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Synthetic-based aphrons: Correlation between properties and filtrate reduction performance
Colloids and Surfaces A: Physicochem. Eng. Aspects 353 (2010) 57–63
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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Synthetic-based aphrons: Correlation between properties and filtrate reduction performance Luciana S. Spinelli a,∗ , Genecy R. Neto a , Layla F.A. Freire a , Vitor Monteiro b , Rosana Lomba b , Ricardo Michel a , Elizabete Lucas a a b
Federal University of Rio de Janeiro, Institute of Macromolecules, Technology Center, Bloco J, Ilha do Fundão, P.O. Box 68525, Rio de Janeiro, Brazil Petrobras Research Center (CENPES), Ilha do Fundão, Quadra 9, Rio de Janeiro, Brazil
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Article history: Received 17 April 2009 Received in revised form 1 October 2009 Accepted 18 October 2009 Available online 24 October 2009 Keywords: Aphrons Microbubbles Surfactants Microscopy Size distribution Filtrate reduction
a b s t r a c t Aphrons fluids, because of their “noninvasive” characteristic, are indicated for drilling zones that have multiple intercalations of depleted formations adjacent to formations that require high-density fluids. Aphrons are colloidal dispersions containing microbubbles, with cores of gas, liquid or emulsion ranging from 10 to 100 m in diameter, that are highly stable due to their high interfacial area and multiple surrounding surfactant layers. This paper presents results of physical–chemical properties, bubble size distribution and filtration of systems containing microbubbles. The aphrons were generated by applying a pressure differential under a high-pressure high-temperature (HPHT) filtration cell. Tests were also run with different types of surfactants, specific for generation of bubbles in an organic medium (ester). The surfactants were analyzed for their surface tension and the dispersions produced were photographed under an optical microscope at 60× magnification. The images obtained were digitized to enable determination of the bubble size distribution using an ImageJ program. The filtrate reduction performance of these fluids was determined by static filtration in synthetic porous media. There was a correlation between the filtration characteristics of the fluids, the bubble size distribution and number of bubbles produced in each base and for each surfactant tested. The results obtained served as a reference to formulate a light, non-water-based drilling fluid containing microbubbles with “noninvasive” characteristics. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Dispersions are mixtures in which a substance spreads out (dispersed phase) in the bulk of another substance (continuous phase). The high interfacial area created between the phases in dispersion permits a rapid transfer of the components from one phase to the other, as occurs for example in gas–liquid and liquid–liquid reaction systems, solvent extraction, flotation, etc. These processes are present in a wide range of industries [1]. Sebba [2] in 1987 defined aphrons as colloidal dispersions containing microbubbles of 10–100 m in diameter, whose cores can be composed on a gas, liquid or emulsion encapsulated by various layers of surfactants. According to Sebba, when the encapsulated phase is a gas, these structures are called colloidal gas aphrons (CGA). Likewise, when the encapsulated core is a liquid, normally oil, they are called colloidal liquid aphrons (CLA). Finally, microbubbles with cores formed of a water–oil emulsion are called colloidal emulsion aphrons (CEA) [2–4]. ∗ Corresponding author. Tel.: +55 21 2562 8266; fax: +55 21 2562 7209. E-mail addresses: [email protected] (L.S. Spinelli), [email protected] (V. Monteiro). 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.10.017
Colloidal gas aphrons are dispersions of microbubbles and differ from regular foams not only regarding their geometric structure, but also in terms of their rheological properties. Normal foams are essentially gas–liquid–gas systems where fine liquid lamellae encircle polyhedral structures that in turn encapsulate the gas phase. Microfoams (aphrons) have much higher liquid phase content around the gas phase and are characterized by tiny and practically spherical bubbles [5]. In general, aphrons are formed by stirring a surfactant solution at a velocity of between 5000 and 10,000 rpm. However, they can also be formed by the action of a pressure difference in a highpressure high-temperature (HPHT) filter press [6]. The surfactants used can be ionic (cationic or anionic) as well as nonionic [2,7–9]. It is important to describe the arrangement of the surfactant molecules in the structure of aphrons. The innermost layer contains surfactants whose hydrophobic groups are inside the core and hydrophilic groups that are outside it. The external layer (protective layer) has surfactants whose hydrophobic and hydrophilic groups are arranged in the opposite order [2–4]. Despite a number of published studies, there is no conclusive evidence on their structure. However, the theory on aphrons is based mainly on the stability of these systems. The electrostatic
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repulsion when ionic surfactants are used and the steric repulsion when nonionic ones are used contribute to the stability of aphrons, which can be influenced by various parameters, such as the surfactant type and concentration and stirring time and speed, among others [2,8,10,11]. The covering of the microbubbles by various surfactant monolayers retards their coalescence by reducing the moment of shock caused by the collision of the microbubbles [5]. Better knowledge of the structure of aphrons, such as the number of surfactant layers and thicknesses of the interfaces, would be of great value to optimize them for various processes. Despite the relative lack of knowledge about the structure of the stabilization mechanism of dispersions, aphrons have excellent properties, such as large interfacial area in relation to volume, high stability, flow properties similar to those of water (CGA, for example, can be easily pumped from one place to another without collapsing) and significant cost advantages in various uses [8,10,12–14]. Because of these properties, aphrons have found applications in many areas. Most studies have focused on techniques of effective separation for recovery of substances of high aggregate value and also on investigation of the effects of operational parameters on their separation performance [12]. 1.1. Drilling fluids Drilling fluids containing aphrons in an aqueous medium have already been used in oilfields. The aphrons are generally incorporated in the drilling fluid at the surface, using conventional fluid mixing equipment. However, it is believed that at shallow depths, they can be directly incorporated at the drill bit [15]. The potential of aphrons as components of drilling fluids rests in their ability to reduce the invasion of the fluid in the rock and to minimize the damages to the formation, due to their high power to seal off depleted zones [16]. When aphrons penetrate the depleted zone, the pressure differential between their internal and the external medium causes them to expand, favoring the aggregation of bubbles. This results in a micro-environment of bubbles that seal off the depleted formation. This generates enough energy to prevent the invasion of fluids, or filtrate, into the depleted zone. Besides this, there is no formation of filter cake, which reduces the instances when drilling equipment gets stuck in the well and also mitigates corrosion problems [16]. For aphrons to be used in drilling fluids, they need to have a certain degree of stability. For this reason, the encapsulating film must have certain properties: (1) the film must not be too thin, otherwise it will tend to break under pressure; and (2) the protective layer must have a minimum viscosity. The water molecules tend to diffuse outside the film and inside the liquid solution, which contributes to destabilize the film. However, the transfer rate of the water from the film is inversely proportional to the viscosity. Consequently, viscosifiers are generally added, such as a biopolymer, which are incorporated into the structure of the aphrons [16,17]. 2. Experimental The surfactants used in this study to produce aphrons dispersions in an ester base were: a. commercials nonionic polymeric fluorochemical surfactants NOVEC FC-4432 and NOVEC FC-4430 (3 M do Brazil); b. poly(ethylene oxide)—poly(propylene oxide) (PEO-PPO) block copolymers called L7 and L10 with different number of units of ethylene oxide (EO) and propylene oxide (PO), as shown in Fig. 1 (donated by Oxiteno);
c. two surfactants produced in the laboratory by saponification reactions using a commercial ester as reagent. The fluids were mixed with organophilic clay (that has particle size lower than 10 m) and two viscosifier additives, Versa and Liovac 419. The first of these additives has already been used in drilling fluid formulations, while the second, an ester-based viscosifier, was donated by Miracema-Nuodex. The organic phase utilized, based on synthetic ester obtained from vegetable fatty acid utilized, was commercial Ultralub 5391 (from Oxiteno). The surfactants synthesized in the laboratory were obtained by reaction under reflux in a round-bottom flask containing a 1:1:1 mixture of ester: ethanol: 30 wt% KOH solution. The reflux was performed for 30 min at 353 K, after which the system was cooled to room temperature and then an aliquot was used in liquid form as a non-precipitated surfactant (NPS) and another was dried at room temperature for 65 h until it became pasty, that was called dry surfactant (DS). 2.1. Evaluating the surfactants’ surface tension According to another article by our laboratory group [6], surfactants that generate aphrons must be used at concentrations above the critical micelle concentration (CMC). Therefore, the water soluble surfactants used were evaluated regarding surface tension in function of the concentration to obtain the CMC and determine the minimal concentration of each surfactant used in fluids preparation (called for us standard concentration—std.conc.). This is defined as being a concentration greater than the CMC. The measurements were made in a Krüss K10ST digital tensiometer, at room temperature, that uses the ring method in your measurements. The surfactant solution concentration was dependent of each surfactant behavior. 2.2. Preparation of the fluids The fluids were prepared by mixing the organic phase at different concentrations of organophilic clay and viscosifiers (Versa and Liovac 419) in a Hamilton Beach blender. Then the fluid was aged in a heat-controlled shaker for 8 h at 338 K. This formulation is a base for drilling fluids. We produced two types of fluids, one containing a 95:5 ratio of ester:water and the other without water. The microbubbles were incorporated in the base drilling fluid by quickly mixing the recently prepared base fluids with the specific surfactants also in a Hamilton Beach blender, and then passing this mixture through a HPHT filter press, without a filter element, under a pressure differential of 1380 kPa. The surfactants were used at different concentrations, varying of standard concentration (std.conc.) to 5, 10, 20 and 30 times of this value. 2.3. Characterization of the fluids The base fluids were characterized as to viscosity in a Fann 35A viscosimeter, to obtain Fann readings, in specific angular velocity, within the recommended range for drilling fluids. The fluids prepared containing microbubbles (aphrons) were characterized as to bubble size distribution and average size under an optical Olympus SZH10 Research Stereo microscope at 60× magnification. The documentation photos were taken with a Nikon Coolpix 5400 digital camera and the images were processed using the Image J. program coupled to the “AnalyzeParticles” tool. The graphs were plotted with the aid of the LabPlot program, by counting the microbubbles in a specific area unit as described in the literature for similar programs [6]. To obtain more images of each batch of aphrons produced, we made observations under an optical microscope while positioning
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Fig. 1. Structures of PEO–PPO block copolymers.
the slide in three different positions, and from these images we plotted three size distribution graphs for each of the images individually and one graph for the mean of the three images. Each batch was made in triplicate to observe the repeatability in producing aphrons. The stability of these systems was evaluated by observing the bubbles number and the bubbles size changing in function of time: 1, 2 and 24 h. The density of the fluids and aphrons was obtained by use of a mud balance (in kg/m3 ). 2.4. Performance test of the aphrons on filtrate reduction The aphrons’ performance as filtrate-reducing elements was tested through a procedure adapted from the Petrobras N-2607 standard [18]. First the ceramic filtration disks were saturated in an organic medium (ester) to remove the air present in the disks’ pores. Then, to normalize the results, the base organic medium (ester) was passed through the HPHT filtration cell containing disks with pore size of 10 m and permeability of 950 mD, under a pressure differential of 690 kPa, and the mass was evaluated as a function of time. This procedure was due to the fact the ceramic disks, although they have the same permeability according to the manufacturer, may or may not have precisely the same pore distribution. The test itself consisted of passing the base fluid and aphrons through the filtration cell containing the ceramic filtration disk saturated with ester, also under a pressure differential of 690 kPa. The fluid mass expelled from the filter press per unit of time was then evaluated.
DS) were not evaluated, because in preliminary tests they did not promote the formation of microbubbles. Only for the FC-4432 and FC-4430 surfactants (Fig. 2) was it possible, from the discontinuity in the curve, to obtain CMC values (≈2 kg/m3 for FC-4432 and ≈0.7 kg/m3 for FC-4430). The CMC values of the other two surfactants (Fig. 3) could not be determined because they presented different behavior of surface action than the majority ones in which it was not possible to ascertain whether the discontinuities were related to the formation of micelles. For example, in the surface tension graph of the L10 surfactant, two changes in slope can be observed: one a small reduction of tension at around 50 mN/m, which then remains constant until a concentration of 0.3 kg/m3 , followed by another reduction of tension. It is not possible to state whether the first or second discontinuity is related to the formation of micelles. The behavior of the surfactant L10 is related with their structure, as published before [19]. In relation to NPS, this behavior is probably due to the presence of small amount of impurities from the preparation process of this surfactant in the lab. Based on the CMC values obtained, we set the standard concentration used for the fluorated surfactants above this value: for FC-4432 it was 3 kg/m3 and for FC-4430 it was 1 kg/m3 . For the other two surfactants, L10 and NPS, we set the standard concentration at 1 kg/m3 .
3.2. Evaluation of the viscosity of the base fluids
Figs. 2 and 3 show the curves of the surface tension versus the logarithm of the concentration of four of the surfactants: Novec FC4432, Novec FC-4430, NPS and L10. The other surfactants (L7 and
The ester-based fluids produced in our laboratory were obtained by varying the concentration of organophilic clay, Versa and Liovac 419. The fluids’ viscosity was measured using a Fann viscosimeter after they remained in a shaker bath for approximately 8 h (fluid aging). Two test fluids were also aged in a roller oven to compare their viscosities with those of the other fluids, of the same formulation, that were aged in a shaker bath, to confirm whether aging in a shaker bath is compatible and can be used in place of a roller oven, the device normally employed to age drilling fluids by Petrobras.
Fig. 2. Evaluation of surface tension of FC-4432 and FC-4430 surfactants.
Fig. 3. Evaluation of surface tension of NPS and L10 surfactants.
3. Results 3.1. Evaluation of the surface tension of the surfactants
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L.S. Spinelli et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 353 (2010) 57–63 Table 2 Composition of ester/water in 95:5 rate-based fluid and results of Fann readings.
Table 1 Composition of pure ester-based fluids and results of Fann readings. Fluid
Clay concentration (kg/m3 of ester)
Versa concentrationa
1 2b 3 4 5 6 7 8 9 10
60 60 120 80 40 60 40 80 90 90
0.074 – 0.075 – – 0.075 0.075 0.075 – 0.075
a b
Fann readings 600 rpm
3 rpm
43 108 140 83 27 42 32 78 94 97
8 14 64 23 3 5 4 21 30 30
Versa volume per ester volume. Fluid 2 also contain 1.3 kg per ester volume (m3 ).
Table 1 shows the compositions of the base fluids produced, together with the Fann readings obtained at 600 and 3 rpm (maximum and minimum speeds of a Fann viscosimeter). These values were compared with the viscosity range normally observed for common drilling fluids at CENPES/Petrobras: for 600 rpm, the readings were in the range of 130–100 and for 3 rpm they were between 21 and 13. Of all the fluids prepared, only fluids 2 and 8 had Fann readings within the range recommended for drilling fluids. Nevertheless, we only chose formulation 8 for use in the next tests for production of aphrons. We decided not to use Liovac 419 because it is a very viscous additive that is hard to handle and not commonly used in drilling fluids. Fluids 1 and 2 which were also aged in the roller oven had Fann readings in the same range as those aged in the shaker bath. This indicates that the shaker bath satisfactorily simulates the action of a roller oven in aging drilling fluids. The clay concentration in formulation 8 is considerably high (80 kg/m3 ), producing fluids with a very large quantity of solids, which can impair their use when passing through porous disks. Therefore, with starting from formulation we tried to reduce the clay concentration and keep the viscosity within the desired range. To do this, we added a small concentration of water to the ester in an ester:water ratio of 95:5, while maintaining the concentration of Versa and decreasing that of clay according to Table 2. The only fluid that presented values within the recommended range was fluid 13 (with 52 kg/m3 ). So we used the formulations 8 and 13 to produce aphrons with different surfactant types and concentrations.
Fluid
Clay concentration (kg/m3 of ester)
Versa concentrationa
11 12 13 14
60 56 52 40
0.075 0.075 0.075 0.075
a
Fann readings 600 rpm
3 rpm
119 110 94 49
26 25 23 5
Versa volume per ester volume.
3.3. Evaluation of the density of aphrons produced Aphrons were produced using a pure ester medium and a emulsion ester:water 95:5 medium, varying the type and concentration of surfactant. In the both cases, densities varies between 720 and 841 (kg/m3 ), characterizing a light non-water-based drilling fluids. 3.4. Size distribution and average size of the microbubbles In an attempt to obtain aphrons in a pure ester medium (without water), we observed foams (with relatively large bubbles) formed at the fluid surface, when using Novec FC-4430, Novec FC-4432 and L10 as surfactants, even when using viscosifying additives. Fig. 4 shows the example of large bubbles formed at the fluid surface using a L10 as a surfactant. With the use of the other surfactants, L7, DS and NPS, no bubbles were formed. In an attempt to obtain incorporated bubbles inside the liquid fluid we have done a previous treatment of the fluid, while maintaining it in the shaker bath for at least 8 h at a temperature of 338 K. To do this, we prepared two types of aphron fluids utilizing Novec FC-4430 as the surfactant at a concentration of 10 kg/m3 : (1) containing only clay, at a concentration of 60 kg/m3 ; and (2) containing clay at this same concentration along with Versa. In these tests we managed to obtain bubbles inside the fluid (able to be analyzed for size and size distribution) (Figs. 5 and 6, respectively). The addition of Versa caused an increase in the number of microbubbles produced and a reduction in their size (from 90 to 61 m). It can also be observed, by the bubble number against diameter curve profile, a decreasing of the bubble size distribution for the systems containing Versa. Since it would not be possible to show all micrographs and the respective bubble number against diameter curves, it will be assumed that the difference between the higher and lower sizes represents the size distribution in terms of distribution width (very small amounts of bubbles were not considered).
Fig. 4. Ester-based aphrons with L10 (at 10 kg/m3 ) and organophilic clay: (a) general aspect of becker system and (b) image of foam formed at the fluid surface.
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Fig. 5. Ester-based aphrons with Novec FC4430 (at 10 kg/m3 ) and organophilic clay: (a) image of microbubbles treated by Image J. and (b) size distribution of bubbles with number and average size data.
Fig. 6. Ester-based aphrons with Novec FC4430 (at 10 kg/m3 ), organophilic clay and Versa: (a) image of microbubbles treated by Image J. and (b) size distribution of bubbles with number and average size data.
Nevertheless, this type of fluid did not present in the Fann readings range (read with Fann viscosimeter) commonly found in drilling fluids, according to 3.2 item. Therefore, we produced aphrons with fluid 8, using Novec FC-4430 at 10 kg/m3 of concentration, where the average bubble size increased from 61 to 130 m. On the other hand, the aphron fluids prepared using a emulsion ester:water 95:5 medium with a smaller concentration of organophilic clay, fluid 13, had sizes varying from 60 to 80 m, depending on the type and concentration of surfactant used to produce the aphrons, presenting a size range lower than that produced with a pure ester medium. In terms of stability, aphrons produced with ester:water 95:5 emulsion were constituted of bubbles that increased their size extremely fast, indicating low stability. On the other hand, aphrons based on pure ester presented a slow bubble size increasing, and bubble breaking was only observed after 24 h.
tion (std.conc.) for each type of surfactant (such as in L10 [std.conc.] and L10 [5 × std.conc.]). In this test it can be seen that the use of the L10 (poly(ethylene oxide)–poly(propylene oxide) block copolymer) to generate aphrons led to the formation of structures capable of significantly
3.5. Performance of the aphrons in filtrate reduction We tested fluid 8 as a filtrate reducer, but the filter element retained a large volume of solids, which made it impossible to conclude the test due to the very large quantity of clay. We then tested only fluid 13 with different surfactant types and concentrations. Fig. 7 shows the results obtained in the filtrate reduction tests for all the aphrons fluids prepared with the fluid 13. The legend summarizes the surfactant and concentration used to prepare the aphrons as being the product of a value and a standard concentra-
Fig. 7. Graph of normalized rate of base fluid and aphrons passing by 10 m filter element in function of time.
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Table 3 Results of number, average size, size distributiona and normalized rates at two times: 10 and 45 s.
Base fluid NPS [std.conc.] NPS [5 × std.conc.] NPS [10 × std.conc.] NPS [20 × std.conc.] NPS [30 × std.conc.] L10 [std.conc.] L10 [5 × std.conc.] L10 [10 × std.conc.] L10 [20 × std.conc.] L10 [30 × std.conc.] N30 [std.conc.] N30 [10 × std.conc.] N32 [std.conc.] a
Number of bubbles
Average size (m)
Size distribution (m)a
– 274 561 534 491 838 186 258 213 372 341 270 346 465
– 86.8 62.6 59.1 68.1 62.6 85.2 78.9 72.3 62.5 66.5 87.7 65.2 70.2
– 200 160 190 200 190 180 190 160 170 190 190 200 190
Rate at 10 s 0.48 0.46 0.39 0.37 0.37 0.38 0.26 0.19 0.37 – 0.43 0.37 0.64 0.39
Rate at 45 s 0.32 0.45 0.26 0.27 0.27 0.29 0.20 0.17 0.28 – 0.32 0.27 0.22 0.17
Difference between the higher and lower microbubbles size.
reducing the filtrate in relation to the fluid, at concentrations of L10 [std.conc.] and L10 [5 × std.conc.]. As the concentration increased, the filtrate reduction rates decreased and were comparable with the filtrate reduction of aphrons produced with the surfactant prepared in the laboratory from ester at concentrations of NPS [10 × std.conc.] and NPS [20 × std.conc.]. For this reason, we believe there is an optimal concentration for use of each surfactant to generate aphrons. The behavior of the block copolymer is due to the fact it has alternating blocks of hydrophobic and hydrophilic chains, which is different than the structure of all the other surfactants used. Both the fluorated surfactants and the NPS have a structure with polar segments (ionic or nonionic) linked directly to a large hydrophobic segment composed of a hydrocarbon chain. The differentiated structure of L10 favors its low solubility in water and great affinity for ester, factors that may be behind the formation of more stable bubbles. There was a correlation between the properties of the aphrons produced and their action as filtrate-reducing agents (Table 3). An increase in the number of bubbles and a reduction in their size made them more efficient in reducing the filtrate in the sample. This occurred when there was a fivefold increase above the standard surfactant concentration for the same surfactant. Besides this, the greater the surfactant concentration, mainly starting at ten times the standard level, the narrower the bubble size distribution the lower the filtrate reduction efficiency. Based on these last results, we can suggest evaluating aphrons prepared with surfactants of the same family (PEO-PPO block copolymers with alternating hydrophilic and hydrophobic groups) and varying the number of oxide propylene oxide units for the purpose of increasing the aphrons’ efficiency in controlling the invasion of fluids even more. An interesting fact is that this type of surfactant is already being used in the petroleum industry in areas such as demulsification and flocculation and could also gain space for production of aphron systems to enhance the performance of drilling fluids. Besides this, the change of the aqueous phase of the emulsion system to brine would be interesting to evaluate the effect of the presence of salts on the efficiency of aphrons production and filtrate reduction. 4. Conclusions The use of HPHT filtration cell with controlled pressure was efficient to prepare aphrons structures, which were confirmed by visual appearance, optical microscopy and particle size. The variation of surfactant type and concentration produced systems having different characteristics in terms of microbubbles amount per area unit, size and size distribution. Microbubbles hav-
ing small sizes, high quantity and wide size distribution produced aphrons more efficient in reducing the filtrate. A filtrate reduction efficiency of 60% was obtained using a CH3 –PEO–PPO–OH block copolymer at relatively low concentrations which was used as a reference to formulate a light, non-water-based drilling fluid containing microbubbles with “noninvasive” characteristics. Acknowledgments The authors acknowledge the financial support of the Coordinating Office for Improvement of University Researchers (CAPES), the National Council for Scientific and Technological Research (CNPq) and the National Petroleum Agency/Office to Finance Studies and Projects/Oil and Natural Gas Sector Fund (ANP/FINEP/CTPETRO), besides Oxiteno do Brasil, 3M do Brasil and Miracema-Nuodex for supplies some surfactants, organic medium (ester) and viscosifier. References [1] R.B. Worden, A.B. Scranton, Method for forming reversible colloidal gas or liquid aphrons and compositions produced, PI 6022727, 2000. [2] F. Sebba, Foams and biliquid foams-aphrons. Wiley, Chichester, 1987 (chap.5). In: P. Jauregi, S. Gilmour, J. Varley, Characterization of colloidal gas aphrons for subsequent use for protein recovery, Chem. Eng. J. 65 (1997) 1–11. [3] G.J. Lye, D.C. Stuckey, Structure and stability of colloidal liquid aphrons, Colloids Surf. A 131 (1998) 119–136. [4] T. Deng, Y. Dai, J. Wang, A new kind of dispersion—colloidal emulsion aphrons, Colloids Surf. A 266 (2005) 97–105. [5] R.C.G. Oliveira, Remediac¸ão de Subsolos Contaminados por Compostos Orgânicos a partir da Injec¸ão de Soluc¸ões de Surfatantes e de Espumas, Doctoral thesis—Postgraduate Program in Engineering, Federal University of Rio de Janeiro, Brazil, 2004. [6] L.S. Spinelli, A. Bezerra, A. Aquino, E.F. Lucas, V. Monteiro, R. Lomba, R.C. Michel, Composition, size distribution and characteristics of aphron dispersions, Macromol. Symp. 295 (2006) 243–249. [7] P. Jauregi, J. Varley, Colloidal gas aphrons: potential applications in biotechnology, Trends Biotechnol. 17 (1999) 389–395. [8] T. Deng, Stabilization and characterization of colloidal gas aphrons dispersion, J. Colloid Interface Sci. 261 (2003) 360–365. [9] E.H.A. Mansur, Y. Wang, Y. Dai, Removal of suspension of fine particles from water by colloidal gas aphrons (CGA), Sep. Purif. Technol. 48 (2006) 71– 77. [10] R.W. Alves, Extrac¸ão de corantes de urucum por processos adsortivos utilizando argilas convencionais e colloidal gas aphrons, Doctoral thesis—Postgraduate Program in Engineering, Federal University of Santa Catarina, Brazil, 2005. [11] H. Tseng, L. Pilon, G.R. Warrier, Rheology and convective heat transfer of colloidal gas aphrons in horizontal mini-channels, Int. J. Heat Fluid Flow 27 (2006) 298–310. [12] P. Jauregi, S. Gilmour, J. Varley, Characterization of colloidal gas aphrons for subsequent use for protein recovery, Chem. Eng. J. 65 (1997) 1–11. [13] M. Noble, A. Brown, P. Jauregi, A. Kaul, J. Varley, Protein recovery using gas–liquid dispersions, J. Chromatogr. B 711 (1998) 31–43.
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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Synthetic-based aphrons: Correlation between properties and filtrate reduction performance Luciana S. Spinelli a,∗ , Genecy R. Neto a , Layla F.A. Freire a , Vitor Monteiro b , Rosana Lomba b , Ricardo Michel a , Elizabete Lucas a a b
Federal University of Rio de Janeiro, Institute of Macromolecules, Technology Center, Bloco J, Ilha do Fundão, P.O. Box 68525, Rio de Janeiro, Brazil Petrobras Research Center (CENPES), Ilha do Fundão, Quadra 9, Rio de Janeiro, Brazil
a r t i c l e
i n f o
Article history: Received 17 April 2009 Received in revised form 1 October 2009 Accepted 18 October 2009 Available online 24 October 2009 Keywords: Aphrons Microbubbles Surfactants Microscopy Size distribution Filtrate reduction
a b s t r a c t Aphrons fluids, because of their “noninvasive” characteristic, are indicated for drilling zones that have multiple intercalations of depleted formations adjacent to formations that require high-density fluids. Aphrons are colloidal dispersions containing microbubbles, with cores of gas, liquid or emulsion ranging from 10 to 100 m in diameter, that are highly stable due to their high interfacial area and multiple surrounding surfactant layers. This paper presents results of physical–chemical properties, bubble size distribution and filtration of systems containing microbubbles. The aphrons were generated by applying a pressure differential under a high-pressure high-temperature (HPHT) filtration cell. Tests were also run with different types of surfactants, specific for generation of bubbles in an organic medium (ester). The surfactants were analyzed for their surface tension and the dispersions produced were photographed under an optical microscope at 60× magnification. The images obtained were digitized to enable determination of the bubble size distribution using an ImageJ program. The filtrate reduction performance of these fluids was determined by static filtration in synthetic porous media. There was a correlation between the filtration characteristics of the fluids, the bubble size distribution and number of bubbles produced in each base and for each surfactant tested. The results obtained served as a reference to formulate a light, non-water-based drilling fluid containing microbubbles with “noninvasive” characteristics. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Dispersions are mixtures in which a substance spreads out (dispersed phase) in the bulk of another substance (continuous phase). The high interfacial area created between the phases in dispersion permits a rapid transfer of the components from one phase to the other, as occurs for example in gas–liquid and liquid–liquid reaction systems, solvent extraction, flotation, etc. These processes are present in a wide range of industries [1]. Sebba [2] in 1987 defined aphrons as colloidal dispersions containing microbubbles of 10–100 m in diameter, whose cores can be composed on a gas, liquid or emulsion encapsulated by various layers of surfactants. According to Sebba, when the encapsulated phase is a gas, these structures are called colloidal gas aphrons (CGA). Likewise, when the encapsulated core is a liquid, normally oil, they are called colloidal liquid aphrons (CLA). Finally, microbubbles with cores formed of a water–oil emulsion are called colloidal emulsion aphrons (CEA) [2–4]. ∗ Corresponding author. Tel.: +55 21 2562 8266; fax: +55 21 2562 7209. E-mail addresses: [email protected] (L.S. Spinelli), [email protected] (V. Monteiro). 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.10.017
Colloidal gas aphrons are dispersions of microbubbles and differ from regular foams not only regarding their geometric structure, but also in terms of their rheological properties. Normal foams are essentially gas–liquid–gas systems where fine liquid lamellae encircle polyhedral structures that in turn encapsulate the gas phase. Microfoams (aphrons) have much higher liquid phase content around the gas phase and are characterized by tiny and practically spherical bubbles [5]. In general, aphrons are formed by stirring a surfactant solution at a velocity of between 5000 and 10,000 rpm. However, they can also be formed by the action of a pressure difference in a highpressure high-temperature (HPHT) filter press [6]. The surfactants used can be ionic (cationic or anionic) as well as nonionic [2,7–9]. It is important to describe the arrangement of the surfactant molecules in the structure of aphrons. The innermost layer contains surfactants whose hydrophobic groups are inside the core and hydrophilic groups that are outside it. The external layer (protective layer) has surfactants whose hydrophobic and hydrophilic groups are arranged in the opposite order [2–4]. Despite a number of published studies, there is no conclusive evidence on their structure. However, the theory on aphrons is based mainly on the stability of these systems. The electrostatic
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repulsion when ionic surfactants are used and the steric repulsion when nonionic ones are used contribute to the stability of aphrons, which can be influenced by various parameters, such as the surfactant type and concentration and stirring time and speed, among others [2,8,10,11]. The covering of the microbubbles by various surfactant monolayers retards their coalescence by reducing the moment of shock caused by the collision of the microbubbles [5]. Better knowledge of the structure of aphrons, such as the number of surfactant layers and thicknesses of the interfaces, would be of great value to optimize them for various processes. Despite the relative lack of knowledge about the structure of the stabilization mechanism of dispersions, aphrons have excellent properties, such as large interfacial area in relation to volume, high stability, flow properties similar to those of water (CGA, for example, can be easily pumped from one place to another without collapsing) and significant cost advantages in various uses [8,10,12–14]. Because of these properties, aphrons have found applications in many areas. Most studies have focused on techniques of effective separation for recovery of substances of high aggregate value and also on investigation of the effects of operational parameters on their separation performance [12]. 1.1. Drilling fluids Drilling fluids containing aphrons in an aqueous medium have already been used in oilfields. The aphrons are generally incorporated in the drilling fluid at the surface, using conventional fluid mixing equipment. However, it is believed that at shallow depths, they can be directly incorporated at the drill bit [15]. The potential of aphrons as components of drilling fluids rests in their ability to reduce the invasion of the fluid in the rock and to minimize the damages to the formation, due to their high power to seal off depleted zones [16]. When aphrons penetrate the depleted zone, the pressure differential between their internal and the external medium causes them to expand, favoring the aggregation of bubbles. This results in a micro-environment of bubbles that seal off the depleted formation. This generates enough energy to prevent the invasion of fluids, or filtrate, into the depleted zone. Besides this, there is no formation of filter cake, which reduces the instances when drilling equipment gets stuck in the well and also mitigates corrosion problems [16]. For aphrons to be used in drilling fluids, they need to have a certain degree of stability. For this reason, the encapsulating film must have certain properties: (1) the film must not be too thin, otherwise it will tend to break under pressure; and (2) the protective layer must have a minimum viscosity. The water molecules tend to diffuse outside the film and inside the liquid solution, which contributes to destabilize the film. However, the transfer rate of the water from the film is inversely proportional to the viscosity. Consequently, viscosifiers are generally added, such as a biopolymer, which are incorporated into the structure of the aphrons [16,17]. 2. Experimental The surfactants used in this study to produce aphrons dispersions in an ester base were: a. commercials nonionic polymeric fluorochemical surfactants NOVEC FC-4432 and NOVEC FC-4430 (3 M do Brazil); b. poly(ethylene oxide)—poly(propylene oxide) (PEO-PPO) block copolymers called L7 and L10 with different number of units of ethylene oxide (EO) and propylene oxide (PO), as shown in Fig. 1 (donated by Oxiteno);
c. two surfactants produced in the laboratory by saponification reactions using a commercial ester as reagent. The fluids were mixed with organophilic clay (that has particle size lower than 10 m) and two viscosifier additives, Versa and Liovac 419. The first of these additives has already been used in drilling fluid formulations, while the second, an ester-based viscosifier, was donated by Miracema-Nuodex. The organic phase utilized, based on synthetic ester obtained from vegetable fatty acid utilized, was commercial Ultralub 5391 (from Oxiteno). The surfactants synthesized in the laboratory were obtained by reaction under reflux in a round-bottom flask containing a 1:1:1 mixture of ester: ethanol: 30 wt% KOH solution. The reflux was performed for 30 min at 353 K, after which the system was cooled to room temperature and then an aliquot was used in liquid form as a non-precipitated surfactant (NPS) and another was dried at room temperature for 65 h until it became pasty, that was called dry surfactant (DS). 2.1. Evaluating the surfactants’ surface tension According to another article by our laboratory group [6], surfactants that generate aphrons must be used at concentrations above the critical micelle concentration (CMC). Therefore, the water soluble surfactants used were evaluated regarding surface tension in function of the concentration to obtain the CMC and determine the minimal concentration of each surfactant used in fluids preparation (called for us standard concentration—std.conc.). This is defined as being a concentration greater than the CMC. The measurements were made in a Krüss K10ST digital tensiometer, at room temperature, that uses the ring method in your measurements. The surfactant solution concentration was dependent of each surfactant behavior. 2.2. Preparation of the fluids The fluids were prepared by mixing the organic phase at different concentrations of organophilic clay and viscosifiers (Versa and Liovac 419) in a Hamilton Beach blender. Then the fluid was aged in a heat-controlled shaker for 8 h at 338 K. This formulation is a base for drilling fluids. We produced two types of fluids, one containing a 95:5 ratio of ester:water and the other without water. The microbubbles were incorporated in the base drilling fluid by quickly mixing the recently prepared base fluids with the specific surfactants also in a Hamilton Beach blender, and then passing this mixture through a HPHT filter press, without a filter element, under a pressure differential of 1380 kPa. The surfactants were used at different concentrations, varying of standard concentration (std.conc.) to 5, 10, 20 and 30 times of this value. 2.3. Characterization of the fluids The base fluids were characterized as to viscosity in a Fann 35A viscosimeter, to obtain Fann readings, in specific angular velocity, within the recommended range for drilling fluids. The fluids prepared containing microbubbles (aphrons) were characterized as to bubble size distribution and average size under an optical Olympus SZH10 Research Stereo microscope at 60× magnification. The documentation photos were taken with a Nikon Coolpix 5400 digital camera and the images were processed using the Image J. program coupled to the “AnalyzeParticles” tool. The graphs were plotted with the aid of the LabPlot program, by counting the microbubbles in a specific area unit as described in the literature for similar programs [6]. To obtain more images of each batch of aphrons produced, we made observations under an optical microscope while positioning
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Fig. 1. Structures of PEO–PPO block copolymers.
the slide in three different positions, and from these images we plotted three size distribution graphs for each of the images individually and one graph for the mean of the three images. Each batch was made in triplicate to observe the repeatability in producing aphrons. The stability of these systems was evaluated by observing the bubbles number and the bubbles size changing in function of time: 1, 2 and 24 h. The density of the fluids and aphrons was obtained by use of a mud balance (in kg/m3 ). 2.4. Performance test of the aphrons on filtrate reduction The aphrons’ performance as filtrate-reducing elements was tested through a procedure adapted from the Petrobras N-2607 standard [18]. First the ceramic filtration disks were saturated in an organic medium (ester) to remove the air present in the disks’ pores. Then, to normalize the results, the base organic medium (ester) was passed through the HPHT filtration cell containing disks with pore size of 10 m and permeability of 950 mD, under a pressure differential of 690 kPa, and the mass was evaluated as a function of time. This procedure was due to the fact the ceramic disks, although they have the same permeability according to the manufacturer, may or may not have precisely the same pore distribution. The test itself consisted of passing the base fluid and aphrons through the filtration cell containing the ceramic filtration disk saturated with ester, also under a pressure differential of 690 kPa. The fluid mass expelled from the filter press per unit of time was then evaluated.
DS) were not evaluated, because in preliminary tests they did not promote the formation of microbubbles. Only for the FC-4432 and FC-4430 surfactants (Fig. 2) was it possible, from the discontinuity in the curve, to obtain CMC values (≈2 kg/m3 for FC-4432 and ≈0.7 kg/m3 for FC-4430). The CMC values of the other two surfactants (Fig. 3) could not be determined because they presented different behavior of surface action than the majority ones in which it was not possible to ascertain whether the discontinuities were related to the formation of micelles. For example, in the surface tension graph of the L10 surfactant, two changes in slope can be observed: one a small reduction of tension at around 50 mN/m, which then remains constant until a concentration of 0.3 kg/m3 , followed by another reduction of tension. It is not possible to state whether the first or second discontinuity is related to the formation of micelles. The behavior of the surfactant L10 is related with their structure, as published before [19]. In relation to NPS, this behavior is probably due to the presence of small amount of impurities from the preparation process of this surfactant in the lab. Based on the CMC values obtained, we set the standard concentration used for the fluorated surfactants above this value: for FC-4432 it was 3 kg/m3 and for FC-4430 it was 1 kg/m3 . For the other two surfactants, L10 and NPS, we set the standard concentration at 1 kg/m3 .
3.2. Evaluation of the viscosity of the base fluids
Figs. 2 and 3 show the curves of the surface tension versus the logarithm of the concentration of four of the surfactants: Novec FC4432, Novec FC-4430, NPS and L10. The other surfactants (L7 and
The ester-based fluids produced in our laboratory were obtained by varying the concentration of organophilic clay, Versa and Liovac 419. The fluids’ viscosity was measured using a Fann viscosimeter after they remained in a shaker bath for approximately 8 h (fluid aging). Two test fluids were also aged in a roller oven to compare their viscosities with those of the other fluids, of the same formulation, that were aged in a shaker bath, to confirm whether aging in a shaker bath is compatible and can be used in place of a roller oven, the device normally employed to age drilling fluids by Petrobras.
Fig. 2. Evaluation of surface tension of FC-4432 and FC-4430 surfactants.
Fig. 3. Evaluation of surface tension of NPS and L10 surfactants.
3. Results 3.1. Evaluation of the surface tension of the surfactants
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L.S. Spinelli et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 353 (2010) 57–63 Table 2 Composition of ester/water in 95:5 rate-based fluid and results of Fann readings.
Table 1 Composition of pure ester-based fluids and results of Fann readings. Fluid
Clay concentration (kg/m3 of ester)
Versa concentrationa
1 2b 3 4 5 6 7 8 9 10
60 60 120 80 40 60 40 80 90 90
0.074 – 0.075 – – 0.075 0.075 0.075 – 0.075
a b
Fann readings 600 rpm
3 rpm
43 108 140 83 27 42 32 78 94 97
8 14 64 23 3 5 4 21 30 30
Versa volume per ester volume. Fluid 2 also contain 1.3 kg per ester volume (m3 ).
Table 1 shows the compositions of the base fluids produced, together with the Fann readings obtained at 600 and 3 rpm (maximum and minimum speeds of a Fann viscosimeter). These values were compared with the viscosity range normally observed for common drilling fluids at CENPES/Petrobras: for 600 rpm, the readings were in the range of 130–100 and for 3 rpm they were between 21 and 13. Of all the fluids prepared, only fluids 2 and 8 had Fann readings within the range recommended for drilling fluids. Nevertheless, we only chose formulation 8 for use in the next tests for production of aphrons. We decided not to use Liovac 419 because it is a very viscous additive that is hard to handle and not commonly used in drilling fluids. Fluids 1 and 2 which were also aged in the roller oven had Fann readings in the same range as those aged in the shaker bath. This indicates that the shaker bath satisfactorily simulates the action of a roller oven in aging drilling fluids. The clay concentration in formulation 8 is considerably high (80 kg/m3 ), producing fluids with a very large quantity of solids, which can impair their use when passing through porous disks. Therefore, with starting from formulation we tried to reduce the clay concentration and keep the viscosity within the desired range. To do this, we added a small concentration of water to the ester in an ester:water ratio of 95:5, while maintaining the concentration of Versa and decreasing that of clay according to Table 2. The only fluid that presented values within the recommended range was fluid 13 (with 52 kg/m3 ). So we used the formulations 8 and 13 to produce aphrons with different surfactant types and concentrations.
Fluid
Clay concentration (kg/m3 of ester)
Versa concentrationa
11 12 13 14
60 56 52 40
0.075 0.075 0.075 0.075
a
Fann readings 600 rpm
3 rpm
119 110 94 49
26 25 23 5
Versa volume per ester volume.
3.3. Evaluation of the density of aphrons produced Aphrons were produced using a pure ester medium and a emulsion ester:water 95:5 medium, varying the type and concentration of surfactant. In the both cases, densities varies between 720 and 841 (kg/m3 ), characterizing a light non-water-based drilling fluids. 3.4. Size distribution and average size of the microbubbles In an attempt to obtain aphrons in a pure ester medium (without water), we observed foams (with relatively large bubbles) formed at the fluid surface, when using Novec FC-4430, Novec FC-4432 and L10 as surfactants, even when using viscosifying additives. Fig. 4 shows the example of large bubbles formed at the fluid surface using a L10 as a surfactant. With the use of the other surfactants, L7, DS and NPS, no bubbles were formed. In an attempt to obtain incorporated bubbles inside the liquid fluid we have done a previous treatment of the fluid, while maintaining it in the shaker bath for at least 8 h at a temperature of 338 K. To do this, we prepared two types of aphron fluids utilizing Novec FC-4430 as the surfactant at a concentration of 10 kg/m3 : (1) containing only clay, at a concentration of 60 kg/m3 ; and (2) containing clay at this same concentration along with Versa. In these tests we managed to obtain bubbles inside the fluid (able to be analyzed for size and size distribution) (Figs. 5 and 6, respectively). The addition of Versa caused an increase in the number of microbubbles produced and a reduction in their size (from 90 to 61 m). It can also be observed, by the bubble number against diameter curve profile, a decreasing of the bubble size distribution for the systems containing Versa. Since it would not be possible to show all micrographs and the respective bubble number against diameter curves, it will be assumed that the difference between the higher and lower sizes represents the size distribution in terms of distribution width (very small amounts of bubbles were not considered).
Fig. 4. Ester-based aphrons with L10 (at 10 kg/m3 ) and organophilic clay: (a) general aspect of becker system and (b) image of foam formed at the fluid surface.
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Fig. 5. Ester-based aphrons with Novec FC4430 (at 10 kg/m3 ) and organophilic clay: (a) image of microbubbles treated by Image J. and (b) size distribution of bubbles with number and average size data.
Fig. 6. Ester-based aphrons with Novec FC4430 (at 10 kg/m3 ), organophilic clay and Versa: (a) image of microbubbles treated by Image J. and (b) size distribution of bubbles with number and average size data.
Nevertheless, this type of fluid did not present in the Fann readings range (read with Fann viscosimeter) commonly found in drilling fluids, according to 3.2 item. Therefore, we produced aphrons with fluid 8, using Novec FC-4430 at 10 kg/m3 of concentration, where the average bubble size increased from 61 to 130 m. On the other hand, the aphron fluids prepared using a emulsion ester:water 95:5 medium with a smaller concentration of organophilic clay, fluid 13, had sizes varying from 60 to 80 m, depending on the type and concentration of surfactant used to produce the aphrons, presenting a size range lower than that produced with a pure ester medium. In terms of stability, aphrons produced with ester:water 95:5 emulsion were constituted of bubbles that increased their size extremely fast, indicating low stability. On the other hand, aphrons based on pure ester presented a slow bubble size increasing, and bubble breaking was only observed after 24 h.
tion (std.conc.) for each type of surfactant (such as in L10 [std.conc.] and L10 [5 × std.conc.]). In this test it can be seen that the use of the L10 (poly(ethylene oxide)–poly(propylene oxide) block copolymer) to generate aphrons led to the formation of structures capable of significantly
3.5. Performance of the aphrons in filtrate reduction We tested fluid 8 as a filtrate reducer, but the filter element retained a large volume of solids, which made it impossible to conclude the test due to the very large quantity of clay. We then tested only fluid 13 with different surfactant types and concentrations. Fig. 7 shows the results obtained in the filtrate reduction tests for all the aphrons fluids prepared with the fluid 13. The legend summarizes the surfactant and concentration used to prepare the aphrons as being the product of a value and a standard concentra-
Fig. 7. Graph of normalized rate of base fluid and aphrons passing by 10 m filter element in function of time.
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Table 3 Results of number, average size, size distributiona and normalized rates at two times: 10 and 45 s.
Base fluid NPS [std.conc.] NPS [5 × std.conc.] NPS [10 × std.conc.] NPS [20 × std.conc.] NPS [30 × std.conc.] L10 [std.conc.] L10 [5 × std.conc.] L10 [10 × std.conc.] L10 [20 × std.conc.] L10 [30 × std.conc.] N30 [std.conc.] N30 [10 × std.conc.] N32 [std.conc.] a
Number of bubbles
Average size (m)
Size distribution (m)a
– 274 561 534 491 838 186 258 213 372 341 270 346 465
– 86.8 62.6 59.1 68.1 62.6 85.2 78.9 72.3 62.5 66.5 87.7 65.2 70.2
– 200 160 190 200 190 180 190 160 170 190 190 200 190
Rate at 10 s 0.48 0.46 0.39 0.37 0.37 0.38 0.26 0.19 0.37 – 0.43 0.37 0.64 0.39
Rate at 45 s 0.32 0.45 0.26 0.27 0.27 0.29 0.20 0.17 0.28 – 0.32 0.27 0.22 0.17
Difference between the higher and lower microbubbles size.
reducing the filtrate in relation to the fluid, at concentrations of L10 [std.conc.] and L10 [5 × std.conc.]. As the concentration increased, the filtrate reduction rates decreased and were comparable with the filtrate reduction of aphrons produced with the surfactant prepared in the laboratory from ester at concentrations of NPS [10 × std.conc.] and NPS [20 × std.conc.]. For this reason, we believe there is an optimal concentration for use of each surfactant to generate aphrons. The behavior of the block copolymer is due to the fact it has alternating blocks of hydrophobic and hydrophilic chains, which is different than the structure of all the other surfactants used. Both the fluorated surfactants and the NPS have a structure with polar segments (ionic or nonionic) linked directly to a large hydrophobic segment composed of a hydrocarbon chain. The differentiated structure of L10 favors its low solubility in water and great affinity for ester, factors that may be behind the formation of more stable bubbles. There was a correlation between the properties of the aphrons produced and their action as filtrate-reducing agents (Table 3). An increase in the number of bubbles and a reduction in their size made them more efficient in reducing the filtrate in the sample. This occurred when there was a fivefold increase above the standard surfactant concentration for the same surfactant. Besides this, the greater the surfactant concentration, mainly starting at ten times the standard level, the narrower the bubble size distribution the lower the filtrate reduction efficiency. Based on these last results, we can suggest evaluating aphrons prepared with surfactants of the same family (PEO-PPO block copolymers with alternating hydrophilic and hydrophobic groups) and varying the number of oxide propylene oxide units for the purpose of increasing the aphrons’ efficiency in controlling the invasion of fluids even more. An interesting fact is that this type of surfactant is already being used in the petroleum industry in areas such as demulsification and flocculation and could also gain space for production of aphron systems to enhance the performance of drilling fluids. Besides this, the change of the aqueous phase of the emulsion system to brine would be interesting to evaluate the effect of the presence of salts on the efficiency of aphrons production and filtrate reduction. 4. Conclusions The use of HPHT filtration cell with controlled pressure was efficient to prepare aphrons structures, which were confirmed by visual appearance, optical microscopy and particle size. The variation of surfactant type and concentration produced systems having different characteristics in terms of microbubbles amount per area unit, size and size distribution. Microbubbles hav-
ing small sizes, high quantity and wide size distribution produced aphrons more efficient in reducing the filtrate. A filtrate reduction efficiency of 60% was obtained using a CH3 –PEO–PPO–OH block copolymer at relatively low concentrations which was used as a reference to formulate a light, non-water-based drilling fluid containing microbubbles with “noninvasive” characteristics. Acknowledgments The authors acknowledge the financial support of the Coordinating Office for Improvement of University Researchers (CAPES), the National Council for Scientific and Technological Research (CNPq) and the National Petroleum Agency/Office to Finance Studies and Projects/Oil and Natural Gas Sector Fund (ANP/FINEP/CTPETRO), besides Oxiteno do Brasil, 3M do Brasil and Miracema-Nuodex for supplies some surfactants, organic medium (ester) and viscosifier. References [1] R.B. Worden, A.B. Scranton, Method for forming reversible colloidal gas or liquid aphrons and compositions produced, PI 6022727, 2000. [2] F. Sebba, Foams and biliquid foams-aphrons. Wiley, Chichester, 1987 (chap.5). In: P. Jauregi, S. Gilmour, J. Varley, Characterization of colloidal gas aphrons for subsequent use for protein recovery, Chem. Eng. J. 65 (1997) 1–11. [3] G.J. Lye, D.C. Stuckey, Structure and stability of colloidal liquid aphrons, Colloids Surf. A 131 (1998) 119–136. [4] T. Deng, Y. Dai, J. Wang, A new kind of dispersion—colloidal emulsion aphrons, Colloids Surf. A 266 (2005) 97–105. [5] R.C.G. Oliveira, Remediac¸ão de Subsolos Contaminados por Compostos Orgânicos a partir da Injec¸ão de Soluc¸ões de Surfatantes e de Espumas, Doctoral thesis—Postgraduate Program in Engineering, Federal University of Rio de Janeiro, Brazil, 2004. [6] L.S. Spinelli, A. Bezerra, A. Aquino, E.F. Lucas, V. Monteiro, R. Lomba, R.C. Michel, Composition, size distribution and characteristics of aphron dispersions, Macromol. Symp. 295 (2006) 243–249. [7] P. Jauregi, J. Varley, Colloidal gas aphrons: potential applications in biotechnology, Trends Biotechnol. 17 (1999) 389–395. [8] T. Deng, Stabilization and characterization of colloidal gas aphrons dispersion, J. Colloid Interface Sci. 261 (2003) 360–365. [9] E.H.A. Mansur, Y. Wang, Y. Dai, Removal of suspension of fine particles from water by colloidal gas aphrons (CGA), Sep. Purif. Technol. 48 (2006) 71– 77. [10] R.W. Alves, Extrac¸ão de corantes de urucum por processos adsortivos utilizando argilas convencionais e colloidal gas aphrons, Doctoral thesis—Postgraduate Program in Engineering, Federal University of Santa Catarina, Brazil, 2005. [11] H. Tseng, L. Pilon, G.R. Warrier, Rheology and convective heat transfer of colloidal gas aphrons in horizontal mini-channels, Int. J. Heat Fluid Flow 27 (2006) 298–310. [12] P. Jauregi, S. Gilmour, J. Varley, Characterization of colloidal gas aphrons for subsequent use for protein recovery, Chem. Eng. J. 65 (1997) 1–11. [13] M. Noble, A. Brown, P. Jauregi, A. Kaul, J. Varley, Protein recovery using gas–liquid dispersions, J. Chromatogr. B 711 (1998) 31–43.
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