Page 40 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

24 Gas Wettability of Reservoir Rock Surfaces with Porous Media

greater environmental stability may be considered. In addition, Onda
et al., initially synthesized a waxy substance alkyl ketene dimer, making
use of a heterogeneous nucleation method. The dimer was then placed
on a glass sheet for melting, and finally a super-hydrophobic surface
with fractal structure was obtained when it cooled and solidified. It can
achieve a 174 degrees CA with water.
The roughness at micro and nano scale is an important reason for
generating larger CAs and smaller roll angles. Super-hydrophobicity is
determined by the chemical composition of the surface and rough struc-
ture, which provides the main basis for producing a super-hydrophobic
surface. Currently there are many ways to produce a super-hydrophobic
surface. However, several problems still exist. For example, most of the
methods remain only theoretical and cannot be practically applied
extensively. Some methods produce super-hydrophobic surfaces that
lack stability, etc. As in-depth research continues and new methods are
developed, super-hydrophobic surfaces will be put into industrial pro-
duction for more extensive application.

1.3 CONCEPT AND DEFINITION OF GAS
WETTABILITY
Although colloidal chemistry experiments are usually conducted in the gas
phase (air or inert gas), the typical gas-wet characteristics of a hydrophobic
surface are always neglected. So the gas is generally regarded as a non-wetting
phase [45] in the oil industry. In recent years, the long-range gravitational
attraction between hydrophobic surfaces in liquid phase and gas has been dis-
covered and researched, and gas wettability has garnered more interest by
researchers [1,46].
The essence of wettability is the phenomenon [47] that in “solid/fluid 1/fluid
2” systems, the preferential wetting phase replacing the weaker wetting phase
on solid surface leads to a decrease in Gibbs free energy. Wettability is charac-
terized by decreasing Gibbs free energy on a micro level and represented as a
fluid with strong wettability characteristics replacing the weak one on solid
surfaces at the macro level. It can be seen from the thermodynamics of wetta-
bility that on the one hand it relates to intrinsic physicochemical properties of
solid surfaces, and on the other hand, it is connected with the “fluid pair”
used in wettability evaluations.
In conclusion, gas wettability is defined as the ability of gas to preferentially
cover a solid interface as compared to an immiscible liquid in the “gas/liquid/
solid” system. This definition of gas wettability is consistent with both the tra-
ditional explanation of wettability and with the understanding of scholars in
China and overseas.