Page 91 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Evaluation Methods and Influencing Factors CHAPTER 2 75

matrix to establish the gas wettability evaluation experiment using sessile
method and bubble capture method, respectively. The experimental data illus-
trates the effects of surface (interface) free energy on gas wettability and further
proves the effectiveness of visual quantitative evaluation method of the two
kinds of gas wettability. Based on the relationship between gas wettability and
free energy of solid surface in Sections 4.2.1 and 4.2.2, this section directly
studies the effects of surface energy on gas wettability and observes the phe-
nomenon of gas wettability on low energy surface with high energy surface
and on low energy surface.
1. Experimental Materials
In this experiment, paraffin, plastic, glass, and iron are taken as the
measuring matrix, respectively, and distilled water is taken as the water
phase and depolarized neutral kerosene as the oil phase.
2. Experimental Method
At room temperature set to 20 C, gas wettability of various measur-

ing matrix surfaces is evaluated with sessile drop method. While mea-
suring, the size of liquid drop is 5 μL, contact angle of water is noted as
θ water , and contact angle of neutral kerosene is noted as θ oil . Contact
angle of gas in water (oil) is measured with the bubble capture method,
and the size of bubble is 5 μL. Contact angle of gas in water is noted as
θ gas2water , and that of neutral kerosene is noted as θ gas2oil , respectively,
presenting the wetting ability of matrix surface caused by gas, with
respect to water and kerosene.

2.4.3.1 STUDY OF SESSILE DROP METHOD
In the air, the contact angles of water and kerosene on various measuring
matrices are displayed in Fig. 2.36. From Fig. 2.36, it can be seen that on the
same measuring matrix, the contact angle of water is greater than that of kero-
sene. The change rule of contact angles of water and kerosene on different
measuring matrix is uniform.

104.93 82.99 76.8 Water contact angle 30 30.63 Water contact angle
100
Water contact angle θ water(º) 60 62.52 Oil contact angle θ oil(º) 20 18.75 14.66 9.48
25
80
15
40
10
20
0
Paraffin Plastic Glass Iron sheet 5 0 Paraffin Plastic Glass Iron sheet
Measuring matrice Measuring matrice
FIGURE 2.36
Contact angles of water and oil on various measuring matrices.