Poly (oxypropylene)-amidoamine modified bentonite as potential shale inhibitor in water-based drilling fluids

Applied Clay Science 67–68 (2012) 36–43

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Research paper

Poly (oxypropylene)-amidoamine modified bentonite as potential shale inhibitor in water-based drilling fluids Hanyi Zhong, Zhengsong Qiu ⁎, Weian Huang, Jie Cao School of Petroleum Engineering, China University of Petroleum, Qingdao 266555, China

a r t i c l e

i n f o

Article history: Received 9 January 2012 Received in revised form 7 June 2012 Accepted 7 June 2012 Available online 30 August 2012 Keywords: Water-based drilling fluid Clay hydration Polyamidoamine Inhibition evaluation Bentonite Montmorillonite

a b s t r a c t A series of poly(oxypropylene)-amidoamine (POAA) compounds as potential shale inhibitors were synthesized by condensation of low molar mass polyoxypropylene diamine POP230 with diacids. The synthesized polymer was characterized by Fourier transform infrared spectroscopy (FT-IR) and mass spectrum (MS) analysis. The interaction between the POAA compounds and purified bentonite was investigated via FT-IR, X-ray diffraction (XRD), electrophoretic mobility (EM) measurement, thermogravimetric analysis (TGA), water adsorption test, and scanning electron microscopy (SEM). The POAA compounds were intercalated by the montmorillonite (Mt) with monolayer orientation. The protonated ammonium ions neutralized the negatively charged sites and decreased the electrophoretic mobility. Hydrogen bonds were formed between amide and siloxane groups. The intercalation reduced the water content of the Mt and rendered the clay mineral surface more hydrophobic. The inhibitive properties of the modified Mt were evaluated by inhibition and cuttings hot-rolling dispersion tests. The POAA-Mt exhibited superior shale hydration and dispersion inhibition capacity compared to conventional inhibitors. © 2012 Elsevier B.V. All rights reserved.

1. Introduction In drilling engineering, swelling and dispersion of shales and cuttings led to various problems such as hole collapse, tight hole, stuck pipe, poor hole cleaning, hole enlargement, plastic flow, fracturing, lost circulation, and well control. In addition, the dispersed clay might aggregate on the surface of bit or drilling tools, leading to bit balling and penetration rate reduction (Bol, 1986; Lu, 1985; Sheu and Perricone, 1988). Most of the drilling problems that increased the drilling costs were related to the wellbore stability (Lal, 1999). Shale inhibition was the most important factor in preventing hole problems when drilling in shale formations (Løklingholm, 2002). Oil-based drilling fluids were used to drill water-sensitive formations because of inherent advantages such as excellent inhibition, high temperature stability, and outstanding lubricity (Rojas et al., 2006). However, the expensive costs and adverse effects on environment limited their wide use (Morton et al., 2005). With the increasingly stringent environmental demands, the search for an environmentally friendly water-based drilling fluid to prevent hydration and swelling of clay minerals and to exhibit inhibitive characteristic similar to oil-based drilling fluids became more demanding (Bruton and Mclaurine, 1993; Rosa et al., 2005). Over the past decades, a wide variety of approaches were proposed, like relatively high concentrations of inorganic salts, organic salts and many kinds of polymeric additives (Caenn and Chillingar, 1996; Souza

⁎ Corresponding author. Tel.: + 86 532 86981705; fax: + 86 532 86981936. E-mail address: [email protected] (Z. Qiu). 0169-1317/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2012.06.002

et al., 2010; Stamatakis et al., 1995; Van Oort, 2003; Zhang et al., 2000). Nevertheless, these approaches were not completely successful in inhibiting the hydration of highly water sensitive clays and had various limitations (Young and Ramses, 2006). Among these methods, potassium chloride was the earliest and most widely used agent. When combined with other additives such as partially hydrolyzed polyacrylamide (PHPA) (Steiger, 1981), polyglycol (Brady et al., 1998) and silicates (Guo et al., 2006), effective inhibition would be obtained by synergetic effects. Because of the high concentration required to obtain the satisfactory levels of inhibition, alternative cations that promised to be as effective as potassium ions were needed. This became the starting point for the evaluation of ammonium and amine-based compounds for shale inhibition (Guerrero et al., 2006). Nitrogen derivatives, the simplest is ammonium chloride, were used as shale inhibitors for many years. The history of amine compounds and their properties were reviewed (Patel, 2009; Patel et al., 2007; Schlemmer et al., 2003). A recent advance was the introduction of water-based drilling fluids containing low molar mass polyetheramine compounds (Aldea et al., 2005; Patel et al., 2001a, b; Qu et al., 2009). The ability of polyetheramine to reduce the swelling tendencies of shales was studied (Patel et al., 2007; Wang et al., 2011; Zhong et al., 2011). Based on this inhibitor, a high performance waterbased drilling fluid was designed and applied around the world with great success, which represented a significant step-change improvement over earlier attempts to develop a water-based drilling fluid performing like an oil-based drilling fluid (Guerrero et al., 2006; Patel et al., 2002; Young and Stamatakis, 2006). With the development of computer technologies, computer simulation became a useful tool to understand the underlying principles

H. Zhong et al. / Applied Clay Science 67–68 (2012) 36–43

37

Scheme 1. Preparation of POAA by condensation of POP230 and diacids.

behind clay swelling and determine the interaction between inhibitors and clay minerals. Furthermore, the combination of computer simulation and experimental studies provided an effective way to design novel high performance inhibitors with favorable molecular structures (Anderson et al., 2010a; Bains et al., 2001; Greenwell et al., 2005; Ratcliffe et al., 2009). After analyzing the properties and summarizing the inhibitive actions of various inhibitors with the combination of computer simulation and experimental results, sets of “rule-based” design criteria for clay swelling inhibitors were developed (Anderson et al., 2010b; Suter et al., 2011). Therefore, in this study, we tried to synthesize poly(oxypropylene)-amidoamine (POAA) modified bentonites as potential shale inhibitors. 2. Experimental 2.1. Materials Sodium bentonite was obtained from Xiazijie Bentonite Company, China, and was purified before use. The bentonite was dispersed in deionized water for 24 h to make an 80 g/L dispersions. The dispersions were centrifuged at 8000 r/min for 30 min, and the upper part of the dispersions was recovered. The purified bentonite sample was dried at 105 °C for 24 h and sieved by 200 mesh sieve. The cation exchange capacity was determined to be 1.05 mmol/g by ammonium acetate method. A drilling fluid bentonite was supplied by Weifang Huawei Bentonite Group Co., Ltd, China, following the API standard. Adipic acid, succinic acid, ethane diacid, potassium chloride, potassium formate and sodium formate were purchased from Sinopharm Chemical Reagent Co., Ltd, China, in analytical purity. Ultrahib, a commercial polyamine shale inhibitors, was provided by M-I SWACO in America. (2, 3Epoxypropyl) trimethylammonium chloride (NW-1) was supplied by Shandong Juxin Checmical Co., Ltd, China. Polyoxypropylene diamine

2.2. Synthesis of the POAA compounds The reactions were carried out in a 500 mL four-neck flask equipped with a stirrer and condenser. The flask was immersed into a thermostat oil bath. Nitrogen gas was purged into the flask to remove oxygen. POP230 (230 g, 1 mol) and adipic acid (73 g, 0.5 mol) were added while stirring. The mixture was heated to 140–150 °C for 4 h. During the process, water was removed under the nitrogen atmosphere through a water separator. The reaction product is abbreviated as POP230-AA. With a similar procedure, a series of POP230-amidoamines were prepared from the reaction of POP230 and succinic acid or ethane diacid (abbreviated as POP230-SA and POP230-EA). The FT-IR spectra were recorded by a NEXUS FT-IR spectrometer (Thermo Nicolet Corporation), scanning from 4000 to 400 cm− 1, with 4 cm− 1 resolution in transmission. The molar mass distribution of the POP230-amidoamine was estimated by using 7200 Q-TOF GC/MS mass spectrometer (Agilent, USA). The solution surface tension was measured at 25 °C with the DCAT21 surface/interface tensiometer (Beijing Eastern-Dataphy Instruments Co., Ltd). 2.3. Modified bentonite Purified Na-bentonite (8 g) was dispersed in 1 L of deionized water for 24 h, and POAA compounds with concentrations of 0.2, 0.5, 1.0, 2.0, 3.0, 5.0%(m/v) were added. After stirring for 30 min, the dispersions were allowed to stand for 24 h. The dispersions were centrifuged and washed thoroughly with deionized water for several times. One part of the sediment was used for XRD measurement. The other part was dried in a vacuum oven at 80 °C and ground to powder. Samples were

3500

3000

2500

2000

1500

1500 1380

1630

2970

3620

1110

916 814 798 916 841 798

B

916 841 798

1380

1640 1540

1620 1500 1390

2980 2970

3240

3430 3430

3240

3430

3250

1110

3620

1110

C

1000

Wavenumber(cm ) Fig. 1. FT-IR spectra of POAA and polyoxypropylene diamine. (A) POP230; (B) POP230-AA; (C) POP230-SA; (D) POP230-EA.

4000

3500

3000

2500

2000

1500

1000

798

916

3430

3620

500

-1

1630

A 1110

1370 1300

1510

1640

1700 1560

1640 1550 1450 1370

2970 2880 2970 2880 2970 2870

1590 1460 1370

3370 3290

A

2960 2870

3270

B

1370

3370 3290 3280

C

3620

D

D

4000

(abbreviated as POP230) with the general formula H2NCH(CH3)CH2 [OCH2(CH3)CH]2.6NH2 was purchased from Huntsman Chemical Co.

500

-1

Wavenumber(cm ) Fig. 2. FT-IR of (A) purified Na-bentonite; (B) bentonite modified with POP230-AA; (C) bentonite modified with POP230-SA; (D) bentonite modified with POP230-EA.

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H. Zhong et al. / Applied Clay Science 67–68 (2012) 36–43 -1.6

(a)

d001=1.46 nm 2 θ =6.053

D

d001=1.44 nm 2 θ =6.035

C

-2.0

-8

2

d001=1.46 nm

2θ =6.202

E

Electrophoretic mobility(10 m /Vs)

F

POP230-AA POP230-SA POP230-EA

-1.8

2θ =6.153

d001=1.43 nm 2θ =6.399

-2.2 -2.4 -2.6 -2.8 -3.0 -3.2

B

d001=1.38 nm

-3.4 0

2θ =8.855

A

10

20

30

40

50

Concentration of polymer(g/L)

d001=1.21 nm

Fig. 4. Electrophoretic mobility of modified bentonites in aqueous dispersions. 2

4

6

8

10

12

14

16

o

2Theta ( )

(b)

mixed with KBr and pressed into pellets for FT-IR analysis. The basal spacing of the modified Mt was determined by X-ray diffraction (XRD, X-ray powder diffractometer, X'pert PRO MPD diffractometer CuK alpha 45 kV, 50 mA). Thermal gravimetric analysis (TGA) was performed with the WCT-2D (Beijing Optical Instrument Factory) thermal analyzer at a scan rate of 20 °C/min under nitrogen flow. The Hitachi S-4800 field-emission scanning electron microscope (SEM) was used to study morphological features of the powdered samples. The electrophoretic mobility (EM) measurement was reported previously (Zhong et al., 2011). For the water adsorption test, 1 g of modified bentonite was placed in a sealed glass desiccator with water in the bottom. The amount of water adsorbed was calculated from the mass changes (Montes-H et al., 2003).

2 θ =6.392

F

d 001=1.40 nm 2 θ =6.346

E

d 001=1.39 nm 2 θ =6.356

D

d 001=1.39 nm 2 θ =6.314

C

d 001=1.38 nm 2 θ =6.480

B

d 001=1.36 nm 2 θ =8.855

A 2

4

6

8

o

10

2.4. Inhibitive properties

d 001=1.21 nm 12

14

16

2Theta ( )

(c) 2 θ =6.421

F

d 001=1.38nm 2 θ =6.427

E

d 001=1.38nm

2 θ =6.460

D

d 001=1.38nm

2 θ =6.460 C

d 001=1.37nm 2 θ =6.448

B

d 001=1.37nm 2 θ =8.855

A 2

4

6

8

10

d 001=1.21nm 12

14

Volumes of 400 mL of tap water containing 12 g of inhibitor were reacted with 5%(m/v) drilling fluid bentonite and stirred for 30 min every day. After hot rolling at 70 °C for 16 h, the rheological properties were measured daily before amounts of 20 g drilling fluid bentonite were added. These daily additions of drilling fluid bentonite and hot rolling were carried out until the sample became too viscous to be measured. The rheological properties of the dispersions were measured using a model ZNN-D6 viscometer. The apparent viscosity, plastic viscosity and yield point were calculated from 300 and 600 rpm readings using the API recommended practice of standard procedure for field testing drilling fluids (Recommended Practice, 1988): Apparent viscosity (AV) = φ600/2 (mPa·s) Plastic viscosity (PV) = φ600−φ300 (mPa·s) Yield point (YP) = (φ300 − PV)/2 (N/m 2) For the cuttings hot-rolling dispersion test, 50 g of the shale cuttings (6–10 mesh) obtained from Sha Hejie formation in Shengli oilfield were added to 350 mL formulated solutions in a sealed cell. The cell was hot rolled at 77 °C for 16 h. Then, the cuttings were screened through a 40 mesh sized sieve and washed with 10 mass% KCl solution. The collected cuttings were dried in a vacuum oven at 105 °C for 4 h. The amounts of recovered cuttings were determined (Khodja et al., 2010; Patel, 2009).

16

o

2Theta ( ) Fig. 3. X-ray diffraction patterns of bentonite-POAA at various polymer concentrations (%(m/v)) with dry sample. (a) POP230-AA: (A) 0; (B) 0.2; (C) 0.5; (D) 1.0; (E) 2.0; (F) 3.0;(b) POP230-SA: (A) 0; (B) 0.2; (C) 0.5; (D) 1.0; (E) 2.0; (F) 3.0;(c) POP230EA: (A) 0; (B) 0.2; (C) 0.5; (D) 1.0; (E) 2.0; (F) 3.0.

H. Zhong et al. / Applied Clay Science 67–68 (2012) 36–43

75

100

Surface tension(mN/m)

Mass loss (%)

90

POP230-AA POP230-SA POP230-EA

70

D C B

95

A 85

80

75

70

65 60 55 50 45 40

65 0

200

400

600

800

o

Temperature( C)

3. Results and discussion 3.1. Synthesis and characterization of POAA compounds The condensation of POP230 and diacid in a molar ratio of 2:1 is shown in Scheme 1. The FT-IR spectrum of POP230 showed absorption bands at 1590 cm − 1 corresponding to the N―H bending vibration of the amine group (Fig. 1). In the case of POP230-AA, the absorption of primary amine N―H stretching modes was at 3270 cm− 1. The new band at 1640 cm− 1 indicated the C O stretching vibration. The band at 1550 cm− 1 corresponded to the N―H bending vibration. 1640 cm− 1 and 1550 cm− 1 were the characteristic absorption bands of amide I and amide II (Schmidt et al., 2006). For POP230-SA and POP230-EA, the absorption band of amide I and amide II were observed at 1700, 1560 cm− 1 and 1640, 1510 cm− 1. The appearance of the amide I and amide II bands demonstrated the formation of amide groups. The molar mass distributions of the three polyamideamines were 191–736, 191–661 and 113–621 with the average molar mass values of 508, 476 and 418.

70 60 50 40 30 20

Na-bentonite Na-bentonite-POP230-AA Na-bentonite-POP230-SA Na-bentonite-POP230-EA

10 0 -10 0

50

100

150

35 -4

-3

-2

-1

0

1

lgc(g/L)

Fig. 5. TGA curves of bentonites at POAA concentrations of 0.5%(m/v). (A) purified Nabentonite; (B) bentonite modified with POP230-AA; (C) bentonite modified with POP230-SA; (D) bentonite modified with POP230-EA.

Water adsorption (%)

39

200

250

Time(h) Fig. 6. Adsorbed water content as a function of the testing time at a POAA concentration of 0.5%(m/v).

Fig. 7. Surface tension curves of POAA solutions.

3.2. Interaction of POAA compounds with Mt 3.2.1. FT-IR analysis The FT-IR spectrum of Na-Mt showed absorption band at 3430 cm− 1 and 1630 cm− 1, corresponding to the O―H stretching and bending band of water. 916 cm- 1 is the characteristic bending vibration of Al―OH. For the bentonite-polymer system, the vibrations of the methyl groups were found around 2980 and 2970 cm− 1 as well as that of the vibration bands of C―H groups at about 1380 cm− 1 (Fig. 2). In comparison with the FT-IR spectrum of POAA and POP230-AA, the characteristic bands of amide I and amide II at 1640 cm− 1 and 1550 cm− 1 were shifted to 1630 cm− 1 and 1500 cm− 1. This suggested hydrogen bonds between the amide groups and siloxane groups. For POP230-SA and POP230-EA, the absorption bands of amide I and amide II at 1700, 1560 cm− 1 and 1640, 1510 cm− 1 were shifted to 1640, 1540 cm− 1 and 1620, 1500 cm− 1 also indicating hydrogen bonds (Lin et al., 2007). 3.2.2. XRD patterns The XRD patterns of the bentonite indicated a basal spacing of 1.21 nm. In the case of POP230-AA at a concentration of 0.2%(m/v), the basal spacing increased to 1.38 nm. When the concentration was 0.5%(m/v), the basal spacing increased to 1.43 nm. At higher loadings, the basal spacing changed only slightly with the increasing concentration, demonstrating that the polymer formed a monolayer arrangement in the interlayer space. The monolayer orientation in the interlayer space regardless of the polymer concentration was stabilized by strong hydrogen bonds, which hindered further intercalation (Greenwell et al., 2006). POP230-SA and POP230-EA exhibited the same tendency. However, POP230-AA enlarged the basal spacing to 1.46 nm because of the higher molar mass (Fig. 3). 3.2.3. Electrophoretic mobility measurement The electrophoretic mobility of the purified Na-bentonite was −3.2 (10− 8 m2/Vs). POP230-AA adsorption increased the electrophoretic mobility to −2.6 (10 − 8 m 2/Vs) at about 5 g/L polymer content (Fig. 4). At higher polymer content, the electrophoretic mobility increased towards less negative values. Wang et al. (2010) assumed that the pKa values of POP230 were similar to those of 1,6-hexanediamine (pKa1 = 9.8, pKa2 = 10.9). The pKa values of the polymers would increase after the reaction with the acids. At pH of 8–11 as in our case, a certain part of the molecules would be protonated and interact with the surface charges by electrostatic forces. As a consequence of the polymer adsorption, the hydration of the clay mineral and the degree of dispersion were reduced.

40

H. Zhong et al. / Applied Clay Science 67–68 (2012) 36–43

Fig. 8. SEM photographs of purified and modified bentonites (magnifications 50,000×; 5.0 kV) at a POAA concentration of 0.5%(m/v): (A) purified Na-bentonite; (B) bentonite modified with POP230-AA; (C) bentonite modified with POP230-SA; (D) bentonite modified with POP230-EA.

POP230-EA compensated the negative surface charges to a higher degree than the two other polymers.

of the solution decreased to 38.8, 38.1, and 43.5 mN/m for POP230AA, POP230-SA and POP230-EA.

3.2.4. TGA The mass loss steps observed up to 200 °C were attributed to the desorption of physically adsorbed water, second mass loss step the dehydration of the hydrated exchangeable cations such as Na + and Ca2+. Between 200 and 500 °C, the organic compounds were decomposed (Barick and Tripathy, 2010). The thermal degradation of the modified bentonites differed significantly from that of the purified bentonite between room temperature and 200 °C (Fig. 5). All POAA polymers reduced the water content of the modified bentonite. At 200 °C, the mass loss of pristine bentonite, POP230-AA, POP230-SA and POP230-EA bentonite was 12%, 9%, 7%, and 5%. Thus, the adsorption of POAA reduced the water content of the sample.

3.2.6. SEM observations The purified bentonite showed dense particle aggregates which, after polymer adsorption, changed into extended aggregates forming an open network with pores (Fig. 8). The extended aggregates improved the clay stabilization.

POP230-AA POP230-SA POP230-EA Ultrahib KCl NW-1 NaCOOH KCOOH

2.0 1.9

Basal spacing(nm)

3.2.5. Water adsorption tests The time-dependent adsorption of all samples showed a considerable increase at the initial stage (Fig. 6). Compared with purified bentonite, the amounts of adsorbed water of the modified bentonites were much lower. After 238 h, the amount of water adsorbed by POP230-AA, POP230-SA and POP230-EA bentonite was reduced by about 29%, 27% and 21% compared to the purified bentonite. The reduced affinity of the clay mineral surface to water had favorable impact on clay stabilization (Wang et al., 2011). Because of different hydrophilicity/ hydrophobicity ratios of the three polymers, the affinity to water decreased in the order POP230-EA > POP230-SA > POP230-AA. This was consistent with the results of surface tension measurements (Fig. 7). With increasing concentrations of what, the surface tension

2.1

1.8 1.7 1.6 1.5 1.4 1.3 -1

0

1

2

3

4

5

6

7

8

Concentration of inhibitor(%m/v) Fig. 9. X-ray diffraction patterns of bentonite (wet samples) in the presence of inhibitors.

H. Zhong et al. / Applied Clay Science 67–68 (2012) 36–43

41

Table 1 Rheometer readings of all samples after adding bentonite. Bentonite (%m/v)

Fresh water φ600

φ300

φ3

φ600

KCl φ300

φ3

φ600

Ultrahib φ300

φ3

φ600

PPO230-AA φ300

φ3

φ600

PPO230-SA φ300

φ3

φ600

PPO230-EA φ300

φ3

5 10 15 20 25 30 35

42 186 –

37 167 –

21 91 176

7 18 30 59 162 –

4 11 21 48 145 –

0.5 1 10 24 90 258

3 3 7 20 67 155 –

1.5 2 4 14 62 143 –

0 0 0 3 38 81 224

3.5 6 12 25 271 –

2 3.5 8 20 258 –

0 0.5 2 10 84 237

3.5 6 9 28 171 –

2 3.5 5.5 22 160 –

0 0.5 1 13 52 131

4 5 7 9 13 20 29

2.5 3 4 5 7 12 18

0 0 0.5 0.5 0.5 4 9

– Indicates that the readings were > 300, no further readings were taken.

addition. The inhibition decreased as POP230-EA>Ultrahib>POP230SA>POP230-AA>KCl.

3.3. Inhibitive properties 3.3.1. XRD analysis of wet samples The basal spacing of Na-Mt increased from 1.21 nm to 2.02 nm after thorough hydration (Fig. 9). In the presence of 0.2%(m/v) POP230-AA, it decreased from 2.02 nm to 1.51 nm. At higher polymer concentrations, the basal spacing remained almost constant as a consequence of the polymer monolayer adsorption. The intercalation of POAA prevented water molecules from entering the interlayer space and diminished the water content of the systems, in agreement with the thermogravimetric analysis. Ultrahib as a shale hydration inhibitor, reduced the basal spacing in a similar way. In comparison with other conventional clay swelling inhibitors like KCl, sodium and potassium formate and NW-1, POP230-EA and Ultrahib reduced the basal spacing to a minimum, indicating the best inhibition performance. Furthermore, the POAA compounds reduced the basal spacing of the hydrated samples with relatively low polymer concentrations and were, therefore, superior to KCl and the formates, which generally required high concentrations to achieve ideal suppression. 3.3.2. Bentonite inhibition Measuring the rheological properties of cationic materials was one of the simplest tests for the evaluation of inhibitive properties (Stamatakis et al., 1995). In fresh water without inhibitor, Na-Mt dispersed into colloidal particles (Table 1), which increased the viscosity. When the bentonite content reached 15%(m/v), the fresh water system became too viscous to measure the yield point (Fig. 10). In the presence of inhibitors the yield point changed sharply at different bentonite concentrations. Due to the lower rheological viscosity, POAA addition was more effective than KCl

Fresh water KCl Ultrahib POP230-AA POP230-SA POP230-EA

120

Yield point(Pa)

100

80

3.3.3. Cuttings hot-rolling dispersion tests The inhibitive qualities of the POAA compounds were further evaluated by conventional hot-rolling dispersion tests with highly reactive shales (Table 2). The cuttings recovery in fresh water was 14.2%, indicating high hydration and dispersion. After adding 7% (m/v) KCl, the recovery was 44.5%. At 3% (m/v) Ultrahib addition the recovery was 57.7%, but higher values were reached with the POAA compounds. POP230-EA improved the cuttings recovery to the highest value, indicating the best shale stability.

3.3.4. Inhibition mechanism Scheme 2 depicted the chemical structure and action of POAA. Due to the monolayer arrangement of the polycations in the interlayer space, the silicate layers were diminished the tendency to imbibe water from an aqueous environment. Furthermore, after reaching adsorption saturation, the hydrophobic region of the polymer rendered the clay mineral surface relatively hydrophobic which further hindered the uptake of water.

4. Conclusions According to the rules of designing successful shale inhibitors with respect to molecular structure, POAA compounds with low molar mass were synthesized by condensation of polyoxypropylene diamine POP230 and diacids. The intercalated polymer adopted a monolayer arrangement pulling the adjacent layers together. The interaction between the POAA compounds and the clay mineral mainly included electrostatic interaction, hydrogen bonding and van der Waals interaction, which caused a significant reduction of hydration and swelling. POAA compounds exhibited superior inhibition compared to conventional inhibitors. POP230-EA showed the best inhibitive properties. The POAA compounds were alternatives to other state of the art inhibitors in water-based drilling fluids.

60

Table 2 Cuttings recovery of various inhibitor systems.

40

20

0 0

5

10

15

20

25

30

35

40

Concentration of drilling fluid bentonite(%m/v) Fig. 10. Yield point as a function of the concentration of drilling fluid bentonite in the presence of inhibitors.

Inhibitor

Recovery (%)

Fresh water 3 (% m/v) Ultrahib 7(% m/v) KCl 10 (% m/v) NaCOOH 10 (% m/v) KCOOH 0.5 (% m/v) NW-1 3 (% m/v) POP230-AA 3 (% m/v) POP230-SA 3 (% m/v) POP230-EA

14.2 57.7 44.5 27.1 54.3 44.3 62.6 61.3 65.3

42

H. Zhong et al. / Applied Clay Science 67–68 (2012) 36–43

Scheme 2. Chemical structure of POAA.

Nomenclature API American Petroleum Institute AV Apparent viscosity EM Electrophoretic mobility FT-IR Fourier transform infrared spectroscopy Mt Montmorillonite MS Mass spectrum Na-Mt Sodium montmorillonite NW-1 (2, 3-Epoxypropyl) trimethylammonium chloride PHPA Partially-hydrolyzed polyacrylamide POAA Poly (oxypropylene)-amidoamine POP230-AA Amidation of POP230 and adipic acid POP230-EA Amidation of POP230 and ethane diacid POP230-SA Amidation of POP230 and succinic acid PV Plastic viscosity SEM Scanning electron microscopy TGA Thermogravimetric analysis XRD X-ray diffraction analysis YP Yield point

Acknowledgements This work was financially supported by National Science Foundation of China (No. 41072094), the Fundamental Research Funds for the Central Universities (No. 12CX06023A) and the Outstanding Doctoral Dissertation Training Program of the China University of Petroleum (No. LW110202A).

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