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Article RSE 14005766

Thermal Response Tests and effects of geological heterogeneity

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Rendiconti on-line della Società Geologica Italiana ISSN 2035-8008, vol. 32, pp. 7-14, Novembre-2014.

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F. Colucci (RSE SpA), F. Moia (RSE SpA)

ENERGEOTER 2014 - Electricity from geothermal sources

The thermal response of the ground has been studied by the execution of five ground response tests and the analysis of a significant set of 15 experimental tests. The conductivity and thermal resistance have been estimated in wells with single or double U geothermal probes. The obtained results show the difficulties to evaluate the water and aquifer influences especially in recent alluvial sediments.

The low enthalpy geothermal energy is a technology that can significantly limit the use of fossil fuels and to contribute effectively to reduce greenhouse gas emissions. The closed-loop geothermal probes are easy to install, they 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 response tests have been analyzed with also the tests performed in the experimental field in Milan where two 100 meters deep borehole have been drilled with single U and double U closed-loop geothermal probes configuration. The experimental values have been compared with the theoretical ones based on the local site stratigraphy. In general, the experimental values estimated by using the Thermal Response

Test were more favorable than the theoretical ones, and it must be emphasize that the difference is consistent for a relevant set of cases. Certain thermal conductivity values are particularly high if compared to the expected ones from the local geology and it could be due to ground heterogeneity and groundwater flow can facilitated the heat exchange between borehole and ground. These experimental results seem to indicate that in complex and heterogeneous sedimentary basins as Po plain, it is really difficult to quantify the real deep aquifer contribution in the estimation of ground thermal response.

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