Page 85 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Evaluation Methods and Influencing Factors CHAPTER 2 69

When the bubble phase is stable on the solid interface, Yong’s equation is
satisfied:
γ 5 γ (2.48)
LV
SL SV 1 γ cosθ G
That is,
γ 2 γ 2 A
cosθ G 5 SL SV 5 (2.49)
γ LV γ LV

In the equation, γ —is solid/liquid interface free energy, in mJ=m 2
SL
2
γ —is solid/gas interfacefree energy, in mJ=m .
SV
2
γ —is liquid/solid interfacefree energy, in mJ=m .
LV
2
A—is work of adhesion, in mJ=m .
Eq. (2.49) shows that A and cosθ G form a linear relationship. When adhesion
increases, θ G increases and gas wettability weakens. Evaluation indices of gas
wettability are as follows:
1. Preferential gas-wetting: 0 degrees ,θ G , 90 degrees and γ . γ ,
SL SV
namely A , 0;
2. Intermediate gas-wetting: θ G 5 90 and γ 5 γ , namely A 5 0;

SL SV
3. Nongas-wetting: θ G . 90 degrees and γ , γ , namely A . 0
SL SV
2.4.2.2 EXPERIMENTAL STUDY OF THE EFFECTS OF SURFACE (INTERFACE)
FREE ENERGY ON GAS WETTABILITY
2.4.2.2.1 Effect of Surface (Interface) Free Energy on Gas
Wettability
1. Experimental study of the effects of free energy of solid surface on gas wettability

Based on Tables 2.2 and 2.3, by combining the theoretical derivation in
Section 4.2.1, the relationship between gas wettability states of solid-liquid-gas
system in air and free energy of solid surface and the data (see Table 2.12)of
contact angles of liquid-wetting can be obtained as displayed in Fig. 2.31.
Table 2.12 and Fig. 2.31 show that as the concentration of fluorocarbon polymer
Zonyl8740 increases, free energy of treated glass slide surface, contact angle of liq-
uid, and gas wettability strength present the following rules: As the concentration
of fluorocarbon polymer Zonyl8740 increases, the free energy of treated glass
slide surface gradually decreases, contact angle of liquid on the glass slide surface
increases, and wettability of glass slide surface caused by gas with respect to liquid
increases. Within the range of study, when C Zonyl8740 . 0.1%, the glass slide sur-
face of water/gas/glass slide system shows a capacity for preferential gas-wetting
(ζ gas-water . 0), and gas wettability ζ gas-inn-hexadecane of glass slide of n-hexadecane
/gas/glass slide system gradually increases as C Zonyl8740 increases. That is, gas wet-
tability gradually becomes stronger.