February 14, 2018 Conference paper Open Access

Upscaling of EGS in Different Geological Conditions: a European Perspective

Ghislain Trullenque; Albert Genter; Bernd Leiss; Bianca Wagner; Romain Bouchet; Eric Léoutre; Bruno Malnar; Kristian Bär; Ivan Rajšl

In Europe, only a few industrial geothermal plants based on the Enhanced Geothermal System (EGS) technology (Soultz-sous-Forêts and Rittershoffen in Alsace, France and Insheim in Germany) are operating. Most of them are located in the Upper Rhine Graben and are related to the exploitation of natural fluids trapped in deep fractured hard rocks made of clastic tertiary sediments and/or crystalline rocks.
The European commission decided to further explore and exploit its EGS potential by supporting the development of innovative techniques in different geological conditions. At European scale, these are deep sedimentary basins (e.g. the Southern Permian Basin area, the Pannonian Basin and the various foreland basins of the Alps and the Pyrenees) and the metamorphic and crystalline rocks of the Variscan orogen, which forms most of the bedrock of central and southern Europe. More than 70% of the overall geothermal potential of Europe is located in low permeable bedrock only exploitable by EGS technology, which allows – theoretically – a permanent heat and electricity production at any place. However, for the implementation of enhanced geothermal energy systems into our future energy supply, distribution infrastructures dealing with EGS are crucial. Only EGS makes geothermal energy - heating or heat storage – exploitable at large scale and in view of a significant market penetration.
Until now, main drawbacks of EGS are related to 1) high costs (drilling, CAPEX) and relative low experience due to only very few operating power or heat plants, 2) only very few exploitations due to the lack of available technical solutions of different reservoir types with unexceptional geothermal conditions, 3) highly aggressive fluids causing corrosion or scaling and thus damaging technical installations, and 4) the lack of a clear integration strategy in existing power or heat networks.
These gaps have to be filled by systematic studies associated with site demonstrations in different geological contexts in order to significantly extend the range of EGS in Europe. The MEET project (Multidisciplinary and multi-context demonstration of EGS exploration and Exploitation Techniques and potentials)
aims to:

1. apply EGS techniques to a – in Europe - very common but until now nearly unexploited reservoir type, namely the different rock units of the Variscan orogenic belt. Several research and prospection wells have demonstrated the unexpected presence of hot fluids and sufficient rock permeabilities. We will explore sites, where we already have a strong heat demand for such reservoir types from existing district heating systems which have to be converted to sustainable energy systems,
2. increase the productivity of existing geothermal power plants (Soultz sous Forêts, France) using a fractured granitic basement,
3. as reservoir rock. The re-injection of geothermal fluids with a colder temperature in combination with the latest generation of small-scale ORC units will enhance the heat and electricity production. Solutions have to be developed to avoid the scaling problem, which increases by lowering the fluid temperature,
4. use the hot fluid of mature oil fields, where water is reinjected without using the calories. Such an enhancement through oil barrels and electricity KWh “co-production” of wells could be realized by new low temperature ORC systems, which we aim to test in French oil fields. Ultimately this could lead to a better definition of a value-creating method to assess the conversion of abandoned oil fields.

The proposed different studies clearly aim to enhance the geothermal reservoir types by new exploitation and energy production techniques with the consequence of geographically extending the geothermal heat and electricity production to be supplied to smart energy grids.
The large amount of potential production sites together with the reconversion of existing wells will greatly contribute to lower the costs of geothermal energy making it economically competitive in comparison to conventional fossil and nuclear sources.