A Critical Evaluation of Natural Gas-water Formula Correlations

The performance evaluation of fourteen (14) formula correlations for predicting the water content of natural gas in equilibrium with water, and the suitability of some of these correlations in predicting the water content of natural gas in equilibrium with hydrates, has been presented. Also presented was an evaluation of acid gas and gravity correction factor correlations. The evaluation was achieved by using the cubic plus association equation of state - CPA EoS, published experimental water content data from a tuneable diode laser adsorption spectrometer, and data from the gas processors supplier’s association (GPSA) chart, to validate the results of the correlations. The results of the validation showed that for the prediction of the water content of natural gas in equilibrium with water, the Bukacek correlation was best suited for low pressures of 1 and 2.5 MPa at a temperature range of 9 to 58°C. The modified ideal model (MIM) correlation was the best for pressures of 5 and 10 MPa, at temperature range of 30 to 89.6°C The Aimikhe correlation was best suited for pressures of 7.5 MPa, at a temperature range of 30 to 86°C, while the Khaled’s correlation performed better for high pressures of 25 and 50 MPa, at a temperature range of 30 to 91.5°C. The Maddox correction factor had better accuracy than other acid gas correction factors when accounting for the presence of acid gases. The Mohammadi or Chapoy gravity correction factors were the best correlations for accounting for the presence of heavy components in natural gas. For processed methane-rich natural gas in equilibrium with hydrates at a temperature range of -20 to 10°C, the Lin correlation was best suited for pressures of 2.5 and 5 MPa while the MIM correlation performed better at pressures of 7.5, 15 and 20 MPa.