Page 105 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Gas-wetting Alteration Agent and Gas-wetting CHAPTER 3 89

Table 3.1 Wetting Angle of Cores Obtained After Fluorocarbon
Surfactant Treatment

FC91 Concentration (mg/L) 0 500 1000 2000 3000 5000
Contact angle ( ) Brine 40 93 142 134 140 130

N-decane 10 75 88 89 93 84

1
Table 3.2 Effect of Na on Alteration of Gas Wettability
1
Na Concentration 0 1000 5000 10000 15000 20000 100000 200000
(mg/L)
Contact Brine 140 140 140 144 118 140 132 123
angle ( ) N-decane 93 92 93 83 90 82 91 92

It can be seen from Table 3.1 that the treated core presents intermediate gas
wettability with both hydrophobic and oleophobic ability. Gas wettability first
strengthens and then weakens with the increasing concentration of the fluoro-
carbon surfactant treatment agent. At a concentration of 3000 mg/L, the con-
tact angle of brine/air/sandstone reaches 140 degrees, that of n-decane/air/
sandstone is 93 degrees, and the core surface presents very strong preferential
gas wettability.

3.1.3 Fluorocarbon Surfactant Application Conditions and
Influencing Factors
3.1.3.1 EFFECT OF INORGANIC IONS ON GAS WETTABILITY
The presence of various salts is inevitable in formation of water. The effects of
various inorganic salts on the surface activity of ionic surfactant also differ.
Therefore, the effects of NaCl, CaCl 2 , MgCl 2 , and FeCl 3 on gas wettability of
core sample surface were also investigated.
1
1. Effect of Na on alteration of gas wettability
1
Different concentrations of Na were added to the treatment solution, and the
contact angle of treated core surface to brine and n-decane was measured, as
shown in Table 3.2.
1
It can be seen from Table 3.2 that when the concentration of Na is lower
than 10,000 mg/L, gas wettability is not affected, and when it is increased to
10,000 mg/L, gas wettability of core is slightly weakened, but only to a small
degree. It is concluded that the existence of Na 1 has very little effect on the
alteration of gas wettability of the core.