Thermal conductivity of rocks and regional mapping

ABSTRACT In the low enthalpy geothermal field a proper plant design is fundamental in order to ensure an efficient exchange of heat, avoiding sizing errors of field probes resulting in a loss of energy efficiency or excessive costs. Therefore, it is, among others, important to know the thermal conductivity ( Wm -1 K -1 ) of rocks and sediments involved by ground heat exchangers, providing a distribution map to be associated to other fundamental parameter maps useful for geothermal system planning. Aim of this paper is to highlight the need for a reasoned choice of heat conductivity values to be assigned at regional and local scale. In fact, laboratory measurements in dry and wet conditions give the value belonging to a specific sample. To up-scale the laboratory data to a regional scale we must take into account the different lithologies forming the lithological units represented on geological maps. Moreover, it is necessary to consider the presence of water and the influence of the entire stratigraphic sequence on the subsoil generally involved by geothermal pumps and affected by heat exchange performance. Thermal property tests were carried out in laboratory (dry and wet condition) by using specific equipment, on more than 200 samples collected in four regions of southern Italy (Calabria, Campania, Apulia and Sicily) in the frame of the VIGOR Project, aimed at assessing the values of rocks and loose materials previously obtained from the screening of international literature have been validated by comparison with those directly measured on samples. A were then assigned to the most representative geological units, selected according to the largest areal extent (km