Page 145 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Effect of Gas Wettability on the Surface Properties CHAPTER 4 129

Table 4.2 Contact Angles and Surface Energy of Gas Wetting Rocks
Concentration of Contact Angle ( ) Surface Energy mJ/m 2

Gas-wetting Distilled N- Dispersion Polarity Surface
Alteration Agent Water hexadecane Force Force Energy
(%)
1 101.23 64.53 14.11 2.73 16.83
2 115.14 70.19 12.37 0.39 12.77
3 120.45 74.21 11.17 0.11 11.27
4 122.89 75.38 10.82 0.03 10.85
5 123.32 76.02 10.64 0.03 10.66
6 124.98 80.57 9.35 0.03 9.38
7 124.20 81.31 9.14 0.06 9.21
8 123.84 82.63 8.78 0.10 8.89
9 123.44 84.65 8.25 0.17 8.42
10 124.45 84.75 8.21 0.14 8.35

change. As the treatment concentration increased, the contact angle of water
and oil phases also increased. The contact angle of the distilled water on the
treated core surface reached up to 124.45 , and the contact angle of n-hexade-

2
cane reached 84.75 . The surface energy was reduced to 8.35 mJ/m , and this

is far below the surface tension of general liquids and therefore indicates it is
difficult to wet by liquids. The above results indicate that the gas-wetting alter-
ation agent is adsorbed on the core piece surface, and the stable adsorption
film helps achieve gas-wetting alteration of the core surface.

4.1.2.2.2 Experiment of Quartz Sand Adsorbing Methane
In view of the chemical composition of natural cores, the anisotropy of pore
structure, and the effect of artificial core cement on gas adsorption capacity, a
20 40 mesh quartz sand was used to simulate reservoir rocks, and an AST-
2000 simulation experimental apparatus was used for bulk sample coal bed
gas adsorption/desorption, and methane gas adsorption/desorption of water-
wetting quartz sand and gas-wetting altered quartz sand experiments were con-
ducted. The quartz sand quality measured in every experiment was 2000 g and
adsorption gas was CH 4 . The experimental result is displayed in Table 4.3.

From Table 4.3, it can be seen that water-wetting quartz sand has a certain
CH 4 adsorption capacity. As the pressure gradually increases, gas adsorbtion
capacity rises. When the pressure reaches 6.58 MPa, the adsorbtion capacity is
3
0.19931 m t.
The CH 4 adsorbtion capacity on gas-wetting quartz sand is obviously lower
than that of water-wetting quartz sand. When the equilibrium pressure reaches
2.31 MPa, the apparatus can detect adsorbtion capacity. Under the same equi-
librium pressure, CH 4 adsorbtion capacity on gas-wetting quartz sand is lower
than that of water-wetting quartz sand by one order of magnitude. It is thus