An accurate correlation for calculating natural gas compressibility factors under a wide range of pressure conditions

Abstract

The natural gas compressibility factor is a vital parameter in petroleum engineering calculation. Currently, the calculation models for calculating natural gas compressibility factors in engineering are not accurate and efficient enough. To solve this problem, multivariate nonlinear regression is used to fit the 6988 data of the Standing–Katz chart, a novel empirical formula of natural gas compressibility factors is obtained, which is suitable for the pseudo-reduced pressure range of 0.2 to 30. The mean absolute error, mean relative error and root mean square error between the fitted values and the Standing–Katz chart values are 0.01140, 0.01282 and 0.01663 respectively, hence the fitted values accord well with the chart values. The proposed correlation is verified by 270 measured data of natural gas compressibility factors under low and medium pressure conditions and 219 measured data under high pressure conditions and compared with the other five representative calculation models. The verification result shows that the mean absolute error, mean relative error and root mean square error between the calculated values and the measured values are 0.01962, 0.01626 and 0.02511 respectively, and the proposed correlation is superior to the other five methods because of its higher calculation accuracy. The new correlation is practical and accurate for predicting the natural gas compressibility factor under an extensive range of pressure conditions.

Keywords

• Natural gas
• Empirical correlation
• Compressibility factor
• Standing–Katz​ chart
• Multivariate nonlinear regression