Fracture network characterization and DFN modelling of the Upper Carboniferous, Ruhr Area, Germany

Since coal mining in the Ruhr Area has been ceased, mine water drainage is gradually reduced leading to the rise of formation water and groundwater levels. Rising mine water levels increase the pore pressure and induce stress changes in the subsurface, which may reactivate natural and/or mining-related faults and fractures. As part of the interdisciplinary FloodRisk project, which aims to enhance the understanding of the geomechanical coupling of increased pore pressure and heterogeneous ground movements, we present a geological km-scale 3D model of a former mining area hosted in the Upper Carboniferous. Fault and horizon geometries are constructed based on coal seam mappings from the Geological Survey of NRW. Beside the integration of petrophysical data, a discrete fracture network model (DFN) is implemented to capture the fracture network of the subsurface. Therefore, Upper Carboniferous outcrops were studied by UAV-derived 3D outcrop models to analyse fracture parameters. Fracture network characterization revealed five dominant fracture sets with striking orientations of N-S, NE-SW, ENE-WSW, WNW-ESE and NW-SE. Calculated dilation tendencies provide information on which fracture sets are likely to contribute to fluid flow in the subsurface. A DFN model is stochastically modelled based on these “effective” fracture sets and will be the basis for the construction of a simulation model.