Effect of physical properties estimation on equation-of-state predictions

The aim of this work was to document the influence of various heptanes-plus characterization schemes on equation-of-state predictions. Both the Peng-Robinson and a modified Redlich-Kwong cubic equation were used. Numerous characterization procedures were chosen from the literature. Six reservoir fluids with detailed heptanes-plus analysis were chosen to represent a broad range of fluid types. Pressure-volume-temperature measurements for these fluids were performed over a relatively wide range of conditions. One part of the study dealt with methods for estimating specific gravities and boiling points of petroleum fractions. Equation-of-state predictions were made using critical properties based on the estimated specific gravities and boiling points; these were compared with predictions made using critical properties based on measured specific gravities and boiling points. Another part dealt with various critical property correlations and their influence on equation-of-state predictions. A thorough review of commonly used correlations was presented. Four sets of correlations were compared. Results indicate that relatively small differences in critical properties and acentric factor can result in significant differences in equation-of-state predictions. Finally, a study was performed to document the influence of adjustments in heptanes-plus critical properties, equation-of-state constants (a and b) and binary interaction coefficients. Graphical presentations illustrate the influence of individual andmore » combined adjustments of these parameters.« less