Improved fluid characterization for miscible gas floods

Equations-of-state (EOS) are typically tuned to black-oil PVT data such as constant volume depletion, constant composition expansion, differential liberation, and separator tests. Other PVT data more appropriate for gas injection could include multicontact and swelling tests. The standard method of tuning, however, does not typically incorporate important displacement parameters such as the minimum miscibility pressure or enrichment (MMP or MME) or the likely compositions that result in a reservoir from condensing-vaporizing (CV) displacements. This paper demonstrates an improved reservoir fluid characterization procedure for miscible gas floods that can more accurately represent the interaction of flow and phase behavior. We demonstrate the approach for two displacements, an eleven-component CO ₂ flood and a twelve-component enriched gas flood. The method-of-characteristic (MOC) theory is used to determine the MME (or MMP) of both lumped and unlumped models. The results show that by tuning to the MME/MMP, fewer pseudocomponents are required to characterize the fluid than with conventional tuning methods. For the cases studied, fluids lumped to as few as four pseudocomponents can match well the composition profiles and oil recoveries of the unlumped models.