Page 184 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

168 Gas Wettability of Reservoir Rock Surfaces with Porous Media

(A) (B)

(C)
FIGURE 5.4
Water-displacing-gas front shape in capillaries having different gas wettability. (A) Nongas-wettability (concavity, θ water 5 77.3
degrees), (B) neutral-gas-wettability (plane, θ water 5 95.7 degrees), (C) preferential gas-wettability (convexity, θ water 5 107.5
degrees).

5.1.1.3.2 Characteristics of Water-displacing-gas in Straight
Capillaries Having Different Gas Wettability
It can be seen from (1) that the wall surfaces of capillaries treated by the gas-
wetting alteration agent solution of different concentrations feature different
gas wettability. In the quasistatic condition, the result of the visualization
experiment of capillaries treated with 0%, 0.2%, and 8% gas-wetting alteration
agent solution is as shown in Fig. 5.4.

It can be seen from Fig. 5.4 that in capillary with walls of different gas wetta-
bility, the water-displacing-gas front features different shapes. The water-
displacing-gas front is concave in case of nongas wettable capillary walls, plane
in case of neutral gas wettability, and convex in case of preferential gas wetta-
bility. In the three different gas wettability states, the direction of capillary
force is as shown in Fig. 5.4 P c . In a nongas-wettability state, the capillary force
is the power of water-displacing-gas. In a natural gas wettability state, the cap-
illary force has no effect on water-displacing-gas; and in a preferential gas wet-
tability state, the capillary force equals the resistance of water-displacing-gas.
In addition, the advancing angle measured in capillaries treated by gas-wetting
alteration agent solution of a certain concentration is greater than the contact
angle of water on the quartz slide treated with a solution of the same concen-
tration. This indicates that gas wettability of the same surface increases slightly
in a displacement state compared to an astatic state.