A property characterising agility of the fluid under pressure gradient with account of reservoir permeability and dynamic fluid viscosity:
| (1) | \frac{k_f}{\mu_f} |
where
k_f | formation permeability to fluid "f" |
|---|---|
\mu_f | dynamic viscosity of fluid "f" |
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) | \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] |
and for a case of oil-water fluid :
| (3) | \left<\frac{k}{\mu} \right> = k_{air} \left[ \frac{k_{rw}}{\mu_w} + \frac{k_{ro}}{\mu_o} \right] |
and this is when Perrine model makes the most practical sense.