Phase equilibrium, high pressures, supercritical CO₂, light petroleum, condensate gas.

 

The extreme conditions of pressure, temperature and carbon dioxide composition present in the pre-salt deposits are a challenge related to the exploration and production of these reservoirs and require a deepened technological study to design equipment suitable for these operating conditions. In the context of high concentrations of carbon dioxide, in recent years its use in the tertiary recovery of petroleum has been gaining expression and research in this area is necessary for greater knowledge of the process and ideal conditions for its injection. Thus, the demand for information in the area of phase behavior at high pressures in the presence of carbon dioxide from representative oil systems and from actual oil samples becomes extremely important for the oil industry. This work aims the study of the phase behavior at high pressures of synthetic and representative systems of petroleum using the synthetic visual method and synthetic non visual. The research was divided in two stages. In the first stage, binary systems (CO₂ + cyclohexene and CO₂ + squalane) and a ternary system (CO₂ + cyclohexene + squalane) representative of an oil sample were studied. The thermodynamic modeling was done by applying the cubic state equation of Soave-Reidlich-Kwong, with estimated parameters of Mathias and Copeman for the vapor phase and van der Waals 2 mixing rule.

In the second stage two real samples were studied, one being condensed gas and the other being light petroleum. These samples were characterized and fractionated and later used in the study of phase behavior with binary systems: CO₂ + condensed gas and CO₂ + light petroleum fractions. The thermodynamic modeling was done by applying the cubic state equation of Adachi-Lu-Sugie, with van der Waals mixing rule 1. To obtain all the experimental data an equilibrium cell was used with a sapphire window that allowed the visualization of the phase change. However, the non-visual method was also applied based on the cell volume variation in the phase transition. This method is particularly important in petroleum samples, since these are not translucent. Thus, bubble pressures were determined for the systems at various temperatures and compositions by the two methods. The deviations between the two experimental methods are also presented.