Thermal Response Tests and effects of geological heterogeneity

Francesca Colucci (a) & Fabio Moia (a)
(a) Ricerca sul Sistema Energetico - RSE Spa, Via Rubattino 54, 20134, Milano. E-mail: francesca.colucci@rse-web.it

"The low enthalpy geothermal energy can significantly limit the use of fossil fuels and contribute effectively to reduce greenhouse gas emissions. This source of energy can be exploited through geothermal plants where closed-loop geothermal probes represent the main configuration. These are easy to install, have a simplified authorization procedure and, combined with heat pumps in the GSHP-Ground Source Heat Pumps systems, provide a real support to energy efficiency. For a proper design of complex geothermal plants, it is important to know the ground thermal response in order to properly size the number of vertical probes related to energy that must be provided or disposed. The ground thermal exchange can be estimated by means of the TRT-Thermal Response Test that allows a direct measurement of the subsoil thermal conductivity and thermal resistance of the boreholes. A relevant set of experimental TRT has been analyzed including some tests performed in the experimental field in Milan. The experimental values have been compared with the theoretical ones based on the local site stratigraphy. In general, the experimental values estimated using the TRT were more favourable than the theoretical ones, and it must be emphasize that the difference is consistent for a relevant number of cases. Certain thermal conductivity values are particularly high if compared to the expected ones referred to local stratigraphy. This could be due to ground heterogeneities, and groundwater flow that can facilitate the heat exchange between borehole and ground. These experimental results seem to indicate that in complex and heterogeneous sedimentary basins, such as the Po plain, it is essential to execute TRT in order to quantify the real deep aquifer contribution in the estimation of ground thermal response. Conversely, in the absence of TRT, considering only the theoretical estimates based on the local site stratigraphy, it is really difficult to assess the ground thermal response."

Aquifers, Geothermal energy, GSHP, Low Enthalpy, Thermal Response Test.