In the course of the DGE-ROLLOUT project, the Geological Survey of North Rhine-Westphalia (GD NRW) has finished its third drilling campaign. The drilling site was a quarry in Hastenrath, not far from the Weisweiler lignite-fired power plant, which can be seen on the horizon in the background of the first picture. The targeted rocks, which also occur in some kilometers depth beneath the Weisweiler power plant, reach the surface in Hastenrath. This gives geologists the unique opportunity to study their geothermal properties and to obtain indications of their suitability as hydrothermal target rocks.
In Hastenrath, GD NRW has now obtained 98 meters of drill cores and transported them to their laboratory. The following rock layers are present in the core (from top to bottom): karstified and dolomitic limestones of the Kohlenkalk Group comprising the Vesdre, Pont d'Arcole and Hastière Formations, as well as underlying siltstone/claystone alternations of the Etrœungt Formation and sandstones of the Condroz Group. In addition, the Carboniferous/Devonian boundary was encountered in between the Hastière and Etrœungt Formations. Subsequent to the drilling, comprehensive borehole geophysical investigations were undertaken which are currently being evaluated. Further geochemical and petrophysical laboratory measurements will be planned following a detailed lithostratigraphic description of the drilled rocks.
Supplementing an earlier drilling campaign, GD NRW has now acquired drill core samples of the entire Kohlenkalk Group in Hastenrath which dates to c. 340 to 361 Ma. These Lower Carboniferous rocks, which had been deposited in a former ocean basin, the Rhenohercynian basin, are complemented by several meters of underlying Upper Devonian drill core yielding an age of more than 362 Ma. Considering important geological characteristics (karstification, dolomitization, etc) in the samples of the Kohlenkalk Group it is known that these are generally suitable for the exploitation of geothermal energy, assuming their deep burial and thermal insulation.
At Hastenrath, however, these rocks occur in a geological saddle (anticline) structure directly below the surface. Hence, whereas these rocks are not suited for the generation of geothermal energy in place, their unproblematic accessibility makes them an ideal target for geological investigation and provides crucial information on their geothermal characteristics. Pictures: Fritschle/Becker (GD NRW)
