Towards Sustainable Energy in Svalbard: Geothermal Heat-Flow Insights from Wireline Logs

Reliable estimates of thermal conductivity and radiogenic heat production are essential for robust heat-flow calculations and geothermal assessments. In the high Arctic archipelago of Svalbard, geothermal energy is increasingly considered as an alternative to the present diesel-based energy supply. However, direct measurements of thermal properties are limited to shallow, fully cored research boreholes, while the deeper subsurface—where temperatures suitable for geothermal district heating (~80 °C) are reached at depths of ~2 km beneath the settlement of Longyearbyen—remains poorly constrained. In this study, we derive thermal properties for the Silurian (?) to Paleogene sedimentary succession of onshore Svalbard using wireline logs from eight petroleum exploration boreholes drilled to depths of up to 3.3 km. In addition, we include data from two fully-cored research boreholes. Lithology logs were digitized and used as the basis for thermal modeling. Two approaches were applied: (1) assigning generalized thermal properties based on lithology classes, and (2) calculating thermal properties directly from wireline logs, incorporating lithological information. The resulting thermal conductivity estimates range from 0.4 to 4.2 W m⁻¹ K⁻¹ and show strong lithological control. In the uppermost kilometer, calculated thermal conductivities were compared with laboratory measurements from two fully cored boreholes, revealing consistent lithology-dependent trends, although calculated values are generally slightly lower than measured ones. The derived thermal properties were subsequently used as input for 1D heat-flow modeling of the ten boreholes and a hypothetical deep geothermal borehole beneath Longyearbyen. Calculated heat-flow values range between 60 and 147 mW m⁻², with the highest values obtained for the Raddedalen borehole on Edgeøya. Our results demonstrate that wireline-log-derived thermal properties provide a valuable basis for improving heat-flow estimates and enable a more spatially resolved assessment of the thermal state and geothermal potential of Svalbard.