Deep Geothermal energy - project Optiriss

The southwestern part of Thuringia (central Germany) hosts large subsurface extents of Lower Carboniferous granitoids of the Mid-German Crystalline Rise, overlain by an up to several kilometer thick succession of Lower Permian to Mid-Triassic volcanic and sedimentary rocks. The granitic basement represents a conductivity-controlled ('hot dry rock') reservoir of high potential that could be targeted for economic exploitation as an enhanced geothermal system (EGS) in the future. As a preparatory measure, the federal states of Thuringia and Saxony have jointly funded a collaborative research and development project ('Optiriss') aimed at mitigating non-productivity risks during the exploration of such reservoirs.

3dMGN-SHL_m_Bg

In order to provide structural constraints on the fracture network design during reservoir stimulation, we carry out geometric and kinematic analysis of pre-existing fractures in exposures of the Carboniferous basement and Mesozoic cover rocks within an area of c. 500 km2 around the towns of Meiningen and Suhl, where granitic basement and sedimentary cover are juxtaposed along the southern border fault of the Thuringian Forest basement high. We aim at assessing the reactivation potential of pre-existing fractures in the reservoir during a stimulation phase by carrying out dilation and slip tendency analyses (Morris et al. 1996). For this purpose, constraints on the current strain regime and in-situ stress magnitudes, including borehole data and earthquake focal mechanisms in a larger area, are needed. In-situ stress magnitudes at a reservoir depths are calculated assuming hydrostatic pore pressures and frictional equilibrium along pre-existing fractures. We also compile existing data into a 3D structural model of the area surrounding the target reservoir to improve constraints on the reservoir geometries.


Vertically exaggerated block diagram of the southern Thuringian forest and its southern foreland (Central Germany) with an interpretation of the deep structure. A planned geothermal production and injection well couple at the site Meiningen is also schematically shown (source: modified after Wagenbreth, O. und Steiner, W. 1990. Geologische Streifzüge: Landschaft und Erdgeschichte zwischen Kap Arkona und Fichtelberg: Deutscher Verlag für Grundstoffindustrie).



Papers:

Zinke, C., Navabpour, P., Ustaszewski, K. (2016): Analyse des Bruchflächeninventars in Grundgebirgs- und Rotliegendaufschlüssen am Nordrand des Thüringer Waldes bei Ilmenau (Thüringen) hinsichtlich der Versagenstendenz im rezenten Spannungsfeld. Beitr. Geol. Thüringen, N.F. 22, 137-152.


Final project report:

Hesse, G., Richling, S., Schaubs, A., Will, J., Eckardt, S., Ustaszewski, K., Kasch, N., Siegburg, M., and Thieme, M., 2015, OPTIRISS - Geothermisches Verbundprojekt Thüringen-Sachsen zur Entwicklung einer risikominimierten petrothermalen Explorations- und Erschließungsmethode für geeignete mitteldeutsche Kristallingesteine (Projektteil Thüringen). Abschlussbericht, JENA-GEOS Ingenieurbüro GmbH, 106 pp.


Conference contributions:

Ustaszewski, K., Kasch, N., Zinke, C., Navabpour, P. 2016. On the reactivation potential of preexisting fractures in designing a hot dry rock geothermal reservoir in the Mid-German Crystalline Rise (Central Germany), TSK16, Tektonik - Strukturgeologie - Kristallingeologie, 02-06 March 2016, Bonn, Germany, DOI 10.13140/RG.2.1.1650.9844.

Kasch, N., Ustaszewski, K., Siegburg, M., Navabpour, P., Hesse, G. 2014. Estimating the reactivation potential of existing fractures in subsurface granitoids from outcrop analogues and in-situ stress modeling: implications for EGS reservoir stimulation with an example from Thuringia (Central Germany), AGU Fall Meeting 2014, DOI 10.13140/2.1.1392.6727.

Knörrich, T., Kasch, N., Ustaszewski, K., 2014. 3D Modellierung eines invertierten Grabensystems am Beispiel des Marisfelder Grabens (Südthüringen), GeoFrankfurt2014 conference "Earth System Dynamics", Goethe University, Frankfurt am Main, 21-24 September 2014, Poster presentation, DOI: 10.13140/2.1.1207.9369.

Siegburg, M., Kasch, N., Ustaszewski, K., Navabpour, P., 2014. Evolution of the tectonic activity in southwestern foreland of the Thuringian Forest deduced from the fracture system in the Thüringer Hauptgranit und Muschelkalk. GeoFrankfurt2014 conference "Earth System Dynamics", Goethe University, Frankfurt am Main, 21-24 September 2014, Poster presentation, DOI: 10.13140/2.1.2701.9521.

Thieme, M., Fügenschuh, B., Ustaszewski, K., 2014. Late- to post-Variscan thermal evolution of the south-western Thuringian Forest and its foreland by means of combined fission-track dating of zircon and apatite, GeoFrankfurt2014 conference "Earth System Dynamics", Goethe University, Frankfurt am Main, 21-24 September 2014, Poster presentation, DOI: 10.13140/2.1.4189.8241.

Ustaszewski, K., Kasch, N., Siegburg, M., Navabpour, P., Thieme, M., 2014. Estimating the reactivation potential of existing fractures in subsurface granitoids from outcrop analogues and in-situ stress modeling: implications for EGS reservoir stimulation with an example from Meiningen (Thuringia, Central Germany), EGU General Assembly 2014. Geophysical Research Abstracts, 16, pp EGU2014-3099-1, DOI 10.13140/2.1.1117.5048.



Qualification theses:

Ahlers, S., 2014: Die kinematische Entwicklung der Viernauer-Störungszone südwestlich des Thüringer Waldes, BSc thesis, Friedrich-Schiller-Universität Jena, 63 p.

Knörrich, T., 2014: 3D-Modellierung eines invertierten Grabensystems anhand einer geologischen Geländeaufnahme am Beispiel des Marisfelder Grabens (Südthüringen), diploma thesis, Friedrich-Schiller-Universität Jena, 133 p.

Siegburg, M., 2014: Paläospannungsfeldanalyse im südwestlichen Vorland des Thüringer Waldes, MSc project module, Universität Bremen, 71 p.

Thieme, M., 2015: Thermochronologische Untersuchungen an Granitoiden des Thüringer Hauptgranit und Rotliegendformationen im Thüringer Wald und seinem südwestlichen Vorland, MSc thesis, Friedrich-Schiller-Universität Jena, 161 p.

Winn, S., 2014: Geologische Neukartierung zwischen Benshausen und Zella-Mehlis im Bereich der Südrandverwerfung des Thüringer Waldes, BSc thesis, Friedrich-Schiller-Universität Jena, 49 p.

Zinke, C., 2015: Analyse des Bruchflächeninventars in Grundgebirgs- und Rotliegendaufschlüssen am Nordrand des Thüringer Waldes bei Ilmenau (Thüringen) hinsichtlich der Versagenstendenz im rezenten Spannungsfeld, 65 p.


Project partners:

JENA-GEOS, Jena

Dynardo GmbH, Weimar

DBI Gas- & Umwelttechnik GmbH, Freiberg

TU Bergakademie Freiberg, Lehrstuhl Gebirgs- & Felsmechanik


References:

Morris, A., Ferrill, D.A., Henderson, D.B., 1996. Slip tendency analysis and fault reactivation. Geology 24 (3), 275-278.



Project funding:

Thüringer Aufbaubank Project No. 2012 FE 9080

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