| Abstract |
The transboundary Late Miocene sand and loose sandstone aquifer is the most productive and exploited geothermal aquifer in the Pannonian Basin. In Slovenia, it provides at least 2.3 million m3 of thermal water per year. Exploratory monitoring identified declining trends in piezometric levels between 2009 and 2015, indicating a high risk of overexploitation. Following the establishment of a stricter operational monitoring regime in 2015, when the most concession contracts were signed, the negative trends became less pronounced. Currently, three laws regulate use of geothermal energy, but they are not harmonized in requirements (including reinjection) or reporting. During the COVID-19 years, regional groundwater levels ceased to decline and have now mostly stabilized or are slightly increasing. Only one reinjection well has been in full operation since 2009, while three additional have been supported by substantial subsidies in the last two years, however, they are still in a test phase. As the quantitative status has improved before their construction, a question arises as to whether they are necessary and economically viable. There are also various technical and geological issues regarding the proper design and positioning of such reinjection wells, which we have tried to explore recently. Using numerical modelling, we have evaluated several development scenarios for this geothermal region, from mandatory reinjection for users relying solely on geothermal heat (e.g. district heating, greenhouses) to targeted exploration and reinjection drilling support in most intensively exploited areas. |