Page 84 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

68 Gas Wettability of Reservoir Rock Surfaces with Porous Media

The dispersion part, polarity part, and free energy of solid surface can be
obtained from Eqs. (2.43) and (2.44), which is as follows:

γ d SV 5 466:56 1 1090:8cosθ Oct 2 1557:36cosθ Air (2.45)
64:8 2 50:5cosθ Oct 1 72:1cosθ Air
γ p 5 2550:25ð1 2 cosθ Oct Þ (2.46)
SV
151:5 1 50:5cosθ Oct
γ SV 5 γ d SV 1 γ p SV 5 466:56 1 1090:8cosθ Oct 2 1557:36cosθ Air
64:8 2 50:5cosθ Oct 1 72:1cosθ Air
(2.47)
2550:25ð1 2 cosθ Oct Þ
1
151:5 1 50:5cosθ Oct
Solid/water interface free energy γ SW and solid/n-octane interface free energy
γ SO can be obtained by using the free energy of solid surface calculated from
Eqs. (2.45) (2.47), and the dispersion and polarity parts of free energy in
Eqs. (2.39) and (2.40). At the same time, from Eqs. (3.28) and (3.29), it can
be seen that only the dispersion part γ d SV of solid surface energy is related to
the contact angle θ Air of air bubbles on solid/water interface, and the disper-
sion and polarity parts are not mutually independent. As jointly determined
by the solid surface energy γ , contact angle of air bubbles θ Air and contact
SV
angle of n-octane liquid drops θ Oct .
2. Theoretical study of the effects of free energy of liquid surface and solid/liquid
interface free energy on gas wettability
In the gas-liquid-solid system, the captive bubble method is commonly
used for measuring solid/liquid interface free energy and surface free
energy of liquid. It is extensively used in the medical field [35,36].The
contact angle of the liquid in bubble capture method is the measured
receding angle ðθ R Þ when solid/liquid interface decreases and is replaced
by solid/gas interface, as displayed in Fig. 2.30. The greater the θ R ,the
stronger the capability of gas displacing liquid on a solid surface.
Therefore the contact angle of gas on solid/liquid interface ðθ G Þ is regarded
as representing wettability of the solid/liquid interface due to gas.

FIGURE 2.30
Schematic diagram of bubble capture method (air bubble).