This paper presents a dynamic wettability alteration model based on the Gibbs adsorption isotherm equation. The model is conceptually and thermodynamically developed for ideal surfactant solutions (i.e anionic surfactants) that reduce the surface tension between oil phase and rock formation based on the contact angle in a preferentially oil-wet formation. We assume that interfacial tension (IFT) between oil/water and oil/gas remain unchanged in the presence of surfactants. In order to apply the effect of contact angle on multiphase fluid flow in porous media, existing relative permeability and capillary pressure models are modified to become a function of contact angle to mimic the influence of wettability alteration.

The developed models can be tuned with experimental data including the contact angle, relative permeability, and capillary pressure parameters then they can be used to predict the efficiency of surfactant injection processes in naturally fractured reservoirs accordingly.

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