The Model to Predict the Viscosity of Hydrocarbon Mixtures Containing CO2

The viscosity of hydrocarbon mixtures is essential for CO2 storage applications in depleted oil field. Furthermore, it is necessary to understand the impact of CO2 on characteristics of hydrocarbon mixtures in order to assess the extent to which viscous fingering, gravity segregation, hydrodynamic dispersion and interfacial tension affects influence the local displacement efficiency during miscible gas flooding processes. Whilst the phase behaviour of carbon dioxide/hydrocarbon binary mixtures has been widely reported, empirical data relating to relevant fluid densities and viscosities are frequently absent due to lack of measurements. The extended hard-sphere model (EHS) and the 1-component Extended Hard-Sphere model (1-cEHS) have been modified and tested against experimental data to predict the viscosity of hydrocarbon mixtures containing CO2. The existing expression for the molar core volume and roughness factor for long chain n-alkanes were used. A new correlation for molar core volume V0 of pure CO2 was obtained by the regression of the experimental data. To ensure the validity of CO2 for use in the scheme for n-alkanes, CO2 was regarded as a pseudo n-alkane component which is characterized by an effective molecular weight. For multi-component (CO2/n-C6, C7, C8, C12) and binary systems of CO2/n-alkanes, including n-hexane, n-decane, n-tetradecane, n-hexadecane, and n-octadecane, the mixtures of various CO2 fractions were compared with the results from the existing literature. In most of the available studies, it has not been difficult to identify that the simple mixing rule is usually not the best choice for predicting a mixture’s viscosity. However, the EHS model behaves better than the 1-cEHS model in the limit of low levels of CO2 content.