1 Chapter I Introduction I.1 Backgrounds Previous field studies have shown that poor oil recovery factors are the biggest challenge in developing oil and gas fields. Without the EOR implementation methods, about 65-80% of the OOIP oil remains in the reservoir (Thomas S., 2008). In enhanced oil recovery applications, various chemicals can be additives to modify the interaction of oil-brine-rock in the reserivoir to obtain more favorable conditions for final oil recovery. The widely used chemicals in CEOR include Low Salinity Water/Smart water, surfactants, nanoparticles, polymers, microorganisms, ionic solutions, and combinations of them, which role as injection fluids. Low Salinity Waterflooding is a very attractive mechanism because it offers many advantages from its mechanism, including its low price (compared to other types of chemical EOR), its abundant availability (especially in offshore operations), its ease of application, and its simple feasibility study procedure (Bartels et al., 2019). Results from the BP Laboratory (Lager et al., 2006) showed an average profit of 14% using low-salinity brine. Other studies show varying results from +4% to +40%. Single-well chemical tracer tests conducted by BP Alaska resulted in a decrease in residual oil saturation of 6-12% from OOIP (McGuire et al., 2005). In recent decades, the development of nanotechnology has proven to be an advantage for various fields of science, such as material science, biomedicine, electronics, and the oil and gas industry. Some applications of nanoparticles in the oil and gas industry include applications in the fields of reservoir characterization, exploration, and oil-sensing, additives in drilling mud, mixtures to prevent the formation of hydrate and wax deposits in flow assurance, and mixtures for separating oil from water-oil emulsions in the production water treatment process, as well as applications in enhanced oil recovery. The fact that nanoparticles have a very small size so that they can flow through narrow pores and pore-throats, as well as the properties of their core and surface molecules that are easily modified for a specific purpose, makes nanoparticles an ideal candidate for various EOR applications. 2 Titanium dioxide (TiO2) has become one of the most popular nanomaterials due to its high stability and low cost, and it is believed to have environmentally friendly (non-toxic) properties. A study conducted by Hosseini et al. (2022) showed that 3 wt% TiO 2 could change the wettability of limestone from strongly oil-wet (165.1° and 166.2°) to water-wet (37.6° and 48.2°). Meanwhile, Zargar et al. (2020) reported that the combination of TiO 2/Quartz-nanofluid + 1000 ppm Desalted Water could reduce IFT from 36.4 to 3.5 mN/m, increase viscosity and reduce contact angle from 103⁰ to 48⁰ (stronger water-wet). Combining Low-Salinity Water with nanoparticles (TiO 2 - in this case) can be an interesting alternative in the enhanced oil recovery method. This study aims to investigate the effect of brine salinity (specifically in low salinity concentration) and TiO 2 nanoparticles concentration to the interaction of crude oil-brine-rock (COBR) and the mechanism behind the addition of TiO 2 to LSW in changing the surface charge and interfacial properties in laboratory scale experiments. This information can enrich our knowledge and help us formulate the most beneficial concentration of LSW-TiO 2 nanofluids to maximize oil recovery from subsurface formations. I.2 Problem Statements The problem statements in this study are as follows: 1.