Impact of uncertainty in Utsira formation temperature and salinity on CO2 storage: A field-scale reactive transport simulation study

• The impact of uncertainty in aquifer temperature and salinity is investigated. • Aquifer mineral changes are highly sensitive to uncertainty in aquifer temperature. • Residual and solubility trapping mechanisms are dependent on aquifer temperature. • CO 2 mineralization onset time is controlled by formation temperature. • Salinity highly affects all CO 2 trapping mechanisms except mineral trapping. Saline aquifers offer large storage capacities for carbon dioxide (CO 2 ) geo-sequestration. However, key parameters such as aquifer temperature and brine salinity often remain uncertain, especially in thick formations. These uncertainties can significantly influence the CO 2 reactive transport and trapping. Hence, this study aims to quantify the impact of such uncertainties on CO 2 hydrodynamics and geochemical interactions, utilizing field-scale data of the Sleipner CO 2 storage project, where temperature and salinity are treated as uncertain parameters. A response surface methodology (RSM) was employed to systematically investigate these uncertainties and quantify their impact on CO 2 trapping. To do so, a three-dimensional reactive transport model was constructed to simulate multiphase flow, mineral dissolution and precipitation, and CO 2 trapping mechanisms. The geological model of the Utsira formation was modified to match the plume dynamics. Formation temperatures ranging from 35°C to 41°C and salinities between 0.5 and 2 times that of seawater (33,500 ppm) were tested. Geochemical reactions were modeled using equilibrium and kinetic approaches, with temperature-dependent parameters governing the mineral changes. Proxy models generated with the RSM framework were used to quantify probabilistic uncertainty in the four CO 2 trapping mechanisms. The simulation results showed that CO 2 trapping mechanisms were sensitive to the uncertainty in aquifer temperature and salinity over 300 years. The highest temperature case exhibited the lowest capillary-trapped and solubility-trapped CO 2 . While both mechanisms increased at lower aquifer temperatures. The temperature also had a significant impact on both the onset time of CO 2 mineralization and the total mineral trapping. Lower brine salinity improved dissolution trapping (from 42% at 2S to 50.4% at 0.5S), but mineralization varied minimally with salinity. The brine density contrast in the lower-salinity cases improved convective mixing, promoting CO 2 dissolution. The uncertainty analysis further revealed distinct probabilistic ranges for each trapping mechanism, highlighting the dominant influence of salinity on physical trapping processes and temperature on mineral trapping.