Understanding Permeability measurements, types and Influencing factors

Understanding Permeability measurements, types and Influencing factors

Permeability and Its Types

1. Absolute Permeability: Refers to a material’s ability to allow a single, non-reactive fluid to flow through it. It is an important factor in fields like hydrogeology and petroleum engineering.
2. Effective Permeability: Describes how well a fluid moves through a porous medium that is already saturated with other fluids. For instance, in a reservoir containing both oil and water, each fluid’s permeability will differ.
3. Relative Permeability: This compares the permeability of a material for one fluid relative to another, playing a crucial role in multiphase flows, such as those in oil and gas reservoirs.

Factors Influencing Permeability

1. Porosity: Generally, higher porosity suggests better permeability, though the relationship can be complex, depending on pore size and connectivity.
2. Pore Size Distribution: The distribution and range of pore sizes within a material influence how easily fluids can flow through.
3. Material Composition: Different materials vary in permeability due to their intrinsic properties. For instance, sand is highly permeable, while clay has low permeability.
4. Overburden pressure : When the core is removed from the formation, the confining forces are removed. The rock matrix is permitted to expand in all direction partially changing the shapes of the fluid– flow paths inside the core. Compaction of the core due to overburden pressure may cause as mush as 60 % reduction in the permeability of various formations.
5. Grain size : It was found that the rate of fluid flow is proportion al to the square of the grain diameter , hence the finer sand the smaller the permeability.
6. Reactive liquids: It changes the internal geometry of the porous. Medium, due to precipitation or corrosion.

Methods for Measuring Permeability

1. perm– plug method: The tested samples are usually cut with a diamond drill from the well cores in a direction parallel to the bedding plane of the formations, dried, removing residual oil, then becomes100 % saturated with air. The perm plug is then inserted in a core holder of the permeability device. Samples are mounted in such a way that the sides of the samples are sealed, and a fluid pressure differential can be. Applied across their full length, and the rate of flow of fluid "air" through the plug is observed. Obtaining data "for conditions of viscous flow" at several flow ratesand plotting results as shown in fig (1).
2. Whole – core measurement : The core must be prepared in the same manner as per–plug method preparation. The core is then mounted in a special holding device such as shown in fig: 20 the measurements are the same as for perm–plugs but the calculation are slightly different. Measurements of permeability on long cores generally yield better indication of the permeability than do the small cores especially for rocks which contain fractures as limestone.