Page 309 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

276 Reservoir Ehgineering

IN JECTl ON
WEU

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PRODUCING
WELL

Flgure 5-156. Viscous fingering.
Moblllty and Mobility Ratlo
Mobility of a fluid is defined as the ratio of the permeability of the formation
to a fluid, divided by the fluid viscosity:

(5-217)

where h = mobility, mwcp
k = effective permeability of reservoir rock to a given fluid, md
p = fluid viscosity, cp
When multiple fluids are flowing through the reservoir, relative permeabilities
must be used along with viscosities of the fluids. By convention, the term
mobility ratio is defined as the mobility of the displacing fluid divided by the
mobility of the displaced fluid. For waterfloods, this is the ratio of water to
oil mobilities. Thus the mobility ratio, M, for a waterflood is:

(5-218)

where k, and km, are relative permeabilities to water and oil, respectively, po is
oil viscosity and pw is water Viscosity. Prior to 1957, there was no accepted