Page 102 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

86 Gas Wettability of Reservoir Rock Surfaces with Porous Media

improves wettability and permeability of the medium. Also, fluorine alkane
compounds feature special chemical stability when fluorine is introduced. The
fluoropolymer is adsorbed on the surface of materials and is not easily
removed by leaching and evaporation, thereby ensuring better durability.
Based on established gas wettability evaluation methods, this chapter studies
several gas-wetting alteration materials and their mechanisms.

3.1 GAS-WETTING ALTERATION AGENT—
FLUOROCARBON SURFACTANT
3.1.1 Introduction of Fluorocarbon Surfactant
Surfactant refers to a surface active agent that is adsorbed on interfaces and
has high capacity and efficiency to reduce surface and interfacial tension. It is
widely used in civilian fields and industrial circles, such as food, medicine,
pesticides, textile, chemicals, adhesives, ore-dressing, oil field chemicals,
papermaking, leather, photosensitive material, cleaning supplies, cosmetics,
etc. At present, surfactants are considered the “industrial monosodium gluta-
mate,” and the industry has developed as an important branch of fine
chemicals.
In commonly used surfactants, the hydrophobic group is hydrocarbon and the
molecule contains elements such as oxygen, nitrogen, sulphur, chlorine, bro-
mine, and iodine, etc. Such frequently used surfactants are called hydrocarbon
or common surfactants. Surfactants that also contain elements such as fluo-
rine, silicon, phosphorus, and boron, in addition to the above elements con-
tained in the molecule, are called special surfactants [1].

Fluorocarbon surfactants are among the most important special surfactants.
When the hydrogen atoms in the hydrocarbon chain of common surfactants
are partially or completely substituted with fluorine atoms, then such surfac-
tants having a fluorocarbon-based hydrophobic group are known as fluorocar-
bon surfactants. Such surfactants play an important role that cannot be
replaced by hydrocarbon surfactants. The hydrophilic group of a fluorocarbon
surfactant is basically the same as that of a common surfactant. Its classifica-
tion is identical to that of the hydrocarbon surfactant, and is also classified
based on ionicity.
Fluorocarbon surfactants are the most active surfactants, and have the
unique property of being amphiphobic with three highs; i.e., high surface
activity, high chemical stability and high thermal stability. They also possess
hydrophobic, oleophobic, and antifouling properties. Compared to hydro-
carbon surfactants, fluorocarbon surfactants mainly possess the following
advantages [2 4]:
1. High surface activity: Fluorocarbon surfactants have the highest surface
activity among all surfactants, which is also their most important