About this project
Mining operations typically extend below the groundwater table, requiring continuous pumping to keep workings dry. When a mine is closed and pumping stops, groundwater gradually floods the voids, creating a thermally stable reservoir with potential as a low-enthalpy geothermal energy source. Realizing this potential, however, requires a in-depth quantitative understanding of the coupled flow and heat transport processes that govern the system.
The DIETER project (https://www.iws.uni-stuttgart.de/en/lh2/research/projects/dieter/) aims to develop a comprehensive hardware- and software-based monitoring system for two flooded mines located near Bad Ems. Alongside extensive field investigations and monitoring activities, one of the project's subprojects focuses on the development of a physics-based numerical model. The model is intended to improve the understanding of the governing hydraulic and thermal processes within the two study sites while at the same time providing a transferable framework that can be applied to other flooded mine systems. Within this context, the present work contributes to the development of a process-based, coupled multidimensional numerical model implemented in the open-source simulation tool DuMux.
The central modeling challenge lies in the fundamentally different flow regimes present: free and sometimes turbulent flow within the mine voids, and slow Darcy-type flow through the surrounding host rock. To capture both regimes, the model couples one-dimensional pipe flow in the mine network with three-dimensional porous medium flow in the host rock. This coupling is realized via an embedded approach using sink and source terms, which enables fully independent meshing of the two domains.
The exchange terms driving mass and energy transfer between the two domains are formulated as functions of the respective primary variable differences. For mass exchange, the driving force is the pressure difference between the pipe and porous medium domains, a coupling that has already been successfully implemented and tested in DuMux. In this project we want to extend the coupling to include the energy exchange, where the convective heat flux is governed by the local Nusselt number.
The resulting model can serve as a tool for detailed analysis of the geothermal potential of flooded mines and as a reference tool for the validation of reduced-order models.