Page 205 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Effect of Gas Wettability on Capillaries CHAPTER 5 189

Table 5.2 Effect of Gas Wettability on Displacement Characteristic of Gas-Displacing Water
Experiment Core Time When Oil Gas Breakthrough Saturation of Initial Contact
Number Number Appears (min) Pressure (MPa) Residual Oil (%) Angle of Gas ( )

No. 1 0 1 93 1.24 65.3 138.4
7 1 68 1.09 57.8 94.2
No. 2 0 1 111 1.25 65.5 138.4
15 1 54 0.78 37.8 69.0

wettability of treated core surface also increases. The gas wettability of core
slices treated with gas-wetting alteration agent solution of same concentration
in gas/water system, is greater than in gas/oil system. During the experiment,
the smaller the initial contact angle of bubbles on the solid surface in liquid-
phase, the faster the bubble on the solid surface disappears.

From Fig. 5.20, it can be seen that as gas wettability of core columns increases,
gas permeability reduces slightly. The higher the concentration of gas-wetting
alteration agent solution, the relatively greater the gas permeability reduction.
Within the experiment range, the maximum measured gas permeability reduc-
tion in the experiment is 15%. Gas permeability of cores is reduced by 6%
when it is treated with gas-wetting alteration agent solution.

5.3.2 Effect of Core Displacement Characteristic
5.3.2.1 DISPLACEMENT EXPERIMENT OF CORES WITH DIFFERENT GAS
WETTABILITY IN GAS/WATER SYSTEM

The effect of gas wettability on the time when water appears in the cores, gas
breakthrough pressure and saturation of residual water, during gas-displacing-
water process of cores, is as shown in Table 5.2. It can be seen from Table 5.2
that as the initial contact angle of gas on the core surface decreases, the time
when water appears on the cores gradually decreases during the gas-
displacing-water experiment. The pressure of gas breaking through the core is
reduced, and the saturation of residual water gradually reduces. This shows
that with the increase of the gas wettability of the cores, fluid flow increase,
and the resistance to the flow of gas reduced. This conclusion is in accordance
with the result of gas wettability study conducted with single-straight capillar-
ies in Section 1.1. As gas wettability increases, the liquid fluidity increases, and
the capillary force is the power of gas flow. Experiment No.1 is the parallel
experiment of core 0 1 and core 7 1, and Experiment No. 2 is the parallel
experiment of core 0 1 and core 15 1. Gas wettability of core 7 1 is weaker
than that of core 15 1.
From Table 5.2, it can be seen by comparing the experimental results of exper-
iment No. 1 and No. 2, that the gas breakthrough pressure of core 0 1is
unchanged, but the difference between time when the water appears is greater,
which is because the gas wettability of core 15 1 parallel with core 0 1in