Factors affecting Permeability

Factors affecting Permeability

Skin FactorChanges in the permeability of formation.materials such as mud filtrate, cement slurry, or clay particles to enter the formation during drilling, completion or workover operations and reduce the permeability around the wellbore.Definition :Basically the skin is changes in the permeability of formation around the wellbore

This effect is commonly referred to as a wellbore damage and the region of altered permeability is called the skin zone.

This zone can extend from a few inches to several feet from the wellbore.

Many other wells are stimulated by acidizing or fracturing which in effect increase the permeability near the wellbore. The permeability near the wellbore is ALWAYS different from the permeability away from the well where the formation has not been affected by drilling or stimulation.

The skin factor is represented by letter S im darcy formula

well stimulation techniques will normally enhance the properties of the formation and increase the permeability around the wellbore, so that a decrease in pressuresure drop is observed. The resulting effect of altering the permeability around the well bore is called the skin effect.

Signs of Skin factor (S)Positive (+) : pskin > 0, indicates an additional pressure drop due to wellbore damage, i.e., kskin < kformation.

Negative (-): p skin < 0, indicates less pressure drop due to wellbore improvement i.e., kskin > kformation.

ZERO pskin = 0, indicates no changes in the wellbore condition, i.e., kskin = k.

Factors affecting the permeabilityNatural factors : Rock-related factors are basic characteristics, structure or indigenous properties of reservoir rocks such as grain size and shape and clay cementing.

Artificial factors: The type of fluid medium use for permeability measurement as well as the physical and chemical characteristics of major factors affecting absolute permeability.

Rock interaction-induced laboratory artifacts Thermodynamic factors affecting absolute permeability basically consist of temperature effects, based on some literature data. These fall under category of fluid.

laboratory artifacts The mechanincal factors are related to the effect of mechanical stresses or confining pressures on absolute permeability.