Compositional simulation of thermal recovery processes requires V-L-L (vapor/liquid-hydrocarbon/liquid-water) equilibria data to model distillation mechanisms. We have performed steam distillation experiments to obtain 3-phase equilibrium data and equilibrium ratios (K-values) for crude oil pseudo-components.
A laboratory/empirical technique is developed to determine 3-phase K-values of crude oil pseudo-components/water systems at high temperatures and pressures. A 12 API gravity crude oil is used as the test oil for this study. Isochoric steam distillation experiments are performed to obtain the vapor phase compositions for temperatures ranging from 250 to 500 F at equilibrium saturation pressures.
Three experimental models are devised to calculate the 3-phase K-values. These models are,
SWID-1 stage-wise isochoric distillation of type 1; this test is conducted under stepwise increase of temperature between each equilibrium stage.
SWID-2 stage-wise isochoric distillation of type 2; this test is conducted at a constant temperature for all equilibrium stages.
IDA-3 isochoric distillation analysis of type 3; this test uses a constant initial composition in the cell for each equilibrium stage.
Three-phase equilibrium AT-values are computed using the experimental data (SWID-1, SWID-2 and IDA-3) and a compositional material balance model (CMBM). This model uses experimental vapor phase compositions and a correlation for the hydrocarbon solubility in water to calculate the liquid hydrocarbon compositions. The correlations for hydrocarbon solubility in the water phase are based on data and correlations from literature. The pseudo-components are defined using a modified pseudoization technique based on Whitson's characterization scheme.
These results may provide basic separation data that account for steam distillation mechanisms involved in thermal processes. We conclude that 3-phase equilibrium K-values for the oil pseudo-components are a function of pressure, temperature and a weak function of the initial compositions.