A property characterizing agility of the fluid under pressure gradient with account of reservoir permeability and dynamic fluid viscosity:

(1)	$\begin{array}{l}\displaystyle M = \frac{k}{\mu}\end{array}$

where

$\begin{array}{l}k\end{array}$	formation permeability to fluid
$\begin{array}{l}\mu\end{array}$	dynamic viscosity of fluid

In multiphase flow the concept of fluid mobility is not well-defined as phases may flow quite independently from each other and have different dynamic fluid parameters (pressure and velocity).

But for relatively homogeneous multi-phase flow (phases may move at different velocities but occupy the same reservoir space and have the same pressure) the multi-phase mobility may be defined by Perrine model:

(2)	$\begin{array}{l}\displaystyle \left< \frac{k}{\mu} \right> = k_{air} \left[ \frac{k_{rw}}{\mu_w} + \left( 1 + \frac{R_s \, B_g}{B_o} \right) \cdot \frac{k_{ro}}{\mu_o} + \left( 1 + \frac{R_v \, B_o}{B_g} \right) \cdot \frac{k_{rg}}{\mu_g} \right]\end{array}$

and for a case of oil + water fluid (when Perrine model makes the most practical sense):

(3)	$\begin{array}{l}\displaystyle \left< \frac{k}{\mu} \right> = k_{air} \left[ \frac{k_{rw}}{\mu_w} + \frac{k_{ro}}{\mu_o} \right]\end{array}$

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Fluid Mobility

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