# Flow Dynamics of Sulfate-Modified Water/Polymer Flooding in Micromodels with Modified Wettability
## 1 Introduction
With the gathered observations, it was concluded that a spiked amount of SO\({}_{4}\)\({}^{2-}\) worked effectively to design modified water, possibly contributing to the additional oil. Additional evaluations also helped us to find the difference between low salinity and modified water through core plugs and the role of PDI and non-PDI ions [10; 32]. Figure 1: Wettability alteration mechanism of sulfate in sandstone. (**A**) refers to oil-wet; (**B**) refers to water-wet condition of reservoir. According to the literature, the basic requirements for a successful application of low salinity and modified water flood are the same and can be summarized as:  
1. Reservoir should be oil-wet/mix-wet [12; 45; 46]. In an oil-wet/intermediate-wet state, oil polar compounds are attached to the rock surface through ionic interactions. Low-salinity/modified water flooding targets these polar compounds, detaching them from the rock surface, as shown in Figure 1, and hence producing additional oil recovery through wettability alteration from oil-wet/intermediate-wet to water-wet. 2. Existence of polar compounds in the oil [35; 47; 48]. Polar compounds are mainly composed of asphaltene and naphthenic acids (NAs), and act as surface active compounds. These two surface active compounds are known not only to stabilize water-in-crude oil emulsions, but also to constitute the interfacial film at the fluid-fluid interface. Asphaltene is insoluble in low molecular weight alkanes (n-heptane or n-pentane), but soluble in aromatics (toluene). The interfacial viscoelastic layer at the brine-oil interface is produced, due to the slow and irreversible adsorption process of asphaltene at the fluid interface [20; 21; 22]. [PERSON] et al. [49] described the positive effects of asphaltene to develop the oil-brine interface's rheological properties. Another fraction of crude oil is NAs which are composed of cycloaliphatic carboxylic acids (R-COOH) [47; 50]. These NAs are hydrophilic compounds and are accumulated at the oil-brine interface. Further, NAs can also dissociate in the aqueous phase and reach cations present in the brine to form naphthenic salts. These salts can accumulate at the oil-brine interface. However, the role of NAs remains uncertain because some studies claim that NAs improve oil-brine interface elasticity [47], while others claim they soften the interfacial film [51]. 3. High content of divalent cations in the formation brine [2; 52]. Divalent cations provide the bridging connection between negative oil polar compounds and negative-charged rock surface. Mainly, Ca\({}^{2+}\), Mg\({}^{2+}\) play a significant role to create a bond [17], as shown in Figure 1.  
Previously, experiments were performed using core plugs and sand-packs to prove the effectiveness of modified water technology [43; 53]. A study from [PERSON] et al. [54] reveals that injecting modified water in the secondary mode is an intelligent approach, compared to the injection in the tertiary mode. Further, the synergies of modified water in combination with other EOR technologies have also presented the concept of efficient hybrid EOR technologies [55; 56; 57; 58]. Modified water and low salinity water flooding in combination with polymer flood showed promising oil recovery results based on the improved sweep efficiency. This work focuses on describing the flow behavior of  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No. ** & **Mechanism** & **Approach** & **Formation** & **Active Salts** & **Ref. ** \\ \hline
1 &
\begin{tabular}{c} Wettability alteration, \\ DLE, Oil-brine int. \\ Oil-brine interfacial \\ interactions \\ Oil-brine interfacial \\ interactions \\ Oil-brine interfacial \\ interactions \\ Oil-brine interfacial \\ interactions \\ Oil-brine interfacial \\ interactions \\ Oil-brine interfacial \\ interactions \\ Oil-brine interfacial \\ Interfacial \\ Water-in-crude  
oil recovery from the injection of low-salinity/sulfate-modified water in combination with polymer.