**7. Conclusion**

*Enhanced Oil Recovery Processes - New Technologies*

the greater reduction in IFT.

considered as the main mechanism for oil recovery. Moreover, Ding et al. [61] introduced nanoparticle-assisted low-salinity hot water (LSHW) injection for heavy oil recovery. Flooding tests were conducted on silica sand packs saturated with heavy oil to compare the effect of LSW flooding, 0.05 wt% SiO2 nanoparticle-dispersed LSW flooding, and 0.05 wt% Al2O3 nanoparticle-dispersed LSW flooding on oil recovery. They observed higher oil recovery by the injection of NP/LSW than LSW alone. Also, they found that Al2O3 NPs were more effective in recovering oil due to

Generally, the average nanoparticle size, specific surface area, and stability of nanofluids are important in the performance of this hybrid method. The issue of nanofluid stability at low-salinity conditions is challenging and should be considered in the application of this hybrid method. The range of stability constraints (such as zeta potential) of colloidal systems of nanofluids coupled with ions (i.e., LSW) is typically wider so that in the presence of both elements (nanoparticles and

Heavy oil is conventionally recovered by thermal-based approaches. Thermal energy in combination with LSW water flooding, in the form of hot LSW water flooding, can be applied to simultaneously decrease the viscosity of the heavy oil and alter the wettability of the porous media to attain higher oil recovery. Alotaibi et al. and Tang et al. reported lower contact angle and higher oil recovery, respectively, after increasing the displacement temperature in LSW injection [62, 63]. Contrary to this observation, Soraya et al. [64] found lower oil recovery at higher temperatures by tertiary LSW. However, another study [65] demonstrated that the injection of hot LSW yielded significant incremental oil recovery. In this work, hot LSW at a concentration of 200 ppm salinity was injected after hot HSW at a concentration of 15,000 ppm salinity, which yielded about 25% OOIP incremental oil recovery, as shown in **Figure 21**. In addition, in this study the injection of steam

is proposed after hot LSW flooding to further enhance the oil recovery.

low-salinity hot water (LSHW) into silica sand packs to recover heavy oil. Temperatures of 17, 45, and 70°C were applied under different scenarios of high- and low-salinity brines and nanofluids. LSW was found to provide better

A similar trend was reported by Ding et al. by injecting nanoparticle-assisted

ions), longer-lasting stable solutions can be attained [60].

**6. LSW/hot water hybrid EOR technique**

**18**

**Figure 21.**

*Oil recovery by hot HSW and hot LSW [65].*

The main idea of this chapter is to demonstrate the synergistic EOR effects of combining chemical/gas-based/thermal methods with low-salinity water and the related underlying mechanisms in both sandstone and carbonate rocks. Hybrid EOR methods are utilized to bypass or improve operational, environmental, and economical shortcomings of individually implemented methods. Many experimental and modeling studies have confirmed this potential synergy by mentioning wettability alteration toward more water-wet condition as the main mechanism of LSW method.

Lower ion concentration of LSW allows gas (typically CO2) molecules to dissolve in water phase in higher extent which results in gas/oil contact and improved front stability. However, some studies cast doubt on this idea as the more gas dissolves in water, the lower free gas is available to decrease oil viscosity and ultimately improve oil mobility.

Surfactants are known as the agents which are utilized to decrease the IFT, consequently capillary forces, between oil and water in order to enhance microscopic sweep efficiency. LSW provides more detached oil droplets to be produced due to lowered capillary forces by surfactants.

Polymers cause higher oil recovery by increasing water viscosity which lowers mobility ratio after reservoir fluid redistribution by LSW injection due to wettability alteration.

Thermal methods are applied in heavy oil reservoirs to help oil recovery under the mechanism of improved oil mobility, which can be more advantageous if higher detached oil droplets are provided by LSW injection. Lastly, nanoparticles have been introduced to be beneficial as they can improve wettability alteration process by LSW injection.

Despite the extensive promising works mentioned in this chapter, many contradictions, ambiguities, and unexamined issues, especially in carbonate rocks, require more investigation in LSW hybrid methods regarding underlying mechanisms, field implementation viability, operational considerations, and economical feasibility by both experimental and modeling assessments.

*Enhanced Oil Recovery Processes - New Technologies*
