Page 93 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Evaluation Methods and Influencing Factors CHAPTER 2 77

FIGURE 2.39
Contact angles of gas on paraffin surface in water and oil. (A) θ gas2water 5 70.53 degrees (in water) (B) θ gas2oil 5
119.59 degrees (in oil).

displays the measured contact angle when paraffin is put in water and oil,
respectively.
From Fig. 2.38, it can be seen that the order of contact angles of gas in water
from small to big is: paraffin , plastic , glass , iron. Contact angles of gas
on various matrices in neutral kerosene have the same rule, and contact angle
of gas in water is smaller than that of gas in kerosene in the same matrix sur-
face. Paraffin has the strongest gas wettability, iron surface has the weakest,
and gas wettability in water is stronger than in kerosene on the same matrix
surface.
Fig. 2.39 illustrates that gas preferentially wets paraffin surface in water, and
the contact angle is 70.53 degrees. At this stage, the contact angle of air on par-
affin surface is smaller than on other matrix surfaces at 119.59 degrees. This
experimental rule is consistent with gas wettability evaluation conducted by
sessile drop method.

2.4.4 Effects of Surface Roughness on Gas Wettability
1. Experimental Materials
The experimental temperature is 20 C, and the glass slide was as a

test matrix. Distilled water is regarded as water phase, n-hexadecane as
oil phase, and air as gas phase. Hydrofluoric acid (containing 5%
ammonia fluoride) is the treatment agent for surface roughness, and
Zonyl8740 is used to reverse gas wettability.
2. Experimental Method
a. Zonyl8740 solutions with mass concentration of 0.01% and 0.5% is
prepared.
b. HF acid solution is poured into a plastic beaker, and four glass slides
are placed in the beaker. Two glass slides are taken out every 20 sec-
onds, washed with distilled water, and dried.