A new method for determining the natural gas compressibility factor

The compressibility factor (Z-factor) of natural gas, a critical parameter in many engineering calculations related to oil and gas reservoir engineering, is absolutely necessary in numerous engineering applications of oil and gas exploration, development, and chemical engineering, such as oil and gas production, gas metering, pipeline design, estimation of original gas in place, ultimate recovery and so on. Therefore, it is especially crucial to determine this parameter quickly and accurately. Based on the Nishiumi-Saito (1975) equation of state and multivariate nonlinear regression analysis technique, a new Z-factor correlation is presented in this paper, by which gas compressibility factor in the whole pressure range can be precisely predicted with iteration method. The calculated results of the new method proposed here and DPR, HY, DAK correlations commonly used in oil and gas reservoir engineering are compared with standard data of Z-factor. The results of error analysis indicate that for the cases of general pressure range and relatively high pressure range, the average absolute error of the new method is 0.357% and 0.066% respectively, the calculation accuracy of which is distinctly better than the above three classical methods.