GEMSToolbox: A novel modelling tool for rapid screening of mines for geothermal heat extraction

Mine water geothermal heat extraction is a promising technology to provide long-term, zero carbon heating in former coal mining regions. However to allow the technology to develop further, modelling tools which are faster than 3D coupled-process simulators and more site specific than analytical solutions need to be developed. A novel modelling tool, GEMSToolbox, was designed for assessing the feasibility of disused and flooded mine workings for such geothermal heat extraction. The basis of GEMSToolbox is built upon tested, computationally efficient modelling methods, and combines efficient solvers for water flow through the mine workings with fast solution methods for heat exchange between the water in the mine galleries and the surrounding rock mass. It expands and improves on these methods by (1) allowing for arbitrarily complex multi-seam mine geometries, and (2) addressing potential thermal interaction between nearby mine galleries using a novel geometric weighting technique. Fast calculation allows for wide parameter investigation studies that is required given the often uncertain state of disused mine systems. This makes the tool ideally suitable for the feasibility stage of a project for which site-specific yet computationally efficient alternative tools are currently lacking. The tool is demonstrated on a case study using plans from a real mine system and shows how it can be used to evaluate the long-term thermal performance of a mine water geothermal heat scheme.