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In general the surface tension is a tension (pull) existing on the
surface of liquid and directed on a tangent to the surface and
conditioned by the interaction of molecules of liquid.
In oil recovery it is necessary to know the surface tension

of water on the border with oil (σ ), oil and water on the border
o-w
with gas (σ ). It is also necessary to know how the surface tension σ
o-g
changes depending on the pressure difference and oil saturation by

gas.
At increasing temperature the surface tension of the pure liquid on
the border with gas diminishes. The dependence of the surface
tension on the temperature is described by the following equation:

  1(    t ) o , (9.1)
t
where σ and σ is surface tension at temperature t °С and 20 °С
t
o
2
accordingly, mN/m (mJ/m ); γ is temperature coefficient of surface
-1
tension, °С ; t is temperature, °С.
At increasing temperature the surface tension on the border oil-
2
water σ o-w diminishes depending on oil properties to 10 mJ/m and
more. The surface tension of water considerably diminishes after
dissolution of surfactants in it. The magnitude of the surface tension

on the border oil-water σ o-w for a number of oil types at dissolution of
2
surfactants in water diminishes to a few (less than 10) mJ/m .
The surface tension on the border of two liquids (kerosene –

surfactant) is determined by means of the equation:

σ  K  V ρ (   ρ ) , (9.2)
ker surfact ker surfact surfact ker

where σ is the surface tension on the border kerosene –
ker surfact
2
surfactant, mJ/m ; V is the volume of the drop of kerosene in

ker surfact
3
the border with the surfactant solution, m ; K is the capillary
2.
constant, mJ/m kg; ρ is the density of surfactant solution,
surfact
3
3
kg/m ; ρ is the density of kerosene, kg/m (it is recommended to
ker
3
take ρ = 800 kg/m ).
ker

9.3 Equipment, devices, materials and chemical reagents

The following equipment and materials should be used for the
experiment: stalagmometer, kerosene, water solutions of surfactant of
different concentration and distilled water.

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