An Assessment of Deep Geothermal Resources in Norway

Abstract

The Geological Survey of Norway is currently conducting the largest heat flow study of the Norway mainland ever carried out since the 1970’s. In the framework of the Kontiki (NGU-StatoilHydro) and HeatBar (NGU-NFR-StatoilHydro) projects, we measured temperatures in 15 deep drill holes located in the Oslo Region, mid-Norway, Nordland and Finnmark. In contrast with previous heat flow studies, most of our drill holes reach depths exceeding 800 m, allowing for corrected geothermal gradients from paleoclimatic effects and, consequently, for estimating temperatures well below the deepest level reached by the drill holes. The data were primarily used to calculate the relative amount of heat flow produced in the different units of the Norwegian basement and to extrapolate this information to the offshore areas.
In the present contribution, we focus on the geothermal potential of the Norway mainland. Using our calculated heat flow values, recently published thermal properties of a wide range of rocks in Norway and results from previous geological and geophysical studies, we computed underground temperatures at different depths. Relatively low temperatures are predicted down to 5 km in central and northern Norway, restricting the geothermal potential of these regions to the use of low temperature fields (i.e. < 100 °C) for house or, eventually, district heating only. In the Oslo Region, the most populated region of Norway, our calculations point towards much more favorable conditions. We show that, depending mainly on the thickness of the Cambrian-Ordovician cover and, to some extent, on the concentration of radioactive content in the underlying basement, medium temperature geothermal fields (i.e. 100-200°C) could potentially be operated for electricity production in the near future. These preliminary conclusions sound promising but still need to be confirmed by more focused studies.