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Some analytical correlations can be used to approximate the numerical solutions and some of them are brought below. 

These correlations are usually expressed in terms of 

LaTeX Math Inline
bodyq = q (p_{wf})
 or 
LaTeX Math Inline
body\frac{q}{q_{max}} = f (p_{wf})
 as alternative to 
LaTeX Math Block Reference
anchorIPR
.

They are very helpful in practise to design a proper well flow optimization procedure.

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where 

LaTeX Math Inline
body\sigma = \Big \langle \frac{k} {\mu} \Big \rangle \, h = k \, h\, \Big[ \frac{k_{rw}}{\mu_w} + \frac{k_{ro}}{\mu_o} \Big]
 – water-based or water-oil-based transmissbility above bubble point 
LaTeX Math Block Reference
anchorPerrine2phase_alpha
pageLinear Perrine multi-phase diffusion model
,

 

LaTeX Math Inline
body\epsilon = 0.5
 for steady-state SS flow and 
LaTeX Math Inline
body\epsilon = 0.75
 for pseudo-steady state PSS flow.
body\epsilon = 0.5
 for steady-state SS flow and 
LaTeX Math Inline
body\epsilon = 0.75
 for pseudo-steady state PSS flow.


The alternative form of the conatsnt PI WFP – Well Flow Performance is:


LaTeX Math Block
anchor1
alignmentleft
\frac{q}{q_{max}} = 1 -\frac{p_{wf}}{p_R}



Dry Gas IPR

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For gas producers, the fluid compressibility is high and formation flow is essentially non-linear, inflicting the downward trend on the whole WFP – Well Flow Performance plot (Fig. 2).

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LaTeX Math Block
anchor9C1T3
alignmentleft
qa \, q + b \, q^2 = \Psi(p_R) - \Psi(p_{wf})

where 

LaTeX Math Inline
body\Psi
 – is pseudo-pressure function,  
LaTeX Math Inline
bodya
is laminar flow coefficient and
LaTeX Math Inline
bodyb
is turbulent flow coefficient. LaTeX Math Inline
bodya
is laminar flow coefficient and



It needs two well tests at two different rates to assess

LaTeX Math Inline
body\{ q_{max} \, , \, n \}
 or
LaTeX Math Inline
body\{ a \, , \, b
is turbulent flow coefficient
\}
.  

But obviously more tests will make assessment more accruate.


Saturated Oil IPR

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For 2-phase oil-gas formation flow Saturated Oil reservoir with bottom-hole pressure below bubble point 

LaTeX Math Inline
bodyP_{wf} < P_b
  the near-reservoir zone free gas slippage effects inflicting also inflicts the downward trend at the right side of WFP – Well Flow Performance plot (Fig. 3).

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