Page 330 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Spontaneous imbibition 303

(less than 5 days), but in the late time, the two curves rise similarly and
become almost parallel during the very late time. The difference between
the two curves is that WW þ IFT has additional wettability alteration which
makes the capillary pressure work to improve oil recovery in the early time.
In other words, the capillary force dominates in the early time. In these
simulation cases, the IFT is low at 0.0088 mN/m. When the IFT is low,
the capillary number becomes high, resulting in improved relative permeabil-
ities, and the gravity can play its role to produce oil. Note the permeability in
the model is 122 mD.

10.11 Behaviors of different surfactants
Alvarez et al. (2014) as well as Alvarez and Schechter (2017) per-
formed spontaneous imbibition experiments monitored by CT in shale
reservoirs to compare the effects of anionic surfactants and nonionic surfac-
tants. They concluded that anionic surfactants show superior effect on
wettability alteration and oil recovery during spontaneous imbibition.
Liu et al. (2019) compared the capability of wettability alteration of
anionic surfactants and nonionic surfactants. They observed that anionic sur-
factants (sodium alcohol ether sulfate (AES) and sodium C14-16 olefin
sulfonate (AOS)) more significantly altered core wettability toward more
water-wet than nonionic surfactants (alcohol ethoxylate (AEO-9) and
isomeric alcohol ethoxylates (IAE)). Those anionic and nonionic surfactants
reduced the IFT to the similar level as shown in Fig. 10.14. Because the
anionic surfactants have higher capability of wettability alteration, they

Figure 10.14 Measured water-oil IFT values in different surfactant solutions.