26 Oct 2021

26 Oct 2021

Review status: this preprint is currently under review for the journal SE.

Interdisciplinary Fracture Network Characterization in the Crystalline Basement: A case study from the Southern Odenwald, SW Germany

Matthis Frey1, Claire Bossennec1, Lukas Seib1, Kristian Bär1, and Ingo Sass1,2 Matthis Frey et al.
  • 1Technical University of Darmstadt, Institute of Applied Geosciences, Department of Geothermal Science and Technology, Schnittspahnstraße 9, 64287 Darmstadt, Germany
  • 2GFZ German Research Centre for Geosciences, Section 4.8: Geoenergy, Telegrafenberg, 14473 Potsdam, Germany

Abstract. The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal energy in the Upper Rhine Graben and other regions worldwide. The hydraulic properties of the basement, which are one of the key factors for the productivity of geothermal power plants, are primarily controlled by hydraulically active faults and fractures. While the most accurate in situ information about the general fracture network is obtained from image logs of deep boreholes, such data are generally sparse, costly and thus often not openly accessible. To circumvent this problem, an outcrop analogue study with interdisciplinary geoscientific methods was conducted in the Tromm Granite, located in the southern Odenwald at the northeastern margin of the URG. Using LiDAR scanning, the key characteristics of the fracture network were extracted in a total of five outcrops, additionally complemented by lineament analysis of two different digital elevation models. Based on this, discrete fracture network (DFN) models were developed to calculate equivalent permeability tensors under assumed reservoir conditions. The influence of different parameters, such as fracture orientation, density, aperture and mineralization was investigated. In addition, extensive gravity and radon measurements were carried out in the study area, allowing for more precise localization of fault zones with naturally increased porosity and permeability. Gravity anomalies served as input data for a stochastic density inversion, through which areas of increased open porosity were identified. A laterally heterogeneous fracture network characterizes the Tromm Granite, with the highest natural permeabilities expected at the pluton margin, due to the influence of large shear and fault zones.

Matthis Frey et al.

Status: open (until 04 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on se-2021-118', Gerhard Schmidt, 28 Oct 2021 reply
  • RC2: 'Review and Comments on se-2021-118', Anonymous Referee #1, 30 Nov 2021 reply

Matthis Frey et al.

Data sets

Interdisciplinary Dataset on the Fracture Network of the Tromm Granite, Southern Odenwald, SW Germany Matthis Frey, Claire Bossennec, Lukas Seib, Kristian Bär, Ingo Sass

Matthis Frey et al.


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Short summary
The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal energy in the Upper Rhine Graben. Interdisciplinary investigations of relevant reservoir properties were carried out on analogous rocks in the Odenwald. The highest hydraulic conductivities are expected near large-scale fault zones. In addition, the combination of structural geological and geophysical methods allows a refined mapping of potentially permeable zones.