Mesozoic formations in Norway as CO₂-enhanced geothermal systems reservoirs: A pathway to efficient energy production

This article presents a novel analysis of laboratory test results conducted on core samples from the Åre Formation in the Norwegian Sea, as well as the Skagerrak and Ula Formations in the North Sea. The study addresses the critical challenge of utilizing sedimentary rocks from these Mesozoic formations as geothermal reservoirs for Enhanced Geothermal Systems (EGS) technology, with a focus on using supercritical carbon dioxide (CO₂–EGS) as the working fluid in Norway. This is particularly significant given the growing demand for sustainable energy solutions and the urgent need to reduce carbon emissions. A total of ten core samples from the Åre, Ula, and Skagerrak Formations were analyzed to assess their geothermal reservoir potential. Laboratory investigations included petrophysical tests, effective porosity measurements ranging from 1.94 % to 21.52 % (average 11.66 %), conducted using low-field Nuclear Magnetic Resonance (NMR) and Mercury Intrusion Capillary Pressure (MICP). The median pore diameters ranged from 0.031 μm to 3.255 μm (average 0.97 μm by MICP, 1.32 μm by NMR). Permeability values varied widely, from 0.053 to 67.467 mD, reflecting significant heterogeneity in pore structure. Mechanical tests based on ultrasonic P- and S-wave velocities (ranging from 2417 to 5100 m/s and 1355–2570 m/s, respectively) enabled the calculation of dynamic elastic moduli. The average values were: Young’s modulus – 18.91 GPa, bulk modulus – 17.19 GPa, and shear modulus – 7.35 GPa. Skeletal density was higher in Åre and Ula formations (∼2.65 g/cm³) than in Skagerrak (∼2.33 g/cm³), correlating with observed differences in porosity. The analysis revealed that the Ula Formation exhibits the widest parameter variability, with some samples qualifying as both petrothermal and hydrothermal EGS reservoirs, while all Skagerrak samples aligned with hydrothermal classification. Notably, the Åre Formation exhibited the best combination of high elastic parameters, porosity, and versatility, making it a strong candidate for CO₂–EGS development. This study underscores the innovative potential of integrating CO₂ sequestration with geothermal energy production in Norway. It provides a valuable dataset for evaluating sedimentary formations as viable CO₂–EGS reservoirs, offering new opportunities for cleaner, ore efficient energy systems in geologically diverse regions.