DESTRESS focuses on “enhanced geothermal systems” (EGS), thus, petrothermal systems developed through the application of hydraulic stimulation in the deep underground: The injection of high-pressure water leads to the creation of an artificial reservoir, in which fluid circulates and is warmed. In comparison to hydrothermal systems, EGS have the advantage that they don’t rely on the exploitation of existing aquifers, and are thus in principle independent of location. The success of such projects depends on three essential factors: geology, profitability, and society.
Geology – a hard nut to crack
The permeability and productivity of a geothermal reservoir and the possibility of induced seismicity are central to the geologic and economic success of a project. Many earlier deep geothermal wells have failed as a result of low rates of fluid production, which made the projects economically unprofitable. Therefore, DESTRESS is conducting testing at various sites to determine the impact of a combination of hydraulic, thermal, and chemical stimulation methods to enhance the productivity of a geothermal reservoir. Additionally, new drilling technologies are applied: The so-called “multistage stimulation method” generates multiple horizontal side arms branching off from a single wellbore to increase the efficiency of the system. Although small earthquakes are necessary during stimulation to increase the rock permeability to the desired extent, the trick is to produce sufficiently small shocks without triggering earthquakes that could cause damage. To achieve this goal, DESTRESS employs methods like adaptive traffic light systems, which have been intensively studied in Switzerland in recent years. These are based on a dense seismic observation network, combined with statistical and physical prediction models. Coupled with measures that trigger warnings when specific values are exceeded, DESTRESS aims to reduce the seismic risk to an acceptable level.
Geothermal energy projects have relatively high upfront investment costs. Besides sufficient productivity, profitable projects must have acceptable effects on society and the environment. In order to achieve social acceptance and comply with regulatory requirements, a comprehensive analysis and transparent interpretation of the risk associated with geothermal projects is indispensable. Under DESTRESS, innovative approaches and methods are being developed and tested at demonstration sites with different geological conditions. An important element is to make knowledge available to a wide audience in the form of “best practices”. This will make it easier for all who plan or operate an environmentally friendly, economically successful and sustainable geothermal project in Europe or elsewhere.