## 3 Results and Discussion
### Interfacial Tension  
IFT at the oil/chemical contact is one of the crucial factors that affect oil recovery [3,4]. Reducing the IFT at the oil/brine interface can lead to improving the displacement efficiency, and hence, more oil can be produced. Introducing the chelating agent into the oil/brine interface can reduce the interfacial forces, leading to increasing the oil recovery [13,23]. In this work, the reduction in interfacial tension at the oil-brine interface due to the injection of chelating agents was examined. Figure 7 shows the IFT for oil/SW, oil/K\({}_{4}\)GLDA, oil/Na\({}_{4}\)GLDA, and oil/Ca\({}_{2}\)GLDA systems. The injection of GLDA solutions to the oil-brine system reduced the interfacial tension from 15.54 to less than 4 dynes/cm. Among all tested GLDA types, calcium-based solutions (Ca\({}_{2}\)GLDA) showed the lowest IFT value of 1.5 dynes/cm. Compared to the other GLDA types, Ca\({}_{2}\)GLDA can reduce the interfacial tension by around 57%, under the same conditions, revealing that more oil can be recovered by injecting Ca\({}_{2}\)GLDA solutions due to the reduction in capillary pressure. However, it should be noted that the IFT reduction by chelating agent may help for EOR, but the reduction in IFT and enhancement in capillary number are far from those obtained in surfactant-based EOR.  
The changes in capillary conditions due to chemical flooding can be evaluated by determining the capillary number (\(N_{c}\)). Equation (1) can be used to estimate the capillary number [24,25] and was written as:  
\[N_{c}=\frac{\mu_{f}\mu_{f}}{\sigma_{fo}}, \tag{1}\]  
where \(N_{c}\) is the capillary number, \(\mu_{f}\) is the fluid viscosity, \(u_{f}\) is the velocity, and \(\sigma_{fo}\) is the IFT at the fluid-oil contact. In general, the oil movement can be enhanced by increasing the capillary number; consequently, less oil saturation would be achieved, and more oil can be recovered [26,27].  
Figure 6: Pressure drop profiles during the injection of SW followed by Ca\({}_{2}\)GLDA, NA\({}_{4}\)GLDA, and K\({}_{4}\)GLDA.  
The impact of injecting chelating solutions on reducing the capillary pressure forces was estimated by calculating the capillary number before and after introducing the GLDA solutions. All parameters were kept unchanged except the interfacial tension. The interfacial tension experiments indicated that the IFT can be reduced by around 90% using GLDA chelating agent. The IFT reduction will result in raising the capillary number as described by Equation (1), thereby improving the hydrocarbon flow. Figure 8 shows the capillary numbers for the oil/SW, oil/K\({}_{4}\)GLDA, oil/Na\({}_{4}\)GLDA, and oil/Ca\({}_{2}\)GLDA systems. The injection of GLDA chelating agents can raise the capillary number (\(N_{c}\)) by a factor of 10.5 compared to the conventional SW flooding. As observed, \(N_{c}\) was increased from 1.96 \(\times\) 10\({}^{-8}\) to 2.03 \(\times\) 10\({}^{-7}\) by using GLDA injection. The increase in capillary number is mainly due to the reduction in IFT. The injected chelating agents created a small layer at the oil/GLDA contact, and this layer was generated due to the deprotonation of some acid components present in the crude oil. The generated layer led to inducing a surface-active zone in the form of soap, thus lowering the IFT in a way similar to surfactant flooding [13; 18].  
Figure 8: The capillary numbers for oil and SW as well as oil and different types of GLDA salts systems.  
Figure 7: The interfacial tension between oil and SW as well as those between oil and different types of GLDA salts.