Page 68 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

52 Gas Wettability of Reservoir Rock Surfaces with Porous Media

2.3.1.2.1 Experimental Materials
In order to overcome the effect of physicochemical property of the solid phase
on gas wettability in the experiment, distilled water is taken as water phase,
n-hexadecane and neutral kerosene are taken as oil phase, air is taken as gas
phase, and quartz glass slide (1 3 1 3 0.2 cm) and quartz glass capillary
(inner diameter1mm) are used as the measurement matrix. When the
temperature is 20 C, the surface tensionof water σ water is 72.8 mN/m, that of

n-hexadecane σ n2hexadecane is 27.6 mN/m, and that of neutral kerosene σ kerosene
is 24 mN/m. In addition, the glass slide and capillary are made of quartz.
The gas-wet reversalagent is a cationoid fluoropolymer Zonyl8740 produced
by the US-based company DuPont. As the quartz glass surface has negative
electric charges, the surfactant can be absorbed on quartz glass slide and
quartz capillary surface, forming a layer of waterproof, antioil, and gas-
covering protective film.

2.3.1.2.2 Experimental Method
The glass slide and capillary are first cleaned with alcohol, then washed with
distilled water. They are then dried with high pressure nitrogen and sealed for
storage. The cleaned glass slide is put into a Zonyl8740 water solution of dif-
ferent concentrations and soaked for 4 hours before it is taken out. It is then
washed with distilled water, sealed, and dried in the air at room temperature.
The Zonyl8740 water solution of different concentration is imbibed into the
cleaned glass capillary and set aside for 4 hours. Thereafter, it is sealed and
dried in air at room temperature.
Quantitative evaluation of gas wettability in air by sessile drop method is con-
ducted with a JC2000D3 contact angle meter. The measurement interface is
displayed in Fig. 2.16.

The contact angles of distilled water, neutral kerosene, and n-hexadecane on
the surface of the glass slide are measured separatel, and expressed as σ water ,
σ kerosene , and σ n2hexadecane , respectively. During the measurement process, the
size of every liquid drop is 5 μL.

2.3.1.2.3 Experimental Result and Discussion
In the air, when the glass slide is treated with different concentrations of
Zonyl8740 solution, the change rule of the contact angles of ðσ n2hexadecane Þ in
n-hexadecane, ðσ water Þ water, and ðσ kerosene Þ neutral kerosene are as displayed in
Fig. 2.17.

From Fig. 2.17 it can be seen that as Zonyl8740 concentration increases, σ water ,
σ n2hexadecane ,and σ kerosene increase, because Zonyl8740 is a cationoid fluorocar-
bon polymer, which can be absorbed on the surface of the glass slide. While
drying the finished film, the fluorine-containing side chain [ (CF 2 )nCF 3 ]of
polymers spreads towards the air, occupies the interface of polymers and air,
and significantly reduces the surface free energy [28]. However, it is difficult to