Page 152 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

136 Gas Wettability of Reservoir Rock Surfaces with Porous Media

FIGURE 4.8
Diagram of most stable state of models with different wettability adsorbing CH 4 molecules.

Table 4.9 Calculation Result of Molecular Adsorption of H 2 O
Rock Adsorption Adsorption Adsorption Potential Dipole µ,
Wettability Model Distance Re, Well De, kJ/mol Debye
r/nm
Liquid- Liquid- 0.103 2 41.948 2.0323
wetting wetting
rocks
Gas-wetting Gas-wetting 0.303 2 7.320 2.8837
rocks

4.1.3.4.3 Models With Different Wettability Adsorbing H 2 O
Molecules
The calculation result of H 2 O molecules on different wetting models is dis-
played in Table 4.9 and Fig. 4.9.
There is a great difference among adsorption potential wells of H 2 O molecules
on model surfaces with different wettability. The adsorption potential well of
H 2 O molecules on liquid-wetting rock surfaces is up to 241.948 kJ/mol, and
the corresponding adsorption distance is 0.103 nm. It typically has strong
hydrogen-bond energy and hydrogen-bond length, indicating that H 2 O mole-
cules form strong hydrogen bond on liquid-wetting rock surfaces, and is
regarded as semichemical adsorption. However, the depth of adsorption
potential well of H 2 O molecules on gas-wetting rock surfaces is
only 27.320 kJ/mol, and the corresponding adsorption distance is 0.303 nm,
which indicates that the adsorption of gas-wetting rock surfaces of H 2 O mole-
cules is a physical process (surface condensed agglomeration). For rock surface
treated with gas-wetting alteration, the surface has orderly arranged F atoms due
to the gas-wetting alteration agent, which has a tendency to move toward the
surface. The C C bond energy in surface fluorine carbon chain is 360 kJ/mol