| Popis: |
A C7+ characterization procedure reservoir oil mixtures is presented for the PC-SAFT equation of state. The plus fraction of a reservoir fluid composition is split into carbon number fractions and the PNA distribution estimated of each C7+ carbon number fraction. For each component class (P, N, and A) a constant ε parameter is used independent of molecular weight while the parameter m is assumed to increase linearly with molecular weight. The m and ε parameters of the individual component classes are combined into one value, representative of the whole carbon number fraction. To ensure reliable density predictions, the parameter σ is determined to match the density of each carbon number fraction at standard conditions. The procedure has been tested on ten oil compositions originating from the North Sea, Gulf of Mexico, and the Middle East. For those oil mixtures the PC-SAFT equation provides more accurate liquid compressibilities and liquid densities and shows a more correct development in saturation pressure with temperature than the SRK-Peneloux equation. For near critical mixtures, including oil mixtures undergoing gas injection for EOR purposes, the PC-SAFT equation is less suited than a cubic equation. Asphaltenes require lower values of the PC-SAFT m-parameter than non-asphaltene aromatics. Parameter tuning is needed to use the PC-SAFT equation for gas condensate mixtures. |
