Page 215 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Application of Gas Wettability CHAPTER 6 199

Table 6.2 Correlation Table of Oil/water Interfacial Tension
Treating Agent Interfacial Tension (25 C) (25 C) (mN/m)

Water-block resistance agent 0 0.1% 0.2% 0.3% 0.4% 0.5%
ABSN 2.10 0.80 0.65 0.45 0.40 0.40
FCS-08 2.10 0.45 0.32 0.27 0.25 0.25

It can be seen from Table 6.2 that the effect of FCS-08 in reducing oil/water
interfacial tension is better than that of ABSN. When the concentration of
FCS-08 is 0.2%, the oil/water interfacial tension can be reduced to 0.32 mN/m.
The capillary pressure is the function of the interface between immiscible phases
in a porous media. The smaller the interfacial tension between fluids, the lower
the capillary pressure. The above experimental results indicate that the water-
block resistance agent FCS-08 can effectively reduce capillary pressure and the
power of external liquid phase adsorbed onto the porous media. Thus, it can
effectively reduce the intrusion amount of external liquid phases near borehole
zones or fracture surfaces. It can also decrease the liquid phase saturation in
tight reservoirs, improve oil and gas percolation near borehole zones, and effec-
tively reduce the degree of damage caused by water-blocks.

6.1.2.3.2 Alteration Degree of the Wettability of Core Surfaces
An artificial sandstone core slice was placed in grinding jars with FCS-08 water
solution of different concentrations. This was put aside at room temperature
after thoroughly shaking it. It was then shaken every hour and the liquid sam-
ples were extracted at certain time intervals. The emulsion concentration was
then measured with a spectrophotometer. When the concentration didn’t
change any more, adsorption equilibrium was achieved.

The adsorption-equilibrated core slice was washed with distilled water 3 times,

and was placed in an oven at a constant temperature of 100 C. It was then
dried for 24 hours. The contact angle of oil and water phases (n-Hexadecane
represents oil phase and distilled water represents water phase) on the core
slice were measured with a JC2000D3 contact angle meter, respectively. The
volume of drops was 5 μL, and at least 3 different points were chosen and
measured for every sample. The average value was taken. With the measured
contact angle, the surface energy of core slices before and after adsorbing
FCS-08 was calculated using Owens two-liquid method. The surface tension,
dispersion force, and polarity force of distilled water were 72.8, 21.8, and
2
51.0 mJ/m , respectively, and the surface tension, dispersion force, and
2
polarity force of n-Hexadecane were 27.6, 27.6 and 0 mJ/m , respectively. The
results are shown in Table 6.3.
When the water-block resistance agent FCS-08 was adsorbed, the surface
wettability of artificial cores showed obvious changes. As FCS-08