## 3 Results
### Glass Beads-Fluid Interaction
#### 3.2.2 Brine-Surface Interaction  
The effects of salinity during secondary recovery or smart-water flooding relate to the interaction between the phases present in the reservoir. Water chemistry plays a critical role in the recovery improvement, which has been linked to wettability alteration [6; 12; 55]. Sulfate is present as one of the most common ions in natural reservoir waters, and has shown the ability to induce changes in rocks of different lithologies, including sandstone [15; 17; 20]. The T\({}_{2}\) distribution in the case of water is simpler than that of crude oil, typically exhibiting one dominant mode or peak. The appearance of other modes at lower T\({}_{2}\) values is likely associated to water molecules sitting in smaller pores or pore-throats, corners, cranies and other small surface features. Figure 7 shows the water T\({}_{2}\) distribution inside both glass beads packs saturated with 1% Na\({}_{2}\)SO\({}_{4}\). Untreated glass beads are considered naturally water-wet (hydrophilic). For this sample the dominant mode initially located at 1664.5 \(\pm\) 0.1 ms on Day 1 decreases to 1620.1 \(\pm\) 0.1 ms after 21 days of aging, suggesting that the surface is still being altered, though the surfaces only experiences a minute alteration. On the other hand, treated glass beads show a more dramatic shift in the dominant mode location from 2233.1 \(\pm\) 0.1 ms (Day 1) down to 1620.5 \(\pm\) 0.1 ms (Day 21). The inset plots correspond to the non-normalized spectra. For a single fluid occupying the pore space, we do not anticipate a significant decrease in intensity. The two obvious peaks in the two figures are affected similarly in qualitative sense. However, molecules sitting in a smaller spaces are exposed to larger surface-to-volume ratios, which implies more relative surface effects. Figure 6: Diffusion coefficient behavior of treated and untreated glass beads with oil at different aging times at 25 \({}^{\circ}\)C.  
Figure 7: _Cont._Figure 8 shows the results of the T\({}_{2}\) distribution for the interaction between treated (Figure 8a) and untreated (Figure 8b) glass beads with 100% Na\({}_{2}\)SO\({}_{4}\). For the untreated glass beads, the dominant mode remains at the same location, around 1602.5 \(\pm\) 0.1 ms. Treated glass beads exhibit a decrease from 2120.1 \(\pm\) 0.1 ms to 1756.1 \(\pm\) 0.1 ms. In contrast to the effects of low-salinity, the degree of alteration is milder. However, a similar effect is observable on Day 1, confirming the equilibrium process of the sample. However, the dominant mode for low salinity on Day 7 locates at 1808.4 \(\pm\) 0.1 ms, while for high salinity it is located at 1803.1 \(\pm\) 0.1 ms, suggesting that after the equilibrium process both samples approach similar dominant mode locations. The smaller mode is also affected in a qualitative fashion, similarly to the largest mode. Figure 8: _Cont._  
Figure 7: Relaxation time distribution (T\({}_{2}\)) of glass beads saturated with 1% Na\({}_{2}\)SO\({}_{4}\): (**a**) Untreated glass beads aged for 21 days at 25 \({}^{\circ}\)C; (**b**) Treated glass beads aged for 21 days at 25 \({}^{\circ}\)C. Inset plots correspond to non-normalized distributions. Figure 9 shows the diffusion coefficient response as a function of time at two salinities for both treated and untreated glass beads packs. Analogous to previously observed results, when the beads are hydrophilic, the diffusion coefficient decreases (in concert with the T\({}_{2}\) distribution peak value). These results show that regardless of the media, 1% Na\({}_{2}\)SO\({}_{4}\) brine initially leads to a higher diffusion coefficient (2.272 \(\pm\) 0.002 \(\times\) 10\({}^{-9}\) m\({}^{2}\)/s for TGB and 2.234 \(\pm\) 0.002 \(\times\) 10\({}^{-9}\) m\({}^{2}\)/s for GB, respectively) in comparison to that of 100% Na\({}_{2}\)SO\({}_{4}\) (2.124 \(\pm\) 0.002 \(\times\) 10\({}^{-9}\) m\({}^{2}\)/s for TGB and 2.084 \(\pm\) 0.003 \(\times\) 10\({}^{-9}\) m\({}^{2}\)/s for GB, respectively). Dependency on ionic strength has been observed before [41].