## 1 Introduction  
Hydrocarbon extraction from reservoirs involves primary, secondary, and tertiary recovery stages. Enhanced oil recovery (EOR), the tertiary stage, employs several methods to recover trapped hydrocarbons from pores, such as thermal, chemical, miscible, mobility control, and microbial [1]. Parameters such as wettability, interfacial tension, fluid properties, and mobility control the performance of EOR methods [2; 3]. Chemical EOR recovers the trapped oil droplets in pores by changing wettability, fluid properties, mobility ratio, and oil-water interfacial tension (IFT) parameters of reservoir rocks and fluids. For instance, the mobility-control EOR method such as polymer flooding aims to maintain and keep the favorable mobility ratio by which vertical sweep efficiency can be improved. The surfactant flooding technique is directed to injecting chemicals to change the oil-water phase behavior, which reduces IFT between oil and water or, ideally, reaches the Winsor type III microemulsion with ultralow IFT and improves the reservoir fluid flow to the production well [4]. It improves the microscopic sweep efficiency in reservoir pores. The oil recovery performance of surfactants depends on several parameters such as concentration of chemicals, ionic composition of injection water, salinity, and temperature of the system [5; 6]. Consequently, different Winsor type microemulsions form under different conditions of salinity [7]. The Winsor type I is typical for lower salinity systems where most of the chemicals stay in the water phase, therefore IFT reduction is not considerable. The Winsor type II is typical for higher salinity systems where chemicals have higher affinity for the oil phase and IFT can be reduced, but not to the ultralow values. The Winsor type III microemulsion is the three-phase system where oil and water molecules can co-exist as a middle phase by surfactant action. In the middle phase, the IFT between oil and water reaches ultralow values and is usually typical for moderate salinity systems. Hence this type of microemulsion is favorable during surfactant flooding [6; 8]. Surfactant flooding is not a new chemical EOR application. Historically, the first surfactant usage for oil recovery was dated in the 1920s when there was not enough information about chemicals and their impact on the petroleum industry. In the 1960s, surfactants started to be investigated, and in 1968 micellar flood, which consists of petroleum sulfonate based on surfactant mixed with oil and water, was reported, named microemulsion. Later, numerous studies were performed to investigate surfactants for EOR. These studies demonstrated surfactants' ability to reduce IFT between oil and water and even reach ultra-low IFT, which improves microscopic sweep efficiency [9; 10]. However, as with other production methods, surfactant flooding has complications, such as chemical loss by adsorption and/or precipitation in the reservoir and phase trapping [1; 8]. These mechanisms may affect the surfactant flooding process and the performance of the surfactant to recover oil. If the adsorption is high, injecting only surfactant is not economically feasible since the chemical molecules will be adsorbed, and less will be available to form the microemulsion [11; 12]. Several models are available in the literature to estimate surfactant adsorption on rock surface. [PERSON] et al. used the Langmuir Isotherm model and Freundlich models to select a surfactant with lower adsorption density [13]. In the Langmuir Isotherm equation, surfactant adsorption on rock surface is considered as a monolayer process whereas the Freundlich model is used to describe multilayer, reversible adsorption process. In another study, [PERSON] and [PERSON] compared Langmuir, Freundlich, and Linear adsorption models to determine the static and dynamic adsorption of a natural surfactant on a shale-sand rock surface [14]. The results showed a better prediction of adsorption equilibrium with the Freundlich model over a wide surfactant concentration range.