The paper presents a review of the geological and hydrogeological data of the Lower Cretaceous aquifer in the Polish Lowlands and discusses the possibilities for the utilisation of geothermal water resources in existing and new district heating systems. Based on experience related to the use of thermal waters in existing geothermal systems, and using data from the literature, assessments have been made of the energy and environmental effects of the application of low-enthalpy geothermal resources from the Lower Cretaceous aquifer as a source of heat for urban district heating systems. The authors concluded that the implementation of such solutions could result in the production of approximately 4 PJ of geothermal energy annually. To date, these resources have only been developed in three locations—Mszczonów, Uniejów and Poddębice—with the total amount of energy generated annually reaching 100 TJ/year. Similar district heating networks in 120 nearby localities have been also identified. Here, specified geological and hydrogeological conditions enable the extraction of heat from the investigated Lower Cretaceous aquifer, with the aim of using this for heating purposes. To achieve this goal, multiple measures are required, including the following: raising public awareness through appropriate education programmes aimed at the youngest school children; systemic, efficient energy management measures at the central, regional and local levels, and providing financial support and ensuring regulations and laws aimed at improving the development of geothermal resources.

The beginnings of geothermal implementation research in Poland date back to 1989–1993 when the Mineral and Energy Economy Research Institute of the Polish Academy of Sciences (MEERI PAS) launched the first geothermal installation in the Podhale region, using the reconstructed Bańska IG-1 well. The knowledge acquired during these 30 years has highlighted the importance of geothermal energy—among other things, borehole reconstruction operations and the need for their further refinement. The technologies developed have been used in virtually all geothermal heating systems operating in Poland. Examples of successful reconstruction work include the Bańska IG-1 and Biały Dunajec PAN-1 wells operated by the PEC Geotermia Podhalańska S.A. geothermal company. The Mszczonów IG-1 well, which is operated by the Geotermia Mazowiecka S.A. heating company, has also undergone considerable work almost 24 years after its complete closure. Reconstruction processes can also be important in adapting existing wells for geothermal purposes. After World War II, more than 8000 boreholes deeper than 1000 m were drilled in Poland. They were primarily made for the purpose of geological surveys and hydrocarbon exploration. Some of these boreholes can be adapted for operation in geothermal systems. The paper presents selected methods of reconstructing abandoned, disused (not abandoned and not decommissioned) or damaged boreholes in order to use them in the geothermal water extraction process. Four examples of borehole reconstruction, designed and carried out with the participation of MEERI PAS in Kraków, are discussed in more detail.

Geothermal energy, as one of the more well-known renewable energy sources (RES), is used in many operating installations around the world. Depending on the temperature of the geothermal waters in question, the choices range from installations for generating electricity (high-temperature geothermal energy), to the production of thermal energy for use in recreational complexes, to fish farming (low-temperature geothermal energy). Lindal’s diagram determines the possibilities of using warm groundwater for many investment projects. In light of the drive to avoid climate change, it seems that the conventional “one-way” use of geothermal water resources is insufficient. Therefore, this article presents an optimal innovative solution wherein geothermal water is fully utilized in a geothermal cogeneration installation to produce heat and electricity and to provide cooling. In addition, it was proposed to expand the investment with photovoltaic and hydropower plants to ensure greater energy independence by diversifying energy sources and increasing the share of energy supplies based on renewable energy sources. Such a broad approach allows for the implementation of a sustainable development strategy in the field of environmental protection. The proposed solution involves the modernization and expansion of the existing energy generation sources by a heating plant and a geothermal power plant in Chochołowskie Termy (South Poland), as well as the construction of a power plant based on a photovoltaic installation, hydropower setup, and energy storage. The presented innovative solution may be an excellent example of implementation for similar geothermal facilities in the world. The novelty of the system is the approach of assessing and combining the different RES in one project, based on a geothermal plant. Popularizing this solution in the wider scientific environment may have a real impact in terms of the reduction of pollutant emissions.

In deep geothermal boreholes, an effect of temperature (so-called thermal lift) is observed, which results in the volumetric expansion of the fluid extracted. This process results in increased wellhead pressure values being recorded; in the absence of an appropriate correction, hydraulic properties of the reservoir layer cannot be properly determined. As an example of this effect, the Chochołów PIG-1 (CH PIG-1) geothermal borehole situated in Podhale Basin in Poland was used. Hydrodynamic tests including two pumping phases were carried out in the well in order to establish the basic hydraulic properties related to the determination of its operational resources (maximum water extraction value–capacity) and permissible groundwater level. Particular attention was paid to the thermal lift effect in the borehole. The conductivity, which depends on the pumping level, could be two to three times higher with temperature correction than results without any correction. The goal was to analyse the variability of the observed physiochemical properties of the exploited geothermal waters and to determine the correlation between the properties analysed and the temperature of the geothermal water. For the relationship between temperature and the observed pressure at the wellhead, the value of the correlation coefficient was negative (a negative linear relationship was determined), which means that as the temperature increases, the wellhead pressure decreases. The hydrodynamic tests carried out in the CH PIG-1 borehole and the analysis of variability of selected ions and parameters in exploited water were necessary to assess the possibility of increasing the efficiency (Q) of the CH PIG-1 borehole and to determine the water quality and its natural variability. Such information is crucial for the functioning of the recreational complex based on the use of geothermal water. A study of the phenomena affecting the exploitation of hot water from deep boreholes enables their effective exploitation and the use of resources in accordance with the expectations of investors.

Over the last few years, there has been an upsurge in the demand for drinking water and for water used in agriculture, industry, and others. Consequently, research is needed to find new technologies and methods for the comprehensive use of geothermal water sources, to provide for new resources of water. The paper shows the results of preliminary recognition in the case of the possible exploitation of the Jurassic aquifer in the Polish lowlands, considering the security of the adjacent layers. The considerations are based on experience in the exploitation of the resources of the Paris basin in France. Initial conclusions point to a high potential for such a solution, also in the Paris basin scientists are considering the use of previously unmanaged Jurassic resources.

The aim of the presented work was an attempt to verify the geothermal conditions in the Polish Lowlands (Lower Jurassic and Lower Cretaceous reservoir) based on new geological information. The paper presents geothermal conditions in the Polish Lowlands according to the state of recognition at the end of 2022 in order to update the hydrogeothermal conditions in selected regions. Based on the scientific and research works published so far as well as numerous geothermal investments, and geological information from twenty-three new exploratory drilling events performed in the years 2000–2022 (nineteen of which were performed/documented after 2006), the authors undertook to update forecasts of the top surface of Lower Jurassic and Lower Cretaceous formations, the total thickness of these formations and the potential discharge of wells. The analysis was performed using the QGIS Desktop 3.24.1 software, a cross-platform and free open-source geoinformation software application (GIS ) that enables the viewing, editing and analyzing of spatial data and the creation of maps. The correction covered the course of the isolines on all six analyzed maps. The presented analysis made it possible to make a spot correction of the forecasted course of the isoline in relation to the maps published earlier in the Atlas of geothermal resources in the Polish Lowlands. Mesozoic formations developed in 2006, edited by Wojciech Górecki. Information obtained from newly drilled geothermal boreholes enabled the local correction of the forecasted values of individual parameters while maintaining the general trend.