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Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids
CLAY-03875; No of Pages 11 Applied Clay Science xxx (2016) xxx–xxx
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Research paper
Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids Conny Cerai Ferreira a, Gleber Tacio Teixeira b, Elizabeth Roditi Lachter a, Regina Sandra Veiga Nascimento a,⁎ a Laboratório de Fluidos e Materiais Poliméricos Multifásicos- FLUMAT-, Pólo de Xistoquímica, Instituto de Química, Universidade Federal do Rio de Janeiro, Hélio de Almeida St., 40, Cidade Universitária, Rio de Janeiro, Brazil b Petrobras, Setor de Tecnologia de Fluidos de Perfuração, Rod. Amaral Peixoto, 163, Imboassica, Macaé, Rio de Janeiro 27925-290, Brazil
a r t i c l e
i n f o
Article history: Received 16 March 2016 Received in revised form 19 May 2016 Accepted 24 May 2016 Available online xxxx Keywords: Hyperbranched polymer Polyglycerol hydrophobization Shale interaction and inhibition Water-based drilling fluid
a b s t r a c t The oil and gas industry demands drilling fluids that would be able to minimize the wellbore instability faced during the drilling of reactive shales. In this work we describe the synthesis of hydrophobized hyperbranched polyglycerols (HPG) with unique design and properties to be used as non-ionic reactive shale inhibitors. In association with KCl, HPG showed a superior performance in comparison with unmodified hyperbranched polyglycerol and with the commercial clay reactivity inhibitors PEG400 and PDADMAC. Intact cuttings recoveries were around 80%. The proposed inhibition mechanism suggests the formation of a complex between HPGs and K+ ions and its penetration into the clay interlayer spacing to minimize the shale-water interactions and remove water molecules present in the clay galleries. In addition, these aggregates formed by the amphiphilic structures would cause obstruction of the clay minerals pore throats, thereby making it even more difficult for the penetration of water molecules. © 2016 Published by Elsevier B.V.
1. Introduction The oil industry has been showing a large demand for new technologies to overcome the huge problems related to the drilling of wells. Nowadays, whenever possible, water-based drilling fluids (WBM) are employed, since oil based fluids face several environmental restrictions and involve much higher costs (He et al., 2014). However, when waterbased fluids are used, several wellbore stability issues contribute to increase the challenges related to drilling, and these issues are, in large part, related to the water reactivity of some of the shales being drilled. Shales are clay rich sedimentary rocks that can present water sensitivity depending on their crystalline structure, composition, porosity and the existence of cracks and fractures on the rocks surface (Lal, 1999; Gomez and Patel, 2013; Al-Arfaj et al., 2014). Reactive shales, when in contact with WBM, can have their crystalline structure destroyed resulting in severe problems, such as trapping of column and/or well collapse. To deal with the possible damages caused by water, chemical inhibitors are added to the fluid formulation in order to minimize or even prevent the shale crystalline destruction. The literature reports the use of inorganic salts, such as KCl, and CaCl2, water soluble silicates (Gomez and Patel, 2013), cationic hydrophobized polysaccharides (Lopes et al., 2014), ionic liquids (Berry et al., 2009), poly(oxyalkyl)amines (Qu et al., 2009; Wang et al., 2011), poly(oxypropylene)amidoamine (Zhong et al., 2012), others amine ⁎ Corresponding author. E-mail address: [email protected] (R.S.V. Nascimento).
derivatives (Patel et al., 2007; Zhong et al., 2015a, 2015b) and nonionic molecules/polymers (Shadizadeh et al., 2015), all of them presenting advantages and disadvantages. Regarding the environmental requirements for the drilling fluid formulation, amine derivatives such as quaternary alkyl ammonium salts or amine containing polymers are highly efficient shale inhibitors, but present elevated toxicity. Linear non-ionic polymers, such as polyglycols (PEGs) and polyols, although showing low toxicity, present limited field applications (Patel et al., 2007). The hyperbranched polyglycerols are versatile structures which can be produced from glycidol (Sunder et al., 1999) or glycerol carbonate (Rokicki et al., 2005) a monomer obtained from glycerol. The glycerol is a co-product of the biodiesel industry. In Brazil, due to the increasing use of biodiesel, in partial replacement of the diesel obtained from petroleum, its annual production of about 500,000 m3 demands for the development of new uses for the glycerol (ANP, 2016). The hyperbranched polyglycerol and its derivatives have been widely studied, e.g., as potential agents for the controlled release of drugs (Gupta et al., 2012), as sample pretreatment and immunosensors in analytical chemistry fields (Sun et al., 2015) and as additives for the encapsulation of pigments (Wan et al., 2014). Reports from the literature suggest that the use of dendrimers and dendritic polymers can revolutionize fluids properties (Amanullah, 2013). Zhong et al. (2015c, 2016) proposed the use of polyamidoamine dendrimers and reached very good shale cuttings recovery. However, dendrimers demand laborius multistep synthetic procedures, in contrary, polyglycerols are usually produced in simple one-step procedures
http://dx.doi.org/10.1016/j.clay.2016.05.025 0169-1317/© 2016 Published by Elsevier B.V.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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(Parzuchowski et al., 2008). Teixeira et al. (2014) applied hyperbranched polyglycerols obtained from glycerol carbonate, an ecofriendly precursor, in association with KCl, achieving high percentage cuttings recovery with a polymer concentration about 5 wt%. It has been demonstrated that the performance of these hyperbranched structures is superior to the ones obtained with linear PEGs. Also, the literature indicates that the performance of linear non-ionic inhibitors can be improved by increasing the degree of hydrophobicity of the polymers (Souza et al., 2010). In this work we are committed to the development and evaluation of new and unique hyperbranched polymeric structures, the hydrophobized hyperbranched polyglycerols, as reactive shales inhibition additives for water-based drilling fluids. 2. Experimental 2.1. Materials Glycerol 99,5%, dimethyl carbonate – DMC ≥ 99%, potassium methoxide 95%, dodecyl tetradecyl glycidyl ether – DTGE technical grade, Poly(ethylene glycol) 400 Da – PEG400 and Poly (diallyldimethylammonium chloride) – PDADMAC solution 20 wt% in H2O (Mw: 200,000–350,000) medium molecular weight, were all supplied by Sigma-Aldrich. 2.2. Synthesis and characterization Glycerol carbonate – GC and hyperbranched polyglycerol – PG were synthesized following procedures reported by Rokicki et al. (2005), with exception of the purification process, since PG was not purified. Several partially hydrophobized hyperbranched polyglycerols – HPG – were synthesized with different hydrophobization degrees, with molar ratios with respect to polyglycerol PG:DTGE of 1:1; 1:2 and 1:4 in order to obtain the products labeled HPG11, HPG12 and HPG14, respectively. The procedure employed was as follows: at the end of the polyglycerol synthesis, the temperature of the system was reduced to 125 °C, and dodecyl tetradecyl glycidyl ether – DTGE was added at a rate of 5.0 mL/h. The system was kept closed for 24 h under N2 atmosphere. The characterization of the products was performed through Fourier transform infrared spectroscopy – FT-IR, and the measurements were carried out using a Nicolet 740 FT-IR spectrometer, in the range from 4000 to 400 cm− 1. Nuclear magnetic resonance – NMR was also employed and 1H NMR and 13C NMR spectra were recorded in d6-DMSO with a Brucker Advance DPX-300 spectrometer, operating at 300 and 75.4 MHz, respectively. Thermogravimetric analysis (TGA and DTGA) was conducted in a Shimadzu TGA-51 analyzer, at a ramp of 20 °C/min, from room temperature to 800 °C in a high-purity flowing nitrogen atmosphere (20 mL/min). Particle size was measured by Dynamic Light Scattering – DLS in a Malvern zeta sizer nano series Nano-ZS instrument, with water and tetrahydrofuran (THF) as solvent, in glass cells at 25 °C. 2.3. Clays characterization Clay mineral samples (A1, A2 and A3) and the bentonite B1 were obtained from Bentonorte Company (Paraíba, Brazil). All clays were characterized by scanning electron microscopy Hitachi TM3000 with energy dispersive spectroscopy (X-ray microprobe SwiftED) – SEMEDS. The chemical composition were determined in X-ray Fluorescence Spectrometer WDS-2, model AXIOS (Panalytical). The samples were placed at 1000 °C for 16 h, in muffle furnace, and weighed after cooling to verify the loss on ignition-LOI, which is related to the volatile components. Cation exchange capacity- CEC was quantified through the methylene blue test and textural analysis was performed with an ASAP 2010 Micrometrics analyzer, from nitrogen adsorption and desorption at −196 °C. The specific areas and porous diameters were calculated by the BET method and the porous volumes were calculated
using the BJH method. The semi-quantitative mineral compositions were determined by X-ray Diffraction (XRD), using fluorite as internal standard. 2.4. Inhibitive ability evaluation methods 2.4.1. Hot-rolling cuttings dispersion tests This test provides a simulation of the long exposure that the shale cuttings face when in contact with the fluid under average drilling conditions, when cuttings are brought up and removed from the borehole (Patel et al., 2007). In this test, 50.0 g of sized sample A1 were classified employing 4 and 8 mesh sieves, 4.76 and 2.38 mm, respectively. After that, the sample was transferred to a Baroid cell along with 350.0 mL of the formulated drilling fluid. The cell was kept in a rolling oven Fann Instrument Company LW2000 at 66 °C for 16 h. Finally, the cuttings were removed from the cell, washed and transferred to an oven for drying at 80 °C for 24 h. After drying the cuttings, the total amount and the recovered clay percentage were determined according to Eqs. (1) and (2), where Rtotal is the total of cuttings recovered, Wf, Wi and W#8 are the weight of dry clay after and before the rolling process, and the weight recovered in the 8 mesh sieve, respectively, while Rintact is the percentage of recovered intact cuttings.
Rtotal ¼
Wf 100% Wi
Rintact ¼
W#8 100% Wi
ð1Þ
ð2Þ
High recovery percentages, Rtotal and Rintact, indicate that the inhibitor is a good dispersion suppressant and shale inhibitor. Polymer (PG, HPG11, HPG12 and HPG14) aqueous solutions were tested in a concentration range from 0.1 to 3.0 wt% either pure or associated with KCl 1.0 wt%. The HPGs (5.0 wt% combined with 3.0 wt% KCl) were tested using the clay samples A1, A2 and A3 and their performance compared with the ones from solutions of PDADMAC 3.0 wt% and KCl 3.0 wt%. The highly reactive shales A2 and A3 were tested by a modified procedure using 14.3 g of cuttings in 100.0 mL of polymer solution at 66 °C for 4 h. 2.4.2. Bentonite inhibition test The bentonite inhibition test is usually employed as a screening method that helps to evaluate the ability of a chemical compound to prevent bentonite swelling and maintain low rheological profile (Patel et al., 2007). Aqueous dispersions of the polymeric shale inhibitors being developed in this work were used in 8.0 lb/bbl (2.3 wt%), either pure or combined with KCL 1.0 and 3.0 wt%. The polymeric systems performance was compared with the one from water, and from KCl 1.0 and 3.0 wt% solutions. In Baroid cells 350.0 mL of the solutions were treated with 10.0 lb/bbl (2.8 wt%) of bentonite B1 stirred for 10 min. After aging at 66 °C for 16 h, rheological properties were measured in a viscometer Fann Instrument Company 35 A and another amount of bentonite B1 was added to the cell and the procedure repeated until the rheological parameters exceeded the measuring limits. 2.5. Drilling fluids formulation tests The drilling fluids formulation tests were performed according to recommended standard procedures from the American Petroleum Institute- API (Recommended Practice, 2009). The Lubricity test was conducted in a Lubricity Tester 21200 Fann Instrument Company, and the fluid loss was evaluated in a HTHP Filter Press Series 387, Fann Instrument Company, at 25 °C, 100 psi for 30 min.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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2.6. Investigation of the inhibition mechanism In order to better understand the mechanisms involved in the inhibition process and to be able to propose an inhibition model, adsorption isotherms and X-ray diffraction measurements were used, using bentonite as adsorbent material. To this purpose, 0.25 g of bentonite B1 on 150 mesh (0.119 mm) sieve were added to 25 mL of the polymer solution at concentrations of 0 to 0.4 wt% of polymer for the adsorption isotherms and also for the X-ray diffraction experiments. The systems were kept under stirring for 21 h. The dispersion was centrifuged at 2800 rpm for 20 min in a centrifuge Novatecnica NT810 and the supernatant was collected and diluted 10 times with ultrapure water, the resulting solution being analyzed for carbon in a Total Carbon Analyzer, Shimadzu TOC-L. The deposited material was washed 3 times adding a portion of 25 mL of ultrapure water, manually stirring and centrifuging it under the afore mentioned conditions. Finally, the composites were dried at 80 °C for 24 h, collected, pulverized and submitted to X-ray diffraction analysis, the samples were homogeneously distributed on glass sample holders. The d001-value of the composites were obtained with Rigaku Ultima IV diffractometer operating at 40 kV and 20 mA, the Nifiltered Cu Ka radiation (λ = 0.154 nm). Scans were run in the range of 2° to 30° 2theta at a step size of 0.02°. Representative samples were selected for TGA analysis in a Shimadzu TGA-51 analyzer, with a ramp of 20 °C/min, from room temperature to 400 °C, in a high-purity flowing nitrogen atmosphere (20 mL/min). In these experiments, hyperbranched polyglycerol was used for comparison with HPGs. 3. Results and discussion 3.1. Synthesis and characterization The developed process of production of HPG can be considered an interesting synthetic strategy for industrial applications, with economic and environmental advantages, since no solvents or purification steps were used. Several green chemical concepts motivated the choice of routes in this work in order to obtain the target products: the use of glycerol carbonate synthesized from glycerol; the synthesis of PG and HPG based on ring opening polymerization performed through mass reactions; a route not involving purification processes, consequently leaving no residues and making the process more economical. The glycerol carbonate and hyperbranched polyglycerol synthesis reactions (Rokicki et al., 2005) are presented in Fig. 1. The PG was synthesized
3
with a molar mass Mn: 562 Da, Mw: 1155 Da and PDI (Mn/Mw): 2.06. The obtained PG was modified through hydrophobization reactions to obtain a series of amphiphilic hyperbranched structures, as shown in Fig. 2. The ether bond formed confers a relative stability to the polymer, which is necessary for drilling fluids applications, since a fluid is a complex mixture and the conditions of temperature and pressure can be very severe in the well. The FT-IR spectra of DTGE, PG and HPG are shown in Fig. 3. The DTGE spectrum presents characteristic bands for the epoxy ring at 1250, 910 and 760 cm−1 attributed to C\\O bond and, as expected, these bands did disappear in the HPG spectrum. On the other hand, PG and HPG spectra present strong bands at 3400 and 2900 cm−1which are related to hydroxyl groups. The HPG FT-IR spectrum does not show any characteristic bands of epoxy ring indicating that the hydrophobization reaction was completed under the conditions employed. This hypothesis was confirmed by the NMR results shown in Fig. 4, where no epoxy protons signals (2.6 and 2.8 ppm), as well as epoxy carbon signals (44.0 and 51.0 ppm) are observed. In the 13C NMR spectrum, signals between 59.0 to 82.0 ppm are attributed to polyglycerol carbon atoms bonded to oxygen, except peak at 71.0 ppm which is a signal from the carbon atom in the alkyl chain [OCH2(CH2)nCH3]. The substitution degree – SD was calculated from quantitative 13C NMR by the equation: 3ACH3/Aglycerol, where ACH3 and Aglycerol represent the integration area in 14.5 ppm and between 59.0 to 82.0 ppm, without the signal intensity of the alkyl chain aforementioned, respectively. Therefore, the SD for HPG11, HPG12 and HPG14 are 7.0, 13.0 and 26.0% of hydroxyl groups, respectively. The work was carried out only up to this limit of SD because the modified polymers should be relatively water soluble in order to be used as shale inhibitor for water-based drilling fluids. The thermogravimetric analysis results (TGA and DTGA) for HPG presented in Fig. 5 show that the most significant mass loss occurs between 200 to 400 °C, indicating that the modified polyglycerol should not decompose under the standard conditions found in wells. The particle size of the obtained polymeric structures was measured by Dynamic Light Scattering – DLS and the results can be seen in Fig. 6. In an aqueous dispersion containing 0.5 to 2.0 wt/v% of the materials the unmodified polyglycerol PG presents an average size of about 2.5 nm, however, the amphiphilic structures show a size distribution with high dispersion, around 50–80 nm. The visual turbid appearance of the hyperbranched polymers aqueous solutions/suspensions and the magnitude of the particle sizes obtained suggest that such particles are associated in aqueous medium, forming aggregates. This suggestion
Fig. 1. Glycerol carbonate and hyperbranched polyglycerol synthesis reactions (Rokicki et al., 2005).
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 2. Partially hydrophobized hyperbranched polyglycerol synthesis.
is corroborated by the large oscillation observed in the measurements. It is possible to suppose that this association gives rise to the formation of micellar structures such as the ones observed with amphiphilic molecules like the surfactants. To test this possibility, another experiment was conducted, varying the solvent polarity with the purpose of destroying these aggregated structures. A series of solutions containing 1.0 wt% of the amphiphilic polymer in THF:water mixtures were prepared, and the DLS results are shown in Fig. 7. With the 80:20 THF:water mixture, the HPGs particles size were estimated as 3.0 nm approximately, suggesting that the alkyl chains were solvated by THF and the polar core – PG was solvated by water, breaking the aggregates by favoring solute–solvent interactions instead of solute–solute interactions. 3.2. Clay- mineral samples characterization Clay-mineral samples micrographs are presented in Fig. 8 where it is possible to observe the particles morphological differences
among the four clay types employed in the work. The samples were analyzed as selected powder on 150 mesh sieve. Table 1 contains the shales chemical composition (quantified by XRF), the cation exchange capacity and the textural analysis results. The cation exchange capacity (CEC) is a measure of the exchangeable cations (typically sodium, calcium, iron, potassium and magnesium) that neutralize the negatively clay particles. Reactive shales have a CEC higher than 20 meq/100 g (Stephens et al., 2009). The reactivity of shales also depends on their formation process, several properties like mineralogy, porosity, water affinity, e.g., are important to understand shale/fluid interaction and shale stability (Lal, 1999). Tables 2.a. and 2.b. show shales mineral compositions. All of them presented high clay content, smectite was the predominant mineral. Based on the characterization results obtained and on empirical observations, we concluded that the clay samples are highly reactive with water, which is convenient to study the performance of the proposed inhibitors.
Fig. 3. FT-IR spectra of DTGE, PG and HPG.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 4. a)13C NMR and b)1H NMR from HPG, respectively. TMP is 1,1,1-tris(hydroxymethyl)propane used as initiator on PG synthesis.
3.3. Evaluation of the inhibition performance 3.3.1. Cuttings hot-rolling dispersion tests All HPGs were used in the performance tests without any purification process. Fig. 9 shows the recovery for dispersed and intact cuttings, for the different systems containing the partially hydrophobized structures, in the presence and absence of the inhibitor KCl, compared to the results for PG and KCl systems. It can be observed that, in all cases,
the inhibition efficiency increases with the polymer concentration. In aqueous medium, the synthesized polymer structures show a relatively good performance as inhibitors, but the performance is much better in the presence of KCl, probably due to the formation of a complex between the polymers and K+, favoring the polymer interaction with the negatively charged clay layer, as reported previously in the literature for polyglycols and polyols, also non-ionic polymers (Bland et al., 1995; Reid and Dolan, 1995). The results also indicate that the partially
Fig. 5. HPG thermogravimetric analysis.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 6. Effect of polymer concentration on PG and HPG partial size.
hydrophobized molecules are better inhibitors than the PG polymer, probably due to the decreased solubility of the HPGs in comparison to PG and also as a consequence of their increased adsorption on clay (Souza et al., 2010). The relationship between solubility and the amount of adsorbed polymer on the clays surface is demonstrated by the adsorption isotherms shown in Fig. 12. The polymers HPG11 and HPG12 present similarities in their inhibition properties, but HPG14 does not follow this trend, suggesting that perhaps the efficiency of inhibition may be limited by degree of hydrophobization of the non-ionic polymers. Also, the polymer molecule must be sufficiently water soluble to promote a good interaction with the clay mineral. The results shown in Fig. 10 corroborate this observation. Once again, it is possible to note the similarities between the performance of HPG11 and HPG12 and the poor results of the systems containing HPG14, PG and KCl. The HPG11 and HPG12 systems presented promising results in all tested
clays reaching, in many cases, nearly 80% of intact cuttings recovery, showing interesting robustness for future field applications. In particular, for clay A3 the results with HPG12, e.g., indicate intact cuttings recovery around 90%. Those systems proved even competitive performance in comparison with the commercial and highly toxic inhibitor PDADMAC. Also worth noticing is the effect of increasing the KCl concentration from 1.0 to 3.0 wt% and of the polymer concentration (from 3.0 to 5.0 wt%) which, according to Figs. 9 and 10 for the shale A1, represents an increase of 50% for the intact cuttings recovery (from about 40 to 80% recovery). 3.3.2. Bentonite inhibition test The Bentonite Inhibition Test results presented in Fig. 11 show that the systems containing partially hydrophobized polymers in association with KCl exhibit the best inhibition performance. From these results it is possible to observe more clearly the synergism between the non-ionic structures and the salt, as discussed above. A peculiar result was observed for the HPG14 aqueous dispersion, which apparently presented the best performance as inhibitor in comparison with the other materials dispersion in absence of KCl. This could be explained as follows. In the bentonite inhibition test small bentonite powder portions are added to the inhibitor solution being tested, but in the case of the HPG14 dispersion, after the aging, bentonite powder flocculates were formed, that remained even after vigorous stirring in the Hamilton Beach mixer. Perhaps those flocculates interfered on the bentonite interaction with water, making more difficult its swelling, and consequently keeping low, in an artificial way, the rheological properties of the system. However, in the test with KCl it was not possible to observe the referred flocculates. 3.4. Drilling fluids tests
Fig. 7. Effect of THF:water ratio on HPG (1.0 wt%) partial size. Some columns were not plotted because correspond to systems in which the polymer was not soluble on the solvent mixture.
API drilling fluids tests results are presented in Table 3. Analyzing the rheological properties of the fluids it is possible to observe that Fluid 2 shows much higher viscosity values, in different analysis conditions, when compared with the ones for Fluid 1 (base fluid) and this difference
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
C.C. Ferreira et al. / Applied Clay Science xxx (2016) xxx–xxx
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Fig. 8. Shale samples micrographs. a) Shale A1; b) Shale A2; c) Shale A3 and d) Bentonite B1.
Table 1 Clay chemical composition and textural analysis.
Na2O MgO Al2O SiO2 P2O5 K2O CaO TiO2 Fe2O3 LOI
Chemical composition (wt%)
CEC (meq/100 g) Specific area BET (m2/g) Pore volume (cm3/g) Pore diameter (Å)
Shale A1
Shale A2
Shale A3
Bentonite B1
0.62 2.2 21.7 45.7 0.11 0.95 0.42 1.2 7.0 20.0 63.4 81.1 0.12 63.2
0.59 2.1 21.5 49.0 b0.1 1.3 0.34 1.3 6.7 16.8 51.9 53.0 0.09 80.5
0.45 1.9 12.8 58.3 b0.1 0.15 0.36 0.58 7.2 18.1 41.1 107.5 0.21 80.9
2.0 2.4 19.4 48.3 b0.1 0.94 0.86 1.0 7.7 17.0 60.0 80.7 0.07 50.8
CEC = cation exchange capacity; LOI = loss on ignition.
could be a consequence of the PDAMAC addition. In the case of the fluids containing the HPGs, the rheological properties were maintained similar to the ones obtained for the base, indicating that the proposed inhibitors do not have a great effect on those properties. The HPGs improved the fluid lubricity, probably as a consequence of their amphiphilic structure (Nunes et al., 2014). As it has been shown in the cuttings hotrolling dispersion tests for the polymer solutions, the products HPG11 and HPG12 have similar inhibition performances when compared Table 2.a Clay mineralogical composition. Clay content.
Shale A1 Shale A2 Shale A3 Bentonite B1
with the one for the commercial inhibitor PDADMAC. When compared to the non-ionic inhibitor PEG400, the proposed HPG materials show a 20% higher performance in the intact cuttings recovery test. In conclusion, the partially hydrophobized hyperbranched polyglycerols are really promising non-ionic inhibitors for water-based drilling fluids.
Table 2.b Clay mineralogical composition. Mineral content. Sample
Clay fraction (%)
Silt fraction (%)
95.8 95.8 86.4 92.5
4.2 4.2 13.6 7.5
Shale A1 Shale A2 Shale A3 Bentonite B1
Clay fraction
Silt fraction
Smectite (%)
Illite (%)
Kaolinite (%)
Mica (%)
Quartz (%)
Hematite (%)
68.4 60.6 81.0 81.7
7.66 – – 2.16
19.8 25.5 5.44 8.61
– 9.74 – –
4.20 4.19 0.50 7.50
– – 13.1 –
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 9. Cutting recovery. a) Dispersed recovery for polymers aqueous solution; b) Intact recovery for polymers aqueous solution; c) Dispersed recovery for polymers combined with KCI 1.0 wt%; d) Intact recovery for polymers combined with KCI 1.0 wt%. The used shale is A1.
3.5. Inhibition mechanism investigation
Fig. 10. Cuttings recovery tests performed with different shales. a) Disperse cuttings recovery. b) Intact cuttings recovery.
To investigate the inhibition mechanism, adsorption isotherms were prepared in duplicate (R1 and R2) to analyze the polymer aqueous solutions before and after contact with bentonite. The results are presented in Fig. 12, where qe is the polymer mass adsorbed per gram of bentonite, Ce is the polymer equilibrium concentration. It is possible to observe that the adsorbed amount of polymeric material increases with the hydrophobization degree, probably as a consequence of the decrease of the macromolecules solubility in water. This behavior was observed for all the materials prepared in aqueous dispersions, in the same polymer concentration range (0 to 4000 ppm). For non-ionic polymeric structures this behavior was observed in partially hydrophobized polyglycols (Souza et al., 2010). However the isotherm for PG shows the presence of a pseudo-plateau which is not observed for HPGs materials. All systems presented satisfactory fittings to the Freundlich isotherm model with a correlation coefficient greater than 0.99. The inclination of the HPGs isotherms also indicate that the amphiphilic structures have a higher absorption capacity in clay in comparison to the unmodified polymer. Also, the increase of the isotherms inclination with the degree of the HPGs hydrophobization is a clear indication that the bentonite affinity increases with the hydrophobization degree for the polymer concentration range considered. For linear structures the literature (Souza et al., 2010; Volpert et al., 1998) suggests the formation of additional polymer layers by hydrophobic interactions, besides the interaction between (OCH2CH2) groups and the clay surface. However, in the case of the hyperbranched structures only monolayers are observed, and the increase in the adsorption could be associated to the decrease of solubility with the increase of the hydrophobization degree, favoring bentonite-polymer interactions in comparison with the water-polymer interactions, as previously mentioned. The literature also suggests the formation of a stable complex between exchangeable potassium ions on the clay surface and the non-terminal portions of the adsorbed polyol molecules. This leads to the removal of the water
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 11. Bentonite inhibition test: Effect of bentonite concentration on the yield point (1 Ib/bbl = 0.9975 g/350 mL).
molecules and to an increase of the amount of adsorbed polymer for the structures without free hydroxyl groups (Reid and Dolan, 1995). XRD analysis results are presented in Fig. 13 and show the increase of the interlayer spacing, calculated using Bragg's law, for the composites formed with the polymeric structures and bentonite. The increase of the interlayer spacing, for HPG11 and HPG12 composites, is between 0.30–0.40 nm indicating that the way they penetrate and settle inside the interlayer spacing should be very similar. Nevertheless, it is possible to observe a loss of crystallinity for the composites formed by PG and HPG14 in high concentrations, probably due to the polymer penetration in the interlayer, causing delamination of the clay. This result is also a confirmation that PG and HPG14 are not inhibitors in the absence of KCl. In conclusion, the results suggest that the polymer-clay interaction involves the penetration of the molecules, or parts of them, in the interlayer spacing, minimizing the water-clay interaction due to the
Table 3 Drilling fluid formulation results. Fluid 1 (Base)
Fluid 2 (PDADMAC)
Fluid 3 (PEG400)
Fluid 4 (HPG11)
Fluid 5 (HPG12)
350.0 1.0 0.25 5.0 3.5 0.0 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
API results after aging, rolling for 16 h at 66 °C 600 rpm 84 147 300 rpm 59 93 200 rpm 48 71 100 rpm 35 46 6 rpm 13 9 3 rpm 12 7 Gi 12 7 Gf 14 9 pH 9.0 8.5 Lubricity 0.20 0.19 Density (g/mL) 1.15 1.15 Filtrate (mL) 9.1 5.3
83 60 50 38 15 13 13 15 8.5 0.19 1.16 9.4
80 58 48 35 13 10 10 13 9.0 0.15 1.16 7.8
83 59 47 33 10 9 9 10 9.0 0.16 1.16 7.6
Cuttings recovery Disperse (%) Intact (%)
72.5 37.3
84.9 59.3
86.6 59.0
Water (lb/bbl) XG (lb/bbl) NaOH (g) HPA (lb/bbl) KCl (lb/bbl) Inhibitor (lb/bbl) CaCO3 (lb/bbl) Barite (lb/bbl) Lubricant (lb/bbl)
69.3 32.8
81.2 68.3
GX = xanthan gum; HPA = hidroxypropylamide; lb/bbl = 0.9975 g/350 mL.
hydrophobic characteristics of the formed polymer-bentonite composite. As demonstrated by TGA results shown in Table 4, the water loss increases with an increase in the polymer concentration and also in the polymer hydrophobization degree. The third factor to consider is the fact that in aqueous medium the amphiphilic structures are associated, forming aggregates of 50– 80 nm approximately, as shown in Fig. 6. Also, the tested clay-minerals have shown pore diameters of about 50–80 Å, as presented in Table 1, which are much smaller than the aggregates. This could mean that some of these aggregates could be clogging some of the pore throats of these clay-rich minerals, hindering the entry of water into the clay structure. 4. Conclusions In this work it is shown that chemical changes promoted in the polyglycerol (PG) hyperbranched macromolecule through the hydrophobization of its structure, produces amphiphilic polymers which are promising clay reactivity inhibitors for water based drilling fluids formulations. Stable and versatile new amphiphilic materials were synthesized by alkyl chain insertions into hyperbranched polyglycerol structures through ether bond formation. The proposed synthetic route follows green chemistry principles. A series of HPGs was obtained that in association with KCl did show a high performance as clay reactivity inhibitors. When compared with the unmodified PG,
Fig. 12. Adsorption isotherms. Curves were prepared in duplicates, R1 and R2, for each polymer.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 13. XRD spectra of polymer/clay composites. a) PG; b) HPG11; c) HPG12; d) HPG14.
with linear PEG and with the commercial cationic inhibitor PDADMAC, they did show a competitive performance. Finally, an inhibition mechanism is proposed based on the contribution of three processes that Table 4 TGA analysis results for composites water loss. Polymer conc. (wt%)
Water loss (wt%) PG
HPG11
HPG12
HPG14
0.00 0.05 0.20 0.60
9.1 7.1 4.4 3.8
9.1 6.8 4.2 2.2
9.1 5.1 4.0 2.6
9.1 6.7 3.9 1.6
could take place, simultaneously or not: (1) formation of a high affinity for clay complex between HPG and K+ ions, which adsorbs onto the clay surface minimizing shale-water interactions, (2) HPG penetration on the clay interlayer spacing, also minimizing shale-water interactions, (3) formation of aggregates by the amphiphilic structures that would lead to the obstruction of the clay pore throats, thereby making it difficult the entry of water molecules. Acknowledgements The author thanks to the infrastructure of the Institute of Chemistry/UFRJ – Brazil Brazilian Petroleum National Agency – ANP (48610.013790/2009) for financial support.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Reid, P.I., Dolan, B., 1995. Mechanism of shale inhibition by polyols in water based drilling Fluids. SPE International Symposium on Oilfield Chemistry, 14–17 February, San Antonio, Texas. SPE 28960-MS. Rokicki, G., Rakoczy, P., Parzuchowski, P., Sobiecki, M., 2005. Hyperbranched aliphatic polyethers obtained from environmentally benign monomer: glycerol carbonate. Green Chem. 7, 529–539. Shadizadeh, S.R., Moslemizadeh, A., Dezaki, A.S., 2015. A novel nonionic surfactant for inhibiting shale hydration. Appl. Clay Sci. 118, 74–86. Souza, C.E.C., Lima, A.S., Nascimento, R.S.V., 2010. Hydrophobically modified poly(ethylene glycol)as reactive clays inhibitor additive in water-based drilling fluids. J. Appl. Polym. Sci. 117, 857–864. Stephens, M., Gomez-Nava, S., Churan, M., 2009. AADE 2009-NTCE-11-04: Laboratory Methods to Assess Shale Reactivity with Drilling Fluids. National technical conference & exhibition, New Orleans, Lousiana, USA. Sun, F., Luo, X., Kang, L., Peng, X., Lu, C., 2015. Synthesis of hyperbranched polymers and their applications in analytical chemistry. Polym. Chem. 6, 1214. Sunder, A., Hanselmann, R., Frey, H., Mülhaupt, R., 1999. Controlled synthesis of hyperbranched polyglycerols by ring-opening multibranching polymerization. Macromolecules 32, 4240–4246. Teixeira, G.T., Lomba, R.F.T., Francisco, A.D.S., Silva, J.F.C., Nascimento, R.S.V., 2014. Hyperbranched polyglycerols, obtained from environmentally benign monomer, as reactive clays inhibitors for water-based drilling fluids. J. Appl. Polym. Sci. 131, 40384. Volpert, E., Selb, J., Candau, F., Green, N., Argillier, J.F., Audibert, A., 1998. Adsorption of hydrophobically associating polyacrylamides on clay. Langmuir 14 (7), 1870–1879. Wan, D., Liu, H., Jin, M., Pu, H., Wang, G., 2014. Facile Williamson etherification of hyperbranched polyglycerol and subtle core-dependent supramolecular guest selection of the resulting molecular nanocapsule. Eur. Polym. J. 55, 9–16. Wang, L., Liu, S., Wang, T., Sun, D., 2011. Effect of poly(oxypropylene)diamine adsorption on hydration and dispersion of montmorillonite particles in aqueous solution. Colloids Surf. A Physicochem. Eng. Asp. 381, 41–47. Zhong, H., Qiu, Z., Huang, W., Cao, J., 2012. Poly(oxypropylene)-amidoamine modified bentonite as potential shale inhibitor in water-based drilling fluids. Appl. Clay Sci. 67–68, 36–43. Zhong, H., Sun, D., Huang, W., Liu, Y., Qiu, Z., 2015a. Effect of cycloaliphatic amine on the shale inhibitive properties of water-based drilling fluid. Open Fuels Energy Sci. J. 8, 19–27. Zhong, H., Qiu, Z., Sun, D., Zhang, D., Huang, W., 2015b. Inhibitive properties comparison of different polyetheramines in water-based drilling fluid. J. Nat. Gas Sci. Eng. 26, 99–107. Zhong, H., Qiu, Z., Huang, W., Sun, D., Zhang, D., Cao, J., 2015c. Synergistic stabilization of shale by a mixture of polyamidoamine dendrimers modified bentonite with various generations in water-based. Appl. Clay Sci. 114, 359–369. Zhong, H., Qiu, Z., Zhang, D., Tang, Z., Huang, W., Wang, W., 2016. Inhibiting shalehydration and dispersion with amine-terminated polyamidoamine dendrimers. J. Nat. Gas Sci. Eng. 28, 52–60.
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Research paper
Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids Conny Cerai Ferreira a, Gleber Tacio Teixeira b, Elizabeth Roditi Lachter a, Regina Sandra Veiga Nascimento a,⁎ a Laboratório de Fluidos e Materiais Poliméricos Multifásicos- FLUMAT-, Pólo de Xistoquímica, Instituto de Química, Universidade Federal do Rio de Janeiro, Hélio de Almeida St., 40, Cidade Universitária, Rio de Janeiro, Brazil b Petrobras, Setor de Tecnologia de Fluidos de Perfuração, Rod. Amaral Peixoto, 163, Imboassica, Macaé, Rio de Janeiro 27925-290, Brazil
a r t i c l e
i n f o
Article history: Received 16 March 2016 Received in revised form 19 May 2016 Accepted 24 May 2016 Available online xxxx Keywords: Hyperbranched polymer Polyglycerol hydrophobization Shale interaction and inhibition Water-based drilling fluid
a b s t r a c t The oil and gas industry demands drilling fluids that would be able to minimize the wellbore instability faced during the drilling of reactive shales. In this work we describe the synthesis of hydrophobized hyperbranched polyglycerols (HPG) with unique design and properties to be used as non-ionic reactive shale inhibitors. In association with KCl, HPG showed a superior performance in comparison with unmodified hyperbranched polyglycerol and with the commercial clay reactivity inhibitors PEG400 and PDADMAC. Intact cuttings recoveries were around 80%. The proposed inhibition mechanism suggests the formation of a complex between HPGs and K+ ions and its penetration into the clay interlayer spacing to minimize the shale-water interactions and remove water molecules present in the clay galleries. In addition, these aggregates formed by the amphiphilic structures would cause obstruction of the clay minerals pore throats, thereby making it even more difficult for the penetration of water molecules. © 2016 Published by Elsevier B.V.
1. Introduction The oil industry has been showing a large demand for new technologies to overcome the huge problems related to the drilling of wells. Nowadays, whenever possible, water-based drilling fluids (WBM) are employed, since oil based fluids face several environmental restrictions and involve much higher costs (He et al., 2014). However, when waterbased fluids are used, several wellbore stability issues contribute to increase the challenges related to drilling, and these issues are, in large part, related to the water reactivity of some of the shales being drilled. Shales are clay rich sedimentary rocks that can present water sensitivity depending on their crystalline structure, composition, porosity and the existence of cracks and fractures on the rocks surface (Lal, 1999; Gomez and Patel, 2013; Al-Arfaj et al., 2014). Reactive shales, when in contact with WBM, can have their crystalline structure destroyed resulting in severe problems, such as trapping of column and/or well collapse. To deal with the possible damages caused by water, chemical inhibitors are added to the fluid formulation in order to minimize or even prevent the shale crystalline destruction. The literature reports the use of inorganic salts, such as KCl, and CaCl2, water soluble silicates (Gomez and Patel, 2013), cationic hydrophobized polysaccharides (Lopes et al., 2014), ionic liquids (Berry et al., 2009), poly(oxyalkyl)amines (Qu et al., 2009; Wang et al., 2011), poly(oxypropylene)amidoamine (Zhong et al., 2012), others amine ⁎ Corresponding author. E-mail address: [email protected] (R.S.V. Nascimento).
derivatives (Patel et al., 2007; Zhong et al., 2015a, 2015b) and nonionic molecules/polymers (Shadizadeh et al., 2015), all of them presenting advantages and disadvantages. Regarding the environmental requirements for the drilling fluid formulation, amine derivatives such as quaternary alkyl ammonium salts or amine containing polymers are highly efficient shale inhibitors, but present elevated toxicity. Linear non-ionic polymers, such as polyglycols (PEGs) and polyols, although showing low toxicity, present limited field applications (Patel et al., 2007). The hyperbranched polyglycerols are versatile structures which can be produced from glycidol (Sunder et al., 1999) or glycerol carbonate (Rokicki et al., 2005) a monomer obtained from glycerol. The glycerol is a co-product of the biodiesel industry. In Brazil, due to the increasing use of biodiesel, in partial replacement of the diesel obtained from petroleum, its annual production of about 500,000 m3 demands for the development of new uses for the glycerol (ANP, 2016). The hyperbranched polyglycerol and its derivatives have been widely studied, e.g., as potential agents for the controlled release of drugs (Gupta et al., 2012), as sample pretreatment and immunosensors in analytical chemistry fields (Sun et al., 2015) and as additives for the encapsulation of pigments (Wan et al., 2014). Reports from the literature suggest that the use of dendrimers and dendritic polymers can revolutionize fluids properties (Amanullah, 2013). Zhong et al. (2015c, 2016) proposed the use of polyamidoamine dendrimers and reached very good shale cuttings recovery. However, dendrimers demand laborius multistep synthetic procedures, in contrary, polyglycerols are usually produced in simple one-step procedures
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Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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(Parzuchowski et al., 2008). Teixeira et al. (2014) applied hyperbranched polyglycerols obtained from glycerol carbonate, an ecofriendly precursor, in association with KCl, achieving high percentage cuttings recovery with a polymer concentration about 5 wt%. It has been demonstrated that the performance of these hyperbranched structures is superior to the ones obtained with linear PEGs. Also, the literature indicates that the performance of linear non-ionic inhibitors can be improved by increasing the degree of hydrophobicity of the polymers (Souza et al., 2010). In this work we are committed to the development and evaluation of new and unique hyperbranched polymeric structures, the hydrophobized hyperbranched polyglycerols, as reactive shales inhibition additives for water-based drilling fluids. 2. Experimental 2.1. Materials Glycerol 99,5%, dimethyl carbonate – DMC ≥ 99%, potassium methoxide 95%, dodecyl tetradecyl glycidyl ether – DTGE technical grade, Poly(ethylene glycol) 400 Da – PEG400 and Poly (diallyldimethylammonium chloride) – PDADMAC solution 20 wt% in H2O (Mw: 200,000–350,000) medium molecular weight, were all supplied by Sigma-Aldrich. 2.2. Synthesis and characterization Glycerol carbonate – GC and hyperbranched polyglycerol – PG were synthesized following procedures reported by Rokicki et al. (2005), with exception of the purification process, since PG was not purified. Several partially hydrophobized hyperbranched polyglycerols – HPG – were synthesized with different hydrophobization degrees, with molar ratios with respect to polyglycerol PG:DTGE of 1:1; 1:2 and 1:4 in order to obtain the products labeled HPG11, HPG12 and HPG14, respectively. The procedure employed was as follows: at the end of the polyglycerol synthesis, the temperature of the system was reduced to 125 °C, and dodecyl tetradecyl glycidyl ether – DTGE was added at a rate of 5.0 mL/h. The system was kept closed for 24 h under N2 atmosphere. The characterization of the products was performed through Fourier transform infrared spectroscopy – FT-IR, and the measurements were carried out using a Nicolet 740 FT-IR spectrometer, in the range from 4000 to 400 cm− 1. Nuclear magnetic resonance – NMR was also employed and 1H NMR and 13C NMR spectra were recorded in d6-DMSO with a Brucker Advance DPX-300 spectrometer, operating at 300 and 75.4 MHz, respectively. Thermogravimetric analysis (TGA and DTGA) was conducted in a Shimadzu TGA-51 analyzer, at a ramp of 20 °C/min, from room temperature to 800 °C in a high-purity flowing nitrogen atmosphere (20 mL/min). Particle size was measured by Dynamic Light Scattering – DLS in a Malvern zeta sizer nano series Nano-ZS instrument, with water and tetrahydrofuran (THF) as solvent, in glass cells at 25 °C. 2.3. Clays characterization Clay mineral samples (A1, A2 and A3) and the bentonite B1 were obtained from Bentonorte Company (Paraíba, Brazil). All clays were characterized by scanning electron microscopy Hitachi TM3000 with energy dispersive spectroscopy (X-ray microprobe SwiftED) – SEMEDS. The chemical composition were determined in X-ray Fluorescence Spectrometer WDS-2, model AXIOS (Panalytical). The samples were placed at 1000 °C for 16 h, in muffle furnace, and weighed after cooling to verify the loss on ignition-LOI, which is related to the volatile components. Cation exchange capacity- CEC was quantified through the methylene blue test and textural analysis was performed with an ASAP 2010 Micrometrics analyzer, from nitrogen adsorption and desorption at −196 °C. The specific areas and porous diameters were calculated by the BET method and the porous volumes were calculated
using the BJH method. The semi-quantitative mineral compositions were determined by X-ray Diffraction (XRD), using fluorite as internal standard. 2.4. Inhibitive ability evaluation methods 2.4.1. Hot-rolling cuttings dispersion tests This test provides a simulation of the long exposure that the shale cuttings face when in contact with the fluid under average drilling conditions, when cuttings are brought up and removed from the borehole (Patel et al., 2007). In this test, 50.0 g of sized sample A1 were classified employing 4 and 8 mesh sieves, 4.76 and 2.38 mm, respectively. After that, the sample was transferred to a Baroid cell along with 350.0 mL of the formulated drilling fluid. The cell was kept in a rolling oven Fann Instrument Company LW2000 at 66 °C for 16 h. Finally, the cuttings were removed from the cell, washed and transferred to an oven for drying at 80 °C for 24 h. After drying the cuttings, the total amount and the recovered clay percentage were determined according to Eqs. (1) and (2), where Rtotal is the total of cuttings recovered, Wf, Wi and W#8 are the weight of dry clay after and before the rolling process, and the weight recovered in the 8 mesh sieve, respectively, while Rintact is the percentage of recovered intact cuttings.
Rtotal ¼
Wf 100% Wi
Rintact ¼
W#8 100% Wi
ð1Þ
ð2Þ
High recovery percentages, Rtotal and Rintact, indicate that the inhibitor is a good dispersion suppressant and shale inhibitor. Polymer (PG, HPG11, HPG12 and HPG14) aqueous solutions were tested in a concentration range from 0.1 to 3.0 wt% either pure or associated with KCl 1.0 wt%. The HPGs (5.0 wt% combined with 3.0 wt% KCl) were tested using the clay samples A1, A2 and A3 and their performance compared with the ones from solutions of PDADMAC 3.0 wt% and KCl 3.0 wt%. The highly reactive shales A2 and A3 were tested by a modified procedure using 14.3 g of cuttings in 100.0 mL of polymer solution at 66 °C for 4 h. 2.4.2. Bentonite inhibition test The bentonite inhibition test is usually employed as a screening method that helps to evaluate the ability of a chemical compound to prevent bentonite swelling and maintain low rheological profile (Patel et al., 2007). Aqueous dispersions of the polymeric shale inhibitors being developed in this work were used in 8.0 lb/bbl (2.3 wt%), either pure or combined with KCL 1.0 and 3.0 wt%. The polymeric systems performance was compared with the one from water, and from KCl 1.0 and 3.0 wt% solutions. In Baroid cells 350.0 mL of the solutions were treated with 10.0 lb/bbl (2.8 wt%) of bentonite B1 stirred for 10 min. After aging at 66 °C for 16 h, rheological properties were measured in a viscometer Fann Instrument Company 35 A and another amount of bentonite B1 was added to the cell and the procedure repeated until the rheological parameters exceeded the measuring limits. 2.5. Drilling fluids formulation tests The drilling fluids formulation tests were performed according to recommended standard procedures from the American Petroleum Institute- API (Recommended Practice, 2009). The Lubricity test was conducted in a Lubricity Tester 21200 Fann Instrument Company, and the fluid loss was evaluated in a HTHP Filter Press Series 387, Fann Instrument Company, at 25 °C, 100 psi for 30 min.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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2.6. Investigation of the inhibition mechanism In order to better understand the mechanisms involved in the inhibition process and to be able to propose an inhibition model, adsorption isotherms and X-ray diffraction measurements were used, using bentonite as adsorbent material. To this purpose, 0.25 g of bentonite B1 on 150 mesh (0.119 mm) sieve were added to 25 mL of the polymer solution at concentrations of 0 to 0.4 wt% of polymer for the adsorption isotherms and also for the X-ray diffraction experiments. The systems were kept under stirring for 21 h. The dispersion was centrifuged at 2800 rpm for 20 min in a centrifuge Novatecnica NT810 and the supernatant was collected and diluted 10 times with ultrapure water, the resulting solution being analyzed for carbon in a Total Carbon Analyzer, Shimadzu TOC-L. The deposited material was washed 3 times adding a portion of 25 mL of ultrapure water, manually stirring and centrifuging it under the afore mentioned conditions. Finally, the composites were dried at 80 °C for 24 h, collected, pulverized and submitted to X-ray diffraction analysis, the samples were homogeneously distributed on glass sample holders. The d001-value of the composites were obtained with Rigaku Ultima IV diffractometer operating at 40 kV and 20 mA, the Nifiltered Cu Ka radiation (λ = 0.154 nm). Scans were run in the range of 2° to 30° 2theta at a step size of 0.02°. Representative samples were selected for TGA analysis in a Shimadzu TGA-51 analyzer, with a ramp of 20 °C/min, from room temperature to 400 °C, in a high-purity flowing nitrogen atmosphere (20 mL/min). In these experiments, hyperbranched polyglycerol was used for comparison with HPGs. 3. Results and discussion 3.1. Synthesis and characterization The developed process of production of HPG can be considered an interesting synthetic strategy for industrial applications, with economic and environmental advantages, since no solvents or purification steps were used. Several green chemical concepts motivated the choice of routes in this work in order to obtain the target products: the use of glycerol carbonate synthesized from glycerol; the synthesis of PG and HPG based on ring opening polymerization performed through mass reactions; a route not involving purification processes, consequently leaving no residues and making the process more economical. The glycerol carbonate and hyperbranched polyglycerol synthesis reactions (Rokicki et al., 2005) are presented in Fig. 1. The PG was synthesized
3
with a molar mass Mn: 562 Da, Mw: 1155 Da and PDI (Mn/Mw): 2.06. The obtained PG was modified through hydrophobization reactions to obtain a series of amphiphilic hyperbranched structures, as shown in Fig. 2. The ether bond formed confers a relative stability to the polymer, which is necessary for drilling fluids applications, since a fluid is a complex mixture and the conditions of temperature and pressure can be very severe in the well. The FT-IR spectra of DTGE, PG and HPG are shown in Fig. 3. The DTGE spectrum presents characteristic bands for the epoxy ring at 1250, 910 and 760 cm−1 attributed to C\\O bond and, as expected, these bands did disappear in the HPG spectrum. On the other hand, PG and HPG spectra present strong bands at 3400 and 2900 cm−1which are related to hydroxyl groups. The HPG FT-IR spectrum does not show any characteristic bands of epoxy ring indicating that the hydrophobization reaction was completed under the conditions employed. This hypothesis was confirmed by the NMR results shown in Fig. 4, where no epoxy protons signals (2.6 and 2.8 ppm), as well as epoxy carbon signals (44.0 and 51.0 ppm) are observed. In the 13C NMR spectrum, signals between 59.0 to 82.0 ppm are attributed to polyglycerol carbon atoms bonded to oxygen, except peak at 71.0 ppm which is a signal from the carbon atom in the alkyl chain [OCH2(CH2)nCH3]. The substitution degree – SD was calculated from quantitative 13C NMR by the equation: 3ACH3/Aglycerol, where ACH3 and Aglycerol represent the integration area in 14.5 ppm and between 59.0 to 82.0 ppm, without the signal intensity of the alkyl chain aforementioned, respectively. Therefore, the SD for HPG11, HPG12 and HPG14 are 7.0, 13.0 and 26.0% of hydroxyl groups, respectively. The work was carried out only up to this limit of SD because the modified polymers should be relatively water soluble in order to be used as shale inhibitor for water-based drilling fluids. The thermogravimetric analysis results (TGA and DTGA) for HPG presented in Fig. 5 show that the most significant mass loss occurs between 200 to 400 °C, indicating that the modified polyglycerol should not decompose under the standard conditions found in wells. The particle size of the obtained polymeric structures was measured by Dynamic Light Scattering – DLS and the results can be seen in Fig. 6. In an aqueous dispersion containing 0.5 to 2.0 wt/v% of the materials the unmodified polyglycerol PG presents an average size of about 2.5 nm, however, the amphiphilic structures show a size distribution with high dispersion, around 50–80 nm. The visual turbid appearance of the hyperbranched polymers aqueous solutions/suspensions and the magnitude of the particle sizes obtained suggest that such particles are associated in aqueous medium, forming aggregates. This suggestion
Fig. 1. Glycerol carbonate and hyperbranched polyglycerol synthesis reactions (Rokicki et al., 2005).
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 2. Partially hydrophobized hyperbranched polyglycerol synthesis.
is corroborated by the large oscillation observed in the measurements. It is possible to suppose that this association gives rise to the formation of micellar structures such as the ones observed with amphiphilic molecules like the surfactants. To test this possibility, another experiment was conducted, varying the solvent polarity with the purpose of destroying these aggregated structures. A series of solutions containing 1.0 wt% of the amphiphilic polymer in THF:water mixtures were prepared, and the DLS results are shown in Fig. 7. With the 80:20 THF:water mixture, the HPGs particles size were estimated as 3.0 nm approximately, suggesting that the alkyl chains were solvated by THF and the polar core – PG was solvated by water, breaking the aggregates by favoring solute–solvent interactions instead of solute–solute interactions. 3.2. Clay- mineral samples characterization Clay-mineral samples micrographs are presented in Fig. 8 where it is possible to observe the particles morphological differences
among the four clay types employed in the work. The samples were analyzed as selected powder on 150 mesh sieve. Table 1 contains the shales chemical composition (quantified by XRF), the cation exchange capacity and the textural analysis results. The cation exchange capacity (CEC) is a measure of the exchangeable cations (typically sodium, calcium, iron, potassium and magnesium) that neutralize the negatively clay particles. Reactive shales have a CEC higher than 20 meq/100 g (Stephens et al., 2009). The reactivity of shales also depends on their formation process, several properties like mineralogy, porosity, water affinity, e.g., are important to understand shale/fluid interaction and shale stability (Lal, 1999). Tables 2.a. and 2.b. show shales mineral compositions. All of them presented high clay content, smectite was the predominant mineral. Based on the characterization results obtained and on empirical observations, we concluded that the clay samples are highly reactive with water, which is convenient to study the performance of the proposed inhibitors.
Fig. 3. FT-IR spectra of DTGE, PG and HPG.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 4. a)13C NMR and b)1H NMR from HPG, respectively. TMP is 1,1,1-tris(hydroxymethyl)propane used as initiator on PG synthesis.
3.3. Evaluation of the inhibition performance 3.3.1. Cuttings hot-rolling dispersion tests All HPGs were used in the performance tests without any purification process. Fig. 9 shows the recovery for dispersed and intact cuttings, for the different systems containing the partially hydrophobized structures, in the presence and absence of the inhibitor KCl, compared to the results for PG and KCl systems. It can be observed that, in all cases,
the inhibition efficiency increases with the polymer concentration. In aqueous medium, the synthesized polymer structures show a relatively good performance as inhibitors, but the performance is much better in the presence of KCl, probably due to the formation of a complex between the polymers and K+, favoring the polymer interaction with the negatively charged clay layer, as reported previously in the literature for polyglycols and polyols, also non-ionic polymers (Bland et al., 1995; Reid and Dolan, 1995). The results also indicate that the partially
Fig. 5. HPG thermogravimetric analysis.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 6. Effect of polymer concentration on PG and HPG partial size.
hydrophobized molecules are better inhibitors than the PG polymer, probably due to the decreased solubility of the HPGs in comparison to PG and also as a consequence of their increased adsorption on clay (Souza et al., 2010). The relationship between solubility and the amount of adsorbed polymer on the clays surface is demonstrated by the adsorption isotherms shown in Fig. 12. The polymers HPG11 and HPG12 present similarities in their inhibition properties, but HPG14 does not follow this trend, suggesting that perhaps the efficiency of inhibition may be limited by degree of hydrophobization of the non-ionic polymers. Also, the polymer molecule must be sufficiently water soluble to promote a good interaction with the clay mineral. The results shown in Fig. 10 corroborate this observation. Once again, it is possible to note the similarities between the performance of HPG11 and HPG12 and the poor results of the systems containing HPG14, PG and KCl. The HPG11 and HPG12 systems presented promising results in all tested
clays reaching, in many cases, nearly 80% of intact cuttings recovery, showing interesting robustness for future field applications. In particular, for clay A3 the results with HPG12, e.g., indicate intact cuttings recovery around 90%. Those systems proved even competitive performance in comparison with the commercial and highly toxic inhibitor PDADMAC. Also worth noticing is the effect of increasing the KCl concentration from 1.0 to 3.0 wt% and of the polymer concentration (from 3.0 to 5.0 wt%) which, according to Figs. 9 and 10 for the shale A1, represents an increase of 50% for the intact cuttings recovery (from about 40 to 80% recovery). 3.3.2. Bentonite inhibition test The Bentonite Inhibition Test results presented in Fig. 11 show that the systems containing partially hydrophobized polymers in association with KCl exhibit the best inhibition performance. From these results it is possible to observe more clearly the synergism between the non-ionic structures and the salt, as discussed above. A peculiar result was observed for the HPG14 aqueous dispersion, which apparently presented the best performance as inhibitor in comparison with the other materials dispersion in absence of KCl. This could be explained as follows. In the bentonite inhibition test small bentonite powder portions are added to the inhibitor solution being tested, but in the case of the HPG14 dispersion, after the aging, bentonite powder flocculates were formed, that remained even after vigorous stirring in the Hamilton Beach mixer. Perhaps those flocculates interfered on the bentonite interaction with water, making more difficult its swelling, and consequently keeping low, in an artificial way, the rheological properties of the system. However, in the test with KCl it was not possible to observe the referred flocculates. 3.4. Drilling fluids tests
Fig. 7. Effect of THF:water ratio on HPG (1.0 wt%) partial size. Some columns were not plotted because correspond to systems in which the polymer was not soluble on the solvent mixture.
API drilling fluids tests results are presented in Table 3. Analyzing the rheological properties of the fluids it is possible to observe that Fluid 2 shows much higher viscosity values, in different analysis conditions, when compared with the ones for Fluid 1 (base fluid) and this difference
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 8. Shale samples micrographs. a) Shale A1; b) Shale A2; c) Shale A3 and d) Bentonite B1.
Table 1 Clay chemical composition and textural analysis.
Na2O MgO Al2O SiO2 P2O5 K2O CaO TiO2 Fe2O3 LOI
Chemical composition (wt%)
CEC (meq/100 g) Specific area BET (m2/g) Pore volume (cm3/g) Pore diameter (Å)
Shale A1
Shale A2
Shale A3
Bentonite B1
0.62 2.2 21.7 45.7 0.11 0.95 0.42 1.2 7.0 20.0 63.4 81.1 0.12 63.2
0.59 2.1 21.5 49.0 b0.1 1.3 0.34 1.3 6.7 16.8 51.9 53.0 0.09 80.5
0.45 1.9 12.8 58.3 b0.1 0.15 0.36 0.58 7.2 18.1 41.1 107.5 0.21 80.9
2.0 2.4 19.4 48.3 b0.1 0.94 0.86 1.0 7.7 17.0 60.0 80.7 0.07 50.8
CEC = cation exchange capacity; LOI = loss on ignition.
could be a consequence of the PDAMAC addition. In the case of the fluids containing the HPGs, the rheological properties were maintained similar to the ones obtained for the base, indicating that the proposed inhibitors do not have a great effect on those properties. The HPGs improved the fluid lubricity, probably as a consequence of their amphiphilic structure (Nunes et al., 2014). As it has been shown in the cuttings hotrolling dispersion tests for the polymer solutions, the products HPG11 and HPG12 have similar inhibition performances when compared Table 2.a Clay mineralogical composition. Clay content.
Shale A1 Shale A2 Shale A3 Bentonite B1
with the one for the commercial inhibitor PDADMAC. When compared to the non-ionic inhibitor PEG400, the proposed HPG materials show a 20% higher performance in the intact cuttings recovery test. In conclusion, the partially hydrophobized hyperbranched polyglycerols are really promising non-ionic inhibitors for water-based drilling fluids.
Table 2.b Clay mineralogical composition. Mineral content. Sample
Clay fraction (%)
Silt fraction (%)
95.8 95.8 86.4 92.5
4.2 4.2 13.6 7.5
Shale A1 Shale A2 Shale A3 Bentonite B1
Clay fraction
Silt fraction
Smectite (%)
Illite (%)
Kaolinite (%)
Mica (%)
Quartz (%)
Hematite (%)
68.4 60.6 81.0 81.7
7.66 – – 2.16
19.8 25.5 5.44 8.61
– 9.74 – –
4.20 4.19 0.50 7.50
– – 13.1 –
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 9. Cutting recovery. a) Dispersed recovery for polymers aqueous solution; b) Intact recovery for polymers aqueous solution; c) Dispersed recovery for polymers combined with KCI 1.0 wt%; d) Intact recovery for polymers combined with KCI 1.0 wt%. The used shale is A1.
3.5. Inhibition mechanism investigation
Fig. 10. Cuttings recovery tests performed with different shales. a) Disperse cuttings recovery. b) Intact cuttings recovery.
To investigate the inhibition mechanism, adsorption isotherms were prepared in duplicate (R1 and R2) to analyze the polymer aqueous solutions before and after contact with bentonite. The results are presented in Fig. 12, where qe is the polymer mass adsorbed per gram of bentonite, Ce is the polymer equilibrium concentration. It is possible to observe that the adsorbed amount of polymeric material increases with the hydrophobization degree, probably as a consequence of the decrease of the macromolecules solubility in water. This behavior was observed for all the materials prepared in aqueous dispersions, in the same polymer concentration range (0 to 4000 ppm). For non-ionic polymeric structures this behavior was observed in partially hydrophobized polyglycols (Souza et al., 2010). However the isotherm for PG shows the presence of a pseudo-plateau which is not observed for HPGs materials. All systems presented satisfactory fittings to the Freundlich isotherm model with a correlation coefficient greater than 0.99. The inclination of the HPGs isotherms also indicate that the amphiphilic structures have a higher absorption capacity in clay in comparison to the unmodified polymer. Also, the increase of the isotherms inclination with the degree of the HPGs hydrophobization is a clear indication that the bentonite affinity increases with the hydrophobization degree for the polymer concentration range considered. For linear structures the literature (Souza et al., 2010; Volpert et al., 1998) suggests the formation of additional polymer layers by hydrophobic interactions, besides the interaction between (OCH2CH2) groups and the clay surface. However, in the case of the hyperbranched structures only monolayers are observed, and the increase in the adsorption could be associated to the decrease of solubility with the increase of the hydrophobization degree, favoring bentonite-polymer interactions in comparison with the water-polymer interactions, as previously mentioned. The literature also suggests the formation of a stable complex between exchangeable potassium ions on the clay surface and the non-terminal portions of the adsorbed polyol molecules. This leads to the removal of the water
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 11. Bentonite inhibition test: Effect of bentonite concentration on the yield point (1 Ib/bbl = 0.9975 g/350 mL).
molecules and to an increase of the amount of adsorbed polymer for the structures without free hydroxyl groups (Reid and Dolan, 1995). XRD analysis results are presented in Fig. 13 and show the increase of the interlayer spacing, calculated using Bragg's law, for the composites formed with the polymeric structures and bentonite. The increase of the interlayer spacing, for HPG11 and HPG12 composites, is between 0.30–0.40 nm indicating that the way they penetrate and settle inside the interlayer spacing should be very similar. Nevertheless, it is possible to observe a loss of crystallinity for the composites formed by PG and HPG14 in high concentrations, probably due to the polymer penetration in the interlayer, causing delamination of the clay. This result is also a confirmation that PG and HPG14 are not inhibitors in the absence of KCl. In conclusion, the results suggest that the polymer-clay interaction involves the penetration of the molecules, or parts of them, in the interlayer spacing, minimizing the water-clay interaction due to the
Table 3 Drilling fluid formulation results. Fluid 1 (Base)
Fluid 2 (PDADMAC)
Fluid 3 (PEG400)
Fluid 4 (HPG11)
Fluid 5 (HPG12)
350.0 1.0 0.25 5.0 3.5 0.0 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
350.0 1.0 0.25 5.0 3.5 10.5 30.0 30.0 7.0
API results after aging, rolling for 16 h at 66 °C 600 rpm 84 147 300 rpm 59 93 200 rpm 48 71 100 rpm 35 46 6 rpm 13 9 3 rpm 12 7 Gi 12 7 Gf 14 9 pH 9.0 8.5 Lubricity 0.20 0.19 Density (g/mL) 1.15 1.15 Filtrate (mL) 9.1 5.3
83 60 50 38 15 13 13 15 8.5 0.19 1.16 9.4
80 58 48 35 13 10 10 13 9.0 0.15 1.16 7.8
83 59 47 33 10 9 9 10 9.0 0.16 1.16 7.6
Cuttings recovery Disperse (%) Intact (%)
72.5 37.3
84.9 59.3
86.6 59.0
Water (lb/bbl) XG (lb/bbl) NaOH (g) HPA (lb/bbl) KCl (lb/bbl) Inhibitor (lb/bbl) CaCO3 (lb/bbl) Barite (lb/bbl) Lubricant (lb/bbl)
69.3 32.8
81.2 68.3
GX = xanthan gum; HPA = hidroxypropylamide; lb/bbl = 0.9975 g/350 mL.
hydrophobic characteristics of the formed polymer-bentonite composite. As demonstrated by TGA results shown in Table 4, the water loss increases with an increase in the polymer concentration and also in the polymer hydrophobization degree. The third factor to consider is the fact that in aqueous medium the amphiphilic structures are associated, forming aggregates of 50– 80 nm approximately, as shown in Fig. 6. Also, the tested clay-minerals have shown pore diameters of about 50–80 Å, as presented in Table 1, which are much smaller than the aggregates. This could mean that some of these aggregates could be clogging some of the pore throats of these clay-rich minerals, hindering the entry of water into the clay structure. 4. Conclusions In this work it is shown that chemical changes promoted in the polyglycerol (PG) hyperbranched macromolecule through the hydrophobization of its structure, produces amphiphilic polymers which are promising clay reactivity inhibitors for water based drilling fluids formulations. Stable and versatile new amphiphilic materials were synthesized by alkyl chain insertions into hyperbranched polyglycerol structures through ether bond formation. The proposed synthetic route follows green chemistry principles. A series of HPGs was obtained that in association with KCl did show a high performance as clay reactivity inhibitors. When compared with the unmodified PG,
Fig. 12. Adsorption isotherms. Curves were prepared in duplicates, R1 and R2, for each polymer.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Fig. 13. XRD spectra of polymer/clay composites. a) PG; b) HPG11; c) HPG12; d) HPG14.
with linear PEG and with the commercial cationic inhibitor PDADMAC, they did show a competitive performance. Finally, an inhibition mechanism is proposed based on the contribution of three processes that Table 4 TGA analysis results for composites water loss. Polymer conc. (wt%)
Water loss (wt%) PG
HPG11
HPG12
HPG14
0.00 0.05 0.20 0.60
9.1 7.1 4.4 3.8
9.1 6.8 4.2 2.2
9.1 5.1 4.0 2.6
9.1 6.7 3.9 1.6
could take place, simultaneously or not: (1) formation of a high affinity for clay complex between HPG and K+ ions, which adsorbs onto the clay surface minimizing shale-water interactions, (2) HPG penetration on the clay interlayer spacing, also minimizing shale-water interactions, (3) formation of aggregates by the amphiphilic structures that would lead to the obstruction of the clay pore throats, thereby making it difficult the entry of water molecules. Acknowledgements The author thanks to the infrastructure of the Institute of Chemistry/UFRJ – Brazil Brazilian Petroleum National Agency – ANP (48610.013790/2009) for financial support.
Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025
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Please cite this article as: Ferreira, C.C., et al., Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.05.025