Page 65 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Evaluation Methods and Influencing Factors CHAPTER 2 49

Table 2.5 Contact Angle of Quartz Sand Surface Treated With FC911
FC911 Concentration (mg/L) θ ( )

Water Oil
10 . 90.0 15.3
20 . 90.0 23.3
30 . 90.0 67.9
50 . 90.0 75.1
80 . 90.0 86.3
100 . 90.0 85.1
200 . 90.0 . 90.0
300 90.0 . 90.0
500 89.8 . 90.0
1000 89.7 . 90.0

concentration of FC911 is increased to 200 mg/L, the surface of quartz sand
rejects both water and oil, and contact angles are greater than 90 degrees. The
surface of quartz sand changes to gas wettable. When the concentration of
FC911 is 300 1000 mg/L, the contact angle of quartz sand with respect to
water is about 90 degrees and it rejects oil. If the contact angle is greater than
90 degrees, it indicates that the surface of quartz sand is gas wettable.
It can be concluded from the above experimental results that the contact angle
of powder samples can be easily measured by Washburn method. However,
when the contact angle of liquid phase is greater than 90 degrees, the liquid
will not be spontaneously adsorbed in the Washburn tube filled with quartz
sand, and therefore the specific value of contact angle cannot be measured.
When the contact angle of the oil phase and water phase are greater than 90
degrees, it is thought up to the relative gas wetting. Thus this method can only
qualitatively evaluate whether the powder surface is gas wettable, but it cannot
evaluate the degree of gas wettability.

The Washburn method itself has several shortcomings—i.e., the radius of the
capillary with equivalent powder column is closely related to the size and
shape of particles and compactness of filling. It is required that the powder
sample, column filling method, and compactness of powder column must be
the same in every experiment to obtain relatively accurate results with this
method. Obviously, i.e., difficult to achieve.
The experimental results of the above gas wettability evaluations illustrate that
the capillary force method is a simple and accurate method, but when gas wet-
tability is stronger, the degree of gas wettability cannot be quantitatively evalu-
ated. The contact angle method can be used to easily and intuitively
determine whether the solid surface is easily wettable by gas, and it can tell
the degree of gas wettability of the surface based on the size of contact angle
of liquid phase. Hence this method can be used to quantitatively evaluate gas