Standing-Katz Z-Factor Chart
Calculate the gas compressibility factor (Z) using Hall-Yarborough or Dranchuk-Abou-Kassem correlations. Interactive Standing-Katz chart included.
Input Parameters
Hall-Yarborough (1973): iterative solution for reduced density
Z-Factor
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Gas Density Ratio (ρr)
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Method
Hall-Yarborough
Standing-Katz Chart
How this was calculated
Hall-Yarborough: Solves F(Y) = 0 iteratively where Y is the reduced density. Z = 0.06125*Ppr*t/Y, t = 1/Tpr.
DAK: 11-constant equation fit to Standing-Katz chart. Uses Newton-Raphson on reduced density.
Valid range: Tpr: 1.05-3.0, Ppr: 0.2-15 (extended range for DAK).
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Book a free strategy call →Understanding the Standing-Katz Z-Factor Chart
The Standing-Katz chart, published in 1942, is the foundation for natural gas compressibility factor (Z-factor) determination in petroleum engineering. The Z-factor relates the actual volume of gas to the volume it would occupy if it behaved as an ideal gas, through the real gas equation of state: PV = ZnRT. Accurate Z-factor values are essential for gas reserves estimation, gas flow calculations, and gas metering.
The chart uses pseudo-reduced temperature (Tpr) and pseudo-reduced pressure (Ppr) as inputs, which are the ratio of actual conditions to pseudocritical conditions. Several mathematical correlations have been developed to reproduce the chart digitally. The Hall-Yarborough (1973) method uses an iterative approach based on reduced density, while the Dranchuk-Abou-Kassem (1975) method uses an 11-constant equation. Both are accurate for typical reservoir conditions. This calculator implements both methods. All calculations run in your browser. Built by Groundwork Analytics.