Definition - What does Absolute Permeability mean?
Absolute Permeability is the ability of a reservoir rock to allow fluids to flow through its pores. It indicates the flow capacity of formation. It is simply referred to as permeability.
Absolute Permeability is used to analyze the formation rock. Through the combination of permeability data with pore pressure, porosity and other parameters it is possible to estimate the productivity of the formations. It is expressed in Darcy’s and denoted by letter K.
Petropedia explains Absolute Permeability
Absolute Permeability is not possible to be determined directly; it is traditionally measured in a laboratory. The core samples are taken during drilling and the formation fluids from these samples are extracted thoroughly and dried. A set up is arranged that forces the pressure of these samples, which have different flow rates to drop, hence determining the fluid flux. If a single phase fluid is used to determine the permeability of the rock it is referred as Absolute or Intrinsic Permeability (Ka).
With the experimental data a graph of pressure differential against the flow rate is plotted; the slope of the line provides the Absolute permeability. This results an empirical equation known as Darcy flow equation.
Q= K*A*(P1-P2)/µ* L
Where Q =Flow rate, K = permeability, A = area, P1 P2 = pressure drop, L = path length and µ = viscosity
The Absolute Permeability values for tight formations like shale and siltstones will be few microdarcies, while the one for the formations where flows fluid readily such as sandstones, sand and limestone will vary from one millidarcy’s to fifty Darcie’s for the hydraulic fractured rocks.
Factors effecting permeability:
Permeability depends on various factors like-
- The grain size, shape and its distribution.
- The type of formation.
- Porosity of the formation.
- Pressure and type of fluid in formation.
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