Speaker
Description
Over the past decades, more than 30 relatively deep boreholes were drilled onshore in Norway, providing valuable insights into the subsurface thermal pattern across different regions. Thermal logging from these boreholes revealed significant variations in temperature, reflecting the diverse geological and tectonic characteristics of the country.
On the Svalbard archipelago, which exhibits signs of Quaternary magmatic activity, the highest temperatures were recorded, reaching up to 28.2°C at a depth of 800 meters. This region's geothermal gradient is high due to its tectonic activity and magmatic influences, which resulted in the thinning of the lithosphere there. In contrast, the northernmost part of Norway, known for its tectonic quiescence (reflected by thick lithosphere), recorded the lowest temperatures, with measurements slightly exceeding 9°C at a depth of 650 meters. This significant difference indicates the important effect of tectonic activity on subsurface temperatures.
Central Norway’s highest temperature, 22.2°C at 800 meters, was recorded on Innveien island, influenced by the development of nearby offshore deep sedimentary basins. The southwestern part, including areas near Stavanger, shows lower temperatures, such as 17.6°C at 800 meters. This lower temperature is probably a result of the relatively low concentration of radioactive elements in the bedrock of the Rogaland igneous province. The cooling effect of groundwater flow may also partially contribute to the reduced temperature of the uppermost crust in this region.
The area around the Oslo Fjord presents a more complex thermal pattern. Here, temperatures at 800 meters depth range from 16°C to 24°C, reflecting a combination of different geological factors. The primary factor is the difference in radioactive element content. There is a straightforward relationship: the higher the radiogenic heat production of the bedrock, the higher the measured temperature, and vice versa.
These variations in the subsurface temperature indicate the interplay between tectonic evolution, groundwater flow, and subsurface rock composition. Moreover, the paleoclimatic cooling effect also influences boreholes from 300 to 1500 meters deep. This paleoclimatic thermal influence must be carefully considered when evaluating the geothermal potential of any site in Norway. Therefore, a detailed assessment of these factors is essential for planning Norway's first deep geothermal site, ensuring successful geothermal energy utilization for sustainable solutions.
