## 2 Materials and Methods
### Porous Media
#### Microfluidics  
An oil-wet glass-silicon-glass (GSG) micromodel was used for oil recovery experiments as porous media, shown in Figure 3. Regular distribution of circular grains defines the micromodel as being homogeneous and consists of an artificial pore structure. Previously, such homogenous micromodels have been used for several EOR investigations [76; 77; 78]. Figure 3 shows pore-structure images and dimensional measurements of the model, and Table 4 provides porosity and permeability values.  
Figure 3: Micromodels used in this study. Inlet bottom-left and outlet top-right.  
Figure 2: Sketch of core flood experimental setup [4].  
The water-wet micromodel was chemically modified to generate an oil-wet condition. The chemisorption of fluorinated silane was applied on the silicon surfaces and micromodels' inner glass, to establish the oil-wet condition of the micromodel. Initially, silicon and glass showed a contact angle (to water) below 20\({}^{\circ}\), and hence a water-wet condition. After the chemisorption process, the oil-wet condition was established with the increased contact angle of 112\({}^{\circ}\). Micromodel wettability alteration to oil-wet is almost permanent. Only strong bases or acids can attack and damage the adsorbed silane layer.  
A microfluidics-flooding rig from HOT Microfluidics (Goslar, Germany) was used for the flooding experiment. InspIOR is a compact experimental package that includes a micromodel holder, injection pumps, a DSLR camera for imaging, fluid and waste reservoirs, and pressure sensors. An upgraded version of the components and experimental setup, as described by [PERSON] et al. [79], was used for the flooding experiments. Table 4 describes how the injection rate corresponds to field scale injection flux of 1.0 ft./day for the flooding process. Oil-recovery experiments were performed at a system pressure of 1.0 bar (gas) and at room temperature (i.e., 22 \({}^{\circ}\)C), with the following steps:  
* Initially, deionized water injection was performed in a clean micromodel, to remove air bubbles pursued until the differential pressure across micromodel reaches the desired value and stabilizes.
* Micromodel permeability was measured with deionized water, and synthetic seawater saturation was established in micromodel afterward.
* Continuous and increasing oil injection rates were performed to establish initial oil saturation, until no further water could be produced and pressure stabilized.
* Polymer flooding (2000 ppm prepared in B1 and B3) was performed to observe the oil recovery and to gather the pressure data.
* Micromodel images were captured during the flooding process, at different time intervals, and an imaging-processing tool developed in MATLAB (2018b) calculated oil recovery at a specific time interval/image.  
Polymer flooding was performed in micromodel, with connate water saturation, at room temperature, to investigate the impact of salinity and hardness on polymer in situ viscosity and oil recovery. Polymer solutions prepared in B1 and B3 with 2000 ppm were injected into the micromodel, to observe oil recovery. Note that, the addition of sodium sulfate in SSW increased the total dissolved solids but decreased the hardness, as can be seen \(R^{+1}\) in Table 2. Oil recovery and pressure response from polymer injection will support whether the impact of increasing the TDS or the higher hardness is more significant.