3D modelling of the Lower Carboniferous (Dinantian) as an indicator for the deep geothermal potential in North Rhine-Westphalia (NRW, Germany)

Geothermal energy will play a major role in the forthcoming energy and heat transition in Europe. In the scope of the Interreg-funded project DGE-ROLLOUT ("Roll-out of Deep Geothermal Energy in North-West Europe"), the hydro thermal potential of Lower Carboniferous (Dinantian) carbonate rocks is being investigated. There are five areas in North Rhine-Westphalia (NRW), Germany, which provide information about the Lower Carboniferous potential reservoirs: the Aachen region, the Velbert Anticline, the Northern Rhenish Massif, the Lower Rhine Embayment, and the Munsterland Basin. Much is known about the Tournaisian and Visean facies from field investigations of the first three areas, however, the deep subsurface of the last two areas lies in the focus of this investigation. Structural models and borehole information played a major role in the modelling process. In early Carboniferous times, a tropical shallow-water platform developed in the south of the Laurussian shelf forming thick carbonate deposits, which were often affected by karstification. The shelf edge of the large so-called Kohlenkalk platform is located in the transition zone between the Lower Rhine Embayment and the Munsterland Basin. The karstified platform carbonate rocks of the Kohlenkalk facies in the Lower Rhine Embayment provide ideal aquifers for hydrothermal energy exploitation, whereas proximal calciturbiditic deposits and their respective source areas may provide suitable reservoirs within the Kulm facies of the Munsterland Basin. A lithostratigraphic overview of the Lower Carboniferous formations in NRW has been summarised from the current literature, aiming to assist in the quick characterisation of drill cores and outcrop equivalents in NRW and surrounding areas. A digital 3D model of the subsurface was generated providing information about the depth, thickness and structure of the Lower Carboniferous strata in NRW. Consequently, an estimation of the temperature in the deep subsurface was calculated based on an average geothermal gradient of 30 degrees C/km. Temperatures above 100 degrees C are expected in the western part of the Lower Rhine Embayment (Roer Valley Graben) and throughout the Munsterland Basin. Here, it appears to be possible to implement hydrothermal heat and power generation depending on the geotectonic setting.