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

AbstractSaline aquifers offer large storage capacities for carbon dioxide (CO₂) 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 CO₂ reactive transport and trapping. Hence, this study aims to quantify the impact of such uncertainties on CO₂ hydrodynamics and geochemical interactions, utilizing field-scale data of the Sleipner CO₂ 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 CO₂ trapping. To do so, a three-dimensional reactive transport model was constructed to simulate multiphase flow, mineral dissolution and precipitation, and CO₂ 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 CO₂ trapping mechanisms. The simulation results showed that CO₂ 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 CO₂. While both mechanisms increased at lower aquifer temperatures. The temperature also had a significant impact on both the onset time of CO₂ 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 CO₂ 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.