Page 235 - Fundamentals of Enhanced Oil and Gas Recovery

Waterflooding 223

water results in increasing the amount of recovered oil [35]. Different researchers sup-
ported this result that lower salinity of connate water results in more oil production,
for instance, McGuire et al. [44] data and Zhang and Morrow’s [46] data.

7.6.1.3 Effect of Injection Water Salinity
According to the data in open literature a higher oil recovery was obtained when
the salinity of injection water is lower than that of connate water. Moreover, the
injection water salinity was low enough [48,49]. Zhang et al. [48] observed that the
LS of 1500 ppm which was about 5% formation water salinity resulted in sharp
increase in the tertiary recovery and in the differential pressure.

7.6.1.4 Effect of Wettability
Jadhunandan and Morrow [35] found that the wettability related to initial water satu-
ration in the cores. With higher initial water saturation, the cores showed more
water-wet. Moreover, the oil recovery increased from strongly water-wet to a maxi-
mum close to neutral wet, which was agreed by Sharma and Filoco [47]. For the
cores with high initial salinity, LS injection will make the cores more water-wet and
result in a higher oil recovery [45].

7.6.2 Mechanisms Behind Low-Salinity Waterflooding
Seventeen mechanisms of LS waterflooding have been proposed in the literature, as
follows [45]:
1. fine migration [37]
2. mineral dissolution [50]
3. limited release of mixed-wet particles [50]
4. increased pH effect and reduced interfacial tension (IFT) [44]
5. emulsification/snap-off [44]
6. saponification [44]
7. surfactant-like behavior [44]
8. multicomponent ion exchange (MIE) [51]
9. double layer effect [52]
10. particle-stabilized interfaces/lamella [50,53]
11. salt-in effects [54]
12. osmotic pressure [50]
13. salinity shock [50]
14. wettability alteration (more water-wet) [50]
15. wettability alteration (less water-wet) [50]
16. viscosity ratio [50]
17. end effects [50]