The German demosite is situated within the city of Bochum, which is located in the center of the Ruhr Coal District and the municipality belongs to the state North-Rhine Westphalia. The Ruhr coal basin is part of the external fold and thrust belt of the Variscan orogeny in Central Europe. Sedimentary rocks in this region represent mostly the molasse-type sequence of the Upper Carboniferous, basically formed by interlayered sandstones, siltstones, mudstones and coals, with a thickness of more than 6000 m. The Variscan orogenic belt in Western and Central Europe was formed during the Late Palaeozoic convergence of the Euramerican (Laurussia) and Gondwanaland continental masses.
The convergence and collision took place during the Devonian and Carboniferous, with the deformation front migrating northward with time. Sedimentation concurrent with deformation in its surroundings formed the Variscan foredeep and foreland basin, which marks the Ruhr basin of today. The Ruhr basin strikes in southwest-northeast direction and has a length of 150 km and a width of 80 km across the strike. The demonstration site is located within a syncline, that contains a sedimentary sequence that belong to the Bochum and Witten strata. The study area is crosscut by a fracture system that represents the dominant permeable structures.
Figure 1. Geological section and injection well R2.
The task of the Fraunhofer Research Institution for Energy Infrastructures and Geothermal Systems (IEG) is to characterize the Bochum reservoir with regard to the suitability of a possible reinjection of NCGs. By Through a geological model, the influence of an injection on porosity and permeability shall be predicted. This is based on laboratory experiments on the reactivity of the predominant sandstone with synthetic geothermal fluids. In further pilot-scale flow experiments, the flow in the rock is simulated under real conditions. Finally, tests in the subsurface between two boreholes or push- and- pull experiments with a synthetic brine are to record the effects in the reservoir in order to refine the model.
The IEG has the task of designing, building and commissioning a fluid-gas reactor (FGR). This FGR will supply the other experiment components with an artificially generated and gas-enriched brine at elevated pressure and temperature. It will be able to enrich water with CO2 in steady state but also hold a volume of more than one cubic meter. The FGR will be able to maintain a constant outlet pressure for the experiments in the subsurface, so that the flow rate adjusts according to the geological conditions. Furthermore, the FGR will heat the brine to the experimental temperature.
Figure 3. Bochum demosite at Fraunhofer IEG test site.
Figure 4. Well drilling at Bochum demosite.