Measurement and analysis of thermal properties of rocks for the compilation of geothermal maps of Cyprus

Highlights

An extended geological sampling has been carried out in Cyprus and thermal properties have been measured on 135 samples.

A range of values for thermal conductivity, diffusivity and specific heat capacity have been assigned for each type of rock.

The impact on thermal properties of water in samples, the mineralogical composition and the geological age have been studied.

Thermal Conductivity and Thermal Diffusivity Maps of Cyprus have been compiled and are presented.

Abstract

Previous studies in Cyprus classified the island in the category of low enthalpy with high potentials in the usage of geothermal energy for space air-conditioning. Due to the little existing information about the underground thermal properties, an extended geological sampling has been carried out on the island. Measurements of thermal properties have been performed in the laboratory at room temperature for all the collected samples both in their dry and water-saturated state. The impact on thermal conductivity of water in samples, the mineralogical composition, and the geological age of samples have been the objectives of the current study.

Laboratory results of each rock type in Cyprus are found within certain ranges for each thermo-physical property as follows. Thermal conductivity values for dry rock samples vary between 0.4 and 4.2 W m−1 K−1, thermal diffusivity values range between 0.3 and 1.9 × 10−6 m2 s−1 and specific heat capacity values range from 0.5 to 1.5 J K−1 kg−1. Results also show that thermal conductivity and thermal diffusivity under moisture conditions increase for most of the lythotypes. The notable exception is Gypsum (Kalavaso Formation), which exhibits higher thermal response under dry conditions.

Measured thermal properties also present a difference between thermal properties of the lithologies of the Troodos Ophiolite and the Circum Troodos Sedimentary Succession in Cyprus. Mean values of thermal conductivity and thermal diffusivity for dry samples and water-saturated samples have higher values for the lithologies of the Troodos Ophiolite than measured values for the lithologies of the Circum Troodos Sedimentary Succession, mostly due to their mineralogical composition.

Moreover, the geological age of a lithology has been shown to affect its thermal response. Thermal conductivity of reef limestone and calcarenite rocks increases with the geological age of the lithology.

In order to understand and visualize all measured data the Thermal Conductivity and the Thermal Diffusivity Maps of Cyprus have been compiled with the use of a Geographic Information System (GIS) to be available to engineers as a powerful tool for use in the design of thermal engineering systems. From the obtained maps Troodos Ophiolite can be visualized as a separate part by having the highest values.

Keywords

  • Geothermal;
  • Ground thermal properties;
  • Lithologies;
  • Geothermal maps;
  • GIS

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