Modification of Hall-Yarborough Equation of State For Predicting Gas Compressibility Factors

This investigation demonstrates the use of acentric factor as the third parameter in a corresponding states correlation for compressibility factors and a discussion of their application to three different types of gas reservoir. A correlation is presented which provides compressibility factors based on Hall – Yarborough equation of states for use in both two – phase and single-phase hydrocarbon systems. The modified Hall - Yarborough equation employs the acentric factor as an additional parameter to improve its accuracy. This modified equation is as simple as the original form, yet achieves substantially better prediction accuracy, especially at higher pressure. The correlation is based on hydrocarbon compressibility determinations from twenty-two hydrocarbon samples taken from three different types of reservoir systems. Out of the data used 67 percent were from dew point or retrograde gas condensate and bubble point or dissolved gas reservoir, 33 percent were from single phase gas reservoir. Results from the modified Hall – Yarborough equation, the original Hall – Yarborough equation and practically obtained were compared with natural gas components data for three different reservoirs to demonstrate its accuracy and increased application range. The improvement of the modified equation, over the original Hall – Yarborough equation ranges from 0.98% to 7.017% on the average.