High-pressure phase equilibrium and volumetric properties of pseudo-binary mixtures of stock tank oil plus nitrogen/carbon dioxide up to 463K

High-pressure phase equilibrium and volumetric properties are fundamental to developing high-pressure and high -temperature (HPHT) reservoirs. In this work, we extended our previous study on methane (CH4) + stock tank oil (STO) to two other highly asymmetric light gas-STO systems: nitrogen (N2) + STO and carbon dioxide (CO2) + STO. We systematically measured their phase equilibrium and densities at temperatures from (298.15 to 463.15) K and pressures up to 140 MPa. The nitrogen mole fraction varies from 0.20 to 0.31 for the density measurement and from 0.21 to 0.40 for the phase equilibrium measurement. The carbon dioxide mole fraction varies from 0.20 to 0.70 for the density measurement and from 0.21 to 0.70 for the phase equilibrium measurement. We also determined the isothermal compressibilities and pseudo-excess volumes from the experimental densities. The measured data were modeled by the Soave-Redlich-Kwong (SRK) equation of state (EoS), the Peng-Robinson (PR) EoS, their volume translated versions SRK-VT and PR-VT, and the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) EoS. For density, SRK and PR gave large deviations of-16% and-7%, respectively, compared with-3% for PC-SAFT and PR-VT and-1% for SRK-VT. The overall deviations for isothermal compressibility were in the range of 20-34% for all the models, with larger deviations for N2+STO. SRK, PR, and PC-SAFT gave similar small deviations for pseudo-excess volumes. Using the excess volume method, these models could accurately estimate the live oil densities from the STO densities, showing an average deviation of-0.5%. The deviations in predicted saturation pressures varied in a large range (4-16%), with PC-SAFT better for N2+STO and SRK/PR better for CO2+STO. The measured data and model comparison results are valuable for improving the phase behavior description for HPHT reservoir fluids and gas injection processes.