3. Theory
3.1. Mechanism of solvent-
-swelling of a packer
Water-swelling elastomers swell through the absorp-
tion of saline water following the mechanism of osmosis,
while oil-swelling elastomers swell by the absorption of
hydrocarbons through a diffusion process [2, 9]. The
mechanism of swelling can be illustrated like in Figure 2
as a combination of three separate processes, i.e.:
1. Solvent absorption at the polymer surface;
2. Solvent penetration into the polymer, firstly by occu-
pying the pores and free volume and then the solvent
molecules diffusion into the polymer;
3. The polymer structure expands as the solvent trap-
ped in the pores penetrates into the network of the
polymer chains to swell them [10].
https://i.imgur.com/r0tpSTy.png
Figure 2. Absorption of hydrocarbons by elastomer through
a diffusion process
...
3.2. Thermodynamic principles
of swelling
When the thermodynamic properties of oil and rub-
ber polymer are similar, the attraction between their
molecules causes the swelling. The elastomer swells as
a result of an entropy difference between the elastomer
and the environment in which it is being used. This
entropy disparity manifests itself in an effort to achieve
an energy balance by creating a diffusion gradient be-
tween the elastomer and the surrounding fluid.
