Laboratory of Rheology and Mechanics, University of Chlef, BP 151, Chlef 02000, Algeria d

Transcription

1 Water Effect of Oscillatory Behaviour of Light Crude Oil Mohamed MEKKAOUI a, Madjid MERIEM-BENZIANE b,c, N.H. Abdurahman d, Mansour BELHADRI a, Georgios C. Georgiou e a Laboratory of Rheology, transport and Treatment of the complex rheology, University of science and technology- Mohamed Boudiaf, BP. 1505, El M Naour, Oran Algeria b Mechanical Engineering department, University of Chlef BP151, Chlef Algeria c Laboratory of Rheology and Mechanics, University of Chlef, BP 151, Chlef 02000, Algeria d Faculty of Chemical and Natural Resources Engineering, University of Malaysia Pahang (UMP), Malaysia e Department of Mathematics and Statistics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus Abstract Oil companies are increasingly concerned by the recovery of hydrocarbon crude oil field in residual amounts retained in the pockets by injecting large quantities of water. Thus, the objective of this work is to study experimentally the effects of water on the resilience of crude oil. A series of tests of four samples of synthetic crude oil from the Algerian Sahara has been made. Experimental results, expressed in terms of f ( ), revealed the character of Non Newtonian fluid. Depending on the oil field, the emulsions with different water concentrations, their rheological behaviours were described in better way by the Ostwald de Waele and the Herschel Bulkley models. The results of different emulsions were calibrated by the rheological models and it was found that they were obeying the power law with a weak behaviour index and a yield stress. The viscoelastic of emulsions was identified by measuring the rheological properties including non-newtonian viscosity, the elastic modulus, (G ), the loss modulus, (G ), the phase angle (δ) and the complex module G. The results defined that the rheological parameters of emulsions were significantly effected by the chemical composition of water and the nature of crude oils. Index Terms Algerian crude oil, Complex shear modulus,, Non-Newtonian, Viscosity. I. INTRODUCTION Etymologically, the rheology is a discipline which deals with the flow and deformation of materials under the action of stress. The rheological behavior and stability of the emulsions (O/W) will be affected by the proportion of the oil dispersed phase. The formation of emulsion is another problem that occurs in the petroleum industry. Indeed, crude oil is often mixed with water when it comes out from a well. It was developed to describe the properties of materials whose behavior is poorly defined in relation to that of perfect elastic solid and Newtonian fluid [1]. In the case of the petrochemical industry, the rheological study of cooled crude oils at rest is mainly devoted to analyze the effects of stress deformation which is an unavoidable step for determining the conditions and procedure of delivery start of pumping systems of gelled oil in the pipelines. Nowadays rheology is essential in predicting the long-term instability of the emulsions particularly due to flocculation and coalescence. Rapid increase in a storage modulus (G ) upon ageing can be a signal of strong flocculation. The fermentation conditions of substances give a very complex composition of the formed petroleum [2]. Crude oil is a mixture of aliphatic hydrocarbons, aromatic, oxygen, nitrogen and sulfur. It may contain resins, asphaltenes. With a density of 0806, a Specific Gravity (API) between 36 and 44 and a sulfur content of 0.6%, the Algerian oil is a good quality product that meets international standards of marketing [3]. Saturated aromatic oils and resins are unable to form stable emulsions. The molecules that accumulate at the oil-water interface are responsible for the stability of the emulsion [4]. These components form a rigid layer around the droplets of water to prevent their coalescence by establishing a physical barrier [4-5]. The rheology of a fluid remains of great interest in the fields of fluid mechanics research because it allows detailed analysis of physiochemical and mechanical fluid behaviour with its environment. This interest is increasing in the case of petrochemicals and particularly crude oil. Indeed, the water, content of emulsions of oil, plays an important role in the performance of the facilities for the various processing operations. 549

2 If the temperature adversely affects the viscosity and interfacial tension, its decrease results in the formation of particles coagulate causing the deterioration of emulsions. determining the optimum temperature of emulsification and the nature of the emulsifiers are the subject of research in chemical engineering in recent decades [6]. The addition of strong bases is a well-known process in the improvement of oil recovery by reducing its interfacial tension. The time of agitation or sparging must be properly chosen in order to complete emulsification solutions regardless of their concentration [7-8]. During the treatment phases and from the injected water in the tanks containing large quantities of oil in the residual state forms of oil-water emulsions stable. Also, such emulsions can be formed in pipelines during their transportation to the separation plant. Their destabilization is a technical challenge for engineers and researchers. Asphaltenes and resins, contained in oil, are the most important constituents responsible for the stabilization and separation of emulsions. In a solid state, other fine substances such as naphthenic acids, also contribute to the stabilization of emulsions [8]. The presence in the raw oil component such as heavy asphatlènes and resins lead to the formation of interfacial gel criticism. Analysis of the interfacial tension and modulus of elasticity is not sufficient for predicting the stability of oil-water emulsions [8-9]. It is worth mentioning that there are two kinds of crude oils classifications: geochemists and refiners classification. These two classifications have been established taking into account their origin, their geological history and maturity as well as other geochemical parameters [10-16]. In the present study, we examined the rheological properties for four types of crude oil from the Algerian Sahara and its mixture with different percentages were investigated experimentally. These rheological properties include steady flow behavior, yield stress, coefficient of the shear thinning and consistency of the emulsion. A RheoStress RS100 rheometer was employed in all of the rheological examination tests. The heavy crude oil exhibits a non-newtonian shear thinning. Such curves allow us to determine the rheological characteristics of crude oil and to calculate, as accurately as possible the different equipment and pipelines pumping facilities. The analysis of the influence of temperature on the viscosity of emulsions is discussed using synthetic samples of varying water content. The resulting rheograms allow us to determine, according to the percentages of water, the different rheological properties of emulsions, the latter play an important role in the pipelines and storage processes in the refining stations. A. Equipment Used II. EXPERIMENTAL PROCEDURE For each test, maintaining the desired temperature is obtained by a temperature controller type DC30. The samples were tested with a modular rheometer, the Rheostress RS600 by ThermoHaake (Karlsrule, Germany). It is equipped with a cone-plate and coaxial cylinder geometries. Measurements were made using the configuration of the cone-plate combinations having with the following characteristics: diameter 60.00mm, angle 3, distance mm, sample volume 2.00cm3. The temperature was maintained constant at 20±1 C. This rheometer has several operating test modes. It has a universal controlled rate mode, a controlled stress mode, and an oscillation (OSC) test mode. B. Samples Preparation In this study, samples of crude oil from different regions of the Algerian Sahara, Crude oils Sahara (1, 2, 3 and 4) were used to study their rheological characteristics. To determine the behavioural law fluid, we use a rheometer to determine the variation curves of shear stress with shear rates. The rheological tests were conducted at different temperatures (10 C, 20 C, 50 C, 70 C and 90 C). After determining the rheological behavior of crude oil, we prepared emulsions similar to those frequently encountered in petrochemical industry. The rheological tests were performed at 20 C for oil at different water contents (0%, 30%, 50% and 70%). Depending on the concentration of water, the description of the rheological behavior of emulsions (Crude oil-water) can be modelled as the principal laws of the rheology of complex fluids. First experimental tests highlighted the impact of the presence of water in emulsions on rheological behavior. C. Preparation Four different light crude oil samples used in this study were obtained from Sonatrach company Sahara, Algeria. To account for the origin of the different oil fields, the light crude oils are identified by the letters 1, 2, 3 and 4. At a temperature of 20 C, the important factors for classifying the crude oil are specific gravity (API), density (d: 550

3 kg/m3), molecular weight (mw: g/mole), Freezing point (fp: C ), and sulfur content (S). According to their respective mean values (i.e., 40 < API < 49, 0800 < d < 0830, 165< mw <179, -30 < fp <-35, and 0.08 < %S < 0.2), the Algerian crude oil is classified as a light one. The emulsions were prepared at different volume concentrations of water, where the table 1 showed the chemical of water, namely 30%, 50% and 70%. TABLE 1: CHEMICAL CHARACTERISTIC OF WATER Parameters values PH 7.90 O 2 (mg/l) 7.4 M.O (mg/l) 0.13 HCO - 3 (mg/l) Ca ++ (mg/l) Mg ++ (mg/l) NO - 2 (mg/l) Cl-(mg/l) NO - 3 (mg/l) 5.43 NH + 4 (mg/l) 0.03 SO 2-4 (mg/l) To ensure a perfect homogenization, the solution was stirred for 10 minutes, with a magnetic bar stirrer. For each test, maintaining the desired temperature is obtained by a temperature controller type DC30. To study the rheological behavior of different samples, we exploited the performance of the rheometer "RheoStress 600" (Germany), type Z40 DIN, operated at a pressure of 2.5 bar. Once, the thermodynamically stable emulsion is obtained, we measure the different rheological performance by exploiting the rheometer described above. The study of liquid-liquid stability and influence of temperature on the partitioning of coexisting phases are decisive step in choosing the appropriate solvent (liquid-liquid extraction). Thus, to analyze this physicochemical aspect, we left the emulsion to settle for a period of 24 hours in vials after stirring. A. Rheological Behavior of Crude Oil Sahara III. RESULTS AND DISCUSSION In this study, several rheological parameters of Algerian crude oil are determined. This study is important in the petroleum industry where the water content of the crude oil can be as high as 70% in volume, also in petroleum refining operations where generally the water content is low. In order to show the different rheological parameters, several experimental tests were conducted. The Algerian crude oil is more difficult to stabilize, especially for higher water volume fractions. The crude oil apparent viscosity was determined using an advanced rheometer, controlled by a microcomputer. Shear stress as a function of shear rate, for different temperatures (Figure 1), was measured and compared with, the rheological models: the Ostwald law (non Newtonian, n>1) given by equation (1). 551

4 n (1) Where, n and are the stress, flow index and shear rate, while μ is the viscosity of the fluid. Fig.1. Rheogram crude oils: Sahara1, Sahara2, Sahara3 and Sahara4 for different temperatures B. Influence of Temperature on the Viscosity of Crude Oil Sahara Knowing that the viscosity is an intrinsic property of the fluid, we had to reveal its dependence on temperature. For different temperatures, we analyzed the variation of shear stress with strain rate using the rheometer described earlier. This interdependence is viewed through the experimental results presented in Figure 2. Indeed, the increase in temperature is reflected by a consistent decline in the viscosity of crude oil. This trend is confirmed and reduced to temperatures close to room temperature. Initial results show that the rheological properties of crude oil vary greatly with temperature. Strictly speaking and given its liquid state, the variation of the viscosity of crude oil can be described by a law of the form: B log A (2) T Where, A and B are constants characteristic of the fluid. Their values are approximated by plotting in a coordinate system where, A is the appropriate intercept and B is a measure of the slope. Moreover, we can note that at a given temperature, the rheological behavior of the fluid obeys to a law of two or three parameters. 552

5 Fig 2: Variation of the viscosity of crude oils: Sahara1, Sahara2, Sahara3 and Sahara4 depending on the temperature. Values of the constants A and B of the model are shown in Table 2. TABLE 2: VALUES OF MODEL CONSTANTS FOR VARIOUS CRUDE OILS. Crude Oils Sahara A B Crude oil Sahara Crude oil Sahara Crude oil Sahara Crude oil Sahara The four samples exhibit similar rheological behaviours for different temperatures. In addition, and from Table 2, it should be noted that samples of crude oil of Sahara1 and Sahara3 types are characterized by a high viscosities in comparison to those of Sahara2 and Sahara4 samples, respectively. C. Rheological Behavior of the s a) Modeling the rheology of emulsion At a temperature of 20 C, a series of experiments was conducted to analyze the evolution of shear stress as a function of shear rate for emulsions prepared earlier. Knowledge of the rheological behavior of emulsions is fundamental to the modelling of their flow. to identify the model most representative of the behavior of these emulsions, it is more instructive to plot the experimental results obtained throughout the figures given by rheograms (Figure 3) Such results have highlighted a different rheological behavior of a Non-Newtonian fluid. However, the modelling of crude oil is the basis of this analysis and proposes a power law with two parameters for the characterization of these emulsions. The first point that emerges is that the model includes a yield stress which bodes no doubt that the fluids obey to the Ostwald de Waele model, Herschel-Bulkley model, Bingham model and Casson model. Indeed, these models assume that such fluids are schematically at rest, a rigid three-dimensional structure capable of withstanding stresses below the yield stress. Once we move beyond this constraint, the structure is destroyed completely and the fluid begins to flow. It has been demonstrated that the rheological behavior of emulsions is shear thinning with yield stress. They are similar to the behavior of a solid at low shear stresses. However, under the growing influence of shear stress, it can be assimilated to a viscous fluid with a non-linear trend 553

6 . Fig 3: Rheogram emulsions of crude oils: Sahara1, Sahara2, Sahara3 and Sahara 4 for different water contents The experimental results presented in the form of rheograms, have clearly established that crude oil is a Non Newtonian rheological behaviour regardless of its deposit. For different emulsions and according to their water content, each emulsion has been characterized by the calculation of model parameters (yield stress behaviour index n and consistency factor k). These calculations are essentially based on experimental results using polynomial interpolation techniques. By numerically processing the overall results (table 1) and testing the various models (Herschel-Bulkley and Ostwald de Waele), we determined the parameters values. These tests were performed at a temperature of T = 20 C. Figure 3 led us to select the appropriate model which describes, as accurately as possible, the rheological behaviour of the emulsion. The two immiscible phases, thus formed, consist of crude oil and water respectively regardless of the percentage of water. Given the strongly pronounced polarity of water and character of the constituent species saturated oil, it can be argued that there is no chemical reaction that could affect the stability of coexisting phases. Furthermore, we can conclude that the rheological properties of formed emulsions with basis of crude oil from Sahara (1, 2 and 3) types are modelled by the Herschel-Bulkley equation whose expression is: Rheological data were analyzed by the viscometer s software. Flow behavior of emulsion samples with basis of crude oil from Sahara (1, 2 and 3) types are described by fitting the experimentally measured shear stress shear rate data to three different common models namely (Table 3) Power law (Eq. (1)), Herschel Bulkley (Eq. (3)), Bingham (Eq. (4)), and Casson (Eq. (5)): n τ τ k. (3) 0 γ τ τ0 k.γ (4) τ τ0 k.γ (5) Where is the shear stress (Pa), τ 0 the apparent yield stress, the shear rate (s-1), and k as well as a are model constants. 554

7 Composition of the emulsion (v / v) ISSN: Samples 100% OIL Crude oil A TABLE 3: DETERMINATION OF RHEOLOGICAL MODEL PARAMETERS Newton Model Ostwald de Waele model Herschel-Bulkley model k R 2 n k R 2 0 n k R %O-0%W 50%O-50%W A A %O-30%W A % OIL B %O-70%W 50%O-50%W B B %O-30%W B % OIL C %O-70%W 50%O-50%W C C %O-30%W C % OIL D %O-70%W D %O-50%W D %O-30%W D

8 D. Changes in Rheological Parameters of s a) Influence of water content on yield stress We recall that the emulsions have synthesized a water content of 30%, 50%, and 70% respectively. Experimental results have shown that such emulsions obey to a Herschel-Bulkley rheological law type and the yield stress is a function of concentration by volume in water for different samples of crude oil from Sahara (1, 2 and 3). Table4 presents the trend expressing the relationship τ 0 f ( (% V )) and we can see that its value is seriously Ceau affected by the presence of water in the mixture and it depends entirely on the physicochemical properties, uniformity and stability of the emulsion. The yield stresses τ 0 which correspond to emulsions composed of crude from Sahara (1 and 2), have higher values. It appears that their values increase with the volume concentration in water and they are definitely less than 0.6 Pa.s whatever the type of crude oil. However, the one of the crude oils emulsions consisting of Sahara (1, 2 and 3) maintains Non-Newtonian (Ostwald de Waele) model) properties for 100% based on the crude oils. It is found that the activity of the molecule of water is function of the composition of the emulsion and for low compositions; the behaviour of the emulsion is similar to that of crude oil. TABLE 4: EVOLUTION OF THE YIELD STRESS, COEFFICIENT OF THE SHEAR THINNING AND CONSISTENCY OF THE EMULSION s : crude oil Sahara1 % - Water % : crude oil Sahara2 % - Water % : crude oil Sahara3 % - Water % WITH THE CONCENTRATION OF WATER CVeau (%) 0 (Pa) K (Pa.s n ) n 0 0 0, , , , ,2437 0, , ,4147 0,8599 0, ,001 Pa.s (Viscosity of water) , , , , ,5085 0,2389 0, ,568 0,3257 0, ,001 Pa.s (Viscosity of water) , , , , , , , ,1314 1,145 0, ,001 Pa.s (Viscosity of water) 1 b) Influence of water content on the coefficient of the shear thinning The coefficient of the shear thinning is introduced through the index n which denotes the deviation from the law expressing the Herschel-Bulkley model. Evolution of the shear thinning behavior (n<1) index n with the water content is given in table 4. It appears that its value decreased with the volume concentration in water and it is definitely less than unity regardless of the type of the crude oil. We note that the coefficient n is less than 1, so the fluids are non-newtonian behaviour especially in range 0.5 to 0.9. We conclude that their rheological behaviour is similar to a plastic fluid. c) Influence of water content on the consistency of the emulsion The evolution of consistency k relating to the volumic concentration in water for various emulsions is presented in table 4. Note that the consistency increases with the fraction volume of water up to a certain limit depending on crude oil type. In extreme conditions ( C water (% V ) 0. 0, C water (% V ) 100 ), the emulsions have a Newtonian rheological behaviour i.e., n 1. 0, and k is equal to the viscosity of the pure component. 556

9 Knowing that the viscosity of pure water at T = 20 C is 10-3 Pa.s, the results highlight the existence of a maximum in the composition range 0.50 C water (% V ) 1. 00, the emulsions have a Non Newtonian rheological behaviour. However, its location requires a careful sample preparation whose composition varies in this last interval, or that it is not representative of the solutions encountered in industrial scale. E. Analysis of Oscillatory Behavior of s The study of gel formation in the emulsion is of major importance for the production and transportation. The stirring time should be properly chosen in order to complete emulsification solutions regardless of their concentration [15]. Since rheological parameters are sensitive to the change of microstructure produced by a phase transition, it was decided to explore the utility of the oscillatory analysis for lytropic systems. A small amplitude oscillatory experiment can hardly destroy structures of samples and detect the change of microstructure during the change in concentration. The elastic and viscous responses of viscoelastic systems were quantified by undertaking dynamic oscillatory measurements. A sinusoidal strain of frequency x was applied to the viscoelastic system and the corresponding stress was measured (Eq.(6)). For viscoelastic systems, the stress and strain were out of range. The phase angle shift ( ) was measured in terms of the time shift ( t ) between the amplitudes of the oscillating stress ( ) and the 0 strain ( ) [17]. 0 t (6) The values of G and G are described by the following equations: G G cos (7) G G sin (8) G is the complex shear modulus, according to the angular velocity is given by the following equation: G G ig (9) Where G is the elastic modulus, which reflects the elastic response, whereas G is the corresponding loss modulus expressing the viscous response. There were two regimes: Viscous (if G > G ) and Elastic (if G > G ). To describe, illustrate and analyze the viscoelasticity of these emulsions, the complex modulus (G) is measured. A water-in-crude oil emulsion is a detached structure in which the original surfactants of the crude oil, such as naphthenates and resins, can participate to ameliorate the interactions droplet-droplet, fundamentally if: (i) the movement structure is advantageous to increase shear instruments between the aqueous phase and oily phase; (ii) these surfactants are in important applications [18, 19]. Moreover, the intake of these surfactant particles on water oil interface can result in inter particles interactions (between molecules), which will reverse every strain on the interface, growing its elastic modulus and homogenizing the structure, by decreasing the coalescence structure between the water droplets [18, 19]. Hence, the mixture of both phenomena can be concluded from majority rheological capacities in which the system properties of all interfaces interacting can be interpreted though G (storage or elastic modulus), G (lost or viscous modulus) and tan (δ) (damping factor) effectively, with a good relation with the bottle investigations performed [18, 19]. Figs. 4, 5, 6 and 7 show the results obtained for the emulsions (crude oil Sahara1 30%-water 70%, crude oil Sahara1 50%-water 50% and Crude oil Sahara1 70%-Water 30%), proving the influence of the water concentration and oil composition on the internal structure of the emulsions. Concerning the type emulsions evaluated in this work, the one with the minimum water concentrations respectably: Water 30% and Water 50%, exhibited the minimum complex modulus values. This was possibly due to the lower capacity of material placed on the droplet surfaces. According the Derkach and Dílson, the layer of natural surfactants adsorbed at liquid liquid interfaces creates a stress tendency while the emulsion is exposed to shearing, instigating an increase of the elastic component (G ) in the complex modulus (G) [18, 19]. 557

10 a) Stress sweep For the case of various prepared emulsions, the module of the complex module study shows that it is strongly influenced by an oscillatory shear stress as shown in figures 4, 5, 6 and 7. Thus, the width of the linear range of the stress increases with the increase of energy dissipated by viscous effects. In addition, it should be noted that this area is affected by the size of droplets in the emulsion formed according to the stirring speed. The elastic modulus values of these emulsions are always higher than viscous modulus in the range of study. Since the rheological parameters are very sensitive to changes in the microstructure produced by a phase transition, it was decided to investigate the change of microstructure during the change of the concentration of crude oils. Fig 4: Evolution of complex shear modulus of emulsions (crude Oil Sahara1 %-Water %) with the shear stress Fig.5 Evolution of complex shear modulus of emulsions ( Crude oil Sahara2 %-Water %) with the shear stress Fig.6: Evolution of complex shear modulus of emulsions (Crude Oil Sahara3 %-Water %) with the shear stress 558

11 Fig.7: Evolution of complex shear modulus of emulsions (crude Oil Sahara4 %-Water %) with the shear stress Figures 4, 5, 6 and 7 show the sweep diagrams of stress for different liquid-liquid phases. We see that the module and force depend on the geological origin of the emulsions and their compositions in water (30%, 50% and 70%). If the mesophase is characterized by the change in direction of the curve G, we can notice that each composition has four distinct mesophases depending on the origin of light crude oil. In this sense, the defining of stress areas is reflected in the following tables (5 and 6): Composition Of s f TABLE 5: VALUES OF STRESS SWEEP FOR FRACTURE START OF THE STRUCTURE Modulus constraints mesophases depending on the origin of light crude oil Sahara1 (E#1) Sahara2 (E#2) Sahara3 (E#3) Sahara4 (E#4) O30%-W70% Pa Pa Pa Pa O50%-W50% 0.07Pa 0.28 Pa 0.28Pa 0.28 Pa O70%-W30% 0.02 Pa Pa 0.03 Pa 0.04 Pa TABLE 6: VALUES OF STRESS SWEEP FOR FRACTURE OF THE STRUCTURE Modulus constraints mesophases depending on the origin of light crude oil Composition Of s Sahara1 (E#1) Sahara2 (E#2) Sahara3 (E#3) Sahara4 (E#4) O30%-W70% 0.12 Pa 0.20 Pa 0.16 Pa 0.24 Pa O50%-W50% 0.48 Pa 0.40 Pa 0.48Pa 0.48 Pa O70%-W30% 0.07 Pa Pa Pa 0.07 Pa The type of emulsions (E#1, E#2, E#3 and E#4) with a 70% water concentration presented similar curves, with the complex modulus being reliant on the shear stress for values above 7, 19.5, 6,1.55 Pa (Figs.4 to 7) respectably and a more definite elastic than viscous character (G > G ) at diminution shear stresses. The point change for four emulsions at about 2, 5, 2 and 0.5 Pa (Figs.4 to 7) respectably, can relate a transition from flocculated to dispersed droplets. Structures constituting long-chain particles, such as elevation molecular mass hydrocarbons, or so complex as compositions of waters, are liable to entangle [18]. The effect of the emulsion can be examined in terms of water concentration [18, 19] i.e. an increase in particle size, caused by the reducing in solvent separation, increases the emulsion stability. To study the influence of stress sweep for fracture of the structure, the emulsions (crude oil Sahara% -water %) were based the concentration of water (30%, 50% and 70%), at 30% intervals. The results of the complex modulus versus shear stress are presented in Figs.4 to 7. The emulsion (crude oil Sahara% -water %) showed the 559

12 variation of the complex modulus with stress sweep fracture of the structure. As the concentration of water increased (30%, 50% and 70%), there was a gradual move to greater values. Also this was due to the 70% of water for different, the G curve exhibited a yield stress value with a shear stress of 7.3, 19.5, 6,1.55 and 4Pa respectively (Figs.4 to 7). It can also be noticed that at this point a nonlinear region of the viscoelasticity starts and the complex modulus reduction with increasing shear stress. However, for the 30% and 50% concentration of water, G remained constant. The model emulsions with the same water concentrations (crude oil Sahara1 30% -water 70%), (crude oil Sahara2 30% -water 70%), (crude oil Sahara3 30% -water 70%) and (crude oil Sahara4 30% -water 70%)) (Figs. 4 7) respectively, were more influenced by stress sweep for fracture of the structure than the emulsions for the 30% of water concentration (Figs. 4-7). All the curves obtained by stress sweep for fracture of the structure of emulsions1 (E#1), emulsion2 (E#2), emulsion3(e#3) and emulsion4 (E#4) exhibited for 70% of water showed the same profile and values are different from each other. The emulsions stability is related to their elastic behavior. Model emulsions containing higher water content present higher elastic modulus, and so they are more stable[18, 19]. The behavior of water concentration in the different crude oils are closely linked to their interactions with different emulsions elements as that the results from oscillating rheology for emulsion is reasonably related to that for the model system compositing different content of water: (i) the behavior of the emulsion is related to that of the model emulsion with less quantity of water; (ii) emulsion is more effected by the resisting than the model emulsions containing the same quantity of water. IV. CONCLUSION The analysis capacity of a recovering method of buried oil in the deposits as residual amounts, necessarily involves the study of the rheology of the oil and emulsions which might be formed following the injection of substantial water quantities. In this context, we have completed the preparation of synthetic samples of emulsions whose base is the oil from different fields of the Algerian Sahara and to simulate the rheological behaviour of an operating petrochemical plant. For this purpose, we used emulsions of varying oil water content (30%, 50% and 70%). For a fairly exhaustive study of the Algerian oil, we opted for the following fields: Sahara (1, 2, 3 and 4). For a rheostress 600 type rheometer, the study is focused on the analysis of rheological behaviour of emulsions and the influence of temperature on the viscosity of crude oil in an interval spanning a wide range of characteristic conditions of flow [10-90 C]. The obtained experimental results, shown as rheograms f have clearly established that crude oil has a Non Newtonian (Ostwald de Waele) rheological behaviour regardless of its deposit. In addition, a logarithmic type Log f 1 T enabled us to establish the law behaviour of viscosity with temperature. Tests for different emulsions have yielded results that are calibrated by rheological models obeying to the power law with an index of behaviour and a lower yield stress. Arguably, the emulsions are non-newtonian fluids, of a plastic type. Depending on the oilfield, we can distinguish the following rheological behaviour: - Herschel-Bulkley model for the emulsion-based on the crude oil from Sahara (1, 2 and 3). - Ostwald de Waele model for emulsion-based on the crude oil from Sahara4. The shape of the curves shows that the rheological behaviour depends on the percentage of water. Such behaviour is related to the nature of the oil, the physical characteristics, the reservoir lithology and the sedimentary history of the basin. We comprehend that the complex module and force fracture depend on the geological origin of the emulsions and their water compositions (30%, 50% and 70%). If the mesophase is characterized by the change in direction of the curve G, we can notice that each composition has four diverse mesophases reliant on the origin of light f crude oil. To study the effect of aging for different emulsions (Crude oil%- Water %). The results of the complex modulus in function of shear stress are shown in Fig. 2. The petroleum emulsion (E#1) (Fig. 2a) showed a significant variation of the complex modulus with different percentage of water for obtained the behaviour of the materials may detect many information of the material structure. As time passed, there was a gradual shift to higher values. Besides this, on the 30% in the water, the G curve exhibited a yield stress value with a shear stress of 0.2 Pa. As may be seen, at this point a nonlinear region of the viscoelasticity curve starts and the complex modulus declines with increasing shear stress. All the curves obtained during the aging of emulsions E#1 for 70% water and E#2 for 50% water exhibited the same profile and values very near to each other. Among the systems with the same water 560

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