High‑pressure CO2‑rich gas viscosity: experimental measurements and model evaluation

Accurate characterization of the viscosity of CO₂-rich gas mixtures under high-pressure and high-temperature conditions is important for the design and optimization of hydrocarbon processing facilities. Fluids with high-CO₂ content exhibit significant thermal sensitivity and compressibility, directly affecting their rheological behavior and the predictive capability of flow models. This study presents experimental viscosity measurements for a CO₂-rich separator gas sample, obtained using a capillary tube viscometer (CVL1000 - Sanchez) across a wide pressure (100 bar to 900 bar) and temperature (20 °C to 150 °C) range. The experimental data were compared with predictions from five viscosity models: superTRAPP, Pedersen, LBC-PR, LBC-CPA, and LBC-PC-SAFT. The measurements showed good reproducibility, with mean standard deviations between duplicates ranging from 0.0004 cP to 0.0043 cP. The results revealed that viscosity decreases with increasing temperature and increases with rising pressure, which aligns with the expected behavior for gas systems sensitive to thermal agitation and compressibility effects. Predicted viscosities were calculated at the experimental temperatures and pressures for each data point, and the performance of the models was assessed using standard deviation and absolute average deviation (AAD%). Among the evaluated models, superTRAPP exhibited the best overall predictive performance. The Pedersen correlation performed well at mild temperatures and pressures, but exhibited large deviations under high-temperature regimes. The analysis conducted across distinct pressure and temperature groups identified specific regions of sensitivity, highlighting that the selection of viscosity models substantially impacts prediction accuracy under these conditions.