Indirect Methods for Validating Shallow Geothermal Potential Using Advanced Laboratory Measurements from a Regional to Local Scale—A Case Study from Poland

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.

Subsalt Rotliegend Sediments—A New Challenge for Geothermal Systems in Poland

“…In the study, results of industrial volumetric interpretation of basic rock components (quartz, calcite, dolomite, anhydrite, halite, clay minerals) as well as water and gas saturation from many wells were used (Figure 4). The very recent completion of the K-1 well allowed for reliable estimation of the thermal conductivity logs, using commonly described methods [102][103][104][105][106][107], that in the Rotliegend interval were calibrated with laboratory measurements. Available data allowed to apply a mixing law model to calculate bulk TC for the whole drilled section using textbook TC values (Figure 5).…”

“…Because of lack of appropriate data, the correction for pressure was not computed. Open-high-low-close chart of thermal conductivity of selected rocks and reservoir media according to [77,107,[110][111][113][114][115][116][117][118] (OC-blue bars express thermal conductivity values of particular rocks and media used for the calculations performed in the study).…”

Upgrading a District Heating System by Means of the Integration of Modular Heat Pumps, Geothermal Waters, and PVs for Resilient and Sustainable Urban Energy

“…This is connected both with ground and water potential. According to the results obtained during the implementation of the GeoPLASMA-CE project [35], as well as further studies [36], the thermal conductivity of the soil in the geological profile in Krakow up to 100 m b.g.l. differs from 1.65 to 3.4 W/m/K.…”

“…Estimations made within the GeoPLASMA-CE [35] project show that in the area of Krakow a considerable shallow geothermal potential occurs, both in rocks and in groundwater [36]. The evaluated inventory exposed that about 200 small and 24 bigger geothermal heat pump installations with a total capacity of approximately 5 MWt were working in Krakow at the end of 2018, apart from heat pumps with a horizontal heat exchanger and air heat pumps [37].…”