The Heat beneath Our Feet

While coal energy is phased out to decarbonise our energy supply, the water within flooded abandoned mines provide a huge source (2.2 million GWh) of geothermal heat for the future, enough to meet the UK’s heating demand for more than a century. The mine water is only lukewarm (12-20^oC), but by using a heat pump, temperatures can be increased to a more comfortable 40-50^oC. Heat pumps need electricity, but for every kW of electrical input, the heat output is 3-4 kW, making this an efficient energy source. Research has shown that our abandoned mines could meet our heat demands for a century or more, and will deliver economic opportunities to former mining areas.

After abstraction of water from the mine and subsequent heat extraction , the mine water is returned to the subsurface to avoid surface water contamination. Understanding the subsurface to ensure the right location(s) for re-injection of the water is crucial for the thermal evolution of the mine system. In addition, mine water could interact with nearby (potable) aquifers, so a proper understanding of the hydrogeological behaviour of the mined system is required. Therefore, numerical modelling of mine water and surrounding groundwater flow and associated heat exchange is an essential first stage for the successful deployment of these geothermal mine energy systems.

Here, we present numerical modelling results of the thermal evolution of mine water circulation systems. A parameter sensitivity study gives insight in the rate of heat depletion of the mines, and the importance of several model parameters, such as mine tunnel connectivity, mine water flow speed, and water re-injection location.

This project involves collaboration with the Coal Authority and Durham county council in the UK. Available mine plan data offer opportunities to apply the modelling to proposed mine energy sites across coalfields in the UK and further afield. Results will be applied for planned geothermal energy sites at Stanley (county Durham), South Tyneside and Blyth Port in north-east England.