Definition - What does Permeability mean?
Permeability is a measure of connectivity between pore spaces and the ease with which the fluid flows through the connecting pore spaces of the rock. Every formation rock has pore spaces in which oil or gas or water is trapped. Permeability is an important measure to understand a reservoir's production capability or recovery of hydrocarbon from a reservoir. The unit of measurement of Permeability is Darcy or milli Darcy.
Petropedia explains Permeability
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 simply Permeability or Absolute or Intrinsic Permeability (Ka).
The Permeability values for tight formations like shale and silt stones will be few micro darcies, while the one for the formations where flows fluid readily such as sandstones, sand and limestone will vary from one milli darcy’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.