Page 158 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

142 Gas Wettability of Reservoir Rock Surfaces with Porous Media

Table 4.14 Montmorillonite Property Measurement
Relative Amount of Clay Mineral (%) Mixed-layer Ratio (%S)
S I/S I K C C/S I/S C/S
91 / 3 6 / / / /

This section studies the dispersion properties of montmorillonite before and
after the treatment of gas-wetting alteration agent, including Zeta potential,
expansion character, and the changing situation of cation-exchange capacity
(CEC), and discusses the relation and effect mechanism of dispersion charac-
teristics of montmorillonite and gas wettability.

4.2.1 Gas-wetting Alteration of Montmorillonite
100 200 mesh and 200 400 mesh montmorillonite were soaked in different
concentrations of gas-wetting alteration agent solution for 4 hours. When the
gas-wetting alteration agent was fully adsorbed on the montmorillonite sur-

face, the mixed solution was dried in an oven at 105 C for 24 hours. It was
then cooled at room temperature and grounded. The result of montmorillon-
ite properties measured in this experiment is displayed in Table 4.14.
From Table 4.14, based on the x-ray diffraction analysis of the clay mineral, it
can be seen that the main component of the clay mineral sample is montmo-
rillonite, and its relative content is up to 91%. The sample also contains a
small quantity of kaolinite and illite.

4.2.2 Zeta Potential
The montmorillonite was treated with gas-wetting alteration using distilled
water, and turned into a suspension liquid with 1% mass fraction. It was stir-
red for 30 minutes at high speed and then left to stand for 24 hours, and then
stirred again at high speed for 5 minutes. After it was diluted until the mass
fraction became 0.05%, some suspension liquid was taken, and its Zeta poten-
tial was measured with a Zeta Sizer NanoZS. The experiment was conducted at

room temperature (22 6 3 C), and the pH value of the measured suspension
liquid was found to be 7. The change rule of Zeta potential of gas wetting ben-
tonite is displayed in Fig. 4.12.
When Zeta potential of clay is smaller than 260 mV, it exhibits strong disper-
sion. When Zeta potential is 240 mV, it exhibits relatively strong dispersion.
When Zeta potential is around 220 mV, it exhibits probable dispersion. When
Zeta potential is about 210 mV, it does not exhibit dispersion. It can be seen
from Fig. 4.12 that as the concentration of gas-wetting alteration agent gradu-
ally increases, Zeta potential of the treated montmorillonite increases, and
gradually changes to probable dispersion from relatively strong dispersion.
Finally, when the treatment concentration of gas-wetting alteration agent