A reliable fluid characterization achieved through the use of an Equation of State (EOS) is vital to reproduce the phase behaviour of a reservoir fluid and consequently, to improve understanding of the reservoirs EOR potential.

In this case, an EOS model was developed aimed at accurately reproducing the phase behaviour of two reservoir oils in the same field that contain, besides H2S, substantial amounts of organic sulphur components. The tuning of the EOS for both oils was more difficult to achieve than in cases without such level of sulphur components.

The tuning of the Peng-Robinson EOS was achieved with 9 pseudo-components for both oils, following the selection of the lumping scheme considered adequate for reservoir simulation studies. Organic sulphur components are concentrated in the higher range of molecular weights and, consequently, were incorporated into the heavy fraction. The tuned EOS was then used on a 1 D reservoir simulation compositional model to match the available slim tube experiments, to verify the validity of the EOS tuning. Using the compositional simulation of slim tube displacements, minimum miscibility pressure (MMP) was estimated for both oils and different injection gases.

Although a 9 component scheme is adequate for reservoir performance purposes, engineering of surface facilities requires more detail. Therefore, a delumping methodology was developed to allow engineers to estimate detailed fluid composition from the lumped components obtained from reservoir simulation studies. One of the objectives of this study is to obtain a table of variation of the detailed components distributions that can be used for delumping purposes at different stages of the gas injection project.

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