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Phase Behavior and ThermodynamicsGas Properties

Kay Mixing Rule Gas Pseudo-Critical Properties Formula

Tpc=∑iyiTciT_{pc}=\sum_i y_iT_{ci}

Kay Mixing Rule Gas Pseudo-Critical Properties calculates mixture pseudo-critical temperature for gas properties workflows in phase behavior and thermodynamics.

Calculate

How engineers use this formula

Use this formula when the listed inputs (y_1, T_c1, P_c1, y_2, T_c2, P_c2, y_3, T_c3, P_c3, y_4, T_c4, P_c4, y_5, T_c5, P_c5) are known and the assumptions behind the cited gas properties relationship match the engineering case being checked.

Assumptions

  • Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
  • The declared units match the field-unit constants used in the formula.
  • The cited formula applies to the selected petroleum engineering workflow.

Limitations

  • The calculation does not replace a full engineering model or operating procedure.
  • Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.

Common mistakes

  • Mixing unit systems without converting the inputs.
  • Using default example values as field recommendations.
  • Applying the formula outside the source assumptions.

Default example

Using the default inputs, T_pc equals 380.433 °R.

y_1fraction

0.80

T_c1°R

343.0

P_c1psia

666.4

y_2fraction

0.10

T_c2°R

549.8

P_c2psia

706.5

y_3fraction

0.05

T_c3°R

665.7

P_c3psia

616.0

y_4fraction

0.03

T_c4°R

227.2

P_c4psia

492.3

y_5fraction

0.02

T_c5°R

547.6

P_c5psia

1071.0

Inputs

y_1

fraction

Mole Fraction of Component 1, Default Methane

T_c1

°R

Critical Temperature of Component 1, Default Methane

P_c1

psia

Critical Pressure of Component 1, Default Methane

y_2

fraction

Mole Fraction of Component 2, Default Ethane

T_c2

°R

Critical Temperature of Component 2, Default Ethane

P_c2

psia

Critical Pressure of Component 2, Default Ethane

y_3

fraction

Mole Fraction of Component 3, Default Propane

T_c3

°R

Critical Temperature of Component 3, Default Propane

P_c3

psia

Critical Pressure of Component 3, Default Propane

y_4

fraction

Mole Fraction of Component 4, Default Nitrogen

T_c4

°R

Critical Temperature of Component 4, Default Nitrogen

P_c4

psia

Critical Pressure of Component 4, Default Nitrogen

y_5

fraction

Mole Fraction of Component 5, Default Carbon Dioxide

T_c5

°R

Critical Temperature of Component 5, Default Carbon Dioxide

P_c5

psia

Critical Pressure of Component 5, Default Carbon Dioxide

Outputs

T_pc

°R

Mixture Pseudo-Critical Temperature

P_pc

psia

Mixture Pseudo-Critical Pressure

Source and review

reviewed

Kay, W.B. 1936. Density of Hydrocarbon Gases and Vapors at High Temperature and Pressure; summarized in Whitson wiki Real Gas Law.

Source

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