A thermochemical model for CO2-water interfacial tension
Résumé
Interfacial tension (IFT) of the CO2-brine systems is a key parameter to study the fate of CO2 in the context of geological storage in deep aquifers. IFT contributes to the control of the repartition of the fluids in the host rock porosity, and then on the transport properties of the permeable medium, like the specific relative permeabilities. It also plays an important role on the risk of leakage through the cap rock and determines the quality of sealing. In order to include this parameter in modeling studies concerning the short- and long-term behavior of a deep CO2 geological storage, a practical formulation of the CO2-water IFT has been developped in this study. With only one physical meaninful adjusted parameter, the model can describe the CO2-water IFT for temperatures and pressures ranging from 10 to 110°C and 0.1 to 40 MPa, respectively. The model relies on the approach proposed by Rusanov and Prokhorov [1], where a number of required parameters can be calculated a priori from existing equations of state in the CO2-H2O system and geochemical equilibrium constraints. In the proposed model, focus was emphazised on the CO2 mole fraction at the interface in order to describe correctly CO2- water IFT data available in the literature [2,3]. Depending on temperature, results suggest an important increase of the interfacial CO2 mole fraction as a function of CO2 fugacity up to a given value (> 5 MPa). For higher fugacities the interfacial CO2 mole fraction decreases and reaches a plateau. This behavior appears critical for the description of the CO2-water intefacial tension. In combination with our previous work, [4], this new results will allow more comprehensive modeling of IFT of CO2- brines.