Thermally stable imidazoline-based sulfonate copolymers for enhanced oil recover

Article abstract of DOI:10.1039/c5ra15434k

Novel imidazoline-based sulfonate copolymers (noted PAMDSCM and PAMPSCM) were successfully prepared by copolymerization of acrylamide (AM), acrylic acid (AA), 1-acrylamido ethyl-2-oleic imidazoline (ACEIM) with the sodium salts of 3-(diallyl-amino)-2-hydroxypropyl (NDS) or 2-acrylamido-2-methylpropane sulfonic acid (AMPS), respectively. The copolymers were characterized by infrared (IR) spectroscopy, ¹H nuclear magnetic resonance (¹H NMR) spectroscopy, pyrene fluorescence probe spectroscopy, viscosimetry and thermogravimetry (TG). Both PAMDSCM and PAMPSCM copolymers had excellent high-temperature tolerance in comparison with the same concentration of HPAM, and the residual viscosities were 32.0 mPa s and 31.3 mPa s (viscosity retention rates were 38.8% and 37.1%) at 140 °C, respectively. The copolymers possessed superior long-term thermal stability and their residual viscosity rates were up to 81.8% and 63.8% (52.9 mPa s and 47.1 mPa s) lasting 1.5 hours at 100 °C and 170 s^-1, respectively.

Full text of DOI:10.1039/c5ra15434k

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Graphical abstract
Thermally stable imidazoline-based sulfonate polymers for enhanced
oil recovery
Shaohua Gou, Shan Luo, Tongyi Liu, Hong Xia, Dong Jing, Qin Zhang, Shiwei Li，
Zhonghui Li and Qipeng Guo
Novel water-soluble imidazoline-based sulfonate copolymers were synthesized; the
copolymers possess excellent thermal stability and outstanding potential for
application in high-temperature oil recovery.

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ARTICLE
Thermally stable imidazoline‐based sulfonate copolymers for
enhanced oil recovery
naReceived 00th January 20xx,
Accepted 00th January 20xx
Shaohua Gou, *ab Shan Luo,b Tongyi Liu,b Hong Xia,b Dong Jing,b Qin Zhang,b Shiwei Li,b Zhonghui Li
c and Qipeng Guo*d
DOI: 10.1039/x0xx00000x
Novel imidazoline‐based sulfonate copolymers (noted PAMDSCM and PAMPSCM) were successfully prepared by
copolymerization of acrylamide (AM), acrylic acid (AA), 1‐acrylamido ethyl‐2‐oleic imidazoline (ACEIM) with the sodium
salts of 3‐(diallyl‐amino)‐2‐hydroxypropyl (NDS) or 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS), respectively. The
copolymers were characterized by infrared (IR) spectroscopy, 1H nuclear magnetic resonance (1H NMR) spectroscopy,
pyrene fluorescence probe spectroscopy, viscosimetry and thermogravimetry (TG). Both PAMDSCM and PAMPSCM
copolymers had excellent high‐temperature tolerance in comparison with the same concentration of HPAM, and the
residual viscosities were 32.0 mPa∙s and 31.3 mPa∙s (viscosity retention rates were 38.8% and 37.1%) at 140 oC,
respectively. The copolymers possessed superior long‐term thermal stability and their residual viscosity rates were up to
81.8% and 63.8% (52.9 mPa∙s and 47.1 mPa∙s) lasted 1.5 hours at 100 oC and 170 s‐1, respectively.
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property, temperature tolerance and salt resistance.16‐20
1.Introduction
Water‐soluble polymers have been extensively used to maximize
the residual oil in commercial chemical EOR applications.1,
Recently, increasing attention has been paid to multifunctional
polymers, especially imidazole‐ and imidazoline‐containing
polymers which show a wide range of potential applications.21‐26
And the chemical architecture of substituted imidazoline units
2
Hydrophobically associating polymer (HAPAM) thereof contains a
small number of hydrophobic moieties attached directly to the
polyacrylamide (PAM) backbone.3‐5 Those polymers, in comparison
with partially hydrolyzed polyacrylamide (HPAM), have been proved
to be effective in combating high salinity and relieving the
downtrend of viscosity at high‐temperature, which caused by the
association of hydrophobic groups to minimize their exposure to
the solvent.6 Meanwhile, given its unique rheological properties,
hydrophobically associating polymers possess excellent potential in
EOR applications which was extensively reviewed in the work of
Taylor in 1998.7
constituted as the following:
a
five‐membered aromatic
heterocyclic containing two nitrogen atoms at the 1, 3‐positions
(namely, an electron‐rich hydrophilic amidine (N=C‐N) motif), a
hydrophobic alkyl chain and a pendant side chain constituted by
electron‐donor hydrophilic functional group(s) attached to N of the
motif and the C terminal, respectively.27 Although the particular
configuration and characteristic endow imidazoline derivatives with
desirable storage stability, viscosity, dispersibility and corrosion
inhibition performance in various industrial applications, they were
rarely utilized to incorporate into PAM chain for enhanced oil
recovery 28‐33
.
Numerous research efforts have focused on the introduction of
special functional groups that benefit the improvement of water‐
solubility, temperature resistance, anti‐shear property, salt
tolerance and etc.8‐10 Sulfonate groups attached into the PAM chain
Here we report the synthesis and evaluation of imidazoline‐based
sulfonate copolymers (denoted as PAMDSCM and PAMPSCM) with
the functional monomers attached to heterocyclic moieties and
hydrophobic groups via free‐radical copolymerization. The
copolymers were characterized by IR, 1H NMR, TG, and viscosimetry,
respectively. The critical association concentrations of the polymers
solutions were measured by the use of pyrene fluorescence probe.
The corresponding polymers have been further examined on their
unique properties, such as thickening ability, thermal stability, anti‐
shear thinning and salt tolerance.
can improve effectively the performance on confronting harsh
12
environment like high temperature or high salinity.11,
2‐
Acrylamido‐2‐methylpropane sulfonic acid (AMPS), a widely used
monomer, can be copolymerized with acrylamide (AM) to obtain a
water‐soluble sulfonate polymer that effectively improve thermal
stability and salt tolerance.13, 14 However, a safe temperature limit
for AM‐AMPS copolymer is recommended below 90 oC based on the
investigations by Kamal et al.15 In our previous studies, sulfonated
copolymers have been proven to be successfully applied in EOR
applications and possessed high performance on thickening
2.Experimental
2.1 Materials
Acrylamide (AM), acrylic acid (AA), ammonium persulfate
((NH4)2S2O8), sodium bisulfite (NaHSO3), 2‐acrylamido‐2‐
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methylpropane sulfonic acid (AMPS), ethanol, sodium hydroxide (dissolved in deuterium oxide (D2O) solvent) were measured by a
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DOI: 10.1039/C5RA15434K
(NaOH), thionyl chloride, oleic acid, diethylenetriamine, xylene, Bruker AV III‐400 MHz spectrometer (Bruker BioSpin, Switzerland).
epichlorohydrin, and diallyl amine are analytical reagent and used
2.3.3 Intrinsic viscosity [η] measurement. The intrinsic viscosity
directly without further purification. The chemicals were gained
from Chengdu Kelong Chemical Reagent Factory, therein partially
hydrolyzed polyacrylamide (HPAM, 10% degree of hydrolysis,
Mw=1.2×107), was obtained from Sichuan Guangya Polymer
Chemical Co., Ltd.
of polymer solutions was gauged via an Ubbelohde viscometer. The
copolymers were dissolved and diluted to the required
concentration by way of the 1.0 mol/L NaCl solution at a constant
o
temperature bath (30 C). The flux time of polymer solutions were
fain registered with an accuracy of 0.05 s.
2.2 Synthesis
2.3.4 Conversion measurement. The conversion of AM was
2.2.1 Synthesis of ACEIM. Monomer 1‐acrylamido ethyl‐2‐oleic performed with a high‐performance liquid chromatography (HPLC;
imidazoline (ACEIM) was prepared referring to previously reported Shimadzu Co., Japan). The conversion was calculated by the residual
methods.28,
Briefly, an intermediate imidazoline derivative AM of precipitated the polymer in ethanol, following equation 1: 36
34, 35
(aminoethyl oleic imidazoline) was synthesized based on oleic
acid/diethylenetriamine in the ratio of 1:1.2 with xylene carrying
generated water at 200‐220 oC. Then extracted and further purified
with ethyl acetate and deionized water after adding excessive NaCl
saturated solution. Acryloyl chloride (2.172g, 0.024 mol) was slowly
added dropwise to the intermediate product (6.99 g, 0.02 mol)
which dissolved in 20 mL ethanol solution. The reaction was kept a
here W(%) is the conversion of AM suggesting the conversion of
copolymer; WAM is the total weight of AM before reaction; A and A0
are the chromatographic peak areas of the residual AM in ethanol
and the standard sample AM, respectively; C0 is the concentration
of standard sample AM solution; V is the volume of ethanol solution
precipitated by the polymer.
o
temperature range of 0‐10 C for 4‐5 h, and then the mixture was
extracted with dichloromethane after the organic phase was
washed three times with saturated NaCl solution. Finally, brown oil‐
soluble thick liquid, 1‐acrylamido ethyl‐2‐oleic imidazoline (ACEIM)
was further purified by the reduced pressure distillation of the third
2.3.5 Pyrene fluorescence probe. Pyrene fluorescence probe was
utilized to characterize the critical association concentration (CAC)
1
filtrate. The structure of ACEIM is shown in Fig.1. ACEIM: H NMR
of the copolymers by
a
Shimadzu RF‐5301PC pectrofluoro‐
(400 MHz, CDCl3, Fig.3(a)): δ=7.29 (k, H, CH2=CHCO–), 6.25‐6.28 (k,
2H, CH2=CHCO–), 5.92 (h, 2H, (CH2)NCH2CH2N=), 5.33 (f, 2H, –
(CH2)7CH=CH(CH2)7CH3), 4.05‐4.07 (g, 2H, =NCH2CH2N–), 3.38‐3.51
(e, 2H, –NHCH2CH2NCO), 2.75 (d, 2H, –CONHCH2CH2N–), 1.99‐2.22
o
photometer with emission at 335 nm at 25 C. The slit width of
excitation (emission) was fixed at 15.0 nm through a constant scan
speed of 800 nm/min and the spectral range was 350‐580 nm. The
corresponding polymers were diluted to different concentrations
(100‐4000 mg/L), whereby the concentration of pyrene was 2×10‐6
mol/L.
(c,
14H,
–(CH2)7CH=CH(CH2)7CH3),
1.25
(b,
14H,
–
(CH2)7CH=CH(CH2)7CH3), 0.87 (a, 3H, –CH3), ppm.
2.4 TG test
The thermal stability of the polymers was conducted to measure by
a thermogravimetric analyzer (Switzerland, METTLER TOLEDO Co.)
for a flow rate of 20 mL/min at 25‐800 oC. The heating rate of the TG
experiments was 25 oC/min under nitrogen atmosphere.
2.5 Rheological characterization
2.5.1 Temperature resistance test. Temperature resistance tests of
2000 mg/L copolymer solutions were performed at a temperature
range of 25‐140 oC using a rotational rheometer (Haake RheoStress
6000, Germany) at 170 s‐1.
Fig.1 The structure of ACEIM.
2.2.2 Synthesis of Copolymers PAMDSCM and PAMPSCM.
Copolymers PAMDSCM and PAMPSCM were conducted to prepare
by acrylamide (AM), acrylic acid (AA), 1‐acrylamido ethyl‐2‐oleic
imidazoline (ACEIM), and 3‐(diallyl‐amino)‐2‐hydroxypropyl
(NDS)/2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) via free
radical copolymerization in aqueous solution, respectively, and their
synthesis routes are shown in Scheme 1. The optimal
copolymerization conditions are recorded in Table 1. The
copolymerization conditions (Fig.S1) and synthesis routes of the
monomers (Scheme S1) are given in ESI†.
2.5.2 Long‐term thermal stability test. Long‐term thermal stability
of 2000 mg/L copolymer solutions were achieved by deducing the
relationship between apparent viscosity and time using a rotational
rheometer (Haake RheoStress 6000, Germany) lasted 1.5 hours with
a constant temperature of 100 oC at 170 s‐1.
2.5.3 Anti‐shear test. Shear‐tolerance of 2000 mg/L copolymer
solutions were measured by a rotational rheometer (Haake
RheoStress 6000, Germany) with a shear rate rang of 7.34‐1000 s‐1
at 25 oC.
2.3 Characterization
2.3.1 IR. The copolymers were individually characterized by using
WQF‐520 Infrared spectroscopy (Beijing Rayleigh Analytical
Instrument (Group) Co.Ltd, China) in 4400‐400 cm‐1 optical range.
2.5.4 Shear recovery test. Shear recovery performance of 2000
mg/L copolymer solutions were performed with stepped shear rate
2.3.2 1H NMR. The 1H NMR spectra analyses of the polymers
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o
o
(170 s‐1, 510 s‐1 and 850 s‐1) at 25 C by a rotational rheometer (Haake RheoStress 6000, Germany) at 25 C under a frequency (f)
(Haake RheoStress 6000, Germany).
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scanning range of 0.01‐10 Hz, which obeyedDMOIa:x1w0.e10ll3M9/Cod5ReAl 1a5t4l3o4wK
shear frequency.
2.5.5 Viscoelasticity test. The viscoelastic characteristics of the
copolymer (2000 mg/L) were investigated by a rotational rheometer
Scheme 1 Synthesis routes of PAMDSCM and PAMPSCM.
Table 1 Copolymerization conditions of PAMDSCM and PAMPSCM
Monomer (wt%)
Apparent
viscosity
(mPa∙s)a
553.8
Intrinsic
viscosity
(mL/g)b
1178.2
Initiator
(wt%)
Temperature
(oC)
Conversion
(%)c
Copolymer
pH
AM AA ACEIM
NDS
AMPS
PAMDSCM
PAMPSCM
0.4
0.4
7
7
40
40
6.5 3.5
0.1
0.15
1.0
—
—
1.0
95.9
96.5
7
3
571.1
1201.5
a 0.2 wt % polymer solution measured by a Brookfield DV‐III+Pro viscometer at 25 oC
b The intrinsic viscosity was determined according to the reference37
c Conversion (wt%) of AM tested by HPLC
2.6 Salt resistance test.
was initially infused the sand pack to the saturation, and
subsequently injected the simulated crude oil. Then the sand pack
was injected with the synthetic brine until the water content was
above 95 %, and 2000 mg/L copolymer solution was followed to
inject under a flow rate of 0.25 mL/min. The subsequent water
flooding was eventually injected to replace polymer flooding until
no more oil was exhausted. The oil recovery by polymer flooding (E1)
and the oil recovery by water flooding (E2) were determined,
respectively, thus the difference between them is the value of
enhanced oil recovery (EOR).
Salt resistance tests of 2000 mg/L copolymer solutions were
estimated by a Brookfield DV‐III+Pro viscometer (Brookfield, USA)
under different concentration inorganic salt (NaCl, CaCl2 or MgCl2)
o
solutions at 25 C. The composition of synthetic brine in the Long‐
term experiments is shown in Table 2.
Table 2 Composition of synthetic water flooding
‐
2‐
ion
Na+
K+ Ca2+ Mg2+
Cl‐
HCO3
SO4
Total
7225
Concentration
(mg/L)
2231 70
95 226
4026
28
549
3.Results and discussion
3.1 Characteristic analysis
2.7 Core flooding test.
The effect of copolymer flooding on enhanced oil recovery was
fulfilled under simulated high salinity at 85 C. The dimension of
3.1.1 IR analyses Described in Fig.2 are the IR spectra of the
copolymers. The IR spectra presented that the monomer ACEIM was
successfully copolymerized into the backbone of polymer chain
based on characteristic peaks at 3429 cm‐1, 1653 cm‐1, 1561 cm‐1,
1458 cm‐1, 1404 cm‐1, and 1320 cm‐1 in PAMPSCM IR spectrum and
3416 cm‐1, 1653 cm‐1, 1561 cm‐1, 1449 cm‐1, 1403 cm‐1 and 1320 cm‐
1 in IR spectrum of PAMPSCM. As expected, the obvious absorption
peaks occurred at 1117 cm‐1 and 1043 cm‐1 in PAMDSCM IR
o
sand‐filled pipe prepared for the core experiments was about 2.5
cm in diameter and 50 cm in length. The total salinity of simulated
brine across the core flooding experiments was about 7200 mg/L
(see Table 2). The oil phase was prepared by simulated oil (67.4
mPa∙s at 85 oC). The steel cylinders packed by silica sand were dried
for a minimum of 24 hours before performing. The synthetic brine
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spectrum, and that of PAMPSCM IR spectrum was at 1108 cm‐1 and
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‐
1043 cm‐1, implying the successful introduction of –SO3 groups.
Fig.2 IR spectra of obtained copolymers.
3.1.2 1H NMR analyses. 1H NMR spectra of PAMDSCM and
PAMPSCM are shown in Fig.3. As displayed in Fig. 3(b), the chemical
shift value was 7.67 ppm implying characteristic peak of the NH of
[CONHCH2–]. The chemical shift value appeared at 6.82 ppm due to
the NH protons of [–CONH2]. The chemical shift values were about
5.70 ppm and 5.53‐5.56 ppm attributed to –NCH2– of
[(CH2)NCH2CH2N=] and the aliphatic –CH=CH– of [–
CO(CH2)7CH=CH(CH2)7CH3], respectively, suggesting successful
introduction of ACEIM. The peak value at 3.71 ppm was appointed
to –CH2N= proton of the imidazoline ring and the proton of–
CH2SO3Na. The chemical shift value at 0.94 ppm was attributable to
the –CH3 protons of the aliphatic chain of monomer ACEIM. The
protons of the aliphatic –CH2– and polymeric chain were detected
at 1.56‐1.65 ppm. The chemical shift value of –CH– protons of
polymeric chain was at 2.13 ppm. The peaks at 3.36‐3.41 ppm
represented the protons of [CONHCH2CH2–] and [–
CH2CH(OH)CH2SO3Na].
The 1H NMR spectrum of copolymer PAMPSCM is depicted in Fig.
3(c), which was detected the similar morphological characteristic
peaks with the polymer PAMDSCM. And the spectra peaks of
copolymer PAMPSCM can be discovered the characteristic protons
of the functional monomers. Those characteristic shift peaks,
obviously, are indicative of the successful incorporation of the
monomers ACEIM and AMPS. Depicted in ESI† is the 1H NMR
spectrum of monomer NDS (see Fig.S2).
Fig. 3 1H NMR spectra of (a) ACEIM, (b) PAMDSCM and (c)
PAMPSCM.
3.2 Critical association concentration
As a rule, the critical association concentration (cac) is well‐defined
as the concentration that the interchain associations start to
decreases significantly with hydrophobic groups increasing.38‐40 The
ratios of I1 and I3 as a function of different concentrations of the
copolymers in fluorescence spectra (see Fig.S3 and Fig.S4, ESI†)
were calculated, as displayed in Fig. 4(a). From the curves of I1/I3, a
dramatic decrease was detected when the concentrations of
polymer PAMPSCM exceeded 1.25 g/L, in which of polymer
PAMDSCM occurred beyond 1.0 g/L. The decrease of I1/I3 values was
associated with the weakening of the microenvironment polarity
around pyrene molecule, suggesting that pyrene molecules
transferred into the hydrophobic microdomains. And the results are
also verified in the thickening curves of the polymers in Fig. 4(b).
Tackifying effect, one of the most considerable properties, was
evaluated by measuring viscosity variation of the polymers solution
at a concentration range of 100‐4000 mg/L. As depicted in Fig. 4(b),
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a linear increase on apparent viscosity was observed with the formed by the diallyl. Moreover, a sharp weight decline of
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increasing of polymer concentration. Although the viscosity of PAMDSCM was observed beyond 350 oC, whDicOhI:ca10n.1b0e39a/tCt5riRbAu1t5e4d34tKo
HPAM solution started slightly higher than that of PAMDSCM and the hydroxy decomposition of monomer NDS. For HPAM, the first
o
PAMPSCM at low concentration, the viscosities of PAMDSCM and one took place at 25‐211 C with a mass loss of 16.3 wt%. The
PAMPSCM were well above that of HPAM when the concentration second stage with a weight mass of 35.8 wt% occurred at 211‐384
was above 600 mg/L. And from the viscosity curves, the oC caused by the decomposition of the amide groups. The last one
breakthrough points of PAMDSCM and PAMPSCM were about 1.0 occurred beyond 384 oC, suggesting the carbonization of HPAM.
g/L and 1.25 g/L, respectively. It was due in part to the
enhancement on association effect and hydrogen bond, suggesting
the introduction of rigid imidazoline ring, hydrophobic groups and
sulfonate groups.
Fig. 5 Thermal gravimetric curves of the polymers.
Fig. 4 (a) Effect of the copolymers on I1/I3 values; (b) the thickening
properties of the copolymers.
3.3 TG analysis
The TG curves of PAMDSCM, PAMPSCM and HPAM are depicted in
Fig.5. In the TG profiles, the mass loss declined consecutively over
the whole temperature range of 25‐800 oC. For PAMDSCM, the first
weight loss was 12.7 wt% at 25‐242 oC, showing the evaporation of
crystal water existing in the polymers. The second steps appeared at
242‐344 oC with a mass loss of 29.4 wt%, suggesting the thermolysis
Fig. 6 (a) Anti‐shear resistance and (b) shear recovery of the
polymers.
of the amide group, hydrophobic moiety, sulfonate group and
imidazoline ring. The final mass loss beyond 344 oC was about 51.7
3.4 Rheological behavior
wt% corresponding to the decomposition of carbon backbone of the
polymers. For PAMPSCM, the first one with a weight loss of 17.2
wt% occurred at 25‐280 oC. The second stage took place at 280‐583
oC with a mass loss of 44.9 wt%, which may be ascribed to the
decomposition of the amide group, oleic imidazoline moiety and
sulfonate group of the polymer. The final one occurred beyond 583
oC implying the carbonization. From the TG curves, hence, the mass
loss of polymer PAMDSCM was lesser than that of PAMPSCM at 25‐
3.4.1 Anti‐shear resistance. Apparent viscosity dependent on shear
rate for the copolymers are conducted to delineate in Fig. 6(a).
Obviously, it was fantastically discovered the approximate decline
curves of the polymers with the shear rate increasing. The viscosity
of PAMDSCM or PAMPSCM fell abruptly at a shear rate range of
0.01‐400 s‐1 and maintained the continuous‐steady viscosity over
400 s‐1. The viscosity/shear rate curves of copolymers PAMDSCM
and PAMPSCM had superior anti‐shear thinning and the polymers
o
200 C due in part to the additional five‐membered ring structure
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possessed higher residual viscosities (29.1 mPa∙s and 26.7 mPa∙s, introduction of ACEIM unit into PAM chain can effectively improve
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DOI: 10.1039/C5RA15434K
respectively), compared with the corresponding concentration temperature tolerance on account of imidazoline ring within the
HPAM solution (13.3 mPa∙s) at 1000 s‐1. The results were indicated rigid structure.
that the rigid structure of imidazoline monomer succeeded to
induce an increase in viscosity retention rate and improved
effectively anti‐shear resistance of the polymers.
3.4.4 Long‐term thermal stability. Long‐term thermal stabilities of
the polymers are depicted in Fig. 7(b). Obviously, it was discovered
that those initially decreased slowly in viscosity, then kept
3.4.2 Shear recovery. The variations of apparent viscosity as a approximately trend to be stable following the time increasing at
o
function of different gradient shear rates for PAMDSCM and 100 C. As expected, the polymers possessed excellent long‐term
PAMPSCM in aqueous phase are portrayed in Fig. 6(b). As expected, thermal stabilities in comparison to the same concentration HPAM,
it was discovered that the viscosity curves of the polymer solutions which depend on the physical reversibility of association effect of
42
kept approximate viscosity value, which undergone a flipping back the polymers.41,
What needs to be emphasized is that the
and forth in the region of 170 s‐1, 510 s‐1 and 850 s‐1, then back viscosities of 2000mg/L of the polymers and HPAM solutions are
again. The phenomena indicated that the polymers functionalized virtually unanimous; however, the difference of the molecular
imidazoline derivative possessed remarkable improvement on shear weight between HPAM and obtained polymers is tremendous. And
stability on a basis of the reversible supermolecular networks of PAMDSCM held the preferable thermal stability than PAMPSCM
hydrophobically associating polymer.41
solution through 90 min of 100 oC.
Fig.8 (a) Effect of NaCl concentration on apparent viscosity; (b)
Effect of CaCl2 concentration on apparent viscosity; (c) Effect of
MgCl2 concentration on apparent viscosity; (d) long‐term stability of
the polymers in the presence of 7225 mg/L inorganic salt for 30
days.
3.5 Salt resistance
The stabilities of the corresponding polymer solutions against
inorganic salt (Na+, Ca2+ or Mg2+) are shown in Fig.8(a‐c). For the
curves of PAMDSCM and PAMPSCM, it was discovered that the
apparent viscosity presented initially declined rapidly and
subsequently plateaued with the addition of inorganic salt. It also
can calculate that the residual viscosity were 46.2 mPa∙s and 29.3
mPa∙s for PAMDSCM and PAMPSCM in 10 000 mg/L NaCl solution,
respectively, in which the residual viscosity of HPAM was 15.6
mPa∙s. And the tests to resist Ca2+ (Mg2+) for PAMDSCM and
PAMPSCM are shown in Fig. 8 and the residual viscosity were 20.6
mPa∙s and 25.7 mPa∙s (37.1 mPa∙s and 24.6 mPa∙s, respectively) in
2000 mg/L inorganic salt, respectively. The polymers had preferable
improvement on the salt resistance compared with HPAM solution
(2000 mg/L CaCl2: 11.6 mPa∙s; 2000 mg/L MgCl2: 13.6 mPa∙s), which
were associated with the enhancement of internal rotation
resistance due to the introduction of hydrophobic group and
sulfonate groups.
Fig. 7 (a) Effect of temperature on apparent viscosity; (b) the
viscosity‐time curves of the polymers at 100 oC.
3.4.3 Temperature tolerance. The variation of apparent viscosity as
a function of different temperature for PAMDSCM and PAMPSCM in
aqueous phase are depicted in Fig.7(a). At a temperature range of
o
25‐110 C, a continuously slow decrease in viscosity was initially
observed in the approximate decline curves of PAMDSCM and
PAMPSCM. As temperatures continue to rise, it was amazing that an
abruptly decrease was subsequently observed. It could be derived
that polymers PAMDSCM and PAMPSCM possessed the viscosity
residual rate of 76% and 78% at 110 oC, respectively. And the
residual viscosities were 32.0 mPa∙s and 31.3 mPa∙s, respectively,
whereas that of HPAM was 17.5 mP∙s at 140 oC. The phenomena can
be interpreted in terms of the characteristic hydrophobic effect of
hydrophobically associating polymers, suggesting that the successful
6 | J. Name., 2012, 00, 1‐3
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The variations of apparent viscosity of the polymers (2000 mg/L) 3.7 Enhanced oil recovery
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DOI: 10.1039/C5RA15434K
in the presence of inorganic salt were determined by a Brookfield The characteristic parameters for polymer solutions are investigated
o
DV‐III+Pro viscometer at 25 C for 30 days, as shown in Fig.8(d). As in Table 3 under simulated salinity environment in core flooding
observed in the curves, obviously, the viscosities of the polymers tests, which included resistance factor (RF), residual resistance
showed the similar decline tendency with time rising. The factor (RRF), the recovery factor (E1, E2 and EOR value) and etc.
phenomena can be explained the electrostatic charge shielding Obviously, it can be observed that the functionalized copolymers
effect in the presence of salt, hence a collapse of the network possessed superior profile control capability in a comparison with
caused the reduction of the viscosity of the polymers.43, 44 And the same concentration of HPAM solution.
obtained polymers can withstand preferably high salinity in
The results of oil recovery rate as a function of volume injected
comparison to the same concentration HPAM solution on account of (PV) for PAMDSCM, PAMPSCM and HPAM solutions are plotted in
the introduction of sulfonate and oleic imidazoline unit into the Fig.10. The porosity and permeability across the core flooding tests
polymers chain.
were about 35.48% and 203.6 mD, respectively. Besides, the
measurements of the porosity and permeability before and after
the core flooding experiments showed that the difference was
inconspicuous. From the curves, it was derived the oil recovery
factor of PAMDSCM (EOR=12.3%) and PAMPSCM (EOR=10.25%),
whereas that of HPAM was only 6.17 %. Given the unique steady
and dynamic rheological properties of the polymers, relatively high
oil recovery factors were obtained under simulated high
temperature and salinities, thus the results were verified by the
effective improvement of water‐oil mobility ratio.
Fig.9 Viscoelasticity of the polymers.
3.6 Viscoelasticity
The viscoelastic properties of PAMDSCM and PAMPSCM solutions
are depicted in Fig.9. As described in Fig.9, the dynamic viscoelastic
curves of the storage modulus (G׳) and loss modulus (G״)
dependent on the oscillation frequency (f) presented approximate
growth trend that G׳ and G״ initially increased gradually (G׳<G״) in
the region of low‐frequency, and subsequently G׳ surpassed G״ that
elastic behavior predominated accompanying with the frequency
rising. Those are the characteristic viscoelastic behaviors of the
imidazole‐functional sulfonate polymers suggesting the great
potential of enhanced recovery efficiency in EOR applications.
Fig. 10 The results of the core‐flooding experiments.
Table 3 Characteristic parameters of polymer solutions
Core samples
Polymer solutions
PAMDSCM
PAMPSCM
HPAM
RF
RRF
4.02
4.60
1.53
E1 (%)
52.19
50.12
45.32
E2 (%)
39.89
39.87
39.17
EOR (%)
12.30
10.25
6.17
1
2
3
12.53
13.05
4.58
promote remarkably thickening and rheological property on a basis
of the unique structural characteristic of hydrophobic copolymers.
The copolymer solutions had been proven to be more effectively
against the inorganic salt (NaCl, CaCl2 or MgCl2). Additionally, the
EOR results inferred that PAMDSCM and PAMPSCM solutions could
enhance the simulated oil recovery of 12.30% and 10.25%,
respectively. The excellent features signified that the polymers have
great technological potential in high‐temperature oil recovery.
4.Conclusions
Novel imidazoline‐functionalized sulfonate copolymers have been
successfully synthesized in the presence of (NH4)2S2O8‐NaHSO3. The
two copolymers possessed outstanding improvement on high
thermal stability and their viscosity residual rates can be up to
38.8% and 37.1% at 140 oC in comparison with that of 25 oC,
respectively. The polymers solutions also had excellent long‐term
heat stability that their residual viscosity rates could be up to 81.8%
and 63.8% lasted 1.5 hours at 100 C with a shear rate of 170 s‐1,
respectively. Moreover, the copolymers have been confirmed to
o
Acknowledgements
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Paper
RSC advances
Sp., 2002, 16, 705‐712.
The work was financially supported by key projects (natural
View Article Online
31 D. Wang, S. Li, Y. Ying, M. Wang, H. Xiao and Z. Chen, Corros Sci,
DOI: 10.1039/C5RA15434K
sciences) of Sichuan Provincial Education Department (15ZA0051),
Foundation of Youth Science and Technology Innovation Team of
Sichuan Province (2015TD0007) and Southwest Petroleum
University (2014PYZ008, 2014XJZ759). The authors express their
sincere thanks for the financial supporters.
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