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titleDerivation
Panel
borderColorwheat
bgColormintcream
borderWidth7
LaTeX Math Block
anchorcZder
alignmentleft
c = \frac{1}{\rho} \frac{d\rho}{dp}  = \frac{d \ln \rho}{dp} =  \frac{d }{dp} \left(  \ln  \left(\frac{p}{Z} \right)  \right) = \frac{Z}{p} \cdot \frac{d }{dp} \left(\frac{p}{Z} \right) = \frac{Z}{p} \cdot \left( \frac{1}{Z} + p \cdot \frac{d }{dp} \left( \frac{1}{Z} \right)   \right) = \frac{1}{p}  - \frac{1}{Z} \frac{dZ}{dp}

Rewriting 

LaTeX Math Block Reference
anchorcZ
:

LaTeX Math Block
anchorcZ
alignmentleft
\frac{d \ln Z}{dp} = \frac{1}{p} - c(p) \rightarrow \ln \frac{Z}{Z_0} = \ln \frac{p}{p_0} - \int_{p_0}^p c(p) \, dp

which arrives to 

LaTeX Math Block Reference
anchorZ_c
.


The
Z-factor value for Ideal Gas is strictly unit: 

LaTeX Math Inline
bodyZ(T, p) = 1
.

For many real gases (particularly for the most compositions of natural gases) the Z-factoris trending towards unit value (

LaTeX Math Inline
bodyZ \rightarrow 1
) while approaching the STP.

For incompressible fluids  the Z-factor is trending to  for strongly compressible fluids and linear pressure dependence (

LaTeX Math Inline
bodyZ \rightarrow a \cdot p
)  for incompressible fluidswith pressure growth.

Modelling Z-factor 

LaTeX Math Inline
bodyZ(T,p)
as a function of fluidpressure 
LaTeX Math Inline
bodyp
 and temperature 
LaTeX Math Inline
bodyT
 is based on Equation of State.

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