Dynamic vs static assessment of the mine water heat energy potential of coal mines

Flooded coal mines have the potential to provide low-carbon renewable heating, independent of surface weather and temperature conditions. To develop an open-loop mine water heating system, it is essential to estimate the amount of heat available within the mine. This estimation is necessary to determine the potential size of the system, assess whether it meets surface demand, and evaluate its economic viability.

Various methods can be used for this estimation. Static methods, which do not account for the influence of time or the underground spatial geometry, rely on simplified variables. These include calculating the background heat flow over the mine's area, estimating the heat stored in the rock volume surrounding the mine, assessing the heat in the mine's water volume, and determining a realistic flowrate to calculate the potential heat extraction.

In contrast, dynamic modelling methods provide a more comprehensive approach by accounting for changes in heat availability over time and the mine's structural architecture.

Using the GEMSToolbox, we performed dynamic modelling on a real two-seam coal mine map and a simplified grid model with comparable size and properties. The results from these dynamic models were compared with static methods, revealing significant differences in heat estimates, varying by orders of magnitude from 10¹⁰ MJ to 10³ MJ of heat produced over 40 years.

Dynamic modelling also offers additional benefits, such as tracking heat variation over time, analysing the impact of different injection and abstraction points, and assessing potential interference from nearby geothermal systems. These findings underscore the advantages of dynamic modelling in developing and optimising mine water heating systems.