Permeability is a measure of how easily a rock allows fluid to pass through it. The Navier-Stokes equation governs fluid flow through rocks, which is assumed to be laminar. Darcy's law provides an empirical formula to calculate permeability based on factors like flow rate, pressure differences, fluid viscosity, sample length and area. There are three types of permeability: absolute, effective, and relative. Absolute permeability depends on the rock properties alone, effective permeability also considers other fluid phases present, and relative permeability is the ratio of effective to absolute permeability. Permeability is affected by pore size, grain size, shape, packing and other textural properties of the rock.

1. PERMEABILITY OF
ROCKS

2. Permeability
The permeability of rock is a measure of the ease
with which the rock will permit the passage of fluids.
The fundamental physical law which governs this is
the Navier-Stokes equation.
We assume the flow of fluids in rock as laminar.

3. Calculation of permeability
The fluid flow through a cylindrical tube is given by the simplified
Navier-Stokes equation for laminar flow and uncompressible fluids.
The equation can be expressed as:-
About 150 years ago, Darcy carried out several experiments and then
developed an empirical formula that remains the main permeability
formula. Darcy's formula is given as:-
Where
Q= the flow rate
r = the radius of the tube (cm /m)
= the outlet fluid pressure(Pa)
= the inlet fluid pressure(Pa)
m= the dynamic viscosity of the fluid(Pa)
L= length of the tube(cm or m)
k = permeability of the sample(darcy)
A = area of the sample

4. Absolute permeability:-Absolute permeability is an ability to flow
fluid through a permeable rock when only one type of fluid is in the
rock pore spaces.
Effective permeability:-Effective permeability of rock to a fluid phase
(oil, gas, or water) in porous medium is a measure of the ability of that
phase to flow in the presence of other fluid phases.
Relative permeability:-Relative permeability is the ratio of effective
permeability of a particular fluid at a particular saturation to absolute
permeability of that fluid at total saturation. If a single fluid is present
in a rock, its relative permeability is 1.0.
There are three types of permeability:-
1.
2.
3.
Types of Permeability

5. Textural properties-
Amount, distribution and type of clays
Overburden pressure
Impurities in water
High velocity flow effects
Numerous factors affect the magnitude & or direction of the
permeability:-
a. Pore size b. Grain size distribution
c. shape of grains d. Packing of grains
F A C T O R S A F F E C T I N G P E R M E A B I L I T Y O F R O C K S

6. There is a general increase in permeability as grain size increases from very fine to
coarse , permeability increase as sorting progresses from very poor to well sorted.

7. SI unit for permeability is
A particle unit for permeability is darcy(d) or more
commonly the millidarcy(md).(1 darcy = )
UNIT:

8. Thank
you