**3. LSW/polymer hybrid EOR technique**

Polymer flooding, as a well-known and effective EOR method, can also be considered as a complementary method to enhance the capability of LSW flooding as a hybrid approach. Polymer flooding affects the macroscopic sweep efficiency in porous media by improving the displacement mobility ratio. On the other hand, LSW flooding affects the microscopic sweep efficiency by changing CBR interactions and wettability. Hence, the hybrid low-salinity/polymer flooding provides the benefits of both methods and can be considered as a novel EOR approach.

Different injection schemes were experimentally studied and modeled in the literature. LSW can be injected as a preflush before polymer flooding, or polymer can be injected prior to LSW. The first approach is more effective than the second one because the injection of LSW changes the wettability to more water wet, which alters the distribution of the remaining oil saturation in the porous medium. Oil droplets are detached from small pores and accumulated in bigger and middle-sized pores. Hence, the injection of polymer recovers the redistributed oil more easily. Torrijos et al. [21] experimentally investigated the synergy between LSW flooding and polymer flooding in sandstones. Both injection modes were studied by injecting a low-salinity polymer (LSP), which was prepared by dissolving 1000 ppm hydrolyzed polyacrylamide (HPAM) in 1000 ppm NaCl brine as LSW. **Figure 8** shows that the hybrid LSW/LSP provides around 20% higher total oil recovery than the LSP/LSW method.

A similar trend was observed by Alsofi et al. [22] who studied the synergy between LSW/polymer flooding in a carbonate formation. In this work, heavy crude oil, high-salinity (69,000 mg/L) brine, and low-salinity brine (6900 mg/L)

**Figure 8.** *Oil recovery by two combinations of polymer flooding and LSW flooding [21].*

**Figure 9.** *Recovery profile for tertiary hybrid flooding method [22].*

were used. After secondary waterflooding, polymer flooding followed by polymer-LSW flooding provided more than 24% OOIP additional recovery, as shown in **Figure 9**. The same findings were reported by [23–25].

Hence, the sequence of injection affects total oil recovery. Almansour et al. experimentally investigated the hybrid LSW/polymer flooding method in Berea and Bentheimer sandstone samples. Persian Gulf brine and a 10 times diluted sample were used as the high-salinity and low-salinity brines, respectively. The hybrid method recovered more than 12% extra oil by switching from LSW to polymer in the Berea sandstone and more than 29% for the Bentheimer sample. Continuing LSW as the tertiary method and then converting to polymer flooding were also recommended based on their results [26]. Likewise, Tahir et al. showed that injection of polymer after LSW or smart water provides higher oil recovery than the oil recovery obtained by polymer injection before LSW. It is speculated that in this flooding sequence (i.e., polymer flooding before LSW), the LSW may follow the same paths as the polymer fluid, which inhibits the direct contact of LSW with the oil/rock interface. In contrast, the preinjection of LSW can alter the wettability of the rock by direct contact making oil detachment from rock surfaces easier, which aids the displacement of oil in the subsequent polymer flooding stage [27].

In addition to experimental studies, modeling approaches have also confirmed the benefits of hybrid LSW/polymer flooding. Khorsandi et al. [28] developed the first analytical solution for combined LSW/polymer flooding in sandstone to describe the synergy of this hybrid process, which allows recognizing the effective parameters and the mechanisms controlling oil recovery. This hybrid method was

### *Hybrid EOR Methods Utilizing Low-Salinity Water DOI: http://dx.doi.org/10.5772/intechopen.88056*

*Enhanced Oil Recovery Processes - New Technologies*

**Figure 8.**

**Figure 9.**

were used. After secondary waterflooding, polymer flooding followed by polymer-LSW flooding provided more than 24% OOIP additional recovery, as shown in

Hence, the sequence of injection affects total oil recovery. Almansour et al. experimentally investigated the hybrid LSW/polymer flooding method in Berea and Bentheimer sandstone samples. Persian Gulf brine and a 10 times diluted sample were used as the high-salinity and low-salinity brines, respectively. The hybrid method recovered more than 12% extra oil by switching from LSW to polymer in the Berea sandstone and more than 29% for the Bentheimer sample. Continuing LSW as the tertiary method and then converting to polymer flooding were also recommended based on their results [26]. Likewise, Tahir et al. showed that injection of polymer after LSW or smart water provides higher oil recovery than the oil recovery obtained by polymer injection before LSW. It is speculated that in this flooding sequence (i.e., polymer flooding before LSW), the LSW may follow the same paths as the polymer fluid, which inhibits the direct contact of LSW with the oil/rock interface. In contrast, the preinjection of LSW can alter the wettability of the rock by direct contact making oil detachment from rock surfaces easier, which

aids the displacement of oil in the subsequent polymer flooding stage [27].

In addition to experimental studies, modeling approaches have also confirmed the benefits of hybrid LSW/polymer flooding. Khorsandi et al. [28] developed the first analytical solution for combined LSW/polymer flooding in sandstone to describe the synergy of this hybrid process, which allows recognizing the effective parameters and the mechanisms controlling oil recovery. This hybrid method was

**Figure 9**. The same findings were reported by [23–25].

*Recovery profile for tertiary hybrid flooding method [22].*

*Oil recovery by two combinations of polymer flooding and LSW flooding [21].*

**8**

also simulated by Mohammadi and Jerauld [29], who showed higher oil recovery as displayed in **Figure 10** that shows that injection of polymer after LSW gives better performance than polymer injection and stand-alone LSW flooding. Furthermore, this study showed that wettability alteration by LSW and the simultaneous increase in brine viscosity, reduction of the relative brine permeability, and mobility control during polymer flooding improved the fractional flow of the process, as shown in **Figure 11**. The adjustment in fractional flow was also modeled by [30], which confirms the stable shock fronts during LSW/polymer flooding. As polymer cannot invade the inaccessible pore volume, the water remaining after LSW will be immobile in these pores, which reduces the channeling in the formation [31]. Hence, the hybrid method can control the unstable front and the channeling of low-viscosity LSW into the viscous oil. This makes the LSW/polymer hybrid method even more effective in heavy oil formations.

Other injection schemes have also been discussed and studied as reported in the literature. For example, Lee et al. modeled the process of polymer-assisted carbonated LSW flooding (PCLSWF) as a new hybrid method [32]. Different mechanisms are involved during PCLSWF, such as wettability modification by LSW, oil swelling, oil viscosity reduction by the gas, and mobility enhancement by the polymer. Also, higher pressure in the porous media in the presence of polymer leads to more dissolution of CO2 in the brine and more transport of gas to the oil phase. Hence,

### **Figure 10.**

*Oil recovery modeling by hybrid method injection and comparison to other EOR approaches [29].*

**Figure 11.**

*Comparison of fractional flow of high-salinity, low-salinity, polymer, and hybrid flooding by modeling [29].*

PCLSWF showed better performance than LSW flooding, hybrid low-salinity polymer flooding (LSPF), and hybrid carbonated LSW flooding (CLSWF), as shown in **Figure 12** [32]. Another study was conducted by Eikrem to analyze oil recovery by combining low-salinity injection and surfactant/polymer (SP) flooding. Cores with different initial wettability were flooded initially by the high-salinity water (HSW) and then with a surfactant solution in tertiary mode, followed by a polymer injection for mobility control. They found that injecting a 600 ppm HPAM polymer solution after the surfactant injection improved the ultimate recovery of oil [33]. Mjøs observed a similar behavior [34].

Interactions between polymer and LSW affect different governing parameters in the EOR process. Lower salinity has an influence on the polymer injectivity, retention, polymer stability, and rheological factors such as viscosity. Alsofi et al. studied the effect of LSW on the polymer solution properties by single-phase core flooding tests in carbonate samples. Anionic sulfonated polyacrylamide polymer was used as the polymer, and two samples of water with salinity of 244,000 and 24,400 mg/L were used as high- and low-salinity brines, respectively. They found that at lowersalinity concentration, coiling of the polymer backbone is reduced due to lower existing ions in LSW. Therefore, there are more repulsive interactions among the polymer chains causing the expansion of the polymer backbone, which results in higher viscosity of the polymer solution that leads to pressure buildup and slightly lower polymer injectivity [35].

The better solubility of polymer in LSW leads to the alteration of the polymer retention, which is critical for the technical and economical design of the process. In [35], it was indicated that the polymer retention decreased by 10–28%, which was noticeable. Expansion of the polymer chains due to repulsion results in the fitting of fewer polymer molecules on the adsorption rock surface sites, which reduces the retention. In [26], Almansour et al. also confirmed a reduction in the retention of polymer by using LSW. A decrease in polymer adsorption was also reported by [36]. Modeling has also showed that lower concentrations of polymer are required to establish a stable displacement front in the LSW/polymer approach than the HSW/polymer [29].

This synergistic effect also reduces the consumption of polymer, which is a positive point. At lower salinity, a lower polymer concentration is required to achieve the target viscosity, which makes the polymer flooding process more cost-competitive. In addition to the reduction of transportation costs, storage, and polymer handling, this behavior was also confirmed by [22]. Brine salinity also affects the stability of the polymer solution in some special conditions. Levitt et al. [37] showed that at lower ion composition, especially at low calcium concentration, HPAM is more stable at higher temperatures.

### **Figure 12.**

*Oil recovery of PCLSWF compared to other EOR methods in core scale (left) and pilot scale (right). LSWF is LSW flooding, LSPF is low-salinity polymer flooding, and CLSWF shows the carbonated LSW flooding [32].*

### *Hybrid EOR Methods Utilizing Low-Salinity Water DOI: http://dx.doi.org/10.5772/intechopen.88056*

*Enhanced Oil Recovery Processes - New Technologies*

Mjøs observed a similar behavior [34].

lower polymer injectivity [35].

HPAM is more stable at higher temperatures.

PCLSWF showed better performance than LSW flooding, hybrid low-salinity polymer flooding (LSPF), and hybrid carbonated LSW flooding (CLSWF), as shown in **Figure 12** [32]. Another study was conducted by Eikrem to analyze oil recovery by combining low-salinity injection and surfactant/polymer (SP) flooding. Cores with different initial wettability were flooded initially by the high-salinity water (HSW) and then with a surfactant solution in tertiary mode, followed by a polymer injection for mobility control. They found that injecting a 600 ppm HPAM polymer solution after the surfactant injection improved the ultimate recovery of oil [33].

Interactions between polymer and LSW affect different governing parameters in the EOR process. Lower salinity has an influence on the polymer injectivity, retention, polymer stability, and rheological factors such as viscosity. Alsofi et al. studied the effect of LSW on the polymer solution properties by single-phase core flooding tests in carbonate samples. Anionic sulfonated polyacrylamide polymer was used as the polymer, and two samples of water with salinity of 244,000 and 24,400 mg/L were used as high- and low-salinity brines, respectively. They found that at lowersalinity concentration, coiling of the polymer backbone is reduced due to lower existing ions in LSW. Therefore, there are more repulsive interactions among the polymer chains causing the expansion of the polymer backbone, which results in higher viscosity of the polymer solution that leads to pressure buildup and slightly

The better solubility of polymer in LSW leads to the alteration of the polymer retention, which is critical for the technical and economical design of the process. In [35], it was indicated that the polymer retention decreased by 10–28%, which was noticeable. Expansion of the polymer chains due to repulsion results in the fitting of fewer polymer molecules on the adsorption rock surface sites, which reduces the retention. In [26], Almansour et al. also confirmed a reduction in the retention of polymer by using LSW. A decrease in polymer adsorption was also reported by [36]. Modeling has also showed that lower concentrations of polymer are required to establish a stable displacement front in the LSW/polymer approach than the HSW/polymer [29]. This synergistic effect also reduces the consumption of polymer, which is a positive point. At lower salinity, a lower polymer concentration is required to achieve the target viscosity, which makes the polymer flooding process more cost-competitive. In addition to the reduction of transportation costs, storage, and polymer handling, this behavior was also confirmed by [22]. Brine salinity also affects the stability of the polymer solution in some special conditions. Levitt et al. [37] showed that at lower ion composition, especially at low calcium concentration,

*Oil recovery of PCLSWF compared to other EOR methods in core scale (left) and pilot scale (right). LSWF is LSW flooding, LSPF is low-salinity polymer flooding, and CLSWF shows the carbonated LSW flooding [32].*

**10**

**Figure 12.**

Different operational parameters affect the performance of the LSW/polymer hybrid method, which should be considered at the design stage of the flooding process. The main parameters that should be studied are the initial wettability of the rock, smart water design (salinity concentration and composition), and the hybrid method initiation time. Shiran et al. studied the synergy of LSW/polymer flooding by core flooding experiments in sandstone samples [31]. The LSW was obtained by diluting 10 times seawater. Flopaam 3630S polyacrylamide with a hydrolysis degree of 25–30% was added to the LSW in concentrations of 300 and 1000 ppm to prepare the polymer solution. Aluminum citrate was added to the polymer solution to cross-link the polymer chains. This study revealed that the initial wettability of the porous medium was a critical factor affecting the success of the hybrid method, because incremental oil recovery was not observed during the polymer flooding step in the hybrid LSW/polymer injection scheme in core plug samples that were strongly water wet. However, the injection of polymer after LSW was effective for intermediate water-wet core samples, as shown in **Figure 13**. In water-wet formations, there are more adsorption sites available on the rock surfaces; thus, polymer retention is higher, which affects the performance of the method. Moreover, it was observed by [34] that the performance of the hybrid method was better in less water-wet conditions.

Another important parameter in the design of the hybrid method is the appropriate time to switch from conventional waterflooding to the hybrid method. A numerical simulation study of the hybrid LSW/polymer flooding conducted in 1D, 2D, and 3D reservoirs indicated that the hybrid method should be started at water cuts less than or equal to 75% to achieve improvement in oil recovery [30]. Hence, a comprehensive economic study is required to design the optimum case for field applications.

Ion management is a critical parameter to design smart waters and improve the performance of the diluted LSW/polymer flooding. Alteration in ion concentrations and ion types can affect the properties of the polymer solution, which must be considered during the design of hybrid polymer and smart water flooding. Experiments in [27] aimed to study the effect of active ions such as sulfate on the performance of the hybrid methods. The presence of sulfate affects the polymer solution viscosity, as shown in **Figure 14**.

The application of the LSW/polymer flooding offers economical and technical benefits for EOR applications. For example, the water cut is reduced compared to the stand-alone polymer or LSW flooding, as confirmed by simulations conducted

### **Figure 13.**

*Oil recovery during secondary mode LSW flooding followed by polymer flooding and linked polymer solution (LPS) flooding [31].*

### **Figure 14.**

*Polymer steady-state viscosity at different temperatures for different types of solution brines (SSW stands for synthetic seawater) [27].*

by Santo and Muggeridge [30]. Also, the oil recovery by LSW/polymer flooding was established to be slightly better than the conventional surfactant/polymer chemical flooding [22]. This is an important observation because the hybrid method could provide higher oil recovery at a lower cost. The studies reviewed in this section confirm the synergistic effect of combining LSW/polymer flooding.

## **4. LSW/surfactant hybrid EOR technique**

The main mechanism responsible for the effectiveness of LSW in improving oil recovery is the alteration of the wettability of the rock toward more water wet that causes the detachment of oil films from the rock surface. The injection of surfactant reduces the interfacial tension (IFT) between crude oil and brine and alters the wettability of the rock reducing the capillary forces that have trapped oil in the porous media. Therefore, the combination of LSW and low-salinity surfactant (LSS) in LSW flooding could be an efficient approach by combining the effect of oil layer destabilization by LSW and reduction of the IFT by the surfactant. This hybrid method provides higher incremental oil recovery than either stand-alone techniques.

LSW makes the environment more favorable for an effective surfactant flooding, while LSS solubilizes some of the residual oil via Winsor type II microemulsion. Several studies have reported high tertiary oil recovery values by surfactant injection after LSW flooding in both carbonate and sandstone formations. For example, according to [38], 5–7% incremental oil recovery was observed by injection of sodium dodecyl benzene sulfonate surfactant (SDBS) after LSW into sandstones. Similarly, Alameri et al. observed up to 10% incremental oil recovery by LSS after LSW injection into carbonate core samples [39].

Application of the LSW/LSS hybrid method results in lower surfactant consumption, lower operational costs, and fewer operational problems. For instance, it is less challenging to achieve a low IFT during surfactant flooding at low-salinity *Enhanced Oil Recovery Processes - New Technologies*

by Santo and Muggeridge [30]. Also, the oil recovery by LSW/polymer flooding was established to be slightly better than the conventional surfactant/polymer chemical flooding [22]. This is an important observation because the hybrid method could provide higher oil recovery at a lower cost. The studies reviewed in this section

*Polymer steady-state viscosity at different temperatures for different types of solution brines (SSW stands for* 

The main mechanism responsible for the effectiveness of LSW in improving oil recovery is the alteration of the wettability of the rock toward more water wet that causes the detachment of oil films from the rock surface. The injection of surfactant reduces the interfacial tension (IFT) between crude oil and brine and alters the wettability of the rock reducing the capillary forces that have trapped oil in the porous media. Therefore, the combination of LSW and low-salinity surfactant (LSS) in LSW flooding could be an efficient approach by combining the effect of oil layer destabilization by LSW and reduction of the IFT by the surfactant. This hybrid method provides higher incremental oil recovery than either stand-alone

LSW makes the environment more favorable for an effective surfactant flooding, while LSS solubilizes some of the residual oil via Winsor type II microemulsion. Several studies have reported high tertiary oil recovery values by surfactant injection after LSW flooding in both carbonate and sandstone formations. For example, according to [38], 5–7% incremental oil recovery was observed by injection of sodium dodecyl benzene sulfonate surfactant (SDBS) after LSW into sandstones. Similarly, Alameri et al. observed up to 10% incremental oil recovery by LSS after

Application of the LSW/LSS hybrid method results in lower surfactant consumption, lower operational costs, and fewer operational problems. For instance, it is less challenging to achieve a low IFT during surfactant flooding at low-salinity

confirm the synergistic effect of combining LSW/polymer flooding.

**4. LSW/surfactant hybrid EOR technique**

LSW injection into carbonate core samples [39].

**12**

techniques.

**Figure 14.**

*synthetic seawater) [27].*

conditions. Likewise, in these conditions, there is reduced surfactant retention and increased surfactant stability and solubility.

In this hybrid process, the dominant mechanisms for increased oil recovery are wettability alteration by LSW and IFT reduction between the crude oil and brine by LSS. Alagic et al. studied this hybrid method through core flooding tests and analyzed the performance of LSS injection after LSW into sandstone samples. Olefin sulfonate was used as the surfactant in these tests. The results show more than 90% oil recovery of the OOIP when surfactant is injected after LSW. This injection sequence produces higher oil recovery than the injection of surfactant after highsalinity water (74% OOIP), as shown in **Figure 15** [40]. Injection of LSW makes the system more water wet, which aids the detachment of oil droplets and reduces the capillary force, making easier the displacement of oil during the surfactant flooding process. Surfactant injection in a low-salinity environment is more effective, as the presence of the divalent ions contained in high-salinity water attenuates IFT reduction due to the formation of water-in-oil microemulsions.

The achievement of ultralow IFT during LSS is critical; however, several studies have demonstrated that wettability alteration by the hybrid LSW/LSS approach can be very effective. Therefore, in this process, wettability alteration is considered the dominant mechanism for oil recovery. Johannessen et al. [41] used branched C12–13 alcohol-xPO-sulfates as the surfactant, olefin sulfonate as the co-surfactant, and secondary butanol (SBA) as the cosolvent to evaluate the performance of LSW/ LSS flooding from Berea sandstone cores in terms of oil recovery. Two flooding conditions were studied: in the first case, the core was flooded using low-salinity brine corresponding to 0.07 times the seawater salinity (diluted case), and the other one was flooded at the optimum salinity of surfactant flooding obtained from phase behavior screening and IFT measurements (optimum salinity case). The same oil recovery was observed for both cases, as shown in **Figure 16**. Incremental oil recovery beyond expectations by the capillary number changes is explained by the synergistic effect of the low-salinity surfactant flooding, even at IFT values above ultralow IFT values.

The same behavior was observed by Khanamiri et al. during LSW/LSS flooding of sandstone samples [42]. The incremental oil recovery by LSS after LSW was in the range of 2–6% OOIP. They observed that the oil mobilization in the process was mostly due to wettability alteration by LSW and LSS and IFT reduction cannot be considered as the dominant mechanism. As the salinity of the solution was not at the optimum salinity condition, ultralow IFT was not achieved; however, the significant wettability alteration caused by LSS flooding verified from contact angle measurements (quartz crystal microbalance (QCM) on silica-coated crystals) compensated the effect of having a value of IFT higher than the desired ultralow IFT

### **Figure 15.**

*Oil recovery, water cut, and effluent pH during LSW/LSS injection (left) and synthetic seawater (SSW)/LSS flooding (right) [40].*

**Figure 16.**

*Oil recovery and dP profiles for injection of seawater followed by LSW and low-salinity surfactant at diluted case (left) and optimum salinity (right) [41].*

### **Figure 17.**

*Contact angle for deionized water droplet/air/silica after different treatments [42].*

value. **Figure 17** shows the alteration in contact angle for different treated brines. This figure indicates the initial contact angle and the angles after aging in highsalinity water, in LSW, and in LSS. As can be seen, wettability alteration toward water-wet condition occurred for all cases with different types of LSW. However, different ion contents affected the magnitude of wettability alteration.

The effect of surfactant on wettability alteration was also observed by Teklu et al. [43]. They measured the contact angle of different carbonate and sandstone rock disks saturated with oil in low-salinity brine in the presence and absence of nonionic ethoxylated alcohol surfactant. They found that the presence of surfactant decreases the contact angle and makes the system more water wet. Reduction in IFT and alteration of rock wettability by LSS can increase oil recovery in cases when LSW is not effective alone. For example, core flooding experiments conducted by Spildo et al. showed that the application of surfactant-free LSW does not increase oil recovery, while LSS produces incremental oil recovery, as shown in **Figure 18** [44].

These synergistic mechanisms (i.e., wettability alteration and reduction of IFT) in the hybrid LSW/LSS method provide higher oil recovery than the recovery expected from the capillary desaturation curves (CDC). Studies in [44, 45] showed that during the LSS after LSW, the capillary number was about 10<sup>−</sup><sup>4</sup> , which is not high enough to achieve noticeable incremental oil recovery, as observed in the experiments [46]. Hence, oil detachment and redistribution due to rock wettability alteration during LSW make the LSS performance better than the estimation from the CDC.

*Hybrid EOR Methods Utilizing Low-Salinity Water DOI: http://dx.doi.org/10.5772/intechopen.88056*

**Figure 18.**

*Enhanced Oil Recovery Processes - New Technologies*

*case (left) and optimum salinity (right) [41].*

value. **Figure 17** shows the alteration in contact angle for different treated brines. This figure indicates the initial contact angle and the angles after aging in highsalinity water, in LSW, and in LSS. As can be seen, wettability alteration toward water-wet condition occurred for all cases with different types of LSW. However,

*Oil recovery and dP profiles for injection of seawater followed by LSW and low-salinity surfactant at diluted* 

The effect of surfactant on wettability alteration was also observed by Teklu et al. [43]. They measured the contact angle of different carbonate and sandstone rock disks saturated with oil in low-salinity brine in the presence and absence of nonionic ethoxylated alcohol surfactant. They found that the presence of surfactant decreases the contact angle and makes the system more water wet. Reduction in IFT and alteration of rock wettability by LSS can increase oil recovery in cases when LSW is not effective alone. For example, core flooding experiments conducted by Spildo et al. showed that the application of surfactant-free LSW does not increase oil recovery, while LSS produces incremental oil recovery, as shown in **Figure 18** [44]. These synergistic mechanisms (i.e., wettability alteration and reduction of IFT) in the hybrid LSW/LSS method provide higher oil recovery than the recovery expected from the capillary desaturation curves (CDC). Studies in [44, 45] showed

, which is not

different ion contents affected the magnitude of wettability alteration.

*Contact angle for deionized water droplet/air/silica after different treatments [42].*

that during the LSS after LSW, the capillary number was about 10<sup>−</sup><sup>4</sup>

high enough to achieve noticeable incremental oil recovery, as observed in the experiments [46]. Hence, oil detachment and redistribution due to rock wettability alteration during LSW make the LSS performance better than the estimation from

**14**

the CDC.

**Figure 16.**

**Figure 17.**

*Oil recovery and pressure drop profile as a function of pore volume injected into sandstone core during SW/LSW/LSS injection [44].*

Shaddel et al. evaluated the incremental oil recovery obtained from LSW, LSW/ surfactant, and LSW/alkali injection in Berea and Bentheimer sandstones in tertiary mode. Sodium hydroxide and sodium dodecyl sulfate dissolved in 0.01 LSW were used as alkali and surfactant solutions, respectively. The authors considered that the LSW/alkali is a convenient process as a hybrid method due to the lower operation costs [47].

Brine composition is an important variable during the design of surfactant flooding. The retention (i.e., adsorption) of surfactant molecules onto porous media is considered a critical issue; thus, the reduction of surfactant adsorption onto the porous media enhances the quality of a surfactant flooding project from the technical and economical points of view. Glover et al. reported that lowsalinity brine surfactant adsorption is reduced [48]. Lower surfactant retention at lower salinities was also observed in [43, 45]. Additionally, Johannessen et al. [41] observed that the surfactant retention values were lower at very-low-salinity brines than at the optimum salinity condition, as measured by retention tests, which are shown in **Figure 19**. The greater area under the production curve for the LSS condition corresponds to lower surfactant retention. This implies that the hybrid LSW/LSS method is more economically efficient than the injection of surfactant at the ultralow IFT formulation. Tests performed by Araz and Kamyabi showed that precipitation of SDBS surfactant in LSW occurs when salinity concentration is above 1000 ppm [49].

The type and concentration of divalent cations also influence the performance of surfactant flooding. For example, Enge [38] showed that the content of divalent ions in brines affects the precipitation of surfactant. Calcium cations affect the behavior of surfactant adsorption and surfactant precipitation due to interactions with calcium (negative effect) and the stabilization of micelles (positive effect). Hence, there is a limit for divalent cation concentration which must be considered during the LSS design stage. Other properties of surfactant solutions are affected in a low-salinity environment, such as solubility and retention. For instance, Alagic et al. observed that the surfactant solubility is improved in low-salinity brine, especially in the absence of divalent cations [45].

The initial wettability of the porous media is a key parameter in the success of most hybrid LSW EOR methods. Alagic et al. [45] studied the effect of crude oil aging on LSW/LSS flooding in sandstones. They used a sulfonate surfactant added to the low-salinity brine in the LSS injection period. The performance of the LSS

### **Figure 19.**

*Normalized produced surfactant concentration for surfactant in very LSW (LSS) and in water with the optimum salinity (OSS) [41].*

### **Figure 20.**

*Oil recovery of remaining oil (after LSW flooding) in aged (B1, B3) and unaged (B2, B4) sandstone samples for two surfactant concentrations (1 and 0.4 wt%) [45].*

was observed to be better in cores aged by oil. In addition, LSS recovered more oil at a higher concentration of surfactant. **Figure 20** shows the performance of oil recovery in the LSS stage for aged and unaged samples. The same trend was also observed in [33, 34]. Another variable affecting the performance of hybrid methods is the composition of the LSW. Araz and Kamyabi examined the effect of the LSW composition on the performance of core flooding by LSW/LSS in sandstones. They found that alteration in the composition of different ions in LSW and LSS affected oil recovery [49]. Therefore, it is essential to study the effect of ion composition in the LSW/LSS process in terms of oil recovery.

The stability of the displacement front in the LSW/LSS process is a critical issue to achieve a successful recovery. Tavassoli et al. [50] showed that unstable fronts of surfactant floods due to the high velocity result in slow oil recovery. This problem can be solved through the combination of LSW with surfactant/polymer (SP). In this process, three different oil recovery mechanisms are active such as wettability alteration, reduction in IFT, and mobility control. In [51], Wang et al. studied the hybrid low-salinity surfactant/polymer flooding as an EOR method in carbonates.

*Hybrid EOR Methods Utilizing Low-Salinity Water DOI: http://dx.doi.org/10.5772/intechopen.88056*

*Enhanced Oil Recovery Processes - New Technologies*

was observed to be better in cores aged by oil. In addition, LSS recovered more oil at a higher concentration of surfactant. **Figure 20** shows the performance of oil recovery in the LSS stage for aged and unaged samples. The same trend was also observed in [33, 34]. Another variable affecting the performance of hybrid methods is the composition of the LSW. Araz and Kamyabi examined the effect of the LSW composition on the performance of core flooding by LSW/LSS in sandstones. They found that alteration in the composition of different ions in LSW and LSS affected oil recovery [49]. Therefore, it is essential to study the effect of ion composition in

*Oil recovery of remaining oil (after LSW flooding) in aged (B1, B3) and unaged (B2, B4) sandstone samples* 

*Normalized produced surfactant concentration for surfactant in very LSW (LSS) and in water with the* 

The stability of the displacement front in the LSW/LSS process is a critical issue to achieve a successful recovery. Tavassoli et al. [50] showed that unstable fronts of surfactant floods due to the high velocity result in slow oil recovery. This problem can be solved through the combination of LSW with surfactant/polymer (SP). In this process, three different oil recovery mechanisms are active such as wettability alteration, reduction in IFT, and mobility control. In [51], Wang et al. studied the hybrid low-salinity surfactant/polymer flooding as an EOR method in carbonates.

the LSW/LSS process in terms of oil recovery.

*for two surfactant concentrations (1 and 0.4 wt%) [45].*

**16**

**Figure 19.**

**Figure 20.**

*optimum salinity (OSS) [41].*

They observed more recovery by LSW/SP in LSW than HSW/SP. This study confirmed the destabilization of oil layers after LSW injection prior to SP flooding by pressure drop analysis. The pressure drop was more significant due to the formation of an oil bank after LSW injection.

Most of the research conducted in the area of hybrid LSW/LSS or LSW/SP processes has been based on experimental studies. There are few simulation studies published on the effectiveness of the hybrid LSW/LSS method. The lack of modeling and optimization of the process through simulation studies is obvious in this field. In [50], Tavassoli et al. applied UTCHEM-IPhreeqc to model LSW as a function of geochemical reactions and surfactant flooding. Their simulations were in good agreement with experiments carried out by [27]. This study demonstrated the importance of the surfactant selection, injection sequences, and operational parameters such as brine salinity and surfactant solution injection rate to achieve incremental oil recovery. Therefore, more modeling studies are justified.
