Evaluations on Compressibility Factor Calculation Methods for High-Pressure H2S-Containing Natural Gases

The compressibility factor is an essential parameter for natural gas exploitation and processing. The method based on the equation of state (EoS) represents the most popular method for compressibility factor calculations. In this paper, the accuracy of compressibility factor calculations for two traditional cubic-EoSs (Soave-Redlich-Kwong (SRK) EoS, the Peng–Robinson(PR) EoS), the Benedict–Webb–Rubin-Starling (BWRs) EoS, and the Cubic-Plus-Association (CPA) EoS are evaluated based on experimental data for high-pressure H2S-containing natural gases. A total of 234 sets of experimental compressibility factors are applied to validate the above four EoSs, which cover pressures from 70MPa to 131MPa. Results show that for the high-pressure and low H2S content natural gas (35MPa≤P<70MPa, H2S<0.3%), the BWRS EoS yields the best results among the above four EoSs. The average relative deviation (ARD) between the experimental results and the calculated values is 1.07%. For high-pressure and high H2S content natural gas (35MPa≤P<70MPa, H2S≥0.3%), the CPA EoS yields the best results with an ARD of 1.01%. For ultra-high-pressure natural gas (P≥70MPa) without H2S, the BWRS EoS gives the best results with an ARD of 0.32% and the maximum relative deviation is 1.50%.