Pump Tests In Deep Ore Mine Shafts For The Evaluation Of A Possible Geothermal Use
Stemke, Marion Maria; Wieber, Georg
Johannes Gutenberg-Universität Mainz, Germany
In the Rhenish Slate Mountains there are abandoned ore mines with depths of more than 1000 m. After the closure in the middle of the last century, the water in the mine rose up to the level of the receiving water. As a result, water bodies with increased temperatures and a high geothermal potential formed in the underground of the mines. The mines presented here are located in Germany in the state of Rhineland-Palatinate in the town of Herdorf.
Wieber & Streb (2012) developed the variant of extracting mine water from the downstream deep shaft of the San Fernando mine, using it geothermally and then reinjected it into the upstream shaft of the Friedrich Wilhelm mine. The resulting cycle is intended to ensure the regeneration of the geothermal regime. Theoretically, a pumping rate of up to 100 l/s could be achieved for geothermal use. A long-term pumping test was carried out in 2018. The shafts San Fernando Schacht 2 (pump well) and Friedrich-Wilhelm Schacht 2 (injection well) involved in the pumping test each have depths of 930 m and are not connected to each other near the surface, but only via the 830 m level. The composite pit drains freely in the outlet of the Wolf pit. In the period from 2009 to 2010, a discharge of 6.5 to 8 l/s was measured in the summer half-year and 9.4 to 12 l/s in the winter half-year.
The pumping test was carried out in stages with a pumping rate of 8 l/s, 12 l/s and 16 l/s. No significant changes in the water level could be detected in the pump shaft. In the absorption well, however, fluctuations occur which reflect the water inflow from the pump well. In the dewatering adit of the Wolf mine less water flows out with the water withdrawal in the San Fernando shaft. It was found that the water level in Friedrich-Wilhelm shaft slowly decreased again when the water withdrawal was constant over a longer period of time, while at the same time an increase in the amount of water could be observed in the outlet of the Wolf mine. The changes in the flow rate at the Wolf dewatering adit range from dry traps to a sudden increase of up to 21 l/s when the pumps are switched off.
The measured data show that there is at least at times only a limited hydraulic connection between the mines.