Mobility Ratio

Brief

Mobility Ratio determines the relative rate of one fluid to another (etc. water to oil).

$M \le 1$ oil is dominant flowing phase, stable flow.

$M > 1$ water preferentially flows in the reservoir, unstable flow, fingering.

Equation

$M = \frac{k_w/ \mu_w}{k_o/ \mu_o}=\frac{k_{rw}/ \mu_w}{k_{ro}/ \mu_o}=\frac{q_w B_w}{q_o B_o}$

where

$B_o$ = oil formation volume factor, m3/m3

$B_w$ = water formation volume factor, m3/m3

$k_{rw}$ = relative water phase permeability, function of the phase saturation, fraction

$k_o$ = oil phase permeability, function of the phase saturation, fraction

$k_o$ = relative oil phase permeability, function of the phase saturation, mD

$k_w$ = water phase permeability, function of the phase saturation, mD

$M = mobility ratio, fraction :<math> \mu_o$ = oil viscosity, cP

$\mu_w$ = water viscosity, cP

$q_o$ = oil rate, cc/sec

$q_w$ = water rate, cc/sec

Example

Determine Mobility Ratio using the following data: Core is 70% water and 30% oil saturation. Water phase permeability is 248 mD, oil phase permeability is 50 mD. Water viscosity is 1cP, oil viscosity is 3cP.

$M = \frac{248/1}{50/3} =15$

Injected movable pore volume:

$MOPV_{inj} = \frac{W_i * B_{wi}}{MOPV} = \frac{W_i * B_{wi}}{A * h * \phi *(1-S_{wc}-S_{orw})}$

where

$S_{wc}$ = Connate water saturation, fraction

$S_{orw}$ = Residual oil saturation to water, fraction

See Also

• HCPV
• STOIIP
• VRR
• Pattern
• Block
• Mature Water Flood Analysis