Page 154 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

138 Gas Wettability of Reservoir Rock Surfaces with Porous Media

FIGURE 4.10
Diagram of most stable state of models with different wettability adsorbing CO 2 molecules.

There are obvious differences in the adsorption potential wells of carbon diox-
ide molecules on model surfaces with various wettabilities. Carbon dioxide
adsorption of liquid-wetting rock surface is relatively steady, adsorption poten-
tial well is up to 225 kJ/mol, and adsorption distance is about 0.25 nm.
However, on gas-wetting model surfaces, adsorption distance of carbon diox-
ide molecules increased to 0.33 nm, and adsorption potential well decreased
to 210 kJ/mol, which indicates that when the rock surface realized gas-
wetting alteration, its carbon dioxide adsorption capacity weakened, and its
adsorption strength reduced from semichemical adsorption of weak hydrogen
bond to physical process (surface condensed-agglomeration) of van der Waals
forces.
4.1.3.4.5 Models With Different Wettability Adsorbing N 2
Molecules
The calculation result of N 2 molecules on different wetting models is dis-
played in Table 4.11 and Fig. 4.11.
There are some differences in the adsorption potential well of nitrogen mole-
cules on module surfaces with various wettabilities. The adsorption distance of
gas-wetting surface of nitrogen molecules is higher than that of liquid-wetting
surfaces by approximately 0.12 nm, which shows that the nitrogen adsorption
of liquid-wetting rock surfaces is relatively steady. Compared to adsorption
potential well, when rocks realize gas-wetting alteration, the adsorption poten-
tial well reduces sharply, which indicates that the interaction between nitrogen
molecules and gas-wetting surfaces is weak. The data of adsorption potential