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Permeability of rock is characterized by permeability coefficient
k. It is determined by means of Darcy’s law according to which liquid

or gas filtration velocity in porous medium is directly proportional to

pressure gradient and inversely proportional to dynamic viscosity of
liquid or gas:

Q k  P
V    , (3.1)
A  L

where V is liquid or gas filtration velocity, m/s; k is permeability
2
coefficient, m ; P is pressure difference which is created at the ends

of the rock sample under experiment conditions, Pa; A is filtration
2
3
area, m ; Q is the volumetric flow rate of liquid or gas, m /s; L is the
length of the rock sample, m;  is dynamic viscosity of liquid or gas,

Pas.

Permeability coefficient of rock for liquid and gas is determined
by different equations. The equation for determining the permeability

coefficient for liquid under condition of flow (filtration) of an

incompressible liquid according to linear law of filtration (Darcy’s

Q
law) and taking into account that V  has following expression:
A
Q  L 
k  l l , (3.2)
рer.l.
A  P
2
where k is permeability coefficient for liquid, m ; Q is the
рer.l. l
3
volumetric flow rate of liquid (oil, water), m /s; A is filtration area
2  d  2
(cross-sectional area of the rock sample), m ( A  ); d is the
4
diameter of the rock sample of cylindrical form, m;  is pressure
P

difference at the ends of the rock sample, Pa ( P  P 1 - P ); P is inlet
1
2
pressure, Pa; P is outlet pressure, Pa; L is the length of the rock

2
sample, m;  is dynamic viscosity of the liquid (oil, water), Pas.

l
Linear law of Darcy for the case of gas filtration through the rock

sample of cylindrical form due to the fact that gas is compressible (gas

is characterized by inconstancy of volumetric flow rate at pressure

reduction by length of the rock sample) has following expression:

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