Experimental heat flow propagation within porous media using electrical resistivity tomography (ERT)

With increasing numbers of installed systems for the thermal use of the shallow subsurface concerns arise about potential effects on soil and groundwater. So far no consistent economic, political and / or environmental regulations have been established to address these concerns. Furthermore, a lack of fast and effective long-time monitoring method exists to control the environmental impact that may occur at such sites. To address this issue, this study focuses on evaluating the non- invasive geophysical method ‘electrical resistivity tomography’ (ERT), using laboratory measurements to derive a possible efficient monitoring system for shallow geothermal systems. We installed a heat source in an experimental box filled with different porous media, and monitored heat propagation levels. Additionally, electrical resistivity changes were measured to evaluate the correlation between thermal and electrical conductivity. Here, the electrode arrangements correspond to surface multi- column arrays of typical field measurements, which can then be evaluated. Additionally, small electrode chains were installed to monitor the electrical resistivity in different depths and to readjust electrical borehole measurements.