ASSESSMENT OF A SURFACTANT – SciELO Colombia

by TH Fabián-Andrés · 2019 · Cited by 1 — The surfactant-polymer (SP) process is one of the Chemical Summary of Influence of Some Variables on Phase Behavior, Interfacial Tension

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CT&F Vol. 9 Num. 1 June 2019 47ctyf@ecopetrol.com.co ASSESSMENT OF A SURFACTANT- POLYMER FORMULATION APPLIED TO THE CONDITIONS OF ONE COLOMBIAN FIELD Tapias-Hernández, Fabián-Andrés a*; Moreno, Rosangela Barros Zanoni Lopes a a University of Campinas, Campinas, São Paulo, Brazil *email: fabian.tapias@hotmail.com ABSTRACT The surfactant-polymer (SP) process is one of the Chemical Enhanced Oil Recovery (CEOR) methods used in the industry. It has been continuously studied; however, it is still a challenge for the petroleum industry due to the dif˜culty to design the solution to be injected and forecast process performance. This paper is intended to contribute to the design of ˚uids used in an SP process based on some previously known properties and conditions. Hence, reservoir and fluid properties of a Colombian Field were used as reference parameters to select the polymer and surfactant. Then, the effects of salts, temperature, and surfactant on tailor-made polymer solutions were determined through a rheological study. Ostwald-de Waele and Carreau-Yasuda models adjusted the measured viscosity data against shear rate, while Arrhenius equation ˜tted viscosity values at 7,8 s -1 against temperature. The surfactant performance was analyzed using phase behavior tests, and the Chun Huh equations determined the interfacial tension (IFT) values. The Bancroft™s rule was used as a qualitative veri˜cation tool of the kind of micro- emulsion formed. From rheology, we concluded that the viscous modulus is predominant for all polymer solutions, and the ˚uid thickness is reduced due to the presence of divalent cations and raise on temperature, salts or surfactant concentration. On the other hand, the observed phase behavior corresponded to a transition Winsor II to I without ˜nding any Winsor III micro-emulsion. Therefore, some criteria were proposed to select the optimal conditions. For the desired conditions, the reduction of IFT reached values ranging in magnitudes of 10 -3 to 10-4 [mN/m]. These values are usually associated with an improved oil recovery factor. KEYWORDS / PALABRAS CLAVE AFFILIATION EVALUACIÓN DE UNA FORMULACIÓN DE SURFACTANTE- POLÍMERO PARA LAS CONDICIONES DE UN CAMPO COLOMBIANO RESUMEN El proceso de inyección de surfactante-polímero (SP) es uno de los conocidos métodos de recuperación mejorada con químicos (CEOR). Este método ha sido continuamente estudiado; sin embargo, aún constituye un desafío en la industria del petróleo debido a la di˜cultad de diseñar la solución a ser inyectada y predecir su comportamiento. Este trabajo pretende contribuir en el diseño de los ˚uidos a ser usados en un proceso de SP basándose en algunas propiedades y condiciones previamente conocidas. Para ello, las propiedades del yacimiento y del ˚uido de un campo colombiano se utilizaron como parámetros de referencia para seleccionar el polímero y el surfactante. Luego, se determinaron los efectos de las sales, temperatura y el surfactante en soluciones de polímero hechas a medida mediante un estudio reológico. Los modelos de Ostwald-de Waele y Carreau-Yasuda ajustaron los valores de viscosidad medidos en función de la velocidad de corte, mientras que la ecuación de Arrhenius ajustó los valores de viscosidad a 7.8 s -1 en función de la temperatura. El desempeño del surfactante se analizó mediante pruebas de comportamiento de fase, y por medio de las ecuaciones de Chun Huh se determinaron los valores de tensión interfacial (IFT). La regla de Bancroft se usó como una herramienta de veri˜cación cualitativa del tipo de microemulsión formada. A partir de la reología, llegamos a la conclusión de que el módulo viscoso es predominante para todas las soluciones de polímeros, y el aumento de viscosidad del ˚uido se reduce debido a la presencia de cationes divalentes e incrementos en la temperatura, salinidad o concentración de surfactante. Por otra parte, el comportamiento de fases observado correspondió a una transición de Winsor II a I sin encontrar una región de Winsor III. Por lo tanto, se propusieron algunos criterios para seleccionar las condiciones óptimas. Para las condiciones deseadas, la reducción de IFT alcanzó valores que varían en magnitudes de 10 -3 a 10-4 [mN/m]. Estos valores son generalmente asociados con un incremento en el factor de recuperación de petróleo. Surfactant | Polymer | Rheological behavior Phase behavior tests | Interfacial tension. Surfactante | Polímero | Comportamiento reológico Pruebas de comportamiento de fases| Tensión interfacial. ARTICLE INFO : Received : November 08, 2017 Revised : March 31, 2018Accepted : August 21, 2018 CT&F – Ciencia, Tecnologia y Futuro Vol 9, Num 1 June 2019. pages 47 – 63 DOI : https://doi.org/10.29047/01225383.152

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48 The enhanced oil recovery (EOR) methods are a group of techniques applied in reservoir management with the purpose of improving the oil recovery factor that today can be applied at any stage of reservoir development. The EOR methods are divided into three broad categories [1]Œ[4], thermal, miscible and chemical (CEOR) methods. The last group consists in adding chemical products to the injection ˚uids. It encompasses polymer, surfactant/polymer (SP), alkali/surfactant/polymer (ASP) or gel ˚oodings. However, among them, polymer ˚ooding is the most used method in large scale, while the SP and ASP applications are limited for technical reasons, such as the dif˜culty to design and predict the process behavior in the ˜eld, the excessive formation of carbonate or silicate scales, and the formation of strong emulsions in production facilities [5]. A surfactant-polymer (SP) process consists in the addition of surfactant products, to achieve significant interfacial tension reduction and, thus, produce a high capillary number. Also, a polymer solution is used as control mobility agent seeking an increase of areal ef˜ciency [6],[7]. Characterizing the chemical products to be injected and understanding their interactions are key factors for the effectiveness and dynamic performance of the CEOR process [8]-[11]. Therefore, the design of the optimum formulation demands previous studies related to the rheological behavior of the selected polymer, the capability of the chosen surfactant to reduce the IFT, as well as the solution phase behavior evaluation. Therefore, this study is focused on the assessment of the injection blend using Flopaam 3230S and SDS as polymer and surfactant, respectively. It seeks to found an SP formulation suitable to develop an EOR process encompassing a detailed rheological study to determine the influence of temperature, salts and surfactant concentrations on different polymer solutions. Furthermore, phase behavior tests aim to determine solubilization parameters, optimal salinity, type of micro-emulsion and IFT values through Chun Huh equations. 12. The residual oil mobilization mechanisms associated with CEOR process has been linked to a decrease of the capillary forces[12] due to the reduction of IFT [13] and thus, increase of the capillary number. This condition is achieved when interfacial tension reaches values ranging between 10 -3 and 10 -4 [dynes/cm]. Additionally, changes in rock wettability have been documented [14],[15]. Different de˜nitions related to the SP process have been used [4], [16],[17]. The main difference lies in the surfactant concentration, and the way in which the polymer is used during the process. For this work, an SP ˚ooding is characterized for the use of low surfactant concentrations (0.1% to 2% wt) and the addition of polymer in the same solution to increase its viscosity and overcome the viscous instability of low interfacial tension [18]. This approach differs from the Micellar ˚ooding as in that case, the surfactant concentration is 2% up to 12% wt higher, and also from the surfactant ˚ooding where the surfactant is added only on the aqueous phase. Another injection scheme considers a surfactant slug driven by a polymer solution to improve the sweep ef˜ciency and reservoir pressure maintenance [19].The surfactants are amphiphilic molecules, i.e., they have both hydrocarbon portion (nonpolar) or fitailfl and an ionic portion (polar) or fiheadfl [4]. Therefore, they are soluble in both, organic solvents and water. Usually, they are referred to as surface-active agents [20]. At low concentration, they are adsorbed on the surface, or concentrated at the ˚uid/˚uid interface and thus, reduce the surface energy per unit area required to develop the interface between two immiscible ˚uids, also called IFT. This effect takes place directly due to the replacement of solvent molecules at the interface by surfactant molecules i.e., the micelles have solubilized a phase that is immiscible with the solvent. These aggregates in solution are named micro-emulsions (ME).Surfactant dissolved in either water or oil phase tends to partition in some degree into the other phase. It depends on its capability of solubilizing between phases. i.e., a hydrophilic surfactant tends to be preferably soluble into water without excluding that part of it can also solubilize in oil. The partitioning can be characterized by the partitioning coef˜cient (Ke), which is de˜ned as: Where Cso and C sw are the concentration of the solute in the oleic and aqueous phase, respectively. The partitioning coef˜cient depends on temperature, surfactant composition at the interface, ionic strength, pH, oil type and cosolvents used [21],[22]. A partitioning coef˜cient equal to a unity corresponds to the same solubilization of both ˚uids within the micro-emulsion. This condition is associated with the Winsor III behavior and the minimum IFT of the system. The Bancroft™s Rule is an entirely phase-based qualitative method, where an emulsi˜er is more soluble and, constitutes the continuous phase [23]. Therefore, hydrophilic surfactants tend to generate oil in water (o/w) emulsion, whereas lipophilic surfactants will make water in oil (w/o) emulsion. The use of this rule has been recently reported [24]. Several authors [24],[26],[27] have associated micro-emulsions with a high solubilization of oil and water with the low IFT values required to improve the oil recovery. The formation of a micro- emulsion is in˚uenced by different factors such as surfactant nature, brine salinity, temperature, co-solvent types, etc [6],[28]. Hence, three different kinds of micro-emulsion are usually reported in CEOR processes. The ˜rst, known as Winsor I or Lower-phase micro-emulsion is present when the surfactant exhibits good aqueous-phase solubility, and a small quantity of oil is solubilized in the cores of the micelles, i.e., the ME characterizes by an excess oil phase (O) without surfactant and a water-external micro- emulsion phase [29]. In the second case, named Winsor II or Upper-Phase micro-emulsion, the system separates into an oil-external micro-emulsion containing some solubilized water and an excess (1)=

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49Figure 1. Schematic representation of the micro- emulsion types of water phase (W). The last system, called Winsor III or middle- phase micro-emulsion, is more complex due to the existence of a three-phase region consisting of excess oil, micro-emulsion, and excess water [28]. This region is saturated with both oil and water at the temperature and overall composition of the system, and it is important due to the associated ultralow IFT™s values [16]. A schematic representation of the micro-emulsion types is shown in Figure 1.The micro-emulsion behavior as a function of different variables of interest (Water/oil Ratio Œ WOR, salinity, surfactant and co-surfactant concentrations) have been studied through phase behavior tests. These tests are conducted in pipettes, and the primary objective is to ˜nd a chemical formula with high solubilization ratios of oil and water volumes, and to determine the optimum salinity, i.e., the salt concentration where the lowest IFT value is obtained. According to [4],[27], to reach an ultra-low IFT, the solubilization ratio must be greater than 10. One way to quantify the solubilization ratio parameters is shown in equations (2) and (3). Table 1. Summary of Influence of Some Variables on Phase Behavior, Interfacial Tension, and Solubilization Parameters. ˜˚˛˝˙ˆˇˆ˛˝ ˙ˆˇˆ˛˝ ˜˚˛˝ š š˝š˝˜˝˜˝˜˝ME (2)Vom=BA%wt Surfactant (3)Vwm=CA%wt Surfactant (4)om=c(VoVs)2=cVom2 (5) wm=c(VwVs)2=cVwm2 Where A is the aqueous level, B and C are the oil and the water- solubilized level, respectively. The Figure 1 includes the schematic representation of these variables. The IFT values between the micro-emulsion and the ˚uid phases can be obtained according to Chun Huh [30] based on the solubilization ratio parameters, as follows: For the above equations, Huh, found that in EOR process these expressions are consistent with values of c near 0.3. A reasonable agreement between these equations and measurements carried out with a spinning drop are reported [26],[31]. The phase behavior has been extensively studied. Healy et al. [28] explored some physico-chemical properties of multiphase micro- emulsion systems viewing toward understand immiscible aspects of micro-emulsion flooding and develop systematic screening procedures useful for optimal flood design. The relationship between interfacial tension and phase behavior were exposed. Moreover, they showed that the addition of polymer to the brine did not affect the interfacial tension behavior in a signi˜cant manner. In addition, Reed & Healy [32] presented a complete and detailed study on the effects of salinity, brine composition, temperature, surfactant structure, cosolvent, and oil aromaticity on the phase behavior, interfacial tension, and solubilization parameters. Table 1 summarizes the results. Salager [33] also presented a detailed study of the phase behavior, micro-emulsion formation, and interfacial tension. This author presented detailed experimental procedures to characterize the surfactants and to develop the phase behavior tests. The evaluated variables included: surfactant concentration, structure, and composition; aqueous phase salinity; oil structure through the alkane carbon number (ACN) for alkane series, and effective Alkane Carbon Number (EACN) for other hydrocarbons or mixtures; the alcohol type and concentration, WOR and temperature. The process was considered not very sensitive to pressure changes. Table 2 shows the phase behavior results for anionic surfactants. Increasing Variable Phase Behavior* Results VomVwmomwmCy˜˚˛˝˙˝ˆˇ‹‹‹‹‹‹——⁄⁄⁄—⁄⁄———⁄⁄—

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50Scanned Variable (Increase) Ternary Diagram Transition ˜˚˛˝˙˝ˆˇ˜˚˛Table 2. Qualitative Effect of Variables Analyzed on the Phase Behavior of Anionic Surfactants. Micro-emulsion viscosity measurements were conducted for Bennett, Davis, Macosko, & Scriven [34], observing that at a ˜xed shear rate or shear stress and during the transition to Winsor I ˛III˛II. The micro-emulsion viscosity presented two maximum points and a minimum closer to optimal salinity. Close to these maximum values, the ME exhibited non-Newtonian behavior, whereas far away from these points, the micro-emulsion behaved as a Newtonian ˚uid. On the other hand, Thurston, Salager, & Schechter [35] showed a Newtonian behavior of the viscosity in a Winsor I ˛III˛II transition. They also proposed that the birefringence and viscosity are maximized near the salinity that a transition of phase behavior occurs. Similarly, Lopez Salinas [36] performed the micro-emulsion viscosity measurements using a falling-viscometer with multiple ring-shaped and inductive proximity sensors. The micro-emulsion viscosity presented a Newtonian behavior. Moreover, the micro- emulsion viscosity in function of the salinity exhibited two local maxima and a local minimum. The latter in itself is near optimal salinity. Using mixtures of surfactant (anionic and nonionic), polymer, alcohol, water, oil and sodium chloride, Pope, Tsaur, Schechter, & Wang [37] performed static measurements of phase volumes, interfacial tension, viscosities, and phase concentration. They observed a phase behavior transition of Winsor I ˛III˛II for mixtures with and without polymer. They also noted that the anionic surfactants appear to be more compatible with polymers than nonionic ones. Moreover, they reported a little difference in the IFT values with and without polymer. According to them, the polymer only increased the viscosity of the water-rich phase, with little effect on the micro-emulsion phase.Alvestad et al. [10] presented the dynamic behavior of some surfactant systems for EOR applications. They conducted phase behavior studies and core ˚ood recovery process. The surfactant used was synthesized for seawater and heptane at 70°C. Due to this optimization, a cosurfactant not was required. The phase behavior was determined at WOR equal to 20, 10, 4, 2, 1, 1/2 and 1/3 for surfactant concentrations between 0 to 3 [%wt].The results showed a Winsor II˛III˛I transition. The micro-emulsion transition shown in the Figure 1 is considered an ideal representation of the phase behavior, i.e., those multi- phase regions are uniquely de˜ned. The real phase behavior is more complex than that since several middle-phase compositions are founded rather than a single point. The presence of a precipitate in equilibrium with a rich oil micro-emulsion and several liquid crystalline structures with birefringent properties are some indicators of a not typical phase behavior. A complex experimental behavior is reported by Salter [38]. The phase behavior of water/oil/surfactant systems and the basic principles of low-energy emulsi˜cation was reported by Nishimi [39]. According to this study, the surfactants SDS and Disulfosuccionate Sodium Salt (AOT) exhibited only two phases with a phase transition Winsor II˛I at all salt concentrations. Also, pointed out that even at the point of balance between hydrophilicity and lipophilicity, a three-phase state was not observed. Y.Wang [40], presents the results of over forty core ˚ooding test assessment of a surfactant-polymer process in homogeneous and heterogeneous porous media. The IFT behavior for the different formulations evidenced that a tendency associated with the polymer concentration in the solution is non-existing and the IFT values presented a small difference. Nevertheless, in general, the order of magnitude of these values was maintained. Sagi et al., [41], presents an evaluation of surfactants at 25°C for a CEOR process in a carbonate reservoir with salinity of 11.000 ppm of total dissolved solids (TDS). The phase behavior tests showed a transition of Winsor I ˛II without observing Winsor III behavior. Hence, they proposed some criteria to determine de optimal salinity based on the solubilization parameters and assuming that all the surfactant was in the micro-emulsion phase. On the other hand, synthetic polymers and biopolymers have been used in the petroleum industry. The conventional synthetic polymer used is partially hydrolyzed polyacrylamide (HPAM), and a common biopolymer is Xanthan gum [42]. The HPAM is used for most ˜eld projects due to its costs and large-scale production [43]. The HPAM is a copolymer of polyacrylamide (PAM), which is obtained by partial hydrolysis of PAM or by copolymerization of sodium acrylate with acrylamide [44]. The hydrolysis of PAM consists in converting some of the amide groups (CONH 2) to carboxylate groups (COOM). It reduces the adsorption on mineral surfaces. In commercial products, the hydrolysis usually ranges from 15% to 35%. When a monovalent salt (i.e., NaCl, KCl) is added in a homogenous HPAM solution, the carboxylic group is surrounded by the cations, which shield the charge and reduce the carboxylic group repulsion, the hydrodynamic volume becomes smaller and therefore, the viscosity decreases [4]. When divalent salts are present (i.e., MgCl2.6H2O, CaCl 2.2H2O) in an HPAM solution, their effect is more signi˜cant on the viscosity reduction. At high hydrolysis, the solution viscosity decreases sharply until the precipitation of a complex mix of hydrolyzed products and divalent cations occurs [45],[46]. Due to their higher positive charges, divalent ions are more effective in shielding negative charges on the polymer chain than the monovalent ions. Consequently, the polymer coils up at lower divalent ions concentration, and the hydraulic radius of the polymer chain reduces, diminishing the degree of polymer chain entanglement [47],[48].Temperature also influences the rheological behavior of the polymeric solution. Signi˜cant changes are reported for 60 and 90 °C [49]. Different authors [50]-[52] documented that the relationship between the apparent viscosity of polymeric solution and temperature satis˜es the Arrhenius equation: where is the apparent viscosity of the polymeric solution, A is the frequency factor, T is the absolute temperature, ˜E is the viscous activation energy or the activation energy for ˚ow, and R is the universal gas constant. (6)=()

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51Several models describe the rheological behavior of pseudo-plastic ˚uids under the majority of variable conditions [53]. Nevertheless, the most commonly used is the power law model, also called as Ostwald-de Waele law [4], which describes the pseudo-plastic region. Mathematically, the formula is: where is the shear stress (Pa), is the shear rate (s -1), n is the ˚ow behavior index (dimensionless), and K is the consistency index (Pa*s). For pseudaplastic ˚uids, n < 1. The equation describes with good accuracy only the pseudo-plastic regime and cannot be applied for high and low shear rates [20]. A more satisfactory model for the complete shear rate range, capable of ˜tting data in the three regions of the characteristic curves of thinning ˚uids, is the Carreau-Yasuda model [4],[54]. where ˝ is the limiting viscosity at the upper shear rate and is generally taken as water viscosity [4], n is the same as power law index, is a time constant generally taken as 2 [4], 0 is the viscosity at very low shear rates or stress. Nasr-El-Din, Hawkins, Green, & Inst [55] developed an experimental study to determine the effects of various alkalis, surfactants and brine on the viscosity of dilute aqueous solutions of Alco˚ood 1175L and HPAM. They evidenced that the presence of ionic species (NaCl, CaCl2), and anionic surfactants reduced the hydrodynamic size of the polymer molecule (physical change), inducing a detrimental effect on the solution viscosity. They observed that nonionic species presented a negligible effect on the viscosity behavior. The effect of alkalis on rheological behavior is complex as they affect the polymer chain physically (charge shielding) and chemically (hydrolysis). Samanta et al. [11] described the anionic surfactant effects on the rheological behavior. They observed a detrimental effect on the viscosity of HPAM solutions when adding SDS. They con˜rmed that the apparent viscosity of polymer decreases with an increase in the surfactant concentration. Also, Shupe [56] exposed a reduction of viscosity of polyacrylamide solutions and attributed this effect to the increased ionic strength of the surfactant solutions, caused by the content of anionic surfactants themselves and signi˜cant amounts of sodium sulfate. Another important property that must be considered during the design of a CEOR process that includes polymer for operations is the visco-elasticity. Laboratory results have reported an increase in oil recovery when using visco-elastic polymeric solutions [57], [58]. This improvement has been attributed to the elastic properties of the polymeric solutions, and their effects on the displacement ef˜ciency increase [59]-[61] through the expansion and contraction of the polymeric solutions inside the porous ganglia. Urbissinova et al. [61] investigated the effect of both polymer solutions with similar shear viscosity, but different elastic characteristics elucidating a later breakthrough time and higher oil recovery when the polymer with higher elasticity was used. Wei et al. [62] presented a review of the oil displacement mechanism in polymer ˚ooding. They related the elastic properties with a pull (7)= (8)= (+0(1+())1) effect, stripping and oil thread (column ˚ow) as a mechanism to reduce oil residual saturation. Xia et al. [63] compared the displacement ef˜ciencies of visco-elastic HPAM solution and viscous glycerin solutions by ˚ooding at visual macroscopic glass models. The results elucidated the gradual increase of the displacement oil residual ef˜ciency as the viscoelasticity of HPAM solutions and the viscosity of glycerin solutions rises. Zhang et al.[64] showed that the oil recovery of visco-elastic polymer ˚ooding can be enhanced by larger displacement ef˜ciency due to its microscopic roles. Therefore, the injection pressure required increases accordingly if the elastic effect is signi˜cant. Clarke et al. [65] demonstrated the existence of a phenomenon called elastic turbulence. The presence of elastic turbulence will generate a ˚uctuating pressure ˜eld that is observed to destabilize trapped oil drops and thus, recover more oil. Based on the above, this study is aimed at analyzing the behavior of the storage modulus (G™), also named elastic modulus, which is related to Hooke™s law [53]. It is associated with fimemoryfl or elasticity of the polymer solution, which means that the material returns to its original con˜guration when any deforming force is removed. Moreover, the changes caused on the loss modulus (G™™), known as viscous modulus [66], provides information about the viscous properties of the solution. If G™ and G™™ exist simultaneously and are horizontally parallel in an amplitude sweep test (AST), it can be stated that the material has a linear visco-elastic region (LVR) [53],[67]. In the light of the above discussion, we can state that for a successful surfactant-polymer ˚ooding, an entirely rheological behavior study and phase behavior tests of the solutions should be carried out on target conditions to evaluate and determine the better chemical and the corresponding amount should be used. Thus, allowing a better understanding of mechanisms acting during the CEOR process. The target conditions for this work were determined through a previous screening of the method ( Table 3 ). Based on these criteria, the reservoir conditions, petro-physics and ˚uid properties of the San Francisco (SF) ˜eld were selected as references to develop this study. The SF ˜eld was discovered in 1985 and is located 20 km northwest of the city of Neiva in the Upper Magdalena Basin (Colombia). The San Francisco Field is an example of a mature ˜eld producing under a mature water-˚ooding project, with water cut above 90%, an unfavorable mobility ratio [73], [74]. The SF ˜eld is considered a good candidate for a CEOR process. The reservoir temperature is 50 °C, with an initial pressure of 1100 [Psia], at depth of 3000 [ft], a permeability and porosity range of 20-2000 [mD] and 12 Œ 23 %, respectively and a residual oil saturation closer than 0.25. The oil viscosity was determined at reservoir temperature and corresponds to 18.4 [cP]. The reservoir brine composition is shown in Table 4 .The information related to the ˜eld was supplied by the Project fiAdvanced image techniques for reservoir characterization and improvement of the oil recovery factor,fl developed by Universidad Industrial University of Santander (UIS), Ecopetrol S.A and Colciencias. It is important to highlight that the reported information is only a reference for the properties to be experimentally recreated to conduct this work. PAGE - 6 ============ 52 Temperature. (°C) ˜˚˛˝˜˚˛˙ˆ˙˜˚˛˙ˆ˙˜˚˛˙ˆ˙˜˚ˇ˝˜˚ˇ˘ˆ˘˜˚˛˙ˆ˙˜˚ˇ˝˜˚˛˝˝˝“†˝˝˛˝˝˝’˚†˝’˚‘˝’˚š˝’˚˘˝’†˝’˚˘ˇ˝’˚˘˝’˚˘˝’˚˘“’š˝’˚š˝’˚˘“’˚˝ˆ‘’˚˝ˆ˙’˚˝ˆš†’˚˝ˆ˙†’˚˝ˆ˙†’˚˝ˆ˙’˚˝ˆš†˜˚˘˝˝˝˝˝˜˚†˝˝˝˝˜˚†˝˝˝˝˜˚˘†˝˝˝˝˜˚†˝˝˝˝˜˚†˝˝˝˝˜˚˙˝˜˚‘˝˜˚š˝˜˚˙†˜˚˘†˝˜˚“˝˜˚˙†˜˚˙†˚’˚˚š†’˚˚š†’˚š˝˜˚˙†’˚˘‘…ˇ˝—…˘—…ˇ˘—…ˇš—…‘š—Depth (ft)Permeability (mD)Porosity (%)Lithology Clay Oil Saturation*(Fraction) Water Salinity (ppm)Oil Viscosity(cp)APIGravity (°API)Reference ˜˚˛˝˙˛˝˛˚˛˝ˆˇˆ˘ˆˆˆ˜˚˜˛˝SaltMw[g/mol] Brin I: SF Brine Concentration [g/L] Concentration [g/L] Brine II: Cations Brine equivalent to SF Brine Table 3. Screening of an SP process Table 4. Reservoir Brine Composition: San Francisco (SF) Field MATERIALS. A viscosity of 16 - 20 [cP] guided the selection of the oleic phase, which consisted in a mixture of Marlim Field dehydrated oil and Kerosene 28,6 [%wt]. A rheological study determined the proportion of each ˚uid.The last was aimed at keeping the target oil viscosity. The oil density and viscosity were measured as 0.881 [g/cm 3] and 18.5 ± 1 [cP], respectively, at atmospheric pressure and a temperature of 50 °C. The selected polymer was Flopaam 3230S ® from SNF Floerger, which is a synthetic HPAM with an M w of 5 x 106 [g/mol], 30% of hydrolysis degree, and water content of less than 1%[75]. The Sodium dodecyl sulfate (SDS) from LabSynth with MW of 288.373 [g/mol], with purity of 99.23%, was chosen as the surfactant. The polymer was selected because the molecular weight of HPAM is directly related to the permeability of the porous media, and it is threrefore the polymer to be used [76]. On the other hand, the SDS already has been evaluated as a useful surfactant for a CEOR process, with similar oleic phase composition [77],[78]. 3. POLYMER SOLUTION PREPARATION. The polymer solution preparation followed API RP 63. A stock HPAM solution containing 5000 ppm of the polymer was prepared using the synthetic brines (SB) described in Table 4 . The brines were deairated using a vacuum pump, and the HPAM was added to the solutions while agitating them with a magnetic stirrer. The agitation continued for (5 -7) h until the solution reached a homogeneous aspect, and it did not have insoluble particles (˜sheyes). All the HPAM solutions were prepared carefully with the minimum degree of agitation to avoid mechanical degradation of the long-chain molecules. The stock solutions were left still overnight to ensure full hydration. Then, the stock solutions were diluted with SB up to desired concentrations (eleven different levels). The new solutions were put into a beaker and homogenized with a magnetic stirrer at low speed (120 rpm) for 10 minutes. All HPAM solutions were stored in closed containers to minimize oxygen uptake. The preparation of Surfactant-polymer Blend solutions differs from the process exhibited previously, only regarding the kind of solution used to prepare the polymer stock solution and dilute it. In this case, the solution has a mixture of brine and surfactant. The SDS and HPAM concentrations analyzed were 0.5, 1, 1.5 and 2 [%wt] and 5000, 2000, 1500 and 1000 ppm, respectively. RHEOLOGICAL FLUIDS CHARACTERIZATION. In this part, the work was divided into two steps. The ˜rst one focused on the examining the temperature (50 °C) and salts (tests conducted at laboratory temperature aiming to minimize the temperature effect) effects on the rheological and viscoelastic behavior of polymer solutions prepared with both reference ˜eld brines. Therefore, this step aims to select one of them to develop the following activities. The second evaluation study focused on the investigation of the surfactant effect on the rheological behavior of the aqueous solutions. This analysis was conducted only with the brine selected previously. RHEOLOGICAL AND VISCOELASTIC ASSESSMENTS. The rheological and viscoelastic parameters were measured using a rheometer HAAKE MARS III, which is a high precision instrument. The sensor used was the coaxial cylindrical (DG41), whichis preferable for low viscous ˚uids. The temperature was controlled by a THERMO HAAKE C25P refrigerated bath with a Phoenix II 236 KB – 18 Pages