Water-soluble complexes of an acrylamide copolymer and ionic liquids for inhibiting shale hydration

Article abstract of DOI:10.1039/c4nj01741b

Here, we report water-soluble complexes of an acrylamide copolymer and ionic liquids for inhibiting shale hydration. The copolymer, denoted as PAAT, was synthesised via copolymerisation of acrylamide (AM), acrylic acid (AA) and N,N-diallyl-4-methylbenzene

Full text of DOI:10.1039/c4nj01741b

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Water-soluble complexes of an acrylamide
copolymer and ionic liquids for inhibiting shale
Cite this:DOI: 10.1039/c4nj01741b
hydration†
ab
b
a
c
Shaohua Gou,* Ting Yin, Kun Liu and Qipeng Guo*
Here, we report water-soluble complexes of an acrylamide copolymer and ionic liquids for inhibiting shale
hydration. The copolymer, denoted as PAAT, was synthesised via copolymerisation of acrylamide (AM), acrylic
acid (AA) and N,N-diallyl-4-methylbenzenesulfonamide (TCDAP), and the ionic liquids used were 3-methyl
imidazoliumcation-based tetrafluoroborates. X-ray diffraction showed that compared with commonly used
KCl, the water-soluble complex of PAAT with 2 wt% ionic liquid 1-methyl-3-H-imidazolium tetrafluoroborate
(
HmimBF
and effectively inhibit clay swelling. It was also found that the PAAT–HmimBF
could retain 75% of the shale indentation hardness and increase the anti-swelling ratio to 85%. C NMR
revealed that there existed interactions between PAAT and HmimBF . Moreover, the thermal stability of the
PAAT–HmimBF complex is superior to PAAT, suggesting that this water-soluble complex can be used to
inhibit clay and shale hydration in high-temperature oil and gas wells.
4
) could remarkably reduce the d-spacing of sodium montmorillonite in water from 19.24 to 13.16 Å
Received (in Porto Alegre, Brazil)
6th October 2014,
4
complex with 2 wt% HmimBF
4
Accepted 6th January 2015
13
DOI: 10.1039/c4nj01741b
4
4
www.rsc.org/njc
+
4
KCl due to the weak hydration of K , whereas the additive
amount is large, coming to 3–20 wt%. Apart from that, various
1
. Introduction
5
With the urgent demand for energy all over the world, the types of clay hydration inhibitors have been researched, such as
6
development of shale oil and gas is an attractive and challenging low molecular weight polyethylene glycols (PEG), polypropylene
1
7
8
9
area that can make contributions to relieve the energy crisis.
oxides (PPO), mono- and diamines, cationic amine salts, and
10
Shale, which is mainly comprised of clay minerals, will hydrate some charged polymers. Unfortunately, some limitations of
when in contact with water in the environment. The hydration these chemicals such as undesirable solubility, short acting time,
and swelling of clay directly reduces the cementation force and and temperature and/or pH sensitivity have been extensively
5
produces swelling force in rocks, causing the loss of rock documented.
strength and indentation hardness, which could result in the
During the past decades, to reduce the additive amount of
collapse of shale and the failure of production. Therefore, KCl and improve the effectiveness of inhibition, combinations
developing effective shale hydration inhibitors has never been of KCl with various polymers such as PEG, PPO, hydrolysed
2
as crucial as it is today.
polyacrylamide (HPAM) and other high-performance polymers
6
,11,12
The hydration of sodium montmorillonite (MMT) has been have been investigated by numerous researchers.
considered the principal cause of clay hydration and swelling.
Traditionally, the inhibition of clay swelling is achieved using more effectively enhance clay hydration inhibition.
It is
3
believed that synergistic combinations of components could
2
In our previous studies, a series of copolymers were prepared to
13–15
combine with KCl to inhibit clay hydration.
In particular, the
a
b
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,
Southwest Petroleum University, Chengdu, Sichuan 610500, China.
E-mail: shaohuagou@swpu.edu.cn
solution of AM-AA-AOAB-O-b-CD copolymer, which was prepared
with acrylamide (AM), acrylic acid (AA), 1-allyl-3-oil acyloxyimidazole-
1-ammonion bramide (AOAB), and mono-2-O-(allyl oxygen radicals-
Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province,
College of Chemistry and Chemical Engineering, Southwest Petroleum University,
Chengdu, Sichuan 610500, China
2
-hydroxyl propyl)-b-cyclodextrin and 10 wt% KCl, could reduce the
14
d-spacing of MMT from 18.9 to 15.3 Å. However, the additive
amount of KCl needs to be further reduced, and more effective
approaches, particularly those without the use of KCl, are desirable.
In addition, the thermal and chemical stabilities of clay hydration
inhibitors for oil and gas wells drilled under harsh conditions could
be improved by introducing copolymers with specific structures.
c
Polymers Research Group, Institute for Frontier Materials, Deakin University,
Locked Bag 2000, Geelong, Victoria 3220, Australia. E-mail: qguo@deakin.edu.au
Electronic supplementary information (ESI) available: The effect of synthetic
†
conditions on the copolymerisation and intrinsic viscosity of PAAT; the d-spacing
1
13
of MMT in different PAAT–ILs complexes; H NMR and C NMR spectra of
TCDAP and PAAT. See DOI: 10.1039/c4nj01741b
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On the other hand, due to their unique properties such as through a fine fritted funnel. Finally, the CH
NJC
2
2
Cl was removed
high ionic conductivity, thermal stability, chemical stability and under reduced pressure by a rotary evaporator. The obtained
1
recyclability, ionic liquids (ILs) have been widely investigated over TCDAP was a light yellow liquid. Yield: 90%. H NMR (400 MHz,
the past decades for use in many applications by different research CDCl ): 7.69–7.71 (d, 2H, ArH), 7.28–7.31 (d, 2H, ArH), 2.42
3
16,17
groups including our own.
Anionic ILs with strong hydrogen- (s, 3H, Ar–CH ), 3.79–3.81 (d, 4H, CH –N–SO –Ar–), 5.12–5.16
3 2 2
bond accepting characters were employed for the dissolution of (m, 4H, CH
2
QCH–CH
C NMR (100 MHz, CDCl
intercalate into the layer structure of MMT. In addition, ILs were (CH –N–CH ), 118.88 ppm (CH
used to obtain polymer gel membranes due to their high ionic 137.45, 143.22 ppm (Ar–C), 132.69 ppm (CH
2
–), 5.56–5.65 (m, 2H, CH
): 21.45 ppm (Ar–CH
QCH–CH –), 127.16, 129.66,
QCH–CH
2
QCH–CH
2
) ppm.
18
13
cellulose materials. To prepare modified clays, ILs were allowed to
3
3
), 49.34 ppm
19
2
2
2
2
2
2
)
20
conductivity. However, little work has been reported on the (Fig. S3, ESI†).
21,22
utilisation of ILs for clay hydration inhibition.
It has been demonstrated that 3-methyl imidazoliumcation-
ꢀ
2.3 Synthesis of PAAT
based tetrafluoroborate ILs possess devisable cations, and BF
4
2
3
anion is capable of forming hydrogen bonds, which may play TCDAP, OP-10 and deionised water were added to a 250 mL
an important role in the inhibition of clay swelling. In addition, three-neck flask with a magnetic stir bar. After dissolving AM
it is well known that introducing the rigid benzene ring can and AA in deionised water and adjusting the solution pH to a
2
4
ꢀ1
improve the thermal stability of the copolymer. Therefore, a certain value by 1.0 mol L NaOH solution, they were added
series of 3-methyl imidazoliumcation-based tetrafluoroborate ILs into the flask. After 15 min under N atmosphere, ammonium
2
were utilised to inhibit the hydration and swelling of clays in the persulfate and sodium hydrogen sulphite (molar ratio 1 : 1)
present study. Importantly, a novel copolymer with a rigid benzene were added to the flask at a certain temperature for 8 h. The
ring and sulfonamide structure was synthesised to improve the reaction product was washed by ethanol and dried to obtain
thermal stability of the system. The poly(acrylamide-co-acrylic acid- white granular PAAT. The synthetic route is shown in Scheme 1.
co-N,N-diallyl-4-methyl benzenesulfonamide) random copolymer,
denoted as PAAT, was synthesised via the copolymerisation of the
functionalised monomer N,N-diallyl-4-methyl benzenesulfonamide
2.4 Synthesis of PAAT–ILs complexes
(
TCDAP) with acrylamide (AM) and acrylic acid (AA). Water-soluble 3-Methylimidazolium-based tetrafluoroborate ILs were prepared
2
3,25
complexes of PAAT and 3-methylimidazolium-based tetrafluoro- according to previously reported methods.
The structure of
borate ILs were prepared and investigated for potential application the obtained 3-methylimidazolium-based tetrafluoroborate ILs is
as a new type of clay and shale hydration inhibitor.
shown in Fig. 1. PAAT solution was mixed with all kinds of
the prepared 3-methylimidazolium-based tetrafluoroborate ILs
under N2 atmosphere at 50 1C for 4 h. The PAAT–ILs were
obtained after cooling to ambient temperature.
2. Experimental section
2
.1 Materials
Acrylamide (AM), acrylic acid (AA), p-toluenesulfonyl chloride
TsCl), diallylamine (DAP), N-methylimidazole (mim), tetrafluoro-
boric acid, sodium fluoroborate, bromoethane, allyl bromide,
-bromobutane, 1-bromododecane, benzyl bromide, triethylamine
Et N), nonaphenol polyethyleneoxy (10) ether (OP-10), dichloro-
methane (CH Cl ), chloroform (CHCl ), acetone, ammonium per-
sulfate ((NH ), sodium bisulphite (NaHSO ), and KCl were
(
1
(
3
2
2
3
4
)
2
S
2
O
8
3
chemically pure and supplied by Chengdu Kelong Chemical
Reagent Factory, Sichuan, China. Sodium montmorillonite
(MMT) and bentonite were provided by Xinjiang Xiazijie Bentonite
Company, Xinjiang, China. CH Cl was dried using anhydrous
2
2
Scheme 1 Synthetic route of PAAT.
sodium sulphate, and others were used as received without further
purification.
2
.2 Synthesis of N,N-diallyl-4-methylbenzenesulfonamide
TsCl (3.81 g, 0.02 mol) and 10 mL CH Cl were added to a 100 mL
round-bottom flask with a magnetic stir bar. DAP (2.33 g,
.024 mol), Et N (4.04 g, 0.04 mol) and 5 mL CH Cl were
2
2
0
3
2
2
slowly added to the flask in a water-ice bath at 0–5 1C for 6 h.
The crude product was washed sequentially with deionised
water, 1 : 100 dilute HCl, NaOH solution and saturated NaCl and
dried using anhydrous sodium sulphate before it was filtered Fig. 1 Structure of 3-methylimidazolium-based tetrafluoroborate ILs.
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2
.5 Characterisation
indication of the mechanical property of the shale, were deter-
mined according to the following equation:
The apparent viscosities of copolymer solutions were measured
with a Brookfield DV-III + Pro viscometer (Brookfield, USA).
FT-IR spectra were measured with KBr pellets using a WQF-520
Fourier transform infrared spectrometer (Beijing Rayleigh
Analytical Instrument Corporation, China) in the optical range
3
FM ꢂ 10
IH ¼
ꢂ 100%
(2)
A
where the indentation hardness (IH) value is an indication of the
mechanical property of the shale (MPa), FM is the maximum
load before the rock is broken (kN), and A is the contact area
ꢀ1
1
13
of 400–4000 cm by averaging 32 scans. H NMR and C NMR
spectra were recorded by a Bruker AV III-400 NMR spectrometer
2
2
(
mm ). Here, A is 4.446 mm .
(Bruker, Switzerland) in D O and CDCl . Copolymer intrinsic
2 3
viscosity was measured by an Ubbelohde viscometer (Shanghai
Sikeda Scientific Instruments Incorporation, China) at 30 ꢁ
3
. Results and discussion
0.1 1C.
3.1 Synthesis of PAAT
2
.6 X-ray diffractometry (XRD)
The effects of the synthetic conditions on the copolymerisation of
AM, AA and TCDAP were investigated, and the intrinsic viscosity
and the viscosity-average molecular weight were measured. The
results are listed in Table 1 (for details, see Tables S1, S2 and Fig. S1
in ESI†). The structure of PAAT was characterised by FT-IR and
The hybrid MMT mixtures were prepared by adding 0.5 g MMT
to 1 g samples (KCl, ILs, PAAT and PAAT–ILs complex solutions)
at different concentrations. The hybrid mixture suspensions
were kept wet for 2 h. A part of the hybrid MMT mixtures was tested
directly by XRD, and others were dried to constant weight at 40 1C
in vacuum and then tested by XRD. The d-spacing of MMT was
investigated by small-angle XRD diffractometry (X’Pert PRO MPD
1
H NMR spectroscopy, and the results are presented in Fig. 2. The
stretching vibration peaks of –NH– and the CQO bond in the
ꢀ
1
ꢀ1
amide groups appeared at 3435.64 cm
and 1675.85 cm
,
ꢀ1
ꢀ1
respectively. The peaks at 1173.49 cm and 1049.28 cm corre-
(PANalytical B.V., Netherlands)) with a Cu Ka radiation target at
ꢀ1
spond to the stretching vibration of –SO –, suggesting the success-
2
4
0 mA and 40 kV. The scan rate was 1 deg min , the step size
ful copolymerisation of TCDAP monomer. The distinct peaks
around 1.54 ppm and 2.03–2.15 ppm can be assigned to the
was 0.05 degrees, and the scattering angle (2y) ranged from 2 to 8
degrees.
–
CH
at 3.74 ppm is due to the proton of –CH
shift value at 2.49 ppm is attributable to the –CH
Ar–CH in TCDAP, while the peaks at 7.42 ppm and 7.71 ppm,
2
– and –CH– in the polymeric chain, respectively. The peak
–N–CH –. The chemical
protons of
2
.7 Anti-swelling ratio test
2
2
3
Bentonite, which was mainly composed of Na-MMT, was used
due to its remarkable hydration in water. First, 0.5 g bentonite
was soaked in 10 mL sample solution for 2 h at room temperature.
Subsequently, the bentonite phase and the solution phase were
separated by a YuHua model TG-16 supercentrifuge (YuHua
Company, China) at 1500 r min for 15 min. The anti-swelling
ratio of bentonite was then calculated according to the following
equation:
–
3
denoted as d and e in Fig. 2(b), respectively, are attributable
to the protons of the benzene rings. These results verify the
successful preparation of the copolymer PAAT.
ꢀ
1
3.2 Effect of different PAAT–ILs on d-spacing of Na-MMT
The swelling inhibitions of different PAAT–ILs complexes were
investigated by comparing the d-spacing of MMT compared
with water–ILs (see Table S3 and Fig. S2, ESI†). It was found in
our previous works that polymer solutions slightly affected the
d-spacing of Na-MMT with the increasing concentration of
V2 ꢀ V1
B ¼
ꢂ 100%
(1)
V2 ꢀ V0
where B is the anti-swelling ratio (%), V is the volume of swollen
bentonite in distilled water (mL), V is the volume of swollen
bentonite in kerosene (mL), and V is the volume of swollen
bentonite in the sample solution (mL).
29
2
polymer solution. The d-spacing data of MMT in PAAT–ILs
0
are summarised in Table S3 (ESI†). The results indicated that
compared with water–KCl and water–ILs, the PAAT–ILs exhibited
1
significant anti-swelling capacities; for instance, the PAAT–HmimBF
complex resulted in a the smaller d-spacing of 13.16 Å. In addition,
PAAT–ILs with short chain substituents (HmimBF , emimBF
4
2
.8 Temperature resistance test
4
4
The effect of temperature on the apparent viscosities of sample
solutions was tested by using a Haake RS 600 rotational
rheometer (Haake, Germany) at a steady shear rate of 170 s
and AllymimBF ) exhibited excellent clay inhibition of MMT. The
4
d-spacing of MMT enlarged with increasing number of alkyl
Table 1 The optimum synthetic conditions and characteristics of PAAT
ꢀ
1
to simulate injection rates in the range of 30–130 1C.
2
.9 Indentation hardness measurement
Apparenat
Intrinsicb
Molecular
weight
ꢀ1
b
The indentation hardnesses of shale cores were studied by soaking Sample
viscosity (mPa s)
viscosity (mL g
)
6
the cores in solutions of the different samples at 80 1C for 24 h. The
core strength data of the shale were measured with an RTR-1000
rapid triaxial rock testing system (GCTS, USA) in comparison to
PAAT
352.6
1372.00
6.70 ꢂ 10
a
b
The concentration of copolymer was 1 wt%. The intrinsic viscosity
and viscosity-average molecular weight were determined according to
deionised water and KCl. The indentation hardness (IH) values, an ref. 26–28.
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1
Fig. 2 (a) FT-IR spectrum of PAAT and (b) H NMR spectrum of PAAT.
substituents in the PAAT–ILs. BenzylmimBF and C mimBF
4
4
n
3
0,31
(
n 4 6) are essentially insoluble in water.
Fig. 3 XRD patterns of MMT in (a) water–HmimBF
trations of HmimBF and (b) PAAT–HmimBF
concentrations of HmimBF
4
with varying concen-
4
4
complexes with varying
3
.3 Effect of PAAT–HmimBF
4
complex on d-spacing of
4
.
Na-MMT
The effects of PAAT–HmimBF complexes with varying concentra-
4
tions of HmimBF on the d-spacing of MMT were further investi-
4
gated. The results are shown in Fig. 3 and 4. The d-spacing of
MMT was determined to be about 18.60 Å for HmimBF
PAAT–HmimBF complex with 1 wt% HmimBF . The d-spacing of
MMT drastically decreased to about 13.20 Å with 2 wt% HmimBF
The abrupt decrease in d-spacing may occur only under a critical
4
and the
4
4
4
.
32
concentration of ILs. The d-spacing of wet MMT has no obvious
changes with the concentration of HmimBF from 2 to 5 wt%. The
4
d-spacing of corresponding re-dried MMT is higher than that of
untreated MMT (d-spacing = 12 Å). The results suggest that
+
HmimBF
4
intercalated in the MMT interlayer, replacing Na in the
original interlayer of MMT. The intercalation of the ILs confirms the
Fig. 4 The d-spacing of MMT in PAAT–HmimBF
concentrations of HmimBF
4
complexes with varying
different d-spacings of MMT in the different samples (Table S3, ESI†)
4
.
19
due to the size effect and arrangement of ILs.
3
.4 Anti-swelling ratios
The anti-swelling ratios of 0.3 wt% PAAT with different con- concentration is below 2 wt%. At concentrations greater than
centrations of HmimBF
ranging from 1 to 5 wt% were mea- 3 wt%, the clay-swelling inhibition of HmimBF is more effective
sured. The anti-swelling ratios of 1 to 5 wt% KCl solution and than that of KCl at the same concentration. The anti-swelling
to 5 wt% HmimBF
were also measured in comparison with ratio of PAAT–HmimBF complex reaches a maximum of 85%
the PAAT–HmimBF
complexes. The results are shown in Fig. 5. when the concentration of HmimBF is 2 wt%.
4
solution is much higher than that of HmimBF when the
4
4
1
4
4
4
4
The pictures of swollen bentonite in different concentrations of
KCl, HmimBF4 and PAAT with different concentration of
3
.5 Interaction between PAAT and HmimBF
4
1
3
HmimBF are shown in Fig. 6. The anti-swelling ratio increases with Interaction between PAAT and HmimBF was confirmed by
C
4
4
1
3
the addition of KCl as well as HmimBF
reaches about 3 wt% for the PAAT–HmimBF
the anti-swelling ratio is minimal. The anti-swelling ratio of KCl values at 183.81 ppm and 182.60 ppm can be assigned to the
4
. When the concentration NMR. The C NMR spectra of HmimBF
4
, PAAT, and PAAT–
4
complex, its effect on HmimBF complex are presented in Fig. 7. The chemical shift
4
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Fig. 8 Temperature dependence of the apparent viscosities of PAAT and
4
PAAT–HmimBF complex.
Fig. 5 The effect of concentration on anti-swelling ratio.
of 0.2 wt% and an HmimBF concentration of 2 wt%. The apparent
4
viscosity of PAAT gradually reduces with increasing temperature.
Although the viscosity of the solution decreases due to the addition
of HmimBF
the PAAT–HmimBF
addition, the solution viscosity remains almost constant from 60 to
10 1C, which can be ascribed to the strong interaction among
PAAT–HmimBF complexes within this temperature range. At high
temperature, the apparent viscosities of PAAT and PAAT–HmimBF4
complex solutions both decrease greatly because further increasing
the temperature results in the destruction of the interactions among
the polymer molecules.
4
containing organic cations, the apparent viscosity of
4
complex shows an increase from 30 to 60 1C. In
1
Fig. 6 Photographs of swollen bentonite in different samples (a–i: 1 wt%
4
KCl, 2 wt% KCl, 3 wt% KCl, 1 wt% HmimBF
HmimBF , PAAT–1 wt% HmimBF complex, PAAT–2 wt% HmimBF
complex, PAAT–3 wt% HmimBF complex).
4 4
, 2 wt% HmimBF , 3 wt%
4
4
4
4
3.7 Indentation hardness
The hydration and swelling of the clay can lead to the collapse,
fracture and deformation of rock. Indentation hardness analysis
is important for evaluating the performance of clay hydration
inhibitors. The composition of used core mineral is 47.3% illite,
2
7
2.0% illite-montmorillonite mixed-layer, 23.0% chlorite and
.7% kaolinite. The test results are listed in Table 2. The
indentation hardness of origin rocks was about 482.77 MPa,
and the indentation hardness retained in deionised water was
2
1% due to the strong hydration of clay. The indentation hardness
retained 351.06 MPa (73%) with 2 wt% HmimBF , which is
slightly higher than the value of 348.92 MPa (72%) with 3 wt%
complex. KCl. An even higher retained indentation hardness of up to 360.23
MPa (75%) can be obtained using the PAAT–HmimBF complex.
4
1
3
Fig. 7
4 4
C NMR spectra of HmimBF , PAAT and PAAT–HmimBF
4
15
ꢀ
In our previous work, the PANAA copolymer synthesised via
the copolymerisation of AM, AA, N,N-diallylbenzylamine (NAPA),
and 2-(acrylamide)-2-methylpropane-1-sulfonic acid (AMPS) could
retain 74% of the indentation hardness, but it had to be blended
–
COO moieties of PAAT and the PAAT–HmimBF4 complex,
respectively. Obviously, the resonance of the –COO group of
ꢀ
the PAAT–HmimBF
compared to that of PAAT (from 183.04–183.81 ppm to 182.61–
82.82 ppm), which is attributed to the electrostatic interaction.
4
complex shifts towards the higher field
1
This electrostatic interaction could be the driving force of ILs to
exist in the peripheral space of the copolymer chains (Fig. 10a).
Apart from that, it is worth mentioning that hydrogen bonds
Table 2 Results of indentation hardness test
a
Soaking samples Maximum load (kN) Indentation hardness (MPa)
might develop with oxygen atoms in the OQSQO or CQO Water
0.4504
1.5513
1.3252
1.5608
1.6016
101.38
348.92
298.07
351.06
360.23
3
3
KCl
groups of HmimBF (Fig. 10a).
4
PAAT
HmimBF
PAAT–HmimBF
4
3
.6 Temperature resistance
Fig. 8 shows the temperature resistance of 0.2 wt% PAAT and
PAAT–HmimBF
4
a
The concentrations of KCl, HmimBF
4
and copolymer were 3, 2 and
4
complex solutions with a copolymer concentration 0.3 wt%, respectively.
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charges on the clay surfaces (Fig. 10b). In addition, it is believed
that the absorbed copolymer chains of the PAAT–HmimBF
4
complex can prevent further clay hydration by encapsulating
the clay particles and improve the acting time and scour
resistance (Fig. 10b). Meanwhile, hydrogen bonds formed
between water molecules and some groups such as OQSQ O
ꢀ
and –NH
2
groups of PAAT and/or the anion BF
4
of HmimBF
4
could compete with the ones between water molecules and the
silica or alumina functionalities, reducing the ingress of water
2
into MMT.
4. Conclusions
In conclusion, complexes of the copolymer PAAT and the ionic
liquid HmimBF were successfully prepared. The d-spacing of
MMT is significantly reduced from 19.24 to 13.16 Å by PAAT–
HmimBF4 complex, and the PAAT–HmimBF4 complex with
4
Fig. 9 Photographs of original shale core samples before hydration:
(a), (c), (e) and (g) and after soaking in different solutions: (b) water, (d)
HmimBF , (f) PAAT, and (h) PAAT–HmimBF complex.
4
4
2
wt% HmimBF
4
can improve the indentation hardness reten-
tion of shale to 75% and increase the anti-swelling ratio to 85%,
1
3
with 3 wt% KCl. In the present study, the inhibition of clay
hydration by the PAAT–HmimBF complex is significantly
effectively minimising clay hydration and swelling. C NMR
spectra verified the existence of electrostatic interactions and
4
enhanced compared to PAAT (62%). Fig. 9 shows photographs
of core samples of the shale before and after soaking in different
solutions. The original core samples after the hardness test under
external stress show brittle failure. By comparing the photographs
of core samples of the shale before and after soaking in different
solutions, no cracks can be observed on the core samples after
4
hydrogen bonds between PAAT and HmimBF , and the possible
clay hydration and swelling inhibition mechanism has been
presented. It is also shown that PAAT–HmimBF4 complex
exhibits better thermal stability than PAAT, suggesting that it
can be used as a potential clay and shale hydration inhibitor in
high-temperature oil and gas wells.
soaking in HmimBF
These results clearly demonstrate that the PAAT–HmimBF
complex can be potentially used for shale inhibition.
4 4
and PAAT–HmimBF complex solutions.
4
Acknowledgements
The authors gratefully acknowledge the National Natural Science
Foundation of China (U1262209) and Southwest Petroleum
University (No. 2014PYZ011) for financial support.
3
.8 Clay hydration and swelling inhibition mechanism
Fig. 10 depicts the possible mechanism of clay hydration and
swelling inhibition with the PAAT–HmimBF4 complex. The
enhanced clay inhibition can be attributed to the electrostatic
interactions between the cations of HmimBF and the negative
4
Notes and references
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& Exhibition-From
Potential to Production, 2012.
2
R. L. Anderson, I. Ratcliffe, H. C. Greenwell, P. A. Williams,
S. Cliffe and P. V. Coveney, Earth-Sci. Rev., 2010, 98,
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