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

$\mu_o$ = oil viscosity, cP

$\mu_w$ = water viscosity, cP

$q_o$ = oil rate, cc/sec

$q_w$ = water rate, cc/sec

Rule of thumb

$M = 0.333 \mu_o$

Example

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

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

In this case the mobility of water is 15 times higher than the mobility of water.

See Also

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