Saturation-functions models in CO2-brine system: A comparative study

Abstract

CO2 injections into deep saline aquifers create a multiphase flow system within the porous media. In this context, relative permeability and capillary pressure, as saturation functions, are key parameters that control flow dynamics, simulation accuracy, and operational decisions. Since various models have been proposed for the saturation functions, this study aims to assess the existing models and investigate which model performs best under different circumstances. To this end, we first gathered a comprehensive data set to evaluate the existing models. Following that, the nonlinear fitting of experimental data was used to obtain the parameters of each model. Finally, the root-mean-square error and correlation coefficients were used to assess the accuracy of the fit. Based on the results of capillary pressure analysis, the models can be classified into two main categories. The first category includes models with power-law behavior suitable for homogeneous formations (single curvature), such as Brooks-Corey, Li-Horne, Lambda, Thomeer, Leverett J-function, and modified J-function models. The second category includes Van Genuchten, Kosugi, Skelt-Harison, Johnson, and Jing-Van Wunnik, which can be applied to homogeneous and heterogeneous formations (capture more than one curvature). Regarding relative permeability, the L.E.T., Chierici, Van Genuchten, and Corey models exhibit comparable performance across all scenarios. Corey offers simplicity with minimal parameters, while Van Genuchten provides more adaptability for complex data sets with more physically based parameters.