**5. Improving foam stability using nanoparticles**

The previous section shows the instability of foam systems in contact with crude oil at high temperature. Nanoparticles have been examined extensively as a means to stabilize foams used in oil-production operations, including those in high-salinity and high-temperature environments [9, 20–25, 32, 33]. This behavior is due to the nanoparticles' adsorption to the interface between the gas and liquid phases and minimizes the

**133**

**Figure 9.**

*CO2 Foam for Enhanced Oil Recovery Applications DOI: http://dx.doi.org/10.5772/intechopen.89301*

contact area between them; as a result, they can build a strong barrier that prevents bubble coalescence. **Figure 9a** shows a microscopic image for SDS foam system that was stabilized with Al2O3 nanoparticles [32]. It shows the nanoparticle adsorption at the lamella surface. Hence, the nanoparticle-stabilized foams are expected to be durable and highly resistant to unfavorable reservoir conditions including high salinity, high temperatures, and the presence of crude oil. Silica nanoparticles are currently

Nanoparticles' size greatly affect the foam stability. Different experimental results for the usage of silica nanoparticles showed that the smaller the nanoparticle size, the higher the foam stability [32]. The small particle will move faster to the gas–liquid interface compared to the larger nanoparticle size. Hence, the nanoparticle adsorption and concentration in the lamella surface increase and the foam become more stable. This behavior of foam stability with nanoparticle size greatly depends on foam quality, salinity, and nanoparticle hydrophobicity. Larger-size nanoparticles improve the foam stability at foam quality of 70–80%, while smaller size nanoparticles improve the foam stability at quality of 50–60% [9]. In addition, 140 nm silica nanoparticles with contact angle of 86° increased the foam stability

Emrani et al. [21] studied the effect of adding 140 nm silica nanoparticles to AOS foam system. This work achieved a stable foam with an MRF of 8, which was four

*Foam stability improvement by nanoparticles, (a) microscopic image for SDS/Al2O3 foam system [32] and (b) MRF for 0.5 wt% AOS solutions in the absence and presence of 0.1 wt% nanoparticles at 77°F [21].*

regarded as most effective for improving foam stability [20–25].

greater than 100 nm silica nanoparticles with contact angle of 54° [21].

### *CO2 Foam for Enhanced Oil Recovery Applications DOI: http://dx.doi.org/10.5772/intechopen.89301*

*Foams - Emerging Technologies*

**Figure 8.**

*Effect of oil density and viscosity on foam stability [29].*

to be 7.96, 6.68 mN/m, and 231.74 (mN/m)2

lamella drainage and decreases the foam stability.

**5. Improving foam stability using nanoparticles**

the liquid viscosity decreases, which leads to faster drainage. As a result, gas bubbles coalesce faster [31]. In contact with crude oil, the AOS was not able to generate stable foam, where the half-life was 3.9 and 0.45 min at 77 and 150°*F*, respectively. The E, S, and B coefficients for the AOS system at 150°*F* and 800 psi were found

generated foam is not stable. Increasing the pressure to 1200 psi, the values for the three coefficients slightly decreased to 6.67, 5.38 mN/m, and 141.29 (mN/m)2

greater than zero. A positive E value indicates that the oil-entering condition was initially favorable. However, once the oil entered the foam system as an emulsion on the AOS and AOS/SiO2 foam lamellae, it started to spread on the surfaces of the foam bubbles (S > 0) and generated unstable bridges (B > 0) that quickly broke the lamellae and destabilized the foam. The microscopic images of the AOS foam

Similar results were observed by Simjoo et al. [27]. Adding 1 vol% crude oil to different surfactant systems decreases the foam stability and the half-life time. **Figure 7b** shows the change in the foam half-life time due to the presence of crude oil. Regardless of the surfactant type, adding crude oil to the foam increases the

The previous experimental results demonstrate the detrimental effect of crude oil on foam stability [29]. However, regardless of the surfactant used, crude oil with higher hydrocarbon chain lengths has a lower effect on foam stability. **Figure 8** shows the half-life of Coco/SDS (a foam system with a 1:1 mixture of cocobetaine and sodium dodecyl sulfate surfactants) in contact with different crude oils with different densities and viscosities at room temperature. These data show that the higher the density and viscosity, the lower the effect of crude oil on foam stability.

The previous section shows the instability of foam systems in contact with crude oil at high temperature. Nanoparticles have been examined extensively as a means to stabilize foams used in oil-production operations, including those in high-salinity and high-temperature environments [9, 20–25, 32, 33]. This behavior is due to the nanoparticles' adsorption to the interface between the gas and liquid phases and minimizes the

system in contact with crude oil in **Figures 3** and **5** confirm this behavior.

. Based on the flowchart in **Figure 4**, the

, still

**132**

contact area between them; as a result, they can build a strong barrier that prevents bubble coalescence. **Figure 9a** shows a microscopic image for SDS foam system that was stabilized with Al2O3 nanoparticles [32]. It shows the nanoparticle adsorption at the lamella surface. Hence, the nanoparticle-stabilized foams are expected to be durable and highly resistant to unfavorable reservoir conditions including high salinity, high temperatures, and the presence of crude oil. Silica nanoparticles are currently regarded as most effective for improving foam stability [20–25].

Nanoparticles' size greatly affect the foam stability. Different experimental results for the usage of silica nanoparticles showed that the smaller the nanoparticle size, the higher the foam stability [32]. The small particle will move faster to the gas–liquid interface compared to the larger nanoparticle size. Hence, the nanoparticle adsorption and concentration in the lamella surface increase and the foam become more stable. This behavior of foam stability with nanoparticle size greatly depends on foam quality, salinity, and nanoparticle hydrophobicity. Larger-size nanoparticles improve the foam stability at foam quality of 70–80%, while smaller size nanoparticles improve the foam stability at quality of 50–60% [9]. In addition, 140 nm silica nanoparticles with contact angle of 86° increased the foam stability greater than 100 nm silica nanoparticles with contact angle of 54° [21].

Emrani et al. [21] studied the effect of adding 140 nm silica nanoparticles to AOS foam system. This work achieved a stable foam with an MRF of 8, which was four

### **Figure 9.**

*Foam stability improvement by nanoparticles, (a) microscopic image for SDS/Al2O3 foam system [32] and (b) MRF for 0.5 wt% AOS solutions in the absence and presence of 0.1 wt% nanoparticles at 77°F [21].*

times the MRF for AOS foam system. Adding nanoparticles creates a fine texture foam that increases the apparent viscosity and the MRF (**Figure 9b**). Similarly, in a bulk stability test, adding nanoparticles to the AOS foam system tripled the half-life of its original value without nanoparticles [24]. In addition, nanoparticles are adsorb on the interface between the gas and liquid phases, creating thick, solid films that provide a barrier to film thinning and inter-bubble diffusion. Hence, in the presence of crude oil, the spreading of the oil droplets along the foam lamellae decreases and prevents bridge formation. Interfacial tension (IFT) measurements for silica nanoparticle foam system showed that the spreading and bridging coefficients have negative values (−0.69, −4.43 at 1200 psi and 150°*F*), thus evidencing improved foam stability.

Nanoparticle concentration in the interface between the liquid and gas phases is a critical parameter and should increase to a certain threshold to stabilize the foam [34]. **Figure 10** shows the change in foam half-life time with increasing silica nanoparticle concentrations. At low concentrations, the liquid/gas interface is not saturated, and low foam stability is generated. With increased nanoparticle concentration, foam stability increases. However, at higher concentration, nanoparticles agglomerate and form bigger particles that negatively impact the foam stability. Zeta potential measurements in **Figure 10** show a reduction of the absolute zeta potential value with increasing nanoparticle concentration from 0.1 to 0.2 wt%, which indicates a stable suspension. At nanoparticles' concentration higher than 0.2 wt%, nanoparticles become unstable and agglomerate which is indicated by increasing the zeta potential value.

Coreflood experiments by Ibrahim and Nasr-El-Din [23, 24] compared EOR results using an AOS foam system versus a silica-nanoparticle system. **Figure 11** shows total oil recovery after tertiary recovery using different foam systems. A water-assisted gas (WAG) system was able to increase the oil recovery to 60%. AOS generated a weak foam with a similar MRF to that of the CO2/water system, and oil recovery increased by 1.8%. Adding silica nanoparticles to the foam system increased oil recovery to 68.2%.

In a high-salinity environment, the absolute zeta potential for suspensions will decrease [35]. As a result, nanoparticles will have a high affinity to agglomerate. To prevent the instability of nanoparticles in a high-salinity environment, surfacemodified nanoparticles were used to provide steric repulsion between particles.

**135**

**Figure 12.**

**Figure 11.**

*nanoparticles.*

*CO2 Foam for Enhanced Oil Recovery Applications DOI: http://dx.doi.org/10.5772/intechopen.89301*

concentration [36].

Nanoparticle surface wettability is another critical parameter of foam stability. Generally, nanoparticle surfaces should be hydrophilic enough to disperse in water but hydrophobic enough to accumulate at the interface between the water and gas. Nanoparticles coated with 50% SiOH dichlorodimethylsilane generated a stable foam compared to polyethylene glycol (PEG)-coated nanoparticles or dichlorodimethylsilane-coated nanoparticles with higher SiOH% even at 8 wt% NaCl salt

In addition to silica, other types of nanoparticles can also be used to improve foam

stability. About 0.1 wt% Fe2O3 nanoparticles were able to increase the AOS foam half-life time from 1 to 7 h at 75°*F* and 300 psi [37]. However, these nanoparticles tend to aggregate due to their large surface area, which is confirmed by low absolute zeta potential values. An experimental work by Bayat et al. [38] compared the foam stability using SiO2, Al2O3, TiO2, and CuO nanoparticles. They found that the optimum concentration for these nanoparticles was 0.008 wt%. **Figure 12** shows the recovery factor and foam half-life for the four different systems. SiO2 foam had the highest foam

*Total oil recovery for different foam systems with adding 0.5 wt% AOS surfactant and 0.1 wt% silica* 

*Effect of nanoparticle type on the foam stability and oil recovery factor.*

stability and oil recovery compared to the other nanoparticles.

**Figure 10.** *Effect of silica nanoparticle concentrations on foam stability.*

*CO2 Foam for Enhanced Oil Recovery Applications DOI: http://dx.doi.org/10.5772/intechopen.89301*

*Foams - Emerging Technologies*

increasing the zeta potential value.

increased oil recovery to 68.2%.

times the MRF for AOS foam system. Adding nanoparticles creates a fine texture foam that increases the apparent viscosity and the MRF (**Figure 9b**). Similarly, in a bulk stability test, adding nanoparticles to the AOS foam system tripled the half-life of its original value without nanoparticles [24]. In addition, nanoparticles are adsorb on the interface between the gas and liquid phases, creating thick, solid films that provide a barrier to film thinning and inter-bubble diffusion. Hence, in the presence of crude oil, the spreading of the oil droplets along the foam lamellae decreases and prevents bridge formation. Interfacial tension (IFT) measurements for silica nanoparticle foam system showed that the spreading and bridging coefficients have negative values (−0.69,

Nanoparticle concentration in the interface between the liquid and gas phases is a critical parameter and should increase to a certain threshold to stabilize the foam [34]. **Figure 10** shows the change in foam half-life time with increasing silica nanoparticle concentrations. At low concentrations, the liquid/gas interface is not saturated, and low foam stability is generated. With increased nanoparticle concentration, foam stability increases. However, at higher concentration, nanoparticles agglomerate and form bigger particles that negatively impact the foam stability. Zeta potential measurements in **Figure 10** show a reduction of the absolute zeta potential value with increasing nanoparticle concentration from 0.1 to 0.2 wt%, which indicates a stable suspension. At nanoparticles' concentration higher than 0.2 wt%, nanoparticles become unstable and agglomerate which is indicated by

Coreflood experiments by Ibrahim and Nasr-El-Din [23, 24] compared EOR results using an AOS foam system versus a silica-nanoparticle system. **Figure 11** shows total oil recovery after tertiary recovery using different foam systems. A water-assisted gas (WAG) system was able to increase the oil recovery to 60%. AOS generated a weak foam with a similar MRF to that of the CO2/water system, and oil recovery increased by 1.8%. Adding silica nanoparticles to the foam system

In a high-salinity environment, the absolute zeta potential for suspensions will decrease [35]. As a result, nanoparticles will have a high affinity to agglomerate. To prevent the instability of nanoparticles in a high-salinity environment, surfacemodified nanoparticles were used to provide steric repulsion between particles.

−4.43 at 1200 psi and 150°*F*), thus evidencing improved foam stability.

**134**

**Figure 10.**

*Effect of silica nanoparticle concentrations on foam stability.*

Nanoparticle surface wettability is another critical parameter of foam stability. Generally, nanoparticle surfaces should be hydrophilic enough to disperse in water but hydrophobic enough to accumulate at the interface between the water and gas. Nanoparticles coated with 50% SiOH dichlorodimethylsilane generated a stable foam compared to polyethylene glycol (PEG)-coated nanoparticles or dichlorodimethylsilane-coated nanoparticles with higher SiOH% even at 8 wt% NaCl salt concentration [36].

In addition to silica, other types of nanoparticles can also be used to improve foam stability. About 0.1 wt% Fe2O3 nanoparticles were able to increase the AOS foam half-life time from 1 to 7 h at 75°*F* and 300 psi [37]. However, these nanoparticles tend to aggregate due to their large surface area, which is confirmed by low absolute zeta potential values. An experimental work by Bayat et al. [38] compared the foam stability using SiO2, Al2O3, TiO2, and CuO nanoparticles. They found that the optimum concentration for these nanoparticles was 0.008 wt%. **Figure 12** shows the recovery factor and foam half-life for the four different systems. SiO2 foam had the highest foam stability and oil recovery compared to the other nanoparticles.

**Figure 11.**

*Total oil recovery for different foam systems with adding 0.5 wt% AOS surfactant and 0.1 wt% silica nanoparticles.*

**Figure 12.** *Effect of nanoparticle type on the foam stability and oil recovery factor.*
