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

New seismic data and the completion of the K-1 petroleum exploratory well, located close to the axial zone of the Mogilno-Łódź Trough (Polish Lowlands) delivered new insight into local structural, tectonic, facial and thermal variability of this geological unit. In this paper, the two variants of 3D models (SMV1 and SMV2) of Permian-Mesozoic strata are presented for the salt pillow related Kłecko Anticline, while resources assessment was confined to the Rotliegend Enhanced Geothermal System (EGS) type reservoir, that is divided into Playa, Eolian and Fluvial facies-based complexes. Using very conservative assumptions on the methods of the EGS reservoir development, authors assessed that heat in place and technical potential for eolian sandstones are about 386 PJ and ca. 2814 kW, respectively, and for Fluvial 367 PJ and ca. 2850 kW in relation to the volume of 1 km3 at depths of about 5000 m b.s.l. The authors recommend for the further development of the Eolian complex because of its low shale content, influencing the high susceptibility to fracking. The presented research is the first Polish local resources assessment for an EGS reservoir in sedimentary Rotliegend, within thermal anomaly below the salt pillow, which is one of over 100 salt structures mapped in Poland.

Predicting the effective thermal conductivity of unfrozen soils with various water contents based on artificial neural network

The effective thermal conductivity of soils is a crucial parameter for many applications such as geothermal engineering, environmental science, and agriculture and engineering. However, it is pretty challenging to accurately determine it due to soils' complex structure and components. In the present study, the influences of different parameters, including silt content (m_si), sand content (m_sa), clay content (m_cl), quartz content (m_qu), porosity, and water content on the effective thermal conductivity of soils, were firstly analyzed by the Pearson correlation coefficient. Then different artificial neural network (ANN) models were developed based on the 465 groups of thermal conductivity of unfrozen soils collected from the literature to predict the effective thermal conductivity of soils. Results reveal that the parameters ofm_si,m_sa,m_cl, andm_quhave a relatively slight influence on the effective thermal conductivity of soils compared to the water content and porosity. Although the ANN model with six parameters has the highest accuracy, the ANN model with two input parameters (porosity and water content) could predict the effective thermal conductivity well with acceptable accuracy andR²= 0.940. Finally, a correlation of the effective thermal conductivity for different soils was proposed based on the large number of results predicted by the two input parameters ANN-based model. This correlation has proved to have a higher accuracy without assumptions and uncertain parameters when compared to several commonly used existing models.

Characterisation of Ground Thermal and Thermo-Mechanical Behaviour for Shallow Geothermal Energy Applications

Increasing use of the ground as a thermal reservoir is expected in the near future. Shallow geothermal energy (SGE) systems have proved to be sustainable alternative solutions for buildings and infrastructure conditioning in many areas across the globe in the past decades. Recently novel solutions, including energy geostructures, where SGE systems are coupled with foundation heat exchangers, have also been developed. The performance of these systems is dependent on a series of factors, among which the thermal properties of the soil play a major role. The purpose of this paper is to present, in an integrated manner, the main methods and procedures to assess ground thermal properties for SGE systems and to carry out a critical review of the methods. In particular, laboratory testing through either steady-state or transient methods are discussed and a new synthesis comparing results for different techniques is presented. In situ testing including all variations of the thermal response test is presented in detail, including a first comparison between new and traditional approaches. The issue of different scales between laboratory and in situ measurements is then analysed in detail. Finally, the thermo-hydro-mechanical behaviour of soil is introduced and discussed. These coupled processes are important for confirming the structural integrity of energy geostructures, but routine methods for parameter determination are still lacking.