Page 77 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Evaluation Methods and Influencing Factors CHAPTER 2 61

FIGURE 2.25
Soaking process.

FIGURE 2.26
Spreading process.

Table 2.9 Features of Different Wetting Types
Wetting Interfaces That Disappear Interfaces Generated Conditions for
Type During Wetting Process During Wetting Process Spontaneous Progress

Adhesional GL, GS LS W a 5 γ SG 1 γ LG 2 γ SL $ 0
wetting or W a 5 A 1 γ LG
Soaking GS LS W i 5 γ 2 γ $ 0or
SG SL
W i 5 A $ 0
Spreading GS GL、LS S 5 γ SG 2 γ LG 2 γ SL $ 0
or S 5 A 2 γ LG

3. Spreading: The essence of spreading in gas-liquid-solid system is when
solid/liquid interface replaces solid/gas interface, and the surface of the
liquid also spreads, as displayed in Fig. 2.26.
When the spreading area is unit value, the free energy of system S can be cal-
culated based on Eq. (2.18):
S 5 γ SG 2 ðγ LG 1 γ Þ (2.18)
SL

S is spreading coefficient. At constant temperature and pressure, when S $ 0,
liquid spreads automatically on the surface of the solid and continuously
replaces gas on the solid surface.
To summarize, all wetting types are interfacial phenomena in a gas-liquid-
solid system. The process essence is the nature of interface and change in inter-
face energy. See Table 2.9 for features of different wetting types.