Page 82 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

66 Gas Wettability of Reservoir Rock Surfaces with Porous Media

FIGURE 2.29
Form or n-octane liquid drop and air bubble on solid surface in water. (A) Air bubble; (B) N-octane liquid drop.
Nongas-wetting: 21 # ζ gas-liquid , 0,γ solid-gas . γ gas-liquid ,A . 0。σ SO σ SW σ WO .

2.4.2.1.2 Study of the Effects of Surface (Interface) Free Energy
on Gas Wettability Using Bubble Capture Method
1. Theoretical study on the effect of free energy of solid surface on gas wettability

As displayed in Fig. 2.29, the contact angles of air bubbles and n-octane liquid
drops on solid surface are measured in distilled water (θ Air represents the con-
tact angle of air and θ Oct represents the contact angle of n-octane). When the
bubbles and n-octane liquid drops on solid surface in water are stable,
Eqs. (2.35) and (2.36) are obtained based on Yong’s equation.
(2.35)
σ SV 5 σ S 2 π e 5 σ SW 2 σ WV cosθ Air
σ SW 5 σ SO 1 σ WO cosθ Oct (2.36)

In the equation, σ SV —is Solid/air (saturated steam) interfacial tension, in
mN=m

σ S —is surface tension of solids in vacuum, in mN=m.
π e —is steam balance expansion pressure, in mN=m.
σ SW —is solid/water interfacetension, in mN=m.
σ WV —is surface tension of water, in mN=m.
σ SO —is solid/n-octane interfacetension, in mN=m.
σ WO —is water/n-octane interfacetension, in mN=m.
Surface free energy equals surface tension in value. Hence solid/air (saturated
steam) interface free energy is γ SV 5 σ SV , the surface free energy of solid in vac-
uum is γ 5 σ S , solid/water interfacefree energy is γ SW 5 σ SW , surface free
S
energy of water is γ WV 5 σ WV , solid/n-octane interface free energy is γ SO 5 σ SO ,
and water/n-octane interface free energy is γ WO 5 σ WO . As water, air, and
n-octane are immiscible, so, γ SV 5 γ , while assuming that π e 5 0.
S
The following are obtained from Eqs. (2.35) and (2.36):
γ SV 5 γ 2 π e 5 γ SW 2 γ WV cosθ Air (2.37)
S