Page 261 - Enhanced Oil Recovery in Shale and Tight Reservoirs

EOR mechanisms of wettability alteration and its comparison with IFT 243

cationic surfactants (Austad et al., 1998; Standnes et al., 2002), and anionic
surfactants (Sharma and Mohanty, 2013; Seethepalli et al., 2004; Chen and
Mohanty, 2013). Nonionic fluorinated polymeric surfactants were proposed
to treat gas condensate reservoirs to mitigate condensate dropout by altering
wettability to more gas-wetting conditions (Li and Firoozabadi, 2000;
Kumar et al., 2006; Sharma et al., 2018). Ethoxylate sulfates could change
carbonate surfaces from more oil-wet to more water-wet, but they are

not stable at high temperature (e.g., 60 C). At room temperature, Hirasaki
and Zhang (2004) showed that the ethoxy and propoxy sulfates had high
performance in imbibition oil recovery in carbonate cores, when Na 2 CO 3
was added. Sulfonates and carboxylates are thermally stable, but they are
generally poor in altering wettability (Chen and Mohanty, 2015). Sharma
and Mohanty (2013) tested ethoxylate sulfonates for wettability alteration

in hard brine at 100 C and found that water contact angles were reduced

to around 90 C in the best case. Chen and Mohanty (2013, 2014) found
that the divalent scavengers (e.g., EDTA.4Na, Sodium polyacrymide
(NaPA)) sequestered divalent ions in hard brine to free anionic surfactants
to react at the solid-fluid interface to alter wettability of carbonates from
oil-wet to more water-wet. Generally, anionic surfactants are cheaper
than cationic surfactants. A quaternary amine surfactant, BTC 8358 (n-
alkyl dimethyl benzyl ammonium chloride) was found to be effective in
wettability alteration on oil-wet calcite surfaces. A combination of two
Guerbet alkoxy sulfate and one internal olefin sulfonate (IOS) was found
be a strong wettability modifier at a salinity below the optimum salinity.
A mixture of cationic surfactant BTC 8358 and an anionic surfactant Enor-
det A092 (C 16,17 branched IOS to reduce IFT) was also found to have a
good imbibition oil recovery (Chen and Mohanty, 2015).
Liu et al. (2019) compared anionic surfactants and nonionic surfactants in
terms of their capability of wettability alteration. Fig. 9.23 shows the z-po-
tential in these surfactant solutions. It shows that for the same surfactant, the
absolute values of the z-potential increased with surfactant concentration.
The increase for anionic surfactants (sodium alcohol ether sulfate (AES)
and sodium C14-16 alpha olefin sulfonate (AOS)) was much greater than
in nonionic surfactants. At the same concentration, the z-potential (absolute
value) in the anionic surfactant solutions was higher than that in the
nonionic surfactant solutions (alcohol ethoxylate (AEO-9) and isomeric
alcohol ethoxylates (IAE)). The absolute values of the z-potential for the
nonionic surfactant solutions at concentrations of 0.01 wt.%, 0.05 wt.%,
and 0.1 wt.% were less than 20 mV which is close to water’s z-potential.