Characterization, Pressure-Volume-Temperature Properties, and Phase Behavior of a Condensate Gas and Crude Oil

The oil reservoirs are underground and have the oil and gas contained in the porous rock at high temperatures and pressures. Only 5-20% of the oil is withdrawn in primary production. Further recovery can be achieved by injecting carbon dioxide (CO2) that displaces and dissolves part of the remaining oil; this process is called enhanced oil recovery. Although the characterization and fractionation of petroleum are well-known and studied, each oil sample represents a unique multicomponent system; therefore, an individual study of the sample is required. Real samples of condensate gas (CG) and light crude oil (LCO) were collected and analyzed for density, viscosity, atmospheric distillation and fractionation, and aiming characterization. Synthetic visual and non-visual methods for high pressure were successfully applied for bubble point measurements of the systems composed of supercritical CO2 and CG or LCO. Phase envelope calculations were developed on the basis of pseudo components obtained by atmospheric distillation and density values using the Adachi-Lu-Sugie equation of state with van der Waals mixing rule with one interaction parameter (k(ij)) from the literature. Pressure-volume-temperature (PVT) measurements are reported for the systems CG + CO2 and LCO + CO2 as a function of the temperature and pressure and in a wide range of CO2 composition. Crude oil characterization using atmospheric distillation and density measurements was demonstrated to be feasible with accuracy, because the boiling points and specific mass obtained allowed us to propose a series of pseudo components to represent the sample phase behavior studied experimentally. Thus, results suggest that the characterization and fractioning of the samples were effective. Thermodynamic modeling and experimental data presented an average deviation of 3.1% to CG + CO2 and 2.5% to LCO + CO2 systems, indicating reasonable accuracy for petroleum samples.