Evaluation of relative permeability functions as inputs to multiphase flow models simulating supercritical CO2 behavior in deep geologic formations

Multiphase flow models that simulate flow and entrapment behavior of supercritical CO2 (scCO(2)) can be used to design and evaluate CO2 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 CO2 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. (C) 2015 Elsevier Ltd. All rights reserved.