The geothermal and thermal energy storage potential of the crystalline rocks of the German Middle Crystalline High is significant, due to the favorable intrinsic petrophysical properties of the rock and the reservoir. However, only an accurate estimation of the hydraulic and heat transfer properties of the target reservoir can ensure the success of an installation. For the test site at Campus Lichtwiese of the Technical University of Darmstadt, the role of the fracture network affecting the crystalline rock is being investigated in the research projects SKEWS (Solar Coupled Medium Deep Borehole Energy Storage System, BMWK, 03EE4030A-E) and DGE Rollout (Interreg NWE Programme, financed by the European Regional Development Funds (ERDF)). For this purpose, a multidisciplinary approach is used to characterise the architecture of potentially heterogeneous fractured reservoir rocks. This approach includes outcrop analogues, seismic imaging, well logs, all integrated into fracture network modelling applied to a mediumdepth underground thermal energy storage (UTES) geometry. Surface outcrops and similar data from the northern Odenwald are integrated to build a structural model of the subsurface. The near-surface study defines the extension of the weathering profile and its heterogeneity to assess the impact on surface groundwater flow, and potential loading pathways to the surface aquifer. Several cases are analysed, considering the variety of structural configurations observed near the surface. The influence of fracture aperure, and distribution can then be tested to refine the estimate of the overall permeability of the system and its impact on groundwater flow paths and heat flow.