Page 181 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Effect of Gas Wettability on Capillaries CHAPTER 5 165

Air Air
r

P C P
σ Solid-gas P C 2
σ Water-gas θ
σ Solid-water P 1

Water Water

Direction of water-displacing-gas Direction of water-displacing-gas
FIGURE 5.1
Front shape and capillary force of water-displacing-gas in capillaries.

5.1.1.1.2 Water Displacement Experiment in Straight Capillaries
of Different Gas Wettability
Under quasistatic conditions (speed of water-displacing-gas is 0.3 mL/h) in
the water-displacing-gas experiment of capillaries of different gas wettability,
the water-displacing-gas front shows various bending shapes with different
capillary forces. Fig. 5.1 indicates the process of water-displacing-gas in
nongas-wetting capillaries under quasistatic conditions.

From Fig. 5.1, it can be seen that:
(5.1)
P c 5 P 2 P 1 5 2ðσ solid-gas σ solid-water Þ=r 5 2σ water-gas cosθ=r
In formula (5.1), P c —Capillary force;
P 1 and P 2 —Pressure in the front and behind the gas/water interface of
water displacement front, respectively;
σ solid-gas —Tension of solid/gas interface;
σ solid-water —Tension of solid/water interface;
σ water-gas —Surface tension of water;
r—Capillary radius;
θ—Advancing angle of water displacement front.

The water-displacing-gas process under quasistatic conditions is the process of
solid/water interface displacing solid/gas interface. When σ solid-gas . σ solid-water ,
solid/water interface displacing solid/gas interface is a spontaneous process of