Page 134 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

118 Gas Wettability of Reservoir Rock Surfaces with Porous Media

FIGURE 3.30
Combination model of gas-wetting alteration agent and sandstone.

Table 3.19 Calculation Result of Adsorption of Water Molecule on
Various Surfaces
Adsorption Model Adsorption Distance Adsorption Potential
Re nm Well De kJ/mol
#
Sandstone1 —water molecule 0.283 2 39.100
#
Sandstone 2 —water molecule 0.203 2 41.948
Gas-wetting alteration agent 0.405 2 6.886
#
1 —water molecule
Gas-wetting alteration agent 0.410 2 8.532
2#—water molecule

agent is calculated, as also the adsorption potential and adsorption distance.
See Table 3.19 for results

From Table 3.19, it can be seen that the binding capacity of water molecules
with different surfaces varies greatly. The adsorption potential on the surface
of the sandstone model is up to 240 kJ/mol. It is typically hydrogen bond
energy, indicating that the water molecule forms strong hydrogen bonds on
the sandstone surface (the hydrogen bond energy is 25 40 kJ/mol), and,
therefore, the sandstone surface is water-wet. However, the adsorption poten-
tial of the water molecule on the surface of the fluorocarbon gas-wetting alter-
ation agent is only-7 kJ/mol; it is physical adsorption with adsorption distance
about twice that on sandstone surface. It further indicates that gas-wetting
alteration agent can dramatically change the gas wettability of the sandstone,
and the binding capacity with the water molecules is obviously reduced,
accounting for the increase in water-phase contact angle on the sandstone sur-
face after gas-wetting alteration.

REFERENCES
[1] J. Wenxian, Special Surfactant[M], China Light Industry Press, Beijing, 1995.
[2] L. Zhiqi, C. Fu, Fluorinated Surfactant[M], China Light Industry Press, Beijing, 1998.