Page 253 - Enhanced Oil Recovery in Shale and Tight Reservoirs

EOR mechanisms of wettability alteration and its comparison with IFT 235

decreases more significantly. Fig. 9.12 shows that oil recovery will always be
high, or it does not matter whether the wettability is altered or not, as long as
the IFT is low (as shown in the figure when IFT ¼ 0.003 mN/m);
Fig. 9.11A also shows that when the IFT is low, the effect of wettability
alteration is not important any more. Note their core permeability was over
100 mD.
More likely, anionic surfactants reduce IFT, while cationic surfactants
change wettability. While studying imbibition oil recovery in Silurian dolo-
mite cores using surfactants, Chen and Mohanty (2015) combined cationic
surfactants and anionic surfactants. Their experimental data are shown in
Fig. 9.13. The properties of those surfactants are summarized in Table 9.3.
Fig. 9.13A shows that when the 0.2% cationic surfactant BTC 8358 had
spontaneous imbibition oil recovery of 31%. After that, adding 0.02%
anionic surfactant A092 to 0.2% BTC 8358 resulted in 10% incremental
oil recovery to 41.6%. Fig. 9.13B shows that a combination of 0.1% cationic
surfactant BTC 8358 and 0.5% anionic surfactant AS-3 had oil recovery of
46%, 13% higher than that (33%) from 1% anionic surfactant. They claimed
the incremental oil recovery resulted from the synergy of cationic and

Figure 9.13 Synergy of wettability alteration and IFT reduction (Chen and Mohanty,
2015).
Table 9.3 Property data of surfactants.
Surfactant Type IFT, mN/m Wettability alteration
BTC8358 Cationic 3 Oil-wet to
water-wet
A092 Anionic 0.03 No
AS-3 Anionic 0.05 No