An efficient tuning strategy to calibrate cubic EOS for compositional simulation

Abstract

A new strategy for preparing an equation of state for use in compositional simulation is presented. The strategy comprises three major steps: extending the plus fraction and matching the saturation pressure, grouping, and matching of volumetric data. The plus fraction is extended into 45 single carbon number groups (SCN) using a gamma distribution. Then critical pressure, critical temperature, and acentric factor are assigned to each SCN using the best available correlations. The laboratory measured saturation pressure of the fluid is matched by adjusting the molecular weight of the heaviest SCN. The extended composition is grouped into two multiple carbon number groups (MCN) with the intermediates grouped into two pseudocomponents and methane as a pure component. The non-hydrocarbon components are included as required. The critical properties for the grouped components are assigned with a methodology which preserves the coefficients, a and b, of the equation of state which previously matched the saturation pressure. The slight change in the match of the measured saturation pressure caused by the grouping is overcome by adjusting the critical properties of the heaviest MCN. Finally, volumetric data are matched using the volume translation parameters as regression variables.