Abstract
This paper presents a broad overview of laboratory methods for measuring thermal properties and petrophysical parameters of carbonate rocks, and analytical methods for interpreting the obtained data. The investigation was conducted on carbonate rock samples from the Kraków region of Poland in the context of shallow geothermal potential assessment. The measurement techniques used included standard macroscopic examinations; petrophysical investigations (porosity, density); analysis of mineral composition thermal conductivity (TC) and specific heat measurements; and advanced investigations with the use of computed tomography (CT). Various mathematical models, such as layer model, geometric mean, and spherical and non-spherical inclusion models, were applied to calculate thermal conductivity based on mineralogy and porosity. The aim of this paper was to indicate the optimal set of laboratory measurements of carbonate rock samples ensuring sufficient characterization of petrophysical and thermal rock properties. This concerns both the parameters directly characterizing the geothermal potential (thermal conductivity) and other petrophysical parameters, e.g., porosity and mineral composition. Determining the quantitative relationship between these parameters can be of key importance in the case of a shortage of archival thermal conductivity data, which, unlike other petrophysical measurements, are not commonly collected. The results clearly show that the best correlations between calculated and measured TC values exist for the subgroup of samples of porosity higher than 4%. TC evaluation based on porosity and mineral composition correlation models gives satisfactory results compared with direct TC measurements. The methods and results can be used to update the existing 3D parametric models and geothermal potential maps, and for the preliminary assessment of geothermal potential in the surrounding area.
Highlights
Energy policies and climate protection are, in addition to safety issues, some of the most important global challenges at the present time
Selection of a Several laboratory methods allow for the determination of thermal conductivity values
The comparison of the laboratory measured thermal conductivity values with those obtained by mathematical models clearly indicates the impact of both the mineralogy and petrophysical properties of the investigated rocks on the models tested
Summary
Energy policies and climate protection are, in addition to safety issues, some of the most important global challenges at the present time. Despite the current low share in total heat production, Poland is recognized as the fourth largest heat pump market in Europe in terms of annual sales [3] This situation has resulted from raising awareness of environmental issues but is due to the adopted declarations on the reductions of emissions. The development of heat pump technology can assist in the improvement of air conditions and increase the total share of renewable energy sources in Poland’s final energy consumption. Knowledge of the potential of shallow geothermal energy, including thermal conductivity distribution, is an important factor in the sustainable development of the heat pump market and a tool to assist in the reduction of low emissions in Kraków. The authors used the models to calculate thermal conductivity of the Carpathian sandstones [21,22]
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