Evaluation of relative permeability functions as inputs to multiphase flow models simulating supercritical CO 2 behavior in deep geologic formations

Abstract Multiphase flow models that simulate flow and entrapment behavior of supercritical CO 2 (scCO 2 ) can be used to design and evaluate CO 2 sequestration strategies in deep geologic formations. The accuracy of model predictions depends on the constitutive models that relate capillary pressure ( P c ) and relative permeability ( k r ) to phase saturations ( S w ). Any studies to evaluate various constitutive models remain a major challenge, as necessary data are not easy to obtain in field settings. As it is not feasible to create deep formation pressure conditions in the laboratory to keep CO 2 under supercritical conditions, surrogate fluids that mimic the behavior of scCO 2 and brine were used. The k r – S w relationship for the surrogate fluid system was measured independently using long-column and hydrostatic methods. The measured P c – S w data for the same surrogate fluid system was used to derive the k r – S w relationships using the van Genuchten–Mualem model. The relative permeability relationships obtained independently from experiments and derived from measured P c – S w data using the van Genuchten–Mualem constitutive model were then applied to a multiphase model to simulate an injection experiment in an intermediate scale test tank. The comparison demonstrated that the model simulation that used directly measured k r – S w relationships was able to match the experimental observations slightly better than the simulation performed using the empirically derived relative permeability functions. Even though this was a limited study using a homogeneous packing configuration, the results demonstrate the importance of using the correct relative permeability functions in multiphase models used in carbon storage studies.