Page 35 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Concept of Gas Wettability and Research Status CHAPTER 1 19

fractures can be transformed into gas-wet surfaces. In the case, when decom-
pression and discharge are complete, because of the increase of relative perme-
ability of oil and gas and the decrease of the capillary pressure even altered to
driving force, the ability of strata fluid to flow improves significantly. Hence
liquid locking is reduced or relieved. Finally, the gas output and gas produc-
tion rate drastically improve.

In the same year, Peng Haijun et al. [43], worked out problems including seri-
ous water lock and retrograde condensation pollution with fluorine-modified
nano-liquid. The wetting alternation effect of fluorine-modified nano-liquid
was examined, and the optimum working concentration was determined
based on core self-imbibition method and capillary rise experiments. The
experimental results show that the CA of gas-water system is 15 degrees on an
average before wettability change, and it becomes 103 degrees after wettability
change, which indicates that gas-water-glass system is transformed into
intermediate-wet. The alternation effect of fluorine-modified nano-liquid is
better than six other normal wetting alternation agents. The proportion of self-
absorbents increased from 0 to 0.9, the proportion of oil imbibition increased
from 0 to 0.55, and oil lock and water lock were relieved simultaneously. The
optimum concentration of fluorine-modified nano-liquid selected from the
capillary rise experiments in organic solvent is 1%B1.5%. The intermediate
gas-wet alternation mechanism indicates the following: Since the wettability of
solid surface is decided by the chemical composition of the surface and surface
appearance, roughness increases on the surface of pore walls using the nano
particle adsorption method. The low surface energy is then modified and
finally, the intermediate gas-wet surface is formed. When fluorine-modified
nano particles are adsorbed, the surface of pore walls of cores having hydro-
phobic and oleophobic features generate the “slipping” effect in water and oil.
Consequently, the adsorption and collection of oil and water decrease and the
seepage capability is enhanced.

1.2.3 Advancements in Super-Hydrophobic Theory Research
Currently, gas wettability research is still in its early stages, and the basic theo-
retical system is not mature, while gas-wet alternation agents or materials like
fluoropolymers are still relatively simple. This is mainly because the surface
free-energy of fluorine based materials is lower, and the perfluorinated groups
are both hydrophobic and oleophobic, which obviously improves the wetta-
bility and permeability of the respective medium. Furthermore, fluorine alkane
compounds have fluorine-like features that impart a special chemical stability.
When this fluoropolymer is adsorbed on the surface of materials, it is difficult
to remove by drip washing and volatilization; hence it is more durable. A
super amphiphobic surface is required to lower the free surface energy and
increase the roughness. Added to this, certain “concave structures” are also
required [44]. Based on these observations, better materials need to be studied
with respect to gas-wet alternation as well as suitable process control methods
to lay the theoretical foundation for improving the recovery of oil from