Component Partitioning in CO2/Crude Oil Systems: Effects of Oil Composition on CO2 Displacement Performance

Abstract

Abstract Gas chromatography/mass spectrometry (GC/MS) was used to analyze equilibrium phase samples from CO2/crude oil mixtures. K-values, or partitioning coefficients, are presented for over 250 individual components in these CO2/crude oil mixtures. The data show that both molecular size and structure affect the way a molecule partitions into a CO2-rich phase. Multi-ring aromatic compounds partition much less favorably into the CO2-rich phase than other components with similar molecular size or similar GC elution time. Two crude oils which have similar carbon number distributions, but different slim tube displacement behavior, were analyzed by GC/MS. The oil containing a significant quantity of multi-ring aromatics produced a much lower slim tube recovery at given pressure, and had a correspondingly higher minimum miscibility pressure (MMP). Equation of state (EOS) flash calculations and compositional simulations indicate that inclusion of the properties of the multi-ring aromatic compounds in an oil characterization is required if the types of behavior observed experimentally in both the single contact partitioning experiments and in slim tube experiments are to be reproduced numerically for oils containing significant quantities of multi-ring aromatic compounds.