Fracture Network Characterization of the Culm Fold Zone, Western Harz Mountains – Germany, as a Means to Extract Geothermal Reservoir Parameters
Creators: name: Ford, Katherine
name: Leiss, Bernd
name: Wagner, Bianca
name: Sosa, Graciela
Publisher: name: Zenodo
Year: 2020
Subjects: Fracture network
Reservoir parameter
Harz Mountains

description: The focus of this study is to characterize an analogue site for the Variscan metasedimentary and metavolcanic Variscan basement, the potential target reservoir in an unconventional geological setting for the geothermal project of the University of Göttingen. The main outcome of which is to supply district heating for the entire campus. From interpolation of comparable units in the Rhenish Massif with the Harz Mountains, it is likely that the boundary that separates the Variscan autochthonous from the allochthonous zone is striking through the subsurface of the<br> city area of Göttingen. For that reason the analogue site for this project has been chosen as the Western Harz Mountains, paired with the reasonable outcrop situation.<br> To understand and comprise the complex structural parameters that may be found in the expected alternating slate and greywacke units beneath the surface of Göttingen, a 3D conceptual structural model of the Variscan basement must be created as the first step. This contribution will focus on the interactions and changes of different structural parameters across the typical Variscan fold and thrust belt at outcrop scale. To accomplish this, intensive field campaigns and photogrammetry sessions are undertaken for detailed data collection on changes in parameters<br> such as the fracture network, mineralization and lithology across the primary fold and thrust structure. The methodology presented focuses on the characterization of the fracture network through topological analysis. The main parameters defined within the study are connectivity, intensity and level of mineralisation. Then related to how these parameters change in various structural and lithological situations situated along the generalized fold and thrust structure, as a basis for understanding the complexity of the deformation exhibited in the Variscan Fold-and-Thrust belt.<br> Due to the complexity of the lithology and structures exposed in the Western Harz Mountains, a total of 29 outcrops have been categorized, and fracture trace maps have been collected at each defined category. As well as this, a 2.5D approach to fracture network characterisation has been undertaken. Trace maps are created on the bedding plane itself, and adjacent to the planes, this allows for the more holistic quantification of the fracture networks under varying exposure orientations and through the changes in lithology. This statistical approach to data collection will<br> allow for a more generalised view of the interactions between the fracture networks and the lithological and structural framework, such as local-scale folds and faults, which for an analogue study is more suitable.<br> The preliminary results of this study do show a general trend of increased intensity, level of mineralisation and connectivity towards the fold hinge and thrust zone but are however more complex than this hypothesis. A much more detailed study must be undertaken to truly understand how fracture network characteristics are affected by changes in lithological and structural variations. With a detailed characterisation of the fracture network throughout this complex reservoir this is the first step in the creation of the conceptual structural model, following this with petrophysical and chemical parameterisation derived from lab experiments, reservoir models and EGS-exploitation strategies can then be developed and the reservoir potential realised.