| Title | Chrono Thermography - fiber optic-based integrity testing of the backfill of geothermal probes via Distributed Temperature Sensing (DTS) |
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| Authors | Clemens Lehr, Ingo Sass |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | Introduction Backfilling the probe creates a frictional connection between the probe and the surrounding rock. If thermal energy is applied to the probe (heat pulse), heat flows from the fluid in the probe to the surrounding rock via the backfill. At those points where the rock is relatively more thermally conductive, the temperature increase is relatively lower than at those points where the thermal conductivity is relatively poorer. This is because the energy can be transferred more quickly in the rock or dissipated from the probe if the thermal conductivity is better. At those points where the energy cannot flow away as quickly due to relatively poorer thermal conductivity, the temperature is correspondingly higher. Areas that are influenced by groundwater flow also show an apparently higher conductivity, as heat is continuously dissipated from the probe by the groundwater flow. Measuring Method With a thermally stimulated probe (heat pulse test), statements on thermal conductivity, groundwater influence and backfilling can therefore be derived from temperature-depth profiles in correlation with the geology. If the measurements are repeated continuously (chrono-thermography), the graphical representation shows the thermal properties of the space surrounding the probe with high contrast. In the case of vertical flows in the borehole - caused by short circuits between aquifers of different pressure potentials - the mass flow in the faulty backfilled borehole can be estimated using the high-resolution measurement. Anomalies in correlation with the geology can be reliably detected and evaluated using this fiber optic-based method. |