Injection of CO2 into a reservoir for enhanced oil recovery (EOR) results in complex fluid phase behaviour that they require accurate reservoir fluid characterizations by equations of state (EOS) to capture the phase interactions in miscible CO2 floods.

AMAL is a giant Libyan field classified as low shrinkage type of oil and characterized by relatively law solution gas-oil ratio (GOR) of ~ 400 scf/stb and oil gravity of 35° API. The field was producing since 1960's under active bottom water drive that maintained the current reservoir pressure at levels higher than the bubble point pressure.

The main objective of this paper is to establish an EOS model able to characterize AMAL phase behaviour accurately in immiscible and miscible conditions. A model that statically validated against the conventional PVT data and dynamically validated to match the slim-tube experiments.

Three parameters Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state are used to model the Amal phase behaviour. In addition, 1-D slim-tube model is built using commercial compositional simulator to simulate four slim tube experiments.

The main outcome revealed that the match of only the conventional PVT data will not reflect the proper phase behaviour model when it was used to simulate the slim tube experiments. Therefore, further efforts are giving to EOS tuning to match both the conventional and special tests. Also, the lumped compositional model was not so perfect to simulate the hump phenomenon in slim tube experiments like extended model did. Perfect match of all slim tube experiments from immiscible to miscible conditions at pressures of 2000, 3000, 3600 and 4000 psia were achieved indicating the validity and reliability of the realized phase behaviour model. The multiple contact MMP pressure of AMAL field, using CO2 as injection solvent, is around 3140 psia based on measured and predicted results.

The adverse flow effects, such as numerical dispersion and flow effects, are eliminated by the proper selection of the number of grid blocks in the 1-D compositional model and by imposing the concept of interfacial tension (IFT) forces where the base relative perm curves will approach to straight lines as the IFT approaches to zero. The base relative perm curves are back calculated from the immiscible slim tube experiment at 2000 psia (IFT 5.0 dyne/cm2) using graphical techniques (Bardon-Longeron and JonesRoszelle models).[1] [2]

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