Water-soluble carboxymethylchitosan as green scale inhibitor in oil wells

A water-soluble carboxymethylchitosan (CMC) was prepared in water/isopropanol (2/8) medium, at 10 °C, and characterized by UV–vis, FT-IR and NMR techniques. Its performance as an environmentally friendly scale inhibitor in oil wells was evaluated under the physicochemical conditions of oil wells in northeast of Brazil, by using SEM, visual compatibility and dynamic tube blocking test.

Carbohydrate Polymers 215 (2019) 137–142 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Water-soluble carboxymethylchitosan as green scale inhibitor in oil wells a a T a Ruza Gabriela M de A Macedo , Nívia N Marques , Luciana C.S Paulucci , ⁎ João Victor Moura Cunhaa, Marcos A Villettib, Bruno B Castroc, Rosangela de C Balabana, a b c Laboratório de Pesquisa em Petróleo – LAPET, Instituto de Química, Universidade Federal Rio Grande Norte – UFRN, Natal, RN, Brazil Departamento de Física, Universidade Federal de Santa Maria – UFSM, Santa Maria, RS, Brazil Centro de Pesquisa e Desenvolvimento Leopoldo Américo Miguêz de Mello – CENPES/PETROBRAS, Rio de Janeiro, RJ, Brazil A R T I C LE I N FO A B S T R A C T Keywords: Carboxymethylchitosan Scale inhibitor Calcium carbonate Oil industry A water-soluble carboxymethylchitosan (CMC) was prepared in water/isopropanol (2/8) medium, at 10 °C, and characterized by UV–vis, FT-IR and NMR techniques Its performance as an environmentally friendly scale inhibitor in oil wells was evaluated under the physicochemical conditions of oil wells in northeast of Brazil, by using SEM, visual compatibility and dynamic tube blocking test The synthesis conditions led to a degree of carboxymethylation of 0.45 and water-solubility in all pH range studied (1–11) CMC acted as a scale inhibitor of CaCO3 under synthetic brine medium, presenting a minimum inhibitor concentration (MIC) of 170 ppm (1000 psi, T = 70 °C) SEM images showed that CaCO3 crystals were deformed by CMC, which was attributed to effective interactions of CMC through its carboxylate ions and lone pair of electrons on OH and NH2 groups with calcium ions, preventing scale deposition Introduction Inorganic scale formation is one of the most severe problems in petroleum industry, leading to total or partial obstruction of equipment and pipes, causing great damage and economic losses (Kamal, Hussein, Mahmoud, Sultan, & Saad, 2018; Khormali, Sharifov, & Torba, 2018) In this scenario, chemicals are often applied as scale inhibitors, avoiding nucleation or crystal growth One of the most applied types of antiscaling are phosphorus-containing materials, which are highly effective, but are nutrients after discharge to sea, leading to eutrophication, besides of being able to promote calcium phosphate deposition (Zhang, Zhang, Li, Hu, & Hannam, 2010) The growing concern on the utilization of environmentally safe chemicals and legislation control has led to the search for green scale inhibitors, which display nontoxicity, non-bioaccumulation and easy biodegradation (Kumar, Naiya, & Kumar, 2018; Liu, Xue, & Yang, 2017; Mady, Charoensumran, Ajiro, & Kelland, 2018) Polymers have been extensively applied as antiscaling in oil and gas fields, because of their enhanced thermal stability and better environmental compatibility (Younes, El-Maghrabi, & Ali, 2017) In recent years, some biopolymers and their derivatives, such as guar and xanthan gums (Elkholy, El-Taib Heakal, Rashad, & Zakaria, 2018), carboxymethylinulin (Kırboga & Öner, 2012), copolymers of β-cyclodextrins (Liu, Zou, Li, Lin, & Chen, 2016; Gu et al., 2013; Liu, Kan et al., ⁎ 2016), carboxymethylstarch (Wang, Li, & Yang, 2017) and starch-g-poly (acrylic acid) (Yu, Wang, Li, & Yang, 2018) have been evaluated as green scale inhibitors and the results obtained have been considered very promising The presence of hydroxyl and carboxyl groups on the polymer structure provides chelation, dispersion and crystal distortion effects In particular, chitosan, a polysaccharide mainly obtained from deacetylation of chitin, exhibits biocompatibility, biodegradability and hydrophilicity and its degradation products are nontoxic Because of its acid-limited solubility, chitosan has been chemically modified to improve its range of applications and some chitosan derivatives have shown the ability to act as scale inhibitors (Guo et al., 2012; Liang, Zhao, Shen, Wang, & Xu, 2004; Yang et al., 2010; Yang, Xu, Chen, & Sui, 2012; Zhang et al., 2015; Zhao et al., 2010) These studies, however, were performed under mild conditions, very different from the complex environment of petroleum wells The selection of an appropriate chemical to prevent mineral scale in petroleum industry is a challenging task, due to the diversity of parameters that should be taken into account, such as pH, salinity, composition of the water, temperature and pressure of the well, since these conditions combined can completely change the performance of a scale inhibitor The antiscaling product should have the following characteristics: solubility in the medium, stability at the operating conditions and functional groups able to interact with the fouling ions Corresponding author E-mail address: balaban@supercabo.com.br (R.d.C Balaban) https://doi.org/10.1016/j.carbpol.2019.03.082 Received 17 December 2018; Received in revised form 11 February 2019; Accepted 25 March 2019 Available online 25 March 2019 0144-8617/ © 2019 Elsevier Ltd All rights reserved Carbohydrate Polymers 215 (2019) 137–142 R.G.M.d.A Macedo, et al Besides, the concentration applied in the field should be high enough to effectively inhibit scale deposition, but not too high to avoid incompatibility (insolubility in the aqueous medium) or waste of money (2016b, Liu, Kan et al., 2016; Popov et al., 2019) In a recent paper of our group (Macedo, Marques, Tonholo, & Balaban, 2019), carboxymethylchitosan has been proven to act as an excellent corrosion inhibitor in media of high salinity, typical of oil wells This performance was attributed to interactions of eCOOH, eNH2 and eOH groups with the metal surface Knowing that these functional groups can also contribute to scale inhibition processes, the main objectives of this work are to describe the preparation and structural characterization of a water-soluble carboxymethylchitosan and evaluate it as a novel green inhibitor of CaCO3 scale in pipelines used in the oil well installations of the northeast region of Brazil, taking into account the physicochemical conditions of the medium Grasdalen, Tokura, & Smidsrød, 1997): ⎡ DS = ⎣ ( ) (I ) ⎤⎦ + ⎡⎣ ( ) (I ) ⎤⎦ (1) IH Where, I1 is the integral of the hydrogen bonded to anomeric carbon, I8 is the integral corresponding to 3- and 6-substituted OeCH2eCOOD groups, and I9 is integral corresponding to the hydrogens of NeCH2eCOOD groups 2.5 Conductimetric titration Experimental The DS was also determined by conductimetric titration, as presented elsewhere (Bidgoli, Zamani, & Taherzadeh, 2010) CMC (0.1 g) was added to 100 mL of 0.05 M HCl and left under magnetic stirring during 24 h The solution was then titrated with 0.1 M NaOH 2.1 Materials 2.6 UV–vis Low-molecular weight chitosan was obtained from Polymar S.A (Brazil) It has a viscosity-average molecular weight of 3.57 × 104 g/ mol and a degree of deacetylation (DD) of 80%, according to procedure performed previously by our research group (dos Santos Alves, Lima Vidal, & de Carvalho Balaban, 2009) Isopropanol, ethanol, acetic acid, NaOH and HCl were obtained from Synth Salts used in the preparation of the brine, namely, NaCl, KCl, CaCl2, MgCl2, and NaHCO3 were acquired from Sigma-Aldrich Chitosan was purified as described previously (dos Santos Alves et al., 2009), with a mass yield of 72% All the other reagents were used as received The pH-based solubility was estimated on a UV–vis spectrometer from Shimadzu About mg of sample was dissolved in 10 mL of 1% HCl and the resulting solution had pH adjusted by adding 1% NaOH The sample was considered insoluble when the transmittance of its solution at λ =450 nm was ≤ 85% (Chen & Park, 2003; de Abreu & Campana-Filho, 2009; Sashiwa & Shigemasa, 1999) 2.7 Preparation of brine Cationic and anionic species of interest were dissolved separately within individual containers to prevent premature interaction Thus, KCl, MgCl2, CaCl2 and NaCl were successively added to water and the resulting solution was named as “cationic” water; NaHCO3 and NaCl were dissolved in water to obtain the “anionic” water After preparation, the pH of the solutions was adjusted to 8.2 Then, they were filtered through 0.45 μm cellulose acetate membrane, under reduced pressure The mixing ratio of “cationic” and “anionic” water was of 1:1 to all tests, to give final brine composition showed in Table 2.2 Synthesis of carboxymethylchitosan (CMC) Carboxymethylchitosan was prepared as described previously (Chen & Park, 2003), however, with minor modifications (Macedo et al., 2019) In this case, 10 g of chitosan was added to a water/isopropanol (2/8) alcoholic solution containing 13.5 g of NaOH The dispersion was kept under stirring for h, at 10 °C Thereafter, 15 g of monochloroacetic acid was dissolved in 20 mL of isopropanol and added to the reaction mixture The reaction proceeded for h, at 10 °C After this time, 200 mL of 70% aqueous ethanol solution was added to quench the reaction The precipitate was washed with 70–90% ethanol and then with anhydrous ethanol The product obtained was dried under reduced pressure In order to obtain the acidic form of CMC, g of sample was suspended in 100 mL of 80% ethanol Then, 10 mL of 37% HCl was added and the suspension was stirred for 30 min, at room temperature The sample was then filtered and the solid was washed with 70–90% ethanol and dried under vacuum The mass yield was of 87% 2.8 Compatibility test Visual assessment of compatibility between CMC and self-precipitating brine was verified by means of the NACE TM0197 standard (NACE, 2010) Therefore, 50 mL of "cationic" water was added in a 100 mL Schott flask, and 50 mL of "anionic" water was added into another 100 mL Schott flask CMC was dissolved in the "anionic" water at different concentrations All bottles were then kept in oven for h, at 70 °C After this time, the "cationic" and "anionic" waters were mixed and photographed with a Nikon 16.1 Megapixels digital camera, in order to observe if there is formation of precipitate and/or turbidity in the medium The photos were recorded at 0, 1, and 24 h after mixing the waters, and the samples were kept statically under heating at 70 °C 2.3 Infrared spectroscopy Infrared spectroscopy was performed on a Perkin Elmer spectrometer by using an attenuated total reflectance (ATR) accessory For each sample, 12 scans were performed from 650 to 4000 cm−1, with a spectral resolution of cm−1 Table Composition of self-precipitating brine, which simulates a real produced water of a well in the Northeast of Brazil 2.4 Nuclear magnetic ressonance Ions H NMR spectra were obtained at 70 °C on a BRUKER AVANCE 400 MHz spectrometer Chitosan (10 mg/mL) and carboxymethylchitosan (20 mg/mL) were dissolved in D2O/HCl (1%), for 24 h, before analyses The degree of carboxymethylation (DS = degree of substitution) was determined by 1H NMR For that purpose, Eq was employed, based on the method described previously in literature (Mourya, Inamdar, & Tiwari, 2010; Nordtveit Hjerde, Vårum, + Na K+ Ca2+ Mg2+ HCO3− Cl− 138 Concentration (mg/L) 2231 85 152 33 1000 2686 Carbohydrate Polymers 215 (2019) 137–142 R.G.M.d.A Macedo, et al 1020 cm−1 The introduction of carboxymethyl groups on the polysaccharide backbone was evidenced by a peak at 1720 cm−1 on CMC spectrum, which can be attributed to the symmetrical stretch of C]O from COOH group Also, CeO stretching of the CH2COOH group gave rise to a band at 1240 cm−1 (Bidgoli et al., 2010; Chen & Park, 2003; Do Nascimento Marques, Curti, Da Silva Maia, & Balaban, 2013; Doshi, Repo, Heiskanen, Sirviö, & Sillanpää, 2017; Ge & Luo, 2005) The 1H NMR spectra of chitosan and carboxymethylchitosan are shown in Fig Both spectra display a chemical shift at 1.92 ppm, which corresponds to CH3 of the acetamide groups of chitosan The signals at 3.04 and 3.61 ppm refer to the methine protons (CH) of C2 from acetylglucosamine and glucosamine repeat units, respectively The chemical shifts from 3.7 to 3.8 ppm, correspond to the protons of the C3, C4, C5 and C6 carbon atoms The hydrogen bonded to anomeric C1 gives rise to the signals of 4.4–4.8 ppm The structural modification was confirmed by the appearance of signals corresponding to the hydrogens of the 3- and 6-substituted carboxymethyl group at 4.1–4.3 ppm The peak attributed on literature to N-carboxymethyl substitution (3.2 ppm) did not appear, which indicates that the O-carboxymethylchitosan was produced (Chen & Park, 2003; Zheng, Han, Yang, & Liu, 2011) The small change on the experimental procedure in relation to the one reported in literature (Chen & Park, 2003), keeping temperature at 10 °C and increasing the water content, led to solubility of CMC in all pH range studied and mass yield of 87% Meanwhile, chitosan had 100% transmittance at pH < and 85% of transmittance at pH > (Table 2) At acid medium, amino groups become protonated; while at basic medium, carboxylic acid deprotonates and form carboxylate groups; and, at neutral medium, both amino and carboxylic acid groups are under ionic forms, leading to solubility of CMC in all pH range A carboxymethylation degree of 0.45 was found by 1H NMR, similar to the one obtained by conductimetric titration, 0.50 Chen and Park (2003) showed that DS between 0.4 and 0.6 lead to water-soluble carboxymethylchitosans Besides, they demonstrated that the conditions of 2/8 water/isopropanol ratio and 50 °C promoted higher DS (1.1) and mass yield (99.8%), but the products were insoluble at the acid region (good amount of N-carboxymethylation) At the same time, decreasing temperature to 10 °C and decreasing the water/isopropanol ratio to 1/8 promoted a decrease on DS (0.3), decreasing substitution at C2, C3 and C6 positions, leading to a low mass yield (12.8%), but resulting on a water-soluble CMC This last condition resulted on a greater amount of NH2 groups unreacted, which are responsible for solubility of 2.9 Dynamic inhibition efficiency The minimum effective concentration of CMC as scale inhibitor of CaCO3 under dynamic conditions was obtained on a Scaled Solution Ltda's Dinamic Scale equipment, based on the NACE TM31105 standard (NACE, 2005) The procedure evaluates the performance of the scale inhibitor under pressure and temperature equivalent to the actual conditions of oil wells, by using the dynamic tube block test In this work, the inhibitor was considered efficient when its pressure differential did not exceed psi in the minimum of times the blank run (no inhibitor added) or 60 (whichever is greater) "Cationic" and "anionic" waters were injected through pumps (pumps and 2, respectively) into a capillary of 0.8 mm in diameter and m in length A third pump injected into the same capillary a CMC solution solubilized in the "anionic" water, and from it, together with the pump 2, the desired concentration of CMC was dosed by the software of equipment Each run was automatically stopped if the pressure differential reached psi The total flow for the three pumps was maintained at 10 mL/min, under the pressure of 1000 psi and the temperature of 70 °C 2.10 Scanning electron microscopy Changes in morphology of CaCO3 as a function of added CMC was observed with a Hitachi Tabletop scanning electron microscope For this analysis, CMC was solubilized in the “anionic” water, at different concentrations, and the crystals were obtained by mixing the respective “cationic” and “anionic” waters After mixing, the system was allowed to stand for 24 h in an oven, at 70 °C After this time, the system was cooled to room temperature Then, the brines were filtered under vacuum, through 0.45 μm Millipore cellulose acetate membrane The crystals retained on the membrane were collected for analysis Results and discussion 3.1 Characterization of carboxymethylchitosan Fig displays the infrared spectra of chitosan and carboxymethylchitosan Both present bands corresponding to overlapped OeH and NeH stretching at about 3300 cm−1, CeH stretching at about 2900 and 2860 cm−1, peaks at approximately 1650 and 1550 cm−1, corresponding to absorptions of C]O stretching (primary amide) and N-H bending, respectively, besides of stretching of CeOeC bonds at about Fig Infrared spectra of (a) chitosan and (b) carboxymethylchitosan 139 Carbohydrate Polymers 215 (2019) 137–142 R.G.M.d.A Macedo, et al Fig 1H-NMR spectra of chitosan (a) and carboxymethylchitosan (b), both in D2O/HCl (1:1 v/v), at 70 °C eCOOH groups have exhibited higher inhibition efficiency Shorter chains have greater mobility and more easily enters the crystal lattices, disturbing the normal growth of the crystal, while acid groups act on distortion of the crystal lattice via chelating and complexing effects with scale ions Polar functional groups able to bind to scale ions also contribute to higher performance of the inhibitor (Amjad & Koutsoukos, 2014; Elkholy et al., 2018; Wang et al., 2017) Then, the choice of a low molecular weight chitosan would give better mobility and increased performance of CMC as scale inhibitor Taking into account the intended oilfield application, the synthesis conditions were designed to obtain carboxymethylchitosan with the highest degree of O-carboxymethyl substitution, which would give, at the same time, high yield, water-solubility in wide pH range and good amount of polar and chelating groups Table Solubility data (2 g / L) as a function of pH, obtained by UV–vis, at 25 °C pH Chitosan Transmittance (%)* CMC 11 100 100 100 85 85 85 100 100 100 100 100 100 * Transmittance = 100%, indicates solubility; transmittance = 85%, indicates insolubility CMC at acid media In this paper, when the amount of water was increased to 20%, it probably promoted greater attack of the base on the polysaccharide chains, leading to higher active sites for carboxymethylation, whereas, at the same time, keeping a low temperature (10 °C) reduced the velocity of carboxymethylation reaction Thus, we found that the conditions applied in this study were a good alternative to obtain appropriate DS, CMC solubility from acid to basic medium and suitable mass yield Literature has also shown that the performance of a polymer as scale inhibitor depends on its structural parameters, such as molar mass and degree of substitution Lower molar mass and higher amounts of 3.2 Carboxymethylchitosan as scale inhibitor 3.2.1 Compatibility test Compatibility tests evaluate the solubility of the inhibitor in the presence of the cation and its ability to avoid scale deposition Table shows the results of the compatibility test between CMC and self-precipitating water, performed at 70 °C CMC is compatible in the 50–250 ppm range, immediately after preparation However, the formation of precipitate in the bottom of the vials was observed after h of assay at the concentrations of 50 and 100 ppm At concentrations of 500 Table Compatibility test between CMC and self-precipitating brines for formation of calcium carbonate, at 70 °C Time (h) 24 Blank ppt ppt ppt ppt * 50 ppm 100 ppm 150 ppm 250 ppm 500 ppm 1000 ppm limpid ppt ppt ppt limpid ppt ppt ppt limpid limpid limpid limpid limpid limpid limpid limpid turbid turbid turbid turbid turbid turbid turbid turbid * ppt = precipitate 140 Carbohydrate Polymers 215 (2019) 137–142 R.G.M.d.A Macedo, et al Fig Efficiency of dynamic CaCO3 precipitation inhibition at 1000 psi and 70 °C Fig SEM images obtained after compatibility test between self-precipitating brines for CaCO3 formation, at 70 °C (a) Calcium carbonate in the absence of CMC; (b and c) Calcium carbonate in the presence of 170 ppm CMC where there is a constant pressure differential from the beginning to the end of the run (at 170 and 250 ppm) Thus, it would be reasonable to define 170 ppm as the minimal inhibitor concentration (MIC), which is also in the range of CMC concentration for good compatibility with the brines (Table 3) and 1000 ppm, the solutions presented turbidity during the entire test, suggesting incompatibility between CMC and self-precipitating waters for CaCO3 formation, probably due to CMC crosslinking via Ca2+ ions bridges However, when the concentration is 150 and 250 ppm, the precipitate ceases to exist and the solution is clear throughout the assay, suggesting compatibility and possible action as an inhibitor in the formation of calcium carbonate crystals at this range of polymer concentration 3.2.3 Scanning electron microscopy SEM images (Fig 4) refer to CaCO3 precipitates collected after the compatibility test In Fig 4(a), a well-defined crystalline structure in the form of needles and cubes can be observed, comparable to the ones found in literature at this temperature range and which were ascribed to aragonite and calcite, respectively (Yang et al., 2010; Zhao et al., 2010) Fig 4(b and c) displays differences in the structure of the crystals by adding 170 ppm of CMC (minimal inhibition concentration determined by the dynamic efficiency test) In some points, it is possible to observe clusters (circle), whereas, at others, the edges of the cubes are fully deformed (detailed in Fig 4c) Therefore, it is suggested that under these conditions, the CMC causes a morphological deformation in the crystal structure, which difficult their organization and, consequently, minimizes scaling by CaCO3 At the pH of the brine, both amino and hydroxyl groups can bind to Ca2+ through their lone pair of electrons, besides of strong electrostatic interactions between Ca+2 ions and the COO− groups CMC can then occupy the growing points of the initially formed crystals and hinder the arrival of further scaling ions The crystal morphology is then changed, leading to deformation, preventing crystal growth CMC can also interact with calcium ions present in the media via COO−, NH2 and OH groups, preventing the Ca2+ 3.2.2 Dynamic scale inhibition efficiency The efficiency of a scale inhibitor under dynamic conditions can be determined by monitoring the pressure differential during the encounter of incompatible waters in the presence of the inhibitor Fig shows the results obtained by the self-precipitating brine for the formation of CaCO3 in the presence of different concentrations of CMC, at 70 °C and 1000 psi It can be seen that during the blank run, the pressure differential exceeds psi after 15 of testing, due to precipitation of CaCO3, that decreases the diameter of the capillary When 50 ppm of CMC is added, the precipitation time is shifted to approximately 50 min, which indicates the existence of a certain performance of the CMC against the precipitation of CaCO3 When concentration of CMC is increased, the inhibitor become more efficient At a polymer concentration of 100 ppm, the pressure differential is less than psi after h of testing, but at the end of the test a slight increase in pressure differential was observed, which may be related to the precipitation of CaCO3 crystals inside the test tube As the concentration of the polymer increases, it is verified that this slope is minimized, reaching the point 141 Carbohydrate Polymers 215 (2019) 137–142 R.G.M.d.A Macedo, et al arrival at the surface of scale nuclei (Elkholy et al., 2018; Yang et al., 2010; Zhang et al., 2015) sulfate scale prevention using a new mixture of phosphonate scale inhibitors during waterflooding Journal of Petroleum Science & Engineering, 164, 245–258 Kırboga, S., & Öner, M (2012) The inhibitory effects of carboxymethyl inulin on the seeded growth of calcium carbonate Colloids and Surfaces B, Biointerfaces, 91, 18–25 Kumar, S., Naiya, T K., & Kumar, T (2018) Developments in oilfield scale handling towards green technology-A review Journal of Petroleum Science & Engineering, 169, 428–444 Liang, P., Zhao, Y., Shen, Q., Wang, D., & Xu, D (2004) The effect of carboxymethyl chitosan on the precipitation of calcium carbonate Journal of Crystal Growth, 261(4), 571–576 Liu, G., Xue, M., & Yang, H (2017) Polyether copolymer as an 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(2010) Carboxymethyl chitosan and its applications Advanced Materials Letters, 1(1), 11–33 NACE (2005) NACE 31105 dynamic inhibitor evaluation apparatus and procedures in oil and gas production, Vol 24225-SG, Houston, Texas: NACE10 NACE (2010) NACE TM 0197 Laboratory screening test to determine the ability of scale inhibitors to prevent the precipitation of barium sulfate and/or strontium sulfate from solution (for oil and gas production systems) Houston, Texas: NACE12 Nordtveit Hjerde, R J., Vårum, K M., Grasdalen, H., Tokura, S., & Smidsrød, O (1997) Chemical composition of O-(carboxymethyl)-chitins in relation to lysozyme degradation rates Carbohydrate Polymers, 34(3), 131–139 Popov, K., Oshchepkov, M., Afanas’eva, E., Koltinova, E., Dikareva, Y., & Rönkkömäki, H (2019) A new insight into the mechanism of the scale inhibition: DLS study of gypsum nucleation in presence of phosphonates using nanosilver dispersion as an internal light scattering intensity reference Colloids and 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the structural morphology of starch-graft-poly(acrylic acid) on its scale-inhibition efficiency Water Research, 141, 86–95 Zhang, B., Zhang, L., Li, F., Hu, W., & Hannam, P M (2010) Testing the formation of Ca–phosphonate precipitates and evaluating the anionic polymers as Ca–phosphonate precipitates and CaCO3 scale inhibitor in simulated cooling water Corrosion Science, 52(12), 3883–3890 Zhang, H., Cai, Z., Jin, X., Sun, D., Wang, D., Yang, T., Han, X (2015) Preparation of modified oligochitosan and evaluation of its scale inhibition and fluorescence properties Journal of Applied Polymer Science, 132(37) Zhao, D., Zhu, Y., Li, F., Ruan, Q., Zhang, S., Zhang, L., Xu, F (2010) Polymorph selection and nanocrystallite rearrangement of calcium carbonate in carboxymethyl chitosan aqueous solution: Thermodynamic and kinetic analysis Materials Research Bulletin, 45(1), 80–87 Zheng, M., Han, B., Yang, Y., & Liu, W (2011) Synthesis, characterization and biological safety of O-carboxymethyl chitosan used to treat Sarcoma 180 tumor Carbohydrate Polymers, 86(1), 231–238 Conclusions The synthesis of the carboxymethylchitosan was successful, being in agreement with the data presented in the literature Its solubility occurred throughout the pH range studied (1–11), probably due to the synthesis parameters adopted, which gave a degree of substitution of 0.45 CMC was compatible with the CaCO3 self-precipitating brine (150–250 ppm) and the capillary flow test showed that this modified polysaccharide is efficient in controlling the precipitation of CaCO3, presenting a minimum inhibition concentration of 170 ppm, under the conditions of pressure, temperature, pH and salinity oil wells in the northeast of Brazil SEM images showed that CMC modifies the morphology of calcium carbonate crystals in the brine The data suggest a mechanism of interaction of calcium with the polymer chains and/or adsorption of the CMC on the initially formed CaCO3 crystals, favouring the deformation and preventing crystals growth Acknowledgement This study was nanced in part by the Coordenaỗóo de Aperfeiỗoamento de Pessoal de Nível Superior - Brazil (CAPES) Finance Code 001 References Amjad, Z., & Koutsoukos, P G (2014) Evaluation of maleic acid based polymers as scale inhibitors and dispersants for industrial water applications Desalination, 335(1), 55–63 Bidgoli, H., Zamani, A., & Taherzadeh, M J (2010) Effect of carboxymethylation conditions on the water-binding capacity of chitosan-based superabsorbents Carbohydrate Research, 345(18), 2683–2689 Chen, X G., & Park, H J (2003) Chemical characteristics of O-carboxymethyl chitosans related to the preparation conditions Carbohydrate Polymers, 53(4), 355–359 de Abreu, F R., & Campana-Filho, S P (2009) Characteristics and properties of carboxymethylchitosan Carbohydrate Polymers, 75(2), 214–221 Do Nascimento Marques, N., Curti, P S., Da Silva Maia, A M., & Balaban, R D C (2013) Temperature and pH effects on the stability and rheological 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Dynamic inhibition efficiency The minimum effective concentration of CMC as scale inhibitor of CaCO3 under dynamic conditions was obtained on a Scaled Solution Ltda''s Dinamic Scale equipment, based... better mobility and increased performance of CMC as scale inhibitor Taking into account the intended oil? ??eld application, the synthesis conditions were designed to obtain carboxymethylchitosan. .. polymer as scale inhibitor depends on its structural parameters, such as molar mass and degree of substitution Lower molar mass and higher amounts of 3.2 Carboxymethylchitosan as scale inhibitor