Relative Permeability

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Brief

Relative Permeability is the ratio of the effective permeability to base oil permeability measured at connate water saturation[1].

 k_{ro} = k_o/k_{oS_{wc}}
 k_{rw} = k_w/k_{oS_{wc}}

where

 k_{ro} = Oil relative permeability, fraction
 k_{rw} = Water relative permeability, fraction
 k_o = Effective water permeability, mD
 k_w = Effective water permeability, mD
 k_{oS_{wc}} = Effective oil permeability at irreducible oil saturation, mD
 S_{wc} = Connate water saturation, fraction

Related definitions

Effective permeability - oil, water, gas phase permeability when more than one phase is present. Depends on fluids saturations.

Absolute permeability - permeability of the core sample when saturated with one liquid. Independent of fluid. Dependent on pore throat sizes.

Example

Determine the Relative Permeability using the following data[1]:
Core dimensions: A=2 cm2, L=3 cm. PVT: water viscosity = 1 cP, oil viscosity = 3 cP, Bw=1 cc/cc, Bo=1.2 cc/cc.

Absolute permeability

Core is at 100% water and qw=0.553 cc/sec:

Using Darcy's law:

 k_{abs} = \frac{0.553*1*1*3}{2*2} = 0.415 D = 415 mD

Same core at 100% oil and qo=0.154 cc/sec:

 k_{abs} = \frac{0.154*1.2*3*3}{2*2} = 0.415 D = 415 mD

Effective permeability

Same core at 70% water and 30% oil and qw=0.332 cc/sec and qo=0.0184 cc/sec:

 k_w(S_w=0.7)= \frac{0.332*1*1*3}{2*2} = 0.249 D = 249 mD
 k_o(S_w=0.7)= \frac{0.0184*1.2*3*3}{2*2} = 0.049 D = 50 mD

Same core at 30% water and 70% oil and qw=0 cc/sec and qo=0.123 cc/sec:

 k_w(S_w=0.3)= \frac{0*1*1*3}{2*2} = 0 D = 0 mD
 k_o(S_w=0.3)= \frac{0.123*1.2*3*3}{2*2} = 0.332 D = 332 mD

Relative permeability

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

See Also

References

  1. 1.0 1.1 Wolcott, Don (2009). Applied Waterflood Field DevelopmentPaid subscription required. Houston: Energy Tribune Publishing Inc.