Extending residual entropy scaling approach to evaluate the effect of CO2 concentration on the viscosity of aqueous NaCl solutions

Abstract

CO₂ injection alternated with smart water and carbonated water injection are enhanced oil recovery (EOR) methods with a positive environmental effect, as they can trap part of the CO₂ injected into the reservoir. The gas dissolved in the injected brine affects the waterfront, mobility ratio, and stability of the injected fluid coming into contact with unswept oil, increasing oil recovery. In this context, this work aimed to calculate the effect of increased CO₂ concentration on the viscosity of CO₂+brine mixtures. The Residual Entropy Scaling (RES) approach defines viscosity regarding thermodynamic properties, which can be derived from an Equation of State (EoS). In this study, RES model was coupled with the electrolyte Cubic Plus Association (eCPA) and Peng-Robinson-Stryjek-Vera (PRSV) EoS to describe the viscosity of aqueous NaCl solutions. A constant volume correction is also used to improve the density calculation. First, using experimental results from the literature, the adjustable parameters of eCPA and PRSV EoS were tuned to better correlate vapor-liquid equilibrium and density data for systems of interest. Then, the adjusted equations were coupled to the RES model and used to correlate the viscosity of CO₂, H₂O and brine. Both approaches qualitatively reproduced the effect of pressure and temperature on CO₂, H₂O and brine viscosity. However, when applied to CO₂+water and CO₂+brine mixtures, both models failed to predict the increase in viscosity as the CO₂ concentration in the systems increases. Thus, a modification to the RES model's entropic term was proposed by introducing a combination rule with an adjustable binary parameter for the CO₂-water pair. The modified models represented the effect of CO₂ addition on the viscosity of the CO₂+water system and predicted this effect on the CO₂+brine system. However, the deviations between the experimental and calculated viscosity data were smaller when the eCPA EoS was used as a reference model in RES approach.