Viscosity, density, and composition measurements of certain CO2/West Texas oil systems
The shear viscosity coefficients, volumetric properties, and equilibrium phase compositions for mixtures of CO2 and crude oils (both recombined and stock tank oils) in the single phase and equilibrium vapor (dense fluid) and liquid phases are presented. The crude oil systems used in this study are predominantly of West Texas origin. The viscosity measurements were made with a torsionally vibrating quartz-crystal viscometer, developed to measure viscosities of CO2/hydrocarbon systems over a range of conditions from 90°F to 250°F and pressures up to 5000 psia. The crystal viscometer is a part of a continuous phase equilibrium (CPE) apparatus that measures phase behavior and fluid properties of high-pressure fluid mixtures via continuous-multiple-contact fashion. Phase behavior and fluid property trends for all the systems used in the study are identified and discussed. The effects of solution gas, the presence of nitrogen (N2) in the CO2 stream, as well as the dependence of viscosity (μ) on phase density (ρ) and CO2 concentration are also examined. The data are compared to a popular reservoir fluid viscosity correlation that is commonly used for estimating CO2/crude oil viscosities in digital reservoir simulation studies. The correlation is shown to be incapable of predicting, with reasonable accuracy, the viscosities of CO2/crude oil systems.