Page 260 - Enhanced Oil Recovery in Shale and Tight Reservoirs

242 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 9.21 Contact angles when the shale cores were soaked in different surfactant
concentrations for 48 h.

IFT conditions in nonionic surfactants. As s ow decreases, the oil film desorp-
tion does not significantly increase the adhesion work (W)as Fig. 9.22 shows
and as the following equation indicates:

W ¼ðs ow þ s ws ÞA s os A (9.37)
Therefore, the IFT reduction is beneficial to the desorption of oil film or
organic matter from the rock surfaces. In nonionic surfactant solutions, the
oil film or organic matter does not have electrostatic forces to be stripped off.
The shale wettability is altered by adsorption, rather than by the stripping
process through ion-pairs. Thus, the effect of IFT reduction on wettability
alteration is not as effective as in anionic surfactant.

9.7 Surfactant selection for wettability alteration

There are many surfactants that are used to reduce IFT in the surfac-
tant flooding literature. Less discussions have been allocated to surfactants
that are used to change wettability. These surfactants could be nonionic sur-
factants (Standnes et al., 2002; Vijapurapu and Rao, 2004; Xie et al., 2005),

Figure 9.22 Schematic of the stripping process of oil film.