Page 130 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

114 Gas Wettability of Reservoir Rock Surfaces with Porous Media

simulation software. The interaction of gas-wetting alteration agent and sand-
stone surface was calculated using the supramolecular method, as also the
combination and adsorption potential of water molecule on the surface of
sandstone before and after gas wettability alteration treatment. The function-
ing process and mechanism [9] of the surface properties of the reservoir chan-
ged by the gas-wetting alteration agent are explained from the point of
molecular interaction.

3.3.2.1 ESTABLISHMENT OF CALCULATION MODEL
3.3.2.1.1 Establishing Sandstone Model
The standard model of silicon dioxide crystal was used to simulate sandstone
surface. The crystal surface is an infinitely extending plane and information
from this surface cannot be used directly for quantum chemistry calculations
[10]. Thus, the surface of the standard model of silicon dioxide crystal was
simplified into two calculable cluster models, as shown in Fig. 3.24.
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Sandstone model 1 has 68 atoms including 18 Si atoms, 22 O atoms, and 28
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compensated H atoms. Sandstone model 2 has 33 atoms totally, including 5
Si atoms, 16 O atoms, and 12 compensated H atoms.

3.3.2.1.2 Establishing Gas-wetting Alteration Agent Model
For the two kinds of fluorocarbon-wetting alteration agents FC-MMA and FC-
AM-MAA, simplified calculable cluster models were established as the gas-
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wetting alteration agent models 1 and 2 , as shown in Fig. 3.25. The gas-
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wetting alteration agent model 1 has 50 atoms in total, including 16 C atoms,
4 O atoms, 17 H atoms, and 13 F atoms. The gas-wetting alteration agent
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model 2 has 60 C atoms totally, including 19 C atoms, 5 O atoms, 22 H
atoms, 13 F atoms, and 1 N atom.
3.3.2.2 CALCULATION METHOD
One adsorbed molecule M and one surface position S form the surface com-
pound M-S, and the interaction energy can be obtained by calculating gross
energy of the three related systems, i.e., the difference of the three systems:

FIGURE 3.24
Simplified sandstone model.