V-L-L equilibria data and K-values for pseudo-components of a crude oil
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Compositional simulation of thermal recovery processes requires V-L-L (vapor/liquid-hydrocarbon/liquid-water) equilibria data to model distillation mechanism involved in steam flooding. 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 of 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 K-values are computed using the experimental data (SWID-1, SWID-2 and IDA-3) and a compositional material balance model (MBM). The compositional material balance model uses this experimental vapor phase compositions and a correlation for hydrocarbon solubility in water to calculate the liquid hydrocarbon compositions. The correlations for hydrocarbon solubility in the water phase is based on data and correlations from other literature sources. The pseudo-components are categorizes using a modified pseudoization technique based on Whitson's characterization scheme. Results provide data to account for steam distillation mechanism involved in thermal processes. It is concluded 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.
