## 3 Results and Discussion
### Coreflooding  
In this work, the oil recovery from carbonate and sandstone rocks was evaluated using coreflooding experiments. First, the performance of SW flooding to increase the oil recovery was studied by injecting SW bine of 57.3 g/L TDS into the carbonate and sandstone cores. Figure 2 shows the percentage of recovered oil using SW flooding from six core samples. It should be noted that all samples were prepared and treated using the same experimental conditions; hence, the changes in oil recovery can be attributed mainly to the rock types and the petrophysical properties. All the carbonate samples (ILS1-ILS3) showed oil recovery between 37% and 39% of the Original Oil in Place (OOIP), while flooding the sandstone samples (BSS1-BBS3) with SW showed higher oil recovery of around 45-47% of the OOIP. The petrophysical measurements showed that the sandstone samples had a higher rock permeability compared to the carbonate samples; hence, higher oil recovery was obtained for the sandstone samples. The average rock permeabilities were 10 and 75 mD for the carbonate and sandstone samples, respectively. Overall, SW flooding showed higher oil recovery from the sandstone samples compared to that from the carbonate samples, due to the high rock permeability of the sandstone samples. After SW flooding, the chelating agent solutions were injected into the carbonate and sandstone samples by utilizing the same experimental conditions. Figure 3 shows the volume to breakthrough of GLDA solutions during the chemical flooding. In general, a lower volume of the GLDA solution was required for treating the sandstone samples compared to for treating the carbonate samples, which can be attributed mainly to rock permeability. The breakthrough behavior is affected by the rock permeability and heterogeneity. In this work, the rock heterogeneity was minimized by using rock samples from the same formations, then, the breakthrough behavior was controlled mainly by the rock permeability. Higher rock permeability can result in faster breakthrough due to the less flow resistance, and thus a less chemical volume was used. The average PVs to breakthrough were 0.57 and 0.67 PV for the sandstone and carbonate samples, respectively. In addition, in both the sandstone and carbonate samples, Na\({}_{4}\)GLDA and K\({}_{4}\)GLDA showed faster breakthrough compared  
Figure 2: Oil recovery during SW flooding for carbonate (ILS) and sandstone (BSS) samples. to Ca2 GLDA, indicating that higher oil recovery would be achieved using calcium-based GLDA. A faster breakthrough can lead to a poorer sweep efficiency and thus will reduce the oil recovery. Injecting Ca2 GLDA into the carbonate and sandstone samples showed the highest volume to breakthrough, and thus, higher oil recovery would be achieved using Ca2 GLDA. The injected fluid spread along the rock surface and displaced a higher volume of oil, resulting in late breakthrough and better oil recovery. Also, the oil recovery during injection of GLDA solutions into carbonate and sandstone samples was determined, as shown in Figure 4. Higher oil recovery was achieved from the carbonate samples compared to from the sandstone samples, indicating that all types of GLDA solutions work better in a carbonate reservoir. The additional oil recovery varied between 26% and 32% for the carbonate samples, while around 19% to 21% of the OOIP was recovered from the sandstone samples. This could be attributed to the reaction behavior between GLDA solutions and the rock matrix. It is well known that carbonate rocks are more reactant compared to sandstone rocks. GLDA is a weak acid that can dissolve part of the carbonate matrix, similar to the HCI reaction with a slower reaction rate. Therefore, a higher chemical reaction rate will be induced in carbonate rocks compared to in sandstone, leading to higher oil recovery from carbonate formations. Furthermore, Ca2 GLDA showed the highest oil recovery among all tested GLDA types, for both sandstone and carbonate samples.