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10:50-11:10 am - Forum 4

Enhanced Geothermal Systems: Variscan Reservoir Type Characterisations by Outcrop Analogue Studies

Bernd Leiss1,2, Kristian Bär3, Eléonore Dalmais4, Katherine Alexandra Ford1, Albert Genter4, Johanne Klee5, John Reinecker6, Katja Schulz3, Xavier Sengelen7, Ghislain Trullenque5, Aysegül Turan3, Yves Vanbrabant8, Bianca Wagner1,2

1Geoscience Centre of the University of Göttingen, Germany; 2Universitätsenergie Göttingen GmbH, Germany; 3Department of Geothermal Science and Technology, Institut für Angewandte Geowissenschaften der Technischen Universität Darmstadt, Germany; 4Électricité de Strasbourg Géothermie, Schiltigheim, France; 5UniLaSalle, GEOS department, La Salle, France; 6GeoThermal Engineering, Karlsruhe, Germany; 7Laboratoire Géosciences et Environnement Cergy, Cergy Paris Université, France; 8Geological Survey of Belgium, Bruxelles, Belgium

One of the main objectives of the EU-HORIZON 2020-project MEET (Multidisciplinary and multi-context demonstration of EGS exploration and Exploitation Techniques and potentials, GA-number 792037) is to demonstrate the viability and sustainability of ‘Enhanced Geothermal Systems (EGS)’ in unconventional geological settings, which are not primarily predestined for the utilization of deep geothermal systems. In order to cover a wide range of geological settings throughout Europe, we selected four demo sites at different ‘Technology Readiness Levels (TRLs)’, each associated to a different, but representative geological setting within the Variscan orogenic belt. The target horizons for two of the chosen sites are granitic, for two others the metasedimentary and –volcanic rocks of the external fold- and thrust belt, in each case one affected and one not affected by post Variscan extensional tectonics. To finally be able to set-up and parametrize numerical reservoir models and to recommend stimulation measures for the reservoirs, we selected analogue outcrop areas to characterize and quantify the geological structures in 3D, to select samples for a quantification of the petrology as well as the petrophysical and –chemical parameters in the lab. The four Variscan geological settings, the demo sites and the selected outcrop analogue areas are as follows:

- Demo site: Operating geothermal power plant, Soultz sous Forêts, Alsace, France Geological setting: Granitic rocks overprinted by post-variscan fault and graben systems

Outcrop analogue area: Southern Death Valley Fault Zone (far-field, CA, USA), Upper Rhine Graben valley (near-field), Germany

- Demo site: Geothermal power plant under development at the United Downs Deep Geothermal Project (drilling of a doublette just completed), Redruth, UK

Geological setting: Granitic rocks not overprinted by post-variscan extensional tectonics

Outcrop analogue areas: Carnmenellis Granite (near-field) and Cornubian Batholith (far-field), SW-England, UK.

- Demo site: Geothermal power plant aspired to be integrated into the district heating system of the Göttingen University Campus, Germany

Geological setting: Deformed Variscan metasedimentary -volcanic successions overprinted by younger extensional fault and graben systems

Outcrop analogues areas: Western Harz Mountains (near-field) and Rhenish Massif (far-field), Germany

- Demo site: Abandoned gas exploration bore hole for research and conversion for geothermal exploitation in Havelange, Belgium

Geological setting: Deformed Variscan metasedimentary -volcanic successions not overprinted by younger extensional tectonics

Outcrop Analogue areas: Dinant Synclinorium (near-field), Belgium

In addition, we have included core samples from wells reaching into the Variscan crystalline or metamorphic basement below the younger sedimentary cover of the Paris Basin in France to bridge the gap between the outcropping Variscan rocks in Belgium and Southwest-England.

From the variation in TRLs of the demo sites it has become clear, that the type, the quantity and the quality of data available from the reservoirs at the demo sites are also very different. In combination with the diversity in geological settings, the heterogenous Variscan geology, and the site-specific expectations to be met, individual designs of the analogue studies are needed. Nevertheless, based on our results we can present the individual definitions, approaches, results and critical evaluations of our analogue studies at the single sites. To further this, present a complementary discussion, a summarizing conceptual geological model and finally conclusions for a general, multidisciplinary approach of analogue studies for granitic and deformed metasedimentary tectonically overprinted and not overprinted rocks.

Presentation (PDF)

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