STUDY OF THE PHASE EQUILIBRIA BETWEEN PETROLEUM FRACTIONS AND CO2 AT HIGH PRESSURE

Experimental high-pressure phase behavior and thermodynamic equilibrium data are essential for understanding and predicting fluid behavior in the presence of carbon dioxide (CO₂). Due to the compositional complexity of crude oil, the investigation of phase behavior of light, saturates, and aromatics fractions in CO₂-containing systems provides a simplified and systematic approach to represent complex petroleum systems. Such experimental data also enable the estimation of binary interaction parameters, which are critical for thermodynamic modeling. In this study, light, saturate, and aromatic fractions were obtained from a paraffinic crude oil with 0.04 wt.% asphaltenes and an API gravity of 37.65. Fractionation was performed using simulated distillation and ASTM D-2007 procedures, followed by compositional characterization by gas chromatography. Phase equilibrium measurements were carried out using the static–synthetic method at known global compositions and temperatures, employing different mixtures of petroleum fractions with CO₂ and methane. The systems were monitored using visual observation with a SWIR camera, light scattering measurements with a spectrophotometer, and compressibility analysis based on pump volume variation. The obtained compositions ranged from C₃ to C₂₂ for light fractions, C₁₁ to C₃₀₊ for saturates, and C₁₃ to C₃₀₊ for aromatics. The observed phase transitions included vapor–liquid (bubble and dew points), liquid–liquid, liquid–liquid–vapor, solid–liquid, and solid–liquid–vapor equilibria. All experiments were performed in duplicate or triplicate, with deviations below 1 bar. A strong agreement was observed among the applied experimental techniques, with differences also below 1 bar, confirming the reliability and reproducibility of the generated data.