DAK method for natural gas Z-factor calculation can yield relatively more accurate result compared with other methods and therefore is widely used in the petroleum industry.However

our analysis shows that the method generates results with large errors when both pressure and temperature are high.The paper presents a modification of the method based on optimization.Also presented here is an analysis of the relative errors of the calculation results on a two-dimensional plane consisting of isobars and isotherms.The results indicate that

compared with the original DAK method

the revised method can further improve the accuracy of Z-factor for natural gas.