Abstract
In order to describe the phase behavior of a reservoir fluid and calculate its volumetric properties, an EOS requires the values of critical pressure, critical temperature, and acentric factor for each component. There are several correlations in the literature for calculating critical properties and acentric factor for each single carbon number group, SCN.
For heavy ends, accurate properties can be predicted with accurate representation of the critical properties and acentric factor. Direct measurement of the critical properties for heavy ends is not practical. So, characterization of the heavy ends is required.
In tuning EOS after splitting the plus fraction and assigning critical properties and acentric factor for each SCN group, the saturation pressure for the reservoir fluid will be matched at reservoir temperature using the extended composition. Since the experimental measurement for the molecular weight of the plus fraction has some uncertainty, it is reasonable to use the molecular weight of the plus fraction as the tuning variable for matching saturation pressure with the extended composition.
The critical properties and acentric factor for each SCN group extended from the plus fraction were calculated using six different sets of correlations, as discussed above. The main objective of testing these different sets of correlations is to find the set of correlations that will lead to the least adjustment for the molecular weight of the plus fraction when the measured saturation pressure is matched using the extended composition. Results show that using Cavett correlation for calculating critical properties and Riazi and Al- Sahhaf correlation for calculating the acentric factor will lead to the least adjustment in the molecular weight of the plus fraction when saturation pressure is matched with the extended composition.
