A New Forecast Model and Chart for Natural Gas Compressibility Factor

Gas compressibility factor for natural gas system can be determined from Standing and Katz charts using the pseudo critical gas pressures and temperatures. This chart gives accurate values for gas compressibility factor. Reservoir simulation softwares need accurate correlation to estimate the values of this natural gas property, one of the famous correlations is Beggs and Brill. This correlation gives large errors at high gas reservoir pressure. Old correlations give good estimation of gas z factor at low gas reservoir pressures below 6000psia, at high pressures the error starts to appear. In this study, a new accurate gas compressibility factor correlation has been developed which specifically addressed the limitation of other correlations. The equation was developed by regressing 645 data points of measured gas z factor data point from Niger Delta using Matlab. The developed correlation shows superiority as to compare with other evaluated correlations by the statistical parameters applied. The new developed correlation can be used to determine the gas compressibility factor at pressure ranges from 130psia to 14000pia and is a function of pseudo reduced pressure and temperature. A plot of z – factor against reduced pressure (Pr) at isothermal reduced temperature (Tr) was also developed using the equation modeled in this work which yields a chart that mimic conventional Standing and Katz chart. The proposed chart and correlation are applicable at the interval of 1.02 ≤ Tr ≤ 2.2 and 0.1 ≤ Pr ≤ 20. The chart developed in this research work take care of presence of non-hydrocarbon like CO2 and N2