Structural setting for a geothermal system at the eastern boundary of the Roer Valley Rift System – A case study from the Viersen Fault Zone in the vicinity of Straelen, Germany

Geothermal systems have been developed in Paleozoic rocks within the Roer Valley Rift System (RVRS) on the Campine Block in Belgium in the West (e.g. Mol) and the Peel Block in the Netherlands in the East (Tegelen Fault, Californië project). However, no geothermal system has been developed further along the eastern boundary of the RVRS where the tectonically active Viersen Fault Zone (VFZ) is located. This fault zone separates the elevated Krefeld Block from the Venlo Block located near Straelen, Germany. Given the high demand for heat by local greenhouses, the city of Straelen and its surroundings would greatly benefit from geothermal developments. In this study, we aim at characterizing the subsurface structures of the VFZ to estimate the geothermal potential of the Dinantian carbonates, Upper Devonian Condroz sandstones and deeper targets like the Upper/Middle Devonian limestones. This is done by reinterpreting seismic data acquired within the framework of the Californië project, analyzing recently acquired data within the framework of the SCAN project and new gravity measurements performed in the Straelen area. The seismic interpretation indicates fault linkages and relay structures which can be correlated to surface expressions and the recorded gravity measurements. The potential geothermal reservoirs were mapped and horizons were interpolated between the seismic lines with insights provided from gravity results. Our investigations illustrate the previously undescribed segmentation of the Viersen Fault Zone in the Straelen area. This tectonic deformation may promote or enhance fluid flow within the reservoirs in the vicinity of the VFZ similar to the geothermal system developed along the Tegelen Fault in the Netherlands. However, the current permeability of these damage zones in VFZ within the reservoirs requires further local subsurface investigations and in-situ tests through drillings to characterize the hydraulic properties and to map the reservoirs and associated structures in 3D.