Modelling the geometry of abandoned coal mines for inter-seasonal heat and cold underground storage

Wallonia (southern Belgium) experienced intense coal mining in the 19th and 20th centuries. The depths of these abandoned coal mines range from the ground surface to more than 1000 m. These abandoned mines are now being studied as potential reservoirs for inter-seasonal geothermal storage operations as part of the operation of 5th generation heating networks. In the scope of feasibility studies, a major challenge is to reconstruct the geometry of former structures and works, a preliminary but essential step in modelling flows and heat transport underground.

As these mines have long since closed and are no longer accessible, this work is based solely on archive documents such as mining maps from the former collieries and cross-sections held by the mining administration. The information available in these documents is invaluable. However, this information, some of which dates back more than a century, is sometimes difficult to interpret and cannot be considered exhaustive. Moreover, it is not homogeneous and the accuracy of the topographical information varies depending on the source and the time period.

In order to reconstruct a coherent model of the mine workings, galleries and shafts, a geological model constrained by information from archive documents is constructed. Next, the elevation of the boundaries of the mine workings and galleries in layers is adjusted on the layers derived from the geological model in order to preserve the topological links between objects. Finally, a discretised model representing the zones of increased permeability around the workings and galleries is extracted. To carry out all these operations and the associated quality controls, a workflow based on developments in Python and relying on open source libraries has been developed and tested.