Water-Soluble Acrylamide Sulfonate Copolymer for Inhibiting Shale

The retention ratio of apparent viscosity of 2 wt % PANAA solution can reach ... It has been known that over 70% of the formations faced in the petrol...
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Water-Soluble Acrylamide Sulfonate Copolymer for Inhibiting Shale Hydration Xiangjun Liu,† Kun Liu,† Shaohua Gou,*,†,‡ Lixi Liang,† Cheng Luo,† and Qipeng Guo§ †

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China ‡ School of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China § Polymers Research Group, Institute for Frontier Materials, Deakin University, Locked Bag 2000, Geelong, Victoria 3220, Australia ABSTRACT: Here we report a water-soluble acrylamide sulfonate copolymer for inhibiting shale hydrate formation. The copolymer, denoted as PANAA, was synthesized via copolymerization of acrylamide (AM), N,N-diallylbenzylamine (NAPA), acrylic acid (AA), and 2-(acrylamide)-2-methylpropane-1-sulfonic acid (AMPS). The performance of this new water-soluble copolymer for inhibiting shale hydration was investigated for the first time. The retention ratio of apparent viscosity of 2 wt % PANAA solution can reach 61.6% at 130 °C and further up to 72.2% with 12 000 mg/L NaCl brine. The X-ray diffraction studies show that the addition of copolymer PANAA (5000 mg/L), in combination with a low loading of KCl (3 wt %), remarkably reduces the interlayer spacing of sodium montmorillonite (Na-MMT) in water from 19.04 to 15.65 Å. It has also found that these copolymer solutions, blending with KCl, can improve the retention of indentation hardness from 22% to 74% and increase the antiswelling ratio up to 84%. All results have demonstrated that the PANAA copolymer not only has excellent temperatureresistance and salt-tolerance but also exhibits a significant effect on inhibiting the hydration of clays and shale.

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INTRODUCTION It has been known that over 70% of the formations faced in the petroleum drilling are shale formations.1 Unfortunately, the shale, which is mainly comprised of clay minerals, will hydrate when the external water environment has changed. In fact, about 90% of the cases of well-hole collapse happen in shale formations.2 It has been shown that the interlayer spacing expansion and the volume expansion of the clays, which would directly reduce the cementation force and produce swelling force in rocks, are the most important internal factors for the loss of rock strength and indentation hardness.3−5 Over the past decades, the demands for effective shale stabilizers have never stopped. Especially, with the development of shale gas all over the world, such demands have never become as urgent as today.6 Polyacrylamide (PAM) and partially hydrolyzed polyacrylamide (HPAM) are widely used in drilling fluids and their long molecules can absorb on the clay surface to protect the clays from dissolution in water to some extent.7−9 During the past decades, many water-soluble polymers have been used as clay stabilizers in drilling fluid systems to inhibit the hydration and keep the rock strength. The water-soluble polymers used so far include polyacrylonitrile ammonium salt (NH4−HPAN),10 calcium polyacrylate,11 cationic polymers,12,13 zwitterionic polymers,14,15 and polyglycols.16,17 However, most of them showed only very limited ability to inhibite hydration of clays or shale under high temperature and/or salinity conditions.18 Recent efforts have shown that copolymers of acrylamide (AM) or substituted acrylamides with a suitable functional monomer, such as 2-(acrylamide)-2-methylpropane-1-sulfonic acid (AMPS)19 or N,N-diallylbenzylamine (NAPA)20 exhibits considerably improved temperature-resistance and salt-tolerance. © 2014 American Chemical Society

Very recently, we reported two AM sulfonate copolymers of N-phenylmaleimide (N-PMI), modular β-cyclodextrin and AMPS as clay stabilizers and found that these copolymers exhibited remarkable temperature resistance and salt tolerance.21,22 However, modular β-cyclodextrin is not cost-effective and feasibly available at the industry scale. In the present work, a novel water-soluble acrylamide copolymer was designed and investigated for inhibiting shale hydration. The copolymer, denoted as PANAA, was synthesized via radical copolymerization of AM, NAPA, acrylic acid (AA), and AMPS. The structural diversity of the copolymer PANAA, which contains SO3−, benzene rings, N-containing heterocycles, and carboxyl, imparts its excellent temperature resistance and salt tolerance. This new copolymer can effectively inhibit the hydration of clays and the shale.

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EXPERIMENTAL SECTION Materials. AM and AA were analytical reagents, and AM was recrystallized from a water−ethanol mixture. AMPS, ammonium persulfate ((NH 4 ) 2 S 2 O 8 ), sodium sulfite (NaHSO3), alkylphenol ethoxylates (OP-10, used as emulsifier), sodium montmorillonite (Na-MMT, Xinjiang Xiazijie Bentonite Company, China), shale rocks (Sichuan Xujiahe Formation, China), and other chemicals were commercially obatined and used without further purification. NAPA was synthesized according to the method described in a patent.23 Synthesis of Copolymer PANAA. AM (2.8 g), AA (1.2 g), NAPA (0.08 g), and AMPS (0.7 g) were dissolved in degassed Received: Revised: Accepted: Published: 2903

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and deionized water to obtain a solution. Due to the water insolubility of NAPA, OP-10 (0.01 g) was also added as emulsifier. Residual oxygen was removed by nitrogen gas being bubbled through the solution for 30 min under constant stirring at 25 °C. Then NaHSO3-(NH4)2S2O8 (0.004 g, 1/1 molar ratio) solution was slowly added. The reaction was allowed to take place at 40 °C for 6 h. The final solution was clear and highly viscous, and finally the copolymer was precipitated with acetone. The precipitate was dried in vacuum for 10 h to yield the copolymer PANAA. The synthesis reaction was repeated under the same condition. The final yield of the PANAA was 85%. The characteristics of the copolymer PANAA are listed in Table 1.

W% =

intrinsic viscosity

molecular weight

apparent viscosity

PANAA

460 mL g−1

1.2 × 106

635 mL g−1

ACO × V AO

WAM

× 100%

(1)

Here, W% is the conversion of AM or AA, WM is the total weight of AM or AA in the reaction, CO is the concentration of standard sample of AM, AO is the chromatographic peak area of standard sample of AM or AA, A is the chromatographic peak area of the unreacted AM or AA, and V is the solution volume of ethanol in which the copolymer was isolated by precipitation. Morphological Observation. The morphology was investigated using an environmental scanning electron microscope (ESEM, Quanta 450, USA). Solutions (concentration = 5000 mg/L) of HPAM, AM-AA-AMPS (copolymer of AM, AA, and AMPS) and PANAA were prepared and dropped on glass slides to obtain samples for ESEM observation. The samples were allowed to dry at room temperature and were then cryogenically fractured using liquid nitrogen. The fractured surfaces of the samples were observed with the ESEM operating at an accelerating voltage of 20 kV. X-ray Diffractometry (XRD). Na-MMT samples were taken for X-ray diffraction (XRD) measurements. Each solution sample (3 mL) was mixed with Na-MMT (2 g) for 1 h before the measurement. XRD measurements were carried out on a Xray diffractometer (PANalytical, The Netherlands) with a Cu Kα radiation target at 40 mA and 40 kV and a scan rate of 1 deg/min, step size of 0.05 degree, with the scattering angle (2θ) ranged from 2 to 8°. The interlayer spacing of the Na-MMT was calculated according to Bragg’s law. Salts Tolerance Test. The salt tolerance of copolymer solutions was investigated with NaCl, KCl, and CaCl2, respectively. The apparent viscosities of the copolymer PANAA and HPAM solutions under different salt concentrations were determined by using a Brookfield DV-III+Pro viscometer (Brookfield, USA). Temperature Resistance Test. The viscosity of a series of 2 wt % copolymer solutions were tested at both room and elevated temperatures by using a Haake RS600 rotational rheometer (Thermo Haake, Germany). Antiswelling Ratio. The antiswelling ratio (AR) was measured according to the China’s Natural Gas Industry Standard SY/T 5971-94 regarding the evaluation method of clay stabilizer for injection fluid. Bentonite (1 g), which was mainly comprised of Na-MMT and would hydrate drastically in water, was soaked in a polymer solution (20 mL) for 2 h. And then, the solid phase and the liquid phase were separated with a YuHua model TG-16 supercentrifuge (YuHua Company,

Table 1. Characteristics of Copolymer PANAAa copolymer

WM −

a

The intrinsic viscosity and viscosity-average molecular weight was determined according to ref 24 and 25 and the apparent viscosity was tested using a Brookfield DV-III + Pro Viscometer at 30 °C with a polymer concentration of 2 wt %.

Characterization of Copolymer PANAA. Infrared (IR) measurement of monomers and copolymer PANAA were conducted using a Perkin-Elmer 630 FTIR spectrophotometer. All samples were ground well with KBr powder and pressed into disks and then dried at 105 °C for 24 h prior to measurement. IR spectra were recorded at room temperature in the wavenumber range of 4000−500 cm−1 and a minimum of 32 scans at a resolution of 4 cm−1 were signal averaged. NMR experiments of all samples were carried out using D2O as the solvent, and 1HNMR spectra were recorded on a Bruker AV III 400 spectrometer operating at 400 MHz with sodium 2,2dimethyl-isotope 2-silapentane-5-sulfonate (DSS) as the internal reference. The composition of the copolymer PANAA was determined by 1HNMR and high performance liquid chromatography (HPLC, Shimadzu Company, Japan). The molar ratio of (AM +AA), AMPS, and NAPA was obtained from 1HNMR. Furthermore, the molar ratio of AM and AA was determined by the conversions of AM and AA, which were measured by HPLC using ODS column at UV detector (210 nm), H2O/ CH3OH = 90/10 (v/v). The conversions of AM and AA were calculated by the following equation: Scheme 1. Synthesis of acrylamide sulfonate copolymer PANAA

2904

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Figure 1. (a) FTIR spectra of AMPS, AM, AA, and PANAA. (b) 1H NMR spectrum of PANAA. (c) 13C NMR spectrum of PANAA.

where FM is the maximum load before the surface of the rock was broken and A represents the contact area which is 4.446 mm2 here. Thermogravimetric Analysis (TGA). TGA of the samples were equipped with a STA449 F3 synchronous thermal analyzer (Netzsch, Germany) from 30 to 700 °C at a heating rate of 10 °C/min under air atmosphere.

China) under 1500 r/min. At last, the increase of the bentonite volume was measured to calculate AR according to eq2. AR =

VW − VP VW − VO

(2)

where VW and VP are the volume of swollen bentonite in distilled water and in the polymer solution, respectively. VO stands for the volume of bentonite in kerosene. Indentation Hardness of the Shale. Cores of the shale were soaked in polymer or salt solutions at 80 °C for 24 h to simulate the wellbore conditions. Indentation hardness (IH), an indication of the mechanical property of the shale, was measured with a RTR-1000 Rapid Triaxial Rock Testing System (GCTS, USA). The IH values were determined according to eq 3.26 IH =

FM × 1000 A

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RESULTS AND DISCUSSION

Synthesis of Acrylamide Sulfonate Copolymer. The copolymer PANAA was synthesized through copolymerization of AM, NAPA, AA and AMPS as shown in Scheme 1. The molecular weights of copolymer PANAA were measured using GPC. The weight-average molecular weight of the copolymer was Mw = 1.67 × 106 with Mw/Mn = 1.9. The mole ratio of the monomers is AM:AA:APMS:NAPA = 64.04:30.10:5.14:0.73. Infrared analysis was applied to verify the successful preparation of the copolymer PANAA. Figure 1a displays the IR spectra of the monomers and the copolymer PANAA. The IR spectrum of the monomer NAPA shows the characteristic

(3) 2905

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Figure 2. ESEM images of (a) HPAM, scale bar 20 μm, (b) AM-AA-AMPS, scale bar 20 μm, (c) PANAA, scale bar 100 μm, and (d) PANAA, scale bar 20 μm.

bands as expected: the band at 3311 cm−1 is due to the stretching vibration of C−H of the alkene (−CCH2) and the two characteristic peaks at 737 and 694 cm−1 is ascribed to the monosubstituted benzene ring. The double bands at 2930 and 2780 cm−1 are due to the stretching vibrations of the methene. The peak of the stretching vibration of CC can be seen at 1647 cm−1. The IR spectrum of the copolymer PANAA displays the following peaks: −CONH2 and −OH stretching vibration at 3432 cm−1 (the peaks of −CONH2 and −OH overlapped to give a very wide peak); CO stretching vibration at 1665 cm−1; −SO3 stretching vibration at 1240 cm−1suggesting the successful copolymerization of AMPS; characteristic stretching vibration peaks of the single substitution benzene ring at 734 and 692 cm−1 revealing that NAPA is also successfully copolymerized with the other monomers. 1 H NMR and 13C NMR were used to further verify the successful preparation of the copolymer PANAA. The 1H NMR spectrum of copolymer PANAA is shown in Figure1b. The chemical shift value at 1.00−1.11 ppm can be assigned to the −CH3 protons of [−C (CH3)2CH2−SO3Na]. The protons of the aliphatic−CH2− of polymeric chain appear at 1.50 ppm. The proton of the aliphatic −CH− of polymeric chain appears at 2.08 ppm. The characteristic peak at 3.46−3.57 ppm is due to −CH2− of [−C(CH3)2CH2−SO3Na] and [−N−CH2−Ph].

The chemical shift value at 7.69 ppm is due to the protons of the benzene rings, while the weak peak 6.85−7.00 ppm might also come from benzene rings residing in a chemical environment slightly different from the ones absorbing at 7.69 ppm. Due to the exchange between amide protons with D2O, the peaks of NH protons of [−CONH2] is missing. The 13C NMR spectrum of copolymer PANAA is shown in Figure 1c. The C atoms of methyl −CH3 of [−C (CH3)2CH2− SO3Na] appears at 15.9 ppm. The chemical shift value at 34.58 ppm is assigned to the C atoms of −CH2− of polymeric chain. The characteristic peak at 35.9 ppm is due to the C atom of [−C(CH3)2CH2−SO3Na]. The C atom of the aliphatic −CH− of polymeric chain appears at 41.5 ppm. The characteristic peak at 48.5 ppm is due to −CH2− of [−C(CH3)2CH2−SO3Na] and [−N−CH2−Ph]. The peak at 57.48 ppm is ascribed to [-CH2− N−CH2−Ph]. The peaks at 125.8 ppm, 128.6 ppm, 133.1 ppm are attributable to the C atoms on the benzene rings. The strong peaks around 180 ppm are due to the C atoms of [−C O]. These results indicate that the copolymer PANAA was successfully obtained. Morphology of Acrylamide Sulfonate Copolymer. The ESEM images of HPAM, AM-AA-AMPS and PANAA samples are shown in Figure 2. Reticular structures can be found in Figure 2a,b, and the microscopic nets of AM-AA-AMPS have 2906

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copolymer previously used under the same conditions. The worse salt tolerance of the AM/NaAA/AMPS/XBH copolymer can be attributed to the modular β-cyclodextrin, which has many −OH groups and are much more sensitive to electrolyte than the benzyl group in the copolymer PANAA in this study. Temperature Resistance. Considering the needs for use in the underground conditions, the copolymer solution should have not only good salt-tolerance but also good temperatureresistance. Herein, the temperature resistance of the PANAA (2 wt %) was studied under a series of temperatures ranging from 30 to 130 °C (Figure 4). It was found that the apparent

smaller pores and are made of thinner and more evenly distributed filaments than those of HPAM. However, it can be seen from Figure 2c,d that the copolymer PANAA shows rather different morphologies which look like a continuous membrane (Figure 2c). It can be observed that the microscopic structures of PANAA are denser and more regular than those of HPAM and AM-AA-AMPS. Salt Tolerance. We have previously found that the AM/ NaAA/AMPS/XBH copolymer (5000 mg/L) could offer up to 49% and 64.7% retained apparent viscosity in 12 000 mg/L NaCl and 2000 mg/L CaCl2 solutions, respectively.21,22 Herein, it can be seen from Figure 3a that the apparent viscosity of the

Figure 4. (a) Temperature resistance of apparent viscosity of PANAA and HPAM solutions with a polymer concentration of 2 wt %. (b) TGA curve of PANAA. Figure 3. Salt tolerance of the PANAA solutions. (a) Effect of NaCl, KCl, and CaCl2 on apparent viscosity of PANAA; (b) the comparison between PANAA and HPAM.

viscosity decreases slowly and smoothly with the increase of temperature and no sharp loss of viscosity was observed. A relative small loss of apparent viscosity can be observed before 130 °C. 90.6% and 61.6% of the apparent viscosity were retained at 78.8 and 130 °C, respectively. It also can be observed that 91% of the apparent viscosity had recovered when cooling down to 30 °C from 130 °C. This is a significant breakthrough since our recent work in which the apparent viscosity of SAM/N-PMI remained 60% at 85 °C (very close to HPAM) and AM/NaAA/AMPS/XBH (5000 mg/L) remained 75% at 120 °C.21−22 It is interesting to compare the present results with that of 2 wt % solution of HPAM. It can be observed from Figure 4 that the apparent viscosity of HPAM decreases sharply with the increase of temperature. The existence of the NAPA and AMPS in the PANAA copolymer chain makes the copolymer

PANAA solution (5000 mg/L) is decreased with the increase of salt content until a certain concentration and then remains constant. The shrinking was not complete with NaCl and KCl regardless of their concentration because with the addition of CaCl2 the polymer shrank even further. KCl and NaCl have similar influence, and under the salinity of 12 000 mg/L the apparent viscosity remains 72.2% (52 mP.s) and 66.7% (48 mP.s), respectively. However, the effect of CaCl2 is stronger than that of NaCl and KCl. A sharper decrease of the apparent viscosity can be observed and it only remains 59.7% (43 mP.s) of the apparent viscosity under the salinity of 12000 mg/L. These results show that the copolymer PANAA possesses better salt tolerance than the AM/NaAA/AMPS/XBH 2907

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molecules not easy to shrink or break up; the PANAA copolymer has excellent salt tolerance and temperature resistance. As shown in Figure 4b, the TGA diagram of PANAA displayed three stages for the weight loss. The first step occurred in the range of 30−290 °C, with a mass loss of 19.7 wt %, corresponding to the evaporation of intermolecular moisture. The second one took place in the 290−370 °C temperature range with a mass loss of 34.6 wt %, which was ascribed to the imine reaction of the amide groups as well as the decompositions of hydrophobic side chains and cyclodextrin groups. The third thermogravimetry stage occurred beyond 370 °C with the mass loss of 33.5 wt % which could be attributed to the carbonization. Effect of Copolymer PANAA on Inhibiting Na-MMT Hydration. The interlayer space expansion and volume expansion of the clay are the most significant factors influencing the hydration of shale. Na-MMT, which is easier to hydrate in water than other clay minerals, is usually used to analyze the hydration of clays. The interlayer spacing of Na-MMT of shale samples in different solutions was investigated by XRD. The results are listed in Table 2. It can be seen that the addition of PANAA

Figure 5. Effect of polymer on antiswelling ratio. KCl solutions (1 wt %) combined with different loadings of PANAA and PDMDAAC were used in the test.

Indentation Hardness Analysis. The hydration of the clays would have adverse influence on the rock mechanical properties and cause wellbore collapse. The results are summarized in Table 3. It is clear that the addition of the Table 3. Effect of PANAA on Keeping Indentation Hardness of the Shale

Table 2. Interlayer Spacing Comparisons of Different NaMMT Samples polymer/concentration (mg/L)

salt (wt %)

d-spacing (Å)a

b 0 0 PANAA/5000 PANAA/5000

0 0 KCl (3%) 0 KCl (3%)

12.63 19.04 16.97 18.74 15.65

salt (wt %)

maximum load (kN)

indentation hardness (MPa)

0 0 0

2.1464 0.4656 1.3123

482.47 104.66 294.98

0

1.3481

303.03

0

1.364

306.6

NaCl/ 10% KCl/10%

1.4793

332.52

1.5942

358.34

polymer (mg/L) a distilled water PANAA (2000 mg/L) PANAA (6000 mg/L) PANAA (10000 mg/L) PANAA (10000 mg/L) PANAA (10000 mg/L)

a

3 mL of solution samples was mixed with 2g of Na-MMT. bDry NaMMT.

(5000 mg/L) alone only slightly reduce the expansion of interlayer spacing (from 19.04 to 18.74 Å). Our previous work has shown that the addition of 10% KCl significantly reduces the expansion of the interlayer spacing from 18.95 to 15.21 Å.22 In the present system, the addition of PANAA combined with different loadings of KCl remarkably reduces the interlayer spacing from 19.04 to 15.65 Å when combined with lower loading KCl (3 vs 10 wt %). This clearly shows the inhibiting effect of copolymer PANAA on Na-MMT hydration. Effect of PANAA on Antiswelling Ratio. PANAA solutions of different concentrations of (range from 0 to 8000 mg/L) blended with 1 wt % KCl were tested. Clay stabilizer poly(dimethyl diallylammonium chloride) (PDMDAAC), which is widely used for Na-MMT inhibition, was also used for comparison under the same conditions (Figure 5). It is noted that the antiswelling ratios of both polymer solutions are much higher than that of the KCl solution. In addition, the antiswelling ratio is increased with the addition of polymer, and the influence of the polymer concentration becomes very weak when the concentration is over 0.3 wt %. At last the antiswelling ratio reaches 87% when the concentration of PANAA is 0.8 wt %. The antiswelling ability of PANAA is obviously better than PDMDAAC under the same concentration. In general, the mixed solutions of KCl and PANAA are most effective to inhibit the volume expansion of clays.

a

Original rocks before hydration.

PANAA can improve the indentation hardness of the shale in water. However the influence of the concentration of PANAA is not obvious. The highest indentation hardness retained is 306.60 MPa (63%) which is much better than that in distilled water which is only 104.66 MPa (22%). In addition, even better results can be obtained when the PANAA solution is blended with KCl (3%) and NaCl (3%), that to say, up to 358.34 (74%) and 332.52 MPa (69%), respectively. Figure 6 shows photographs of core samples of the shale before and after soaking in different solutions. No collapse, fracture and deformation were observed on the core samples after the cores soaked in polymer solutions. The core samples after the hardness test under external stress (the right side images in Figure 6) shows brittle failure, i.e., the same as that of the original cores. In the previous work,21,22 we found that the retained indentation hardness of the shale cores was 66% in the NaCl 10% solution combined with AM/NaAA/AMPS/XBH (6000 mg/L), this result is close to that of the PANAA copolymer (2000 mg/L) solution, i.e., 61%. On the other hand, the KCl 10% solution combined with AM/NaAA/AMPS/XBH showed better performance (91% retained indentation hardness), which 2908

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temperature resistance and salt tolerance as well as good ability to inhibit the hydration of clays and the shale.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the National Natural Science Foundation of China (Nos. U1262209 and 51274172) for financial support REFERENCES

(1) Tan, B.; Chen, X.; Choi, S. K. Wellbore stability analysis and guidelines for efficient shale instability management. SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, Indonesia, June 7−9, 1999; paper 54356. (2) Friedheim, J.; Guo, Q.; Young, S. Testing And Evaluation Techniques For Drilling Fluids-Shale Interaction And Shale Stability. Presented at the SPE U.S. Rock Mechanics/Geomechanics Symposium, San Francisco, California, June 26−29, 2011; paper 11502. (3) Faruk, C. Interpretation and correlations of clay swelling measurements, SPE Mid-Continent Operations Symposium, 1999, Oklahoma City, Oklahoma, USA (4) Onaisia, A.; Audibert, A.; Biebera, M. T.; Bailey, L.; Denis, J.; Hammond, P. S. X-ray Tomography Vizualization and Mechanical Modelling of Swelling Shale around the Wellbore. J. Petroleum Sci. Eng. 1993, 9, 313−329. (5) Liu, X.-J; Shu, L.; Liu, H.; Wu, X.-L Research on effects of solution salinity and dosage on sodium montmoduonite crystalline interspace. J. Rock Soil Mech. 2011, 1, 79−80. (6) Burns, C.; Topham, A.; Lakani, R. The Challenges of Shale Gas Exploration and Appraisal in Europe and North Africa. Presented at the SPE/EAGE European Unconventional Resources Conference and Exhibition, Vienna, Austria, March 20−22, 2012; paper 151868. (7) Taylor, K. C.; Burke, R. A. Development of a Flow Injection Analysis Method for the Determination of Acrylamide Copolymers in Oilfield Brines. Presented at the SPE International Symposium on Oilfield Chemistry, San Antonio, Texas, February 14−17, 1995; paper 29009. (8) Clark, R. K.; Scheurman, R. F.; Rath, H.; Vanlaar, H. G. Polyacrylamide/Potassium - Chloride Mude for Drilling Water Sensitive Shales. J. Petroleum Technol. 1976, 28, 719−727. (9) Mike, K.; Frederick, L.; Hughes, B. J. Acrylamide/Acrylic Acid Copolymers for Cement Fluid Loss Control. Presented at the SPE Oilfield and Geothermal Chemistry Symposium, Dallas, Texas, January 25−27, 1982; paper 10623. (10) Dautzenberg, G.; Passerini, S.; Scrosati, B.; Croce, F. Characterization of PAN-Based Gel Electrolytes. Electrochemical Stability and Lithium Cyclability. Chem. Mater. 1994, 6, 538−542. (11) Huber, K. Calcium-induced shrinking of polyacrylate chains in aqueous solution. J. Phys. Chem. 1993, 97, 9825−9830. (12) Bruzzano, S.; Sieverling, N.; Wieland, C. W. Cationic Polymer Grafted Starch from Nonsymmetrically Substituted Macroinitiators. Macromolecules 2005, 38, 7251−7261. (13) Kennedy, P. J.; Jacob, S. Cationic Polymerization Astronomy. Synthesis of Polymer Stars by Cationic Means. Acc. Chem. Res. 1998, 31, 835−841. (14) Liu, H.; Xu, H. B. Deep Fluid Diversion for Profile Control and Oil Displacement Technologies. Presented at the SPE International Petroleum Technology Conference, Bangkok, Thailand, February 7− 9, 2012; paper 14217. (15) Wang, J. H.; Sun, J. S.; Bai, L. J. The Novel Model for the Invasion of Particles and the Filtrate of Drilling Fluids. Presented at the International Oil and Gas Conference and Exhibition, Beijing, China, June 8−10, 2010; paper 131912.

Figure 6. Photographs of core samples of the shale (left) and after (right) soaking in different solutions. (a) PANAA (2000 mg/L), (b) PANAA (6000 mg/L), (c) PANAA (10000 mg/L), (d) PANAA (10000 mg/L) + 10 wt % NaCl, and (e) PANAA (10000 mg/L) + 10 wt % KCl.

is attributable to the tight absorption of AM/NaAA/AMPS/ XBH on the shale in KCl solution, resulting an effective protection of the shale from water and keeping the indentation hardness of the rocks.

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CONCLUSIONS In conclusion, we have successfully synthesized a novel watersoluble acrylamide sulfonate copolymer of AM, NAPA, AA, and AMPS. This copolymer exhibits great potential for inhibiting shale hydrate formation due to the presence of sulfonate group, carboxyl and benzyl groups. The addition of PANAA copolymer in combination with a low loading of KCl or NaCl brine significantly increases the retention ratio of apparent viscosity at elevated temperatures and the antiswelling ratio. It also has the ability to keep indentation hardness of the shale and remarkably reduce the interlayer spacing of Na-MMT in water. The PANAA copolymer has shown excellent 2909

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dx.doi.org/10.1021/ie403956d | Ind. Eng. Chem. Res. 2014, 53, 2903−2910