Time-Domain Nuclear Magnetic Resonance Determination of Wettability Alteration: Analysis for Low-Salinity Water  
[PERSON]  
1 Chemical Engineering, University of Wyoming, Laramie, WY 82071, USA; [EMAIL_ADDRESS] (B.X.M.-R.); [EMAIL_ADDRESS] (T.R. ); [EMAIL_ADDRESS] (E.R.S. ); [EMAIL_ADDRESS] (S.A.)  
[PERSON]  
1 Chemical Engineering, University of Wyoming, Laramie, WY 82071, USA; [EMAIL_ADDRESS] 1  
[PERSON]  
2 Center for Economic Geology Research, University of Wyoming, Laramie, WY 82071, USA; [EMAIL_ADDRESS] 2  
[PERSON]  
1 Chemical Engineering, University of Wyoming, Laramie, WY 82071, USA; [EMAIL_ADDRESS] (B.X.M.-R.); [EMAIL_ADDRESS] (T.R. ); [EMAIL_ADDRESS] (E.R.S. ); [EMAIL_ADDRESS] (S.A.)  
[PERSON]  
3 Peterkoeul  
altered by the interaction between the surface and the fluids occupying the pore space [5; 6]. Alteration from oil-wet to slightly water-wet has been purported as the reason leading to an increase in the recovery factor (RF) [7; 8; 9; 10]. Consistent characterization of rock wettability is valuable in enhanced oil recovery studies as this property has been found to correlate with the success of a waterflood [11], including those involving low-salinity water injection [6; 12]. Requirements to adjust reservoir conditions vary depending on lithology. Wettability of sandstone reservoirs can be altered by oil [13; 14], but in a waterflood, the salinity of the injection brine can be much lower than the connate one. Carbonate reservoirs are more influenced by which ions are present. Among them, \(Mg^{+}\), \(Ca^{2+}\), and \({SO_{4}}^{2-}\) are considered potential determining ions [15; 16]. However, sulfate has also shown a positive impact on several low-salinity waterflooding investigations for both sandstone and those focused on the fluids [17; 18; 19; 20]. Wettability can affect multiphase flow properties such as relative permeability, capillary pressure, and residual oil saturation, and consequently its determination is critical [21; 22; 23; 24]. Several methods, including the US Bureau Mines (USBM), imbibition and contact angle, have been the most commonly used ones. Amott cell imbibition and USBM experiments provide data about primary recovery of oil, but can also provide insights into the wettability conditions of the cores in use [25; 26]. On the other hand, contact angle relies on the interaction forces among all fluid phases and solid surfaces of the system of interest (Equation (1)), and measurements help to determine the different conditions required to induce a change in the overall wettability of the reservoir [13; 14]. In this case, the intrinsic or Young's contact angle corresponds to:  
\[cos(\theta)=\frac{\sigma_{bs}-\sigma_{os}}{\sigma_{bo}}, \tag{1}\]  
where \(\sigma_{bs}\) is the stress between the brine and the surface; \(\sigma_{os}\) is the stress between the oil and the surface and \(\sigma_{bo}\) is the interfacial tension between the fluids. A surface with an oil contact angle 0-75\({}^{\circ}\) is considered oil-wet, for an angle 75-105\({}^{\circ}\) the surface is considered intermediate wet, and finally an angle 105-180\({}^{\circ}\) categorizes the surface as water-wet [27]. While the contact angle measurement has made its mark in petroleum research efforts, a technique with less experimental variability and an ability for in situ, non-destructive evaluation would enable this field to grow. Time-domain Nuclear Magnetic Resonance (TD-NMR) has been applied as an advanced technique to study solid-fluid interactions and could serve as a viable alternative [28; 29; 30; 31; 32; 33; 34]. Proton nuclear magnetic resonance (\({}^{1}\)H-NMR) has been explored as a convenient technique to examine rock wettability for many years. The key to interpret the NMR response resides in the sensitivity of relaxation rates, particularly those associated to T\({}_{2}\), which is sensitive to the presence of surfaces [14; 28; 34; 35; 36].