Page 285 - Enhanced Oil Recovery in Shale and Tight Reservoirs

262 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 9.34 Schematic of electric double layer.

and the fluid attached to the particle. The z-potential is the electrokinetic
potential at the slipping plane.
The surface charges at the rock/brine interface determine the magnitude
of the z-potential. When the absolute value of the z-potential is great, the
repulsion between the rock/brine interface and the brine/oil interface is
stronger, which makes the water film more stable and makes it easier for
oil film to be detached from the rock surface, thus, the rock surface is
more water-wet.

9.8.7 Discussion of methods to determine wettability

Refer to Fig. 9.35, the interfacial tensions s and the wettability indices cosq ws
and cos q os at equilibrium in an oil-water-solid system have the following
relationships:
s os s ws
cosq ws ¼ (9.49)
s wo

s ws s os
cosq os ¼ (9.50)
s wo