Page 33 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Concept of Gas Wettability and Research Status CHAPTER 1 17

Studio software in 2011. Based on the theoretical analysis of the molecular
model, the chemical equation and synthetic route of three treatment agents
(HAP, PMP, and OAP) were obtained. Finally, using a CA experiment devel-
oped in-house, the effects of gas-wet alternation of the synthetic agent were
evaluated. The evaluation indicates that the solubility and stability of the three
gas-wet alternation agents are suitable and can reduce the surface energy of
materials. It is to be noted that the CA of oil on the surface of paper is up to
85 degrees when ordinary paper is soaked in 1% of PMP water solution. The
hydrophobicity is very strong and the CA of water on the surface of sandstone
is up to 136 degrees when cotton fiber, nylon fiber, and the surface of sand-
stone are processed with PMP water solution with the same condensation.
In 2011, Ouyang Chuanxiang et al. [38], applied gas wetting alternation tech-
nique in the research on water plugging of a horizontal well and screened out
applicable gas-wet alternation agent WA15 through gas-wet alternation experi-
ment of representative rock samples in the laboratory. This experiment was
aimed at reducing the water imbibition of rock samples to close to 0% from
70% before gas-wet alternation, with good thermal stability and strata compat-
ibility. Successively, the characteristic curves of the three indexes were obtained
based on the comparative study of changes in the water influx, invasion rate,
and water cut, before and after the use of gas-wet alternation agent WA15,
with the established visual water plugging physical model of the horizontal
well. The research results indicate that the gas wetting alternation technique is
applicable for water plugging of horizontal wells, which can retard the water
breakthrough time, improve water-free recovery, and decrease water cut. They
believe that the fundamental principle of gas-wet alternation for water plug-
ging is to translate the wettability of reservoir rocks near the well bottom into
gas-wet (for gas reservoirs) or oil-wet reservoirs (for oil reservoirs) from water-
wet reservoir by injecting gas-wet alternation agents into rocks near the well
bottom. Water changes from the original wetting phase into the non-wetting
phase, and capillary pressure contributes to the resistance of water accessing
the oil/gas reservoirs. Normally, when the differential pressure of production
is less than the threshold pressure of water accessing the rocks, water cannot
access the well bottom, and the purpose of water plugging is achieved. When
gas-wet alternation technique is applied, even the differential pressure of pro-
duction is larger than the threshold pressure of water accessing rocks, water
can access the well bottom, and the intrusion quantity decreases greatly, thus
improving the quantity of oil and gas. This method only changes the wettabil-
ity of rock surfaces around the well bottom. It is different from common water
plugging techniques (common water plugging only plugs water without shut-
off gas and oil), including blocking capillaries and changing permeability,
which in truth only achieve selective water plugging.
In the same year, Yu Hang et al. [39], conducted research on the water plug-
ging effects of gas wetting alternation technique with the numerical simulation
based on the analysis of capillary pressure equation. The results indicate that
when wettability is transformed into neutral gas-wet from strong water-wet,