The first conceptual model for Göttingen demo site has been developed based on the Discrete Fracture Network (DFN) approach as shown in Figure 1 by MEET-partner Technical University of Darmstadt (TUDa). In the first strongly simplified conceptual model set-up, 80 fractures are randomly placed inside a 200 m cube and bounded by 50 m thick isotropic and homogeneous rock resulting in a 300 m fractured reservoir. To better represent the stress and temperature conditions of the subsurface, the reservoir is set from – 600 m to – 900 m deep below sea level.
A pair of geothermal doublet wells are placed on the corner of the reservoir. Constant injection pressure and constant injection temperature are imposed in injection well, whereas only constant production pressure is imposed in production well. The aim of this model is to investigate the performance of an Enhanced Geothermal System (EGS) reservoir, represented by the DFN, by analysing the time until thermal breakthrough occurs at the production well.
Figure 2 depicts the evolution of temperature inside the reservoir in 30 years of injection-production scenario. A similar model implementing Equivalent Permeability Method (EPM) is currently being developed at TUDa to simplify the simulation. The EPM-based model aims to obtain similar simulation result in faster simulation time. To better represent the metamorphic Variscan bedrock below Göttingen, further development of the model will involve geological complexity including intercalated and folded lithological units with distinctly different thermal and mechanical behavior. In these steps real fracture network data from outcrop analogue studies provided by MEET partner University of Göttingen will be used to create lithology and structural position dependent DFNs.
Figure 1: Conceptual model for Göttingen (Germany) demo site
Figure 2: Temperature evolution of the conceptual reservoir after 30 years of constant injection-production scenario