Permeability

Permeability is the property of a formation which allows the fluid to flow through the porous medium.

The unit of permeability is the Darcy:
1 Darcy = 0.987 x 10^-12 m².

Types of permeability:

• Absolute permeability is the measurement of the permeability conducted when a single fluid or phase is present in the rock.
  
• Effective permeability is the permeability of one fluid in the presence of the other immiscible fluids.
  
• Relative permeability is the the ratio of ratio of effective effective permeability to a base permeability such as the absolute absolute permeability of the porous medium.

Note Ko + Kw ≠ K
Sum of the effective permeability to each fluid flowing in the pores is less than absolute permeability of the core sample.

Average permeability

Average permeability is used in upscaling for the equivalent effective permeability:

• Arithmetic average: layer parallel flow (horizontal)
• Geometric average: random distribution
• Harmonic average: layer normal flow (vertical)

External link

PERMEABILITY BASICS
http://www.spec2000.net/15-permbasics.htm