, which took place in Basel, set off unwelcome earthquakes. The geothermal stimulation concept, which the company patented for Switzerland in 2012, involves the creation of a permeable reservoir deep in the geology (crystalline basement) using targeted water injections. As further explained in an article posted on the ‘Think Geoenergy’ website, “the hydraulic stimulation is carried out in sections and in small, staggered steps” in order to lessen the risk of earthquakes. “A sequence of reservoir sections is generated along a horizontally drilled borehole. These are connected with a second, horizontally deviated borehole. The result is a large underground heat exchanger that can be used to produce electricity and extract heat in a geothermal power plant,” the article continues. The success of the stimulation is a milestone in the development of geothermal energy. “We succeeded in increasing the permeability by a factor of 10 to 100 in the compact granite of the Gotthard massif with the help of targeted stimulations, and in measuring and controlling the microseismicity necessary for the development of fissures,” states Geo-Energie Suisse CEO Dr Peter Meier in the same article. “I am convinced that this breakthrough is a key milestone on the way to the first deep geothermal power plant in Switzerland. On the one hand, this is because the permeability achieved in one of the two boreholes corresponds to the transmissivity required for an economic application. On the other hand, and this is central, the microseismicity associated with the stimulations produced a maximum magnitude of -1.8 Mw on the Richter scale which is around 1 million times smaller than in Basel.” Next, the concept will undergo scientific evaluation to inform the future stimulation programme to be conducted at the Haute-Sorne site in the Canton of Jura. GEOTHERMICA (GEOTHERMICA - ERA NET Cofund Geothermal) has supported this research through its ZoDrEx project. The DESTRESS (Demonstration of soft stimulation treatments of geothermal reservoirs) project’s focus has been the optimisation of stimulation treatments while minimising environmental impacts such as earthquakes. Both projects end in 2021. For more information, please see: GEOTHERMICA project website DESTRESS project website
Keywords
GEOTHERMICA, DESTRESS, geothermal, energy, stimulation, reservoir
