Page 151 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Effect of Gas Wettability on the Surface Properties CHAPTER 4 135

Table 4.7 Bond Length of Covalent Bond in Gas-wetting Model
Chemical Bond Chemical Bond Chemical Bond Chemical Bond
Bond Length, Bond Length, Bond Length, Bond Length,
nm nm nm nm
0.13370 C C 0.15098 C F 0.13548 0.13365
End group C F End group C F
0.13402 C C 0.15096 C F 0.13549 0.13372
End group C F End group C F
0.13365 — — — — 0.13403
End group C F End group C F

Table 4.8 Calculating Result of Adsorption Effect of CH 4 Molecules
Rock Wettability Adsorption Model Adsorption Adsorption
Distance, Potential Well D
nm (r), kJ/mol
Liquid-wetting rocks Liquid-wetting (Three 0.261 2 5.490
condensed ring
models)
Liquid-wetting rocks Liquid-wetting (Six 0.228 2 4.834
condensed ring
models)
Gas-wetting rocks Gas-wetting (Three 0.375 2 4.592
carbon atom models)
Gas-wetting rocks Gas-wetting (Six 0.387 2 4.689
carbon atom models)

4.1.3.4.2 Various Wettability Models Adsorbing CH 4 Molecules
The calculation result of CH 4 molecules in models with different wettability is
displayed in Table 4.8 and Fig. 4.8. The adsorption distance of methane gas
on gas-wetting model surfaces is greater than on liquid-wetting model surfaces
by about 0.1 nm, and the adsorption potential well of methane on gas-
wetting model surfaces is slightly lower than on water-wetting surfaces. This
indicates that the methane adsorption capacity of gas-wetting surfaces is weak-
ened due to a sharp decrease in surface energy. In addition, the adsorption
potential well data illustrates that the methane adsorption of liquid-wetting
and gas-wetting rock surfaces is a physical process (surface condensed
agglomeration).