Determination of fluid properties and phase conditions of hydrocarbon mixtures is critical for accurate hydrocarbon measurement, representative sampling, and overall pipeline operation. Fluid properties such as compressibility and density are critical for flow measurement, and determination of the hydrocarbon due point is important to verify that heavier hydrocarbons will not condense out of a gas mixture in changing process conditions.

In the oil and gas industry, equations of state (EOS) are typically used to determine the properties and the phase conditions of hydrocarbon mixtures. EOS are mathematical correlations that relate properties of hydrocarbons to pressure, temperature, and fluid composition. Various software packages are available that use different EOS to calculate a range of natural gas properties and phase conditions. This paper discusses the different EOS that are available, the properties that can be obtained from each EOS, and practical uses of EOS software for natural gas pipeline applications.