Page 83 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Evaluation Methods and Influencing Factors CHAPTER 2 67

Table 2.11 Surface Energy of Measuring Fluids
Fluids Distilled Water N-octane Air
2
Surface free energy ðmJ=m Þ 72.1 21.6 0
2
Dispersion part of surface free energy ðmJ=m Þ 21.6 21.6 0
2
Polarity part of surface free energy ðmJ=m Þ 50.5 0 0
Polarity of fluids Polarity Nonpolarity Nonpolarity
The dispersion part of surface energy or interface energy is noted as superscript d; polarity part is noted as superscript p. For example,
the dispersion part and polarity part of surface tension of water are noted as γ d WV and γ p WV , respectively.

γ SW 5 γ SO 1 γ WO cosθ Oct (2.38)

In Eqs. (2.37) and (2.38), γ WV and γ WO are known quantities (see Table 2.11),
and θ Air and θ Oct can be measured from the apparatus. γ , γ SW ,and γ SO can be
SV
obtained from harmonic Eq. (2.39) in captive bubble two-probe method model
and Eq. (2.40), combining Yong’s Eqs. (2.37) and (2.38).
! p p !
γ γ d γ γ
d
γ 5 γ 1 γ 2 4 SV OV 2 4 SV OV (2.39)
SV
SO
OV
γ d 1 γ d γ p 1 γ p
SV OV SV OV
! p p !
γ γ d γ γ
d
γ 5 γ 1 γ 2 4 SV WV 2 4 SV WV (2.40)
WV
SV
SW
γ d 1 γ d γ p 1 γ P
SV WV SV WV
The surface free energy of water, n-octane, and air and dispersion and polarity
parts of each under an atmospheric pressure at 20 C are displayed in

Table 2.11. The interface free energy γ WO of water/n-octane equalsthe polarity
p
part of surface energy of water ðγ 5 γ 5 50:5mJ=m Þ.
2
WO W
The following are obtained from Eqs. (2.37) (2.40):
p
γ γ d γ γ p γ WV 2 γ WV cosθ Air
d
SV WV
SV WV
γ d 1 γ d 1 γ p 1 γ p 5 4 (2.41)
SV WV SV SV
γ γ d γ γ p γ 1 γ cos Oct 2 γ
p
d
SV OV 1 SV OV 5 OV WO WV cosθ Air (2.42)
p
γ d 1 γ d γ γ p 4
SV OV SV OV
The following results are obtained putting every known quantity into
Eqs. (2.41) and (2.42):
21:6γ d 50:5γ p
SV 1 SV 5 72:1 2 72:1cosθ Air (2.43)
γ d SV 1 21:6 50:5 1 γ p SV 4
21:6γ d SV 21:6 1 50:5cosθ Oct 2 72:1cosθ Air
γ d SV 1 21:6 5 4 (2.44)