Methodology for Stored Heat “Heat In Place” (HIP) assessment of geothermal aquifers – Exemplified by a study of the Arnager Greensand in SW Scania

Sammanfattning: In the sedimentary bedrock of southwest Scania, located in the southernmost part of Sweden, there are several low-enthalpy Mesozoic sandstone aquifers situated at different depths. These aquifers collectively hold the potential for direct-heat geothermal utilization. Given the energy supply challenge across Europe, there is a growing need to characterise the geothermal resources and quantify their energy content. Despite this demand, the assessment of geothermal resources in Sweden has not been performed to any larger extent in comparison to assessment studies of similar geothermal aquifers in Europe. This limitation is concerning, as these aquifers should be acknowledged as national renewable energy assets. This study presents a first-ever geothermal assessment using the stored heat “Heat-In-Place” (HIP) method on the Cretaceous Arnager Greensand over southwest Scania. The results present a set of maps that illustrate the stored heat in the subsurface for the Arnager Greensand, and additional maps detailing the spatial distribution, such as the depth to the formation, thickness, and reservoir temperature. The Arnager Greensand stores a total of 3270 PJ in a range of 1.25 – 4.53 GJ/m2 over SW Scania. The stored heat values are slightly higher with a total of 3610 PJ in the range of 1.37 – 4.99 GJ/m2 in the rock matrix and reservoir fluids separately. The produced maps show the regional geothermal signatures of the Arnager Greensand where the stored heat is particularly marked in the southern parts of the region covering the Falsterbo Peninsula. The relatively greater stored heat in this area can be attributed to the greater thickness of the Arnager Greensand formation. The region from the Falsterbo Peninsula to Malmö and Trelleborg demonstrates relatively greater stored heat values, offering potential for further local geothermal investigations. Its proximity to urban and industrial areas significantly enhances the feasibility of integrating a well-doublet system into a district heating system. Due to the absence of borehole data, the assessment of the stored heat over the Skurup Platform is uncertain. This necessitates additional borehole information to improve the geothermal assessment. In a broader regional context, the stored heat findings indicate that the Arnager Greensand has limited potential as a geothermal reservoir as the stored heat values are lower than those of similar geothermal aquifers in comparable geological settings. Taking into account the Lower Cretaceous sandstones beneath the Arnager Greensand as a combined aquifer with a greater cumulative thickness, the geothermal potential increases over the Lower Cretaceous interval in SW Scania.