Evaluation of high molecular weight surfactants for application in Petroleum Industry

Transcription

1 Evaluation of high molecular weight surfactants for application in Petroleum Industry Mestre, C., Prieto, C., Ribeiro, F. Centro de Investigação da CEPSA, Instituto Superior Técnico Abstract The main objective of this article is to evaluate and characterize LAB C14-C18 surfactant to study the feasibility of possible industrial scale production for purposes of use in enhanced oil recovery (EOR). The characterization process can be divided into four distinct parts. The first part comprises the measurement of critical micelle concentration (CMC) from a solution of 5000 ppm concentration. The second one corresponds to adsorption measures of LAB C14- C18 to various concentrations using kaolinite and sand as adsorbents. Then it was performed the measurement of interfacial tension of LAB C14-C18 with three types of oil, A, B and C oil (from Algeria, Colombia and Nigeria, respectively) and with various co-surfactants and three types of oil. Finally were prepared pipettes with the oil from Algeria and the LAB C14-C18 surfactant with various co-surfactants to form microemulsions. With this study can be concluded that LAB C14-C18 surfactant works for application in enhanced oil recovery processes specially with A oil. This surfactant has a low efficiency value (easier to reduce the interfacial tension), adsorbs very little, minimizing the loss of surfactant by adsorption processes, and delivers ultra low interfacial tensions. Keywords: Surfactant, CMC, Adsorption, Interfacial Tension, Microemulsions, EOR

2 1. Introduction Surfactants are amphiphilic substances because they have in their molecular structure, groups with opposing characteristics. In all the surfactant molecules there are a polar group which has affinity for water and a hydrophobic group which by their non-polar nature has no affinity for water [1, 2, 3]. This amphiphilic structure makes the surfactant capable to reduce the interfacial tension of liquids and form micelles in water, after passing the critical micelle concentration. These two properties are responsible to make the surfactants capable of washing. Dilute solutions of surfactants such as petroleum sulfonates lower the interfacial tension between water and oil contained in reservoirs allowing the mobilization of oil, which otherwise would have remained in the reservoir as residual oil. It is important to note that despite the many applications of surfactants, they present an surfactants at the interface solid/liquid is controlled by the properties of surfactant and the properties of the solid substrate [6, 7]. Producing ultra-low interfacial tension is one of the most important mechanisms for oil recovery with respect to surfactant flooding. For displacement of oil in the pores and capillaries of petroleum reservoir rock, it would appear that it is necessary to reduce interfacial tension between oil and surfactant-water to ultra-low values (<10-2 mn/m). Such ultra-low interfacial tension, which can be achieved with suitable surfactants by adsorbing at the oil-water interface, makes it possible to conduct displacements in the field at capillary numbers several orders of magnitude larger than those existing during water flooding. The relationship between viscous forces of drainage and capillary forces is expressed by capillary number equation 1. increasingly important role in the oil industry, especially in enhanced oil recovery. Enhanced oil recovery is a v N CA (1) generic term for techniques used to increase the amount of oil that can be extracted from an oil field. Using EOR, 30-60% or more of the reservoir s original oil can be extracted compared with 20-40% using primary and secondary recovery [4, 5]. Where is the viscosity of the fluid drag, v the interstitial velocity and the interfacial tension [8]. The enhanced oil recovery methods intended to increase the capillary number by reducing interfacial tension. The phenomena of adsorption are a limiting factor in oil recovery processes due to the retention and loss of surfactant that can occur. Because this phenomenon affects the cost of EOR processes, its study becomes very important. The adsorption of The addition of alkali into many flooding systems plays an important role in reducing interfacial tension. If the surfactant formulation for oil recovery is properly designed it has a high potential to achieve maximum recovery ratio. In the present

3 report the interfacial behaviors of crude oil/surfactant/sodium carbonate were studied. It has been found that exists a correlation between displacement efficiency and the equivalent weight of a sulfonate [9]. Sulfonates with high equivalent weights cause the greatest reduction in interfacial tension but are unfortunately insoluble in water and readily adsorbed [9]. 2. Experimental 2.1 Materials hydrophilic or lipophilic, determined by calculating values for the different regions of the molecule. 2-butanol was used as dissolvent. The salinity is denoted for the salt concentration of the extra adding of sodium carbonate. Table 1- Characteristics and constituents of oils used. Oil A Oil B Oil C Origin Algeria Colombia Nigeria The surfactant used in this study was the LAB C14-C18 figure 1. CH 3 H 3 C n=14-18 API degrees ( C) Saturated (%) Aromatic (%) Resins Asphaltenes SO 3 - Na + Figure 1 - Structure of LAB C14-C Measurement of the critical micelle concentration (CMC) The critical micelle concentration is defined Kaolinite and sand were used as adsorbents for the adsorptions measurements. The crude oils used to measure the interfacial tension between the oil and the aqueous solutions of LAB C14-C18 are showed in Table 1. The co-surfactants were the Neodol 23-1, Neodol 91-8, Neodol 45-7 and Brij 35. These co-surfactants have different hydrophilic-lipophilic values (HLB). The hydrophilic-lipophilic balance of a surfactant is a measure of the degree to which it is as the concentration of surfactants above which micelles form and almost all additional surfactants added to the system turn into micelles. Two other properties of surfactants related to the CMC are effectiveness and efficiency. The efficiency of a surfactant shows how easy is to reduce the tension using this surfactant and effectiveness corresponds to the minimum value obtained of interfacial tension [10]. The critical micelle concentration was measured by the method of Du Nuoy ring using a tensiometer TE3 LAUDA and a 5000 ppm solution. In this method, there is

4 a ring on a surface of a liquid and the force required to separate the ring from the surface is measured. We should ensure that the ring is completely wet for reproducible and meaningful results. It is a simple, fast and high accuracy method [11]. measured with a Spinning Drop Tensiometer where the interfacial tension is calculated by equation 2: 2 ( 2) R (2) Where 1 and 2 are the densities of the 2.3 Measurement of the adsorption with the carbon analyser (TOC) The adsorption of LAB C14-C18 surfactant was measured using sand and kaolinite as adsorbents. Were prepared test tubes with 3g of sand and 10 ml of 500, 1000, 2000, 3000, 4000, 4500 and 5000 ppm of surfactant solutions. The test tubes were put in an oven for 48 hours. Were prepared test tubes with 1g of kaolinite and 10 ml of 59.6, 770, 1774, 2699, 3764, 4852 and 6000 ppm of surfactant solutions. After 48 hours was measured the concentration of these solutions using a carbon analyzer and was calculated the amount adsorbed. From these values were obtained the adsorption isotherms of LAB C14-C Measurement of interfacial tension The interfacial tension was measured using solutions of 5000 ppm concentration of LAB C14-C18 with 2-butanol and the various cosurfactants. Was measured the interfacial tension between these solutions and the oils A, B and C oil from Algeria, Colombia and Nigeria, respectively. These solutions were prepared with different amounts of Na 2 CO 3 in order to find the optimum alkalinity for which the interfacial tension is minimal. Interfacial tensions were phases, the angular velocity and R the radio of the drop [8]. 2.5 Microemulsions The preparation of the microemulsions involved 2.5 ml of A oil and 2.5 ml of surfactant solutions with 2-butanol and the various types of co-surfactants in sealed pipettes. Subsequently the pipettes were put in an oven at 50 C for approximately 24 hours. 3. Results and Discussion 3.1 Measurement of the critical micelle concentration (CMC) Figure 2 shows the results obtained in measuring the CMC of LAB C14-C18 surfactant.

5 ultra-low superficial tension using the LAB C14-C18 surfactant. 3.2 Measurement of the adsorption with the carbon analyser (TOC) Figure 2- Determination of CMC of the LAB C14-C18 surfactant. In zone I surface tension decreases with increasing concentration of surfactant. Most of the surfactant molecules adsorb on the surface water - air and the concentration decreases rapidly (I). In zone II the surface is saturated and the surfactant molecules added should be solubilized in the aqueous phase. In zone III the surface tension remains constant. In this region the solubilization occurs in the form of micelles. The transition between zone II and zone III corresponds to the value of critical micelle concentration. The CMC, effectiveness and efficiency values obtained are shown in Table 2 Surfactant LAB C14- C18 Table 2- Values obtained by CMC measurement. CMC (mmol/l) Effectiveness (mn/m) Efficiency (mmol/l) Low CMC values correspond to effective surfactants. Low values of effectiveness and efficiency lead to a more active surfactant meaning that it is easy to obtain Figure 3 presents the results of adsorption of the LAB C14-C18 surfactant in kaolinite and sand. Figure 3- Adsorption isotherms of the LAB C14- C18 in kaolinite and sand. The amount of adsorption is higher when kaolinite was used. Using this type of adsorbent the adsorption capacity is approximately 3 mg adsorbed / g kaolinite while sand presents an adsorption capacity of about mg adsorbed / g sand. 3.3 Measurement of interfacial tension Figures 4, 5 and 6 present for the different oils (A, B and C), the comparison of interfacial tension of the LAB C14-C18 surfactant without using co-surfactant, only using 2-butanol as a solvent, and using different co-surfactants.

6 Table 3- Interfacial tension and optimum alkalinity values observed for the three types of oils, using LAB C14-C18 with the various cosurfactants. Oil A Figure 4- Interfacial tension of the LAB C14-C18 with the various co-surfactants and A oil. Interfacial Tension (mn/m) Optimum Alkalinity (g/l) 2- butanol Neodol 23-1 Neodol 45-7 Neodol 91-8 Brij Oil B Interfacial Tension (mn/m) Optimum Alkalinity (g/l) Oil C Figure 5- Interfacial tension of the LAB C14-C18 with the various co-surfactants and B oil. Interfacial Tension (mn/m) Optimum Alkalinity (g/l) Figure 6- Interfacial tension of the LAB C14-C18 with the various co-surfactants and C oil. Table 3 summarizes the values of interfacial tension obtained with the various types of oil. From the analyses of figures and data of Table 3, it is possible to verify that the different types of co-surfactants used cause changes in the values of interfacial tension and especially in the great value of alkalinity when compared with the values only with 2-butanol. This is mainly due to the HLB value of each co-surfactant. The use of co-surfactant Neodol 23-1 leads to a decrease of the optimum alkalinity because its HLB value is quite low. If the value of hydrophilic-lipophilic balance is high the

7 substance is more hydrophilic. In this case this value is low and the solution does not allow large concentrations of Na2CO3 because this co-surfactant is poorly soluble in water and slightly resistant to alkalinity. On the other hand, Brij 35 presents the highest HLB value and this is reflected in the highest alkalinities obtained with the three types of oil. Moreover, this is the cosurfactant that produces lower values of interfacial tension. 3.4 Microemulsions The microemulsions are nominated type I or type O/W (oil/water) when all the surfactant is at the bottom of the pipette and it is dissolved in water. On the other hand, Type II or type W/O (water/oil) corresponds to a situation in which all the surfactant is in the upper zone of the pipettes dissolved in oil. In type III microemulsions part of a surfactant is solubilized by water and partly by oil. Table 4 compares the results of optimum alkalinity obtained with the Spinning Drop Tensiometer and with the formation of microemulsions. Tabela 4- Results of optimum alkalinity obtained with the Tensiometer and the formation of microemulsions. LAB C14-C18+2- butanol LAB C14- C18+Neodol 45-7 LAB C14- C18+Neodol 91-8 LAB C14-C18+Brij 35 Optimum alkalinity obtained by the Spinning Drop Tensiometer The measuring of interfacial tension with the Spinning Drop Tensiometer gives the values of ultra low interfacial tension and its optimum alkalinity. So, it is possible to know that, theoretically, the formation of microemulsions occurs at the optimum alkalinity obtained in this method because optimum alkalinity corresponds to the lower interfacial tension values which favors the microemulsions formation. The optimum alkalinity obtained with the Spinning Drop Tensiometer and microemulsions formation should be the same. From table 4 it appears that the expected results are not fulfilled. In the case of microemulsions formed with 2-butanol and the co-surfactant Brij 35 optimum alkalinity is higher than the obtained with the Spinning Drop Tensiometer because to better observe the microemulsion were prepared solutions to 10000ppm, while for measuring with the Spinning Drop Tensiometer were prepared solutions to 5000ppm. On the other hand, Optimum alkalinity obtained by microemulsions formation

8 the oil contains some acids in its constitution and some Na 2 CO 3 is used to neutralize these acids. For the microemulsions formed with the LAB C14- C18 using as co-surfactants Neodol 45-7 and Neodol 91-8 occurs the opposite, alkalinity optimum occurs at a lower concentration. Some authors [7] have conducted studies that indicate that some surfactants exhibit variations in the interfacial tension over a period of time. Period in which the interfacial tension can decrease or increase and where there is a time that corresponds to the ultra low interfacial tension. This suggests that the measurement of interfacial tension with the Spinning Drop Tensiometer was not made at the time corresponding to the ultra low interfacial tension, and therefore, the microemulsions formed at optimum alkalinity values lower. minimizing the loss of surfactant by adsorption processes, and delivers ultralow interfacial tensions. 4. Conclusions LAB C14-C18 surfactant is interesting for application in processes of enhanced oil recovery especially in oil with a structure similar to oil A. This surfactant has a low efficiency value, adsorbs little, thus

9 References [1] Showell, Michael e Francis, Taylor. Handbook of Detergents. Part D: Formulation. Volume 128. [2] Meyers, D. (1988), Surfactant Science and Technology, 20ª edição., VCH Publishers, Inc. New York. [3] Rosen, M. J. (1989), Surfactants and interfacial phenomena, John Wiley & Sons, New York 2ª edição. [4] Seminário Recursos Energéticos Do Brasil: Petróleo, gás, urânio e carvão. Rio de Janeiro 30 de setembro de Clube de Engenharia. [5] M. Baviére. Basic Concepts in Enhanced Oil Recovery Processes. Published for SCI by Elsevier Applied Science. London and New York. [6] Lv, Weifeng, Bazin, Brigitte, Desheng, Ma, Liu, Qingjie, Han, Don, Langyun, Static and Dynamic Adsorption of Anionic and Amphoteric Surfactants with or without presence of Alkali, Journal of Petroleum Science and Engineering (2011, 21 Março) [7] Zhongkui Zhao, Chenguang Bi, Weihong Qiao, Zongshi Li, Lubo Cheng (2006). Dynamic interfacial tension behavior of the novel surfactant solutions and Daqing crude oil. Colloids and Surfaces A: Physicochem. Eng. Aspects 294 (2007) [8] Salager, Jean-Louis (2005). Recuperación Mejorada del Petroleo. Laboratorio de Formulacion, Interfases Reologia y Procesos. Universidade de Los Andes, Mérida Venezuela. [9] E. Raquel e Salager, Jean-Louis (2005). Tensión Interfacial. Laboratorio de Formulacion, Interfases Reologia y Procesos. Universidade de Los Andes, Mérida Venezuela. [10] Salager, Jean-Louis (1993). Surfactants en Solucion Acuosa. Laboratorio de Formulacion, Interfases Reologia y Procesos. Universidade de Los Andes, Mérida Venezuela. [11] C.C.V. Chan, J. A. W. Elliott, and M.C. Williams (2002). Investigation of the dependence of inferred interfacial tension on rotation rate in a spinning drop tensiometer. Journal of Colloid and Interface Science 260 (2003)