# Gas Deviation Factor

## Definition - What does Gas Deviation Factor mean?

Gas Deviation Factor is the ratio of molar volume of gas to that of ideal gas. It is the measure of the amount the gas is deviating from its perfect behavior at similar pressure and temperature. It is an important thermodynamic property used to modify the law of ideal gas to account for the behavior of real gas. When the gas is closer to the phase change, the deviation of the gas from its ideal behavior turns out to be more momentous. It is also known as compressibility factor and compression factor.

## Petropedia explains Gas Deviation Factor

Gas Deviation Factor is generally described as the ratio of the volume a gas actually occupies at a given temperature and pressure to the volume it occupies when it behaves ideally. Natural gas having gas compressibility or deviation factor of 1 behaves in a similar manner like an ideal gas.

It is represented by a symbol āzā which is described in real gas equation of state as:

pV = znRT

If the factor cannot be measured then it can be estimated with the help of correlations. The values of factor (z) are correlated for the blends of reservoir gases over the temperature and pressure ranges detected in the well tests.