Exploring the use of mining shafts with geothermal systems using numerical modelling

As the world transitions to greener sources of energy, understanding how to best plan this transition becomes a critical challenge. A relatively recent approach contributing to the decarbonisation of heating and cooling infrastructure is repurposing abandoned mine networks to deploy geothermal energy technologies. These technologies utilise the subsurface to sustainably provide heating and cooling to buildings and are one of the key renewable technologies contributing to and shaping the decarbonisation of our energy landscape. Different configurations for exchanging heat with the ground can be used, such as closed- or open-loop systems, as well as operational strategies, such as utilising thermal storage, which can affect the subsurface requirements and design of the system.

With mining operations being increasingly shut down, geothermal mine systems not only constitute a sustainable method to providing heating and cooling energy, but also repurpose these abandoned sites and subsurface networks. Additionally, while geothermal energy technologies are generally highly efficient, important barriers to their wider implementation include relatively high capital costs due to subsurface-related uncertainties and the need for earthworks, as well as the dependency on groundwater flow conditions for certain applications. Integration with mines can contribute to overcoming these barriers, such as by minimising required earthworks, by reducing uncertainty through access to high quality data on the state of the subsurface, and by offering advantageous subsurface conditions for a geothermal system that takes advantage of the flow of water through the tunnels.

Integrating geothermal technologies within abandoned mine infrastructure to provide heating and cooling to buildings has been demonstrated and proven in several European countries in recent years. Large-scale projects, such as the Gateshead heat network in the UK (6MW heat pump) and the district heating system in Heerlen, Netherlands, showcase the potential of using flooded subsurface tunnel networks to provide geothermal energy at a large-scale. However, one potential smaller-scale application that has received little attention, and is the focus of this work, is utilising mining shafts.

Abandoned mining shafts are typically covered and flooded, making them a potential low hanging fruit for incorporating geothermal energy applications. While this concept is discussed in literature, more information is needed on the applicability and suitability of different geothermal configurations under different mine shaft conditions. This work contributes towards bridging this gap by utilising advanced finite element modelling methods to simulate a typical mine shaft, adopting a case study from the UK, and investigating in detail the potential energy yields of different geothermal applications under different conditions. Importantly, the effect of natural convection, expected to be significant in a flooded shaft compared to saturated soil, is carefully considered, acknowledging the complexities this introduces due to the difficulty of computational flow modelling at this scale.