A novel water-soluble hydrophobically associating polyacrylamide based on oleic imidazoline and sulfonate for enhanced oil recovery

Article abstract of DOI:10.1039/c5nj01153a

3-(2-(2-Heptadec-8-enyl-4,5-dihydro-imidazol-1-yl)ethylcarbamoyl)acrylic acid (NIMA), 3-(diallyl-amino)-2-hydroxypropyl sulfonate (NDS), acrylamide (AM) and acrylic acid (AA) were successfully utilized to prepare novel acrylamide-based copolymers (named AM/AA/NIMA and AM/AA/NDS/NIMA) which were functionalized by a combination of imidazoline derivative and/or sulfonate via redox free-radical polymerization. The two copolymers were characterized by infrared (IR) spectroscopy, ¹H nuclear magnetic resonance (¹H NMR), viscosimetry, pyrene fluorescence probe, thermogravimetry (TG) and differential thermogravimetry (DTG). As expected, the polymers exhibited excellent thickening property, shear stability (viscosity retention rate 5.02% and 7.65% at 1000 s^-1) and salt-tolerance (10:000 mg L^-1 NaCl: viscosity retention rate up to 17.1% and 10.2%) in comparison with similar concentration partially hydrolyzed polyacrylamide (HPAM). The temperature resistance of the AM/AA/NDS/NIMA solution was also remarkably improved and the viscosity retention rate reached 54.8% under 110 °C. According to the core flooding tests, oil recovery could be enhanced by up to 15.46% by 2000 mg L^-1 of the AM/AA/NDS/NIMA brine solution at 80 °C.

Full text of DOI:10.1039/c5nj01153a

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A novel water-soluble hydrophobically associating
polyacrylamide based on oleic imidazoline and
sulfonate for enhanced oil recovery†
Cite this:DOI: 10.1039/c5nj01153a
ab
b
b
b
b
b
Shaohua Gou,* Shan Luo, Tongyi Liu, Peng Zhao, Yang He, Qinglin Pan and
Qipeng Guo*
c
3-(2-(2-Heptadec-8-enyl-4,5-dihydro-imidazol-1-yl)ethylcarbamoyl)acrylic acid (NIMA), 3-(diallyl-amino)-2-
hydroxypropyl sulfonate (NDS), acrylamide (AM) and acrylic acid (AA) were successfully utilized to
prepare novel acrylamide-based copolymers (named AM/AA/NIMA and AM/AA/NDS/NIMA) which were
functionalized by a combination of imidazoline derivative and/or sulfonate via redox free-radical
1
polymerization. The two copolymers were characterized by infrared (IR) spectroscopy, H nuclear
1
magnetic resonance ( H NMR), viscosimetry, pyrene fluorescence probe, thermogravimetry (TG) and
differential thermogravimetry (DTG). As expected, the polymers exhibited excellent thickening property,
ꢀ1
ꢀ1
shear stability (viscosity retention rate 5.02% and 7.65% at 1000 s ) and salt-tolerance (10 000 mg L
Received (in Victoria, Australia)
7
th May 2015,
NaCl: viscosity retention rate up to 17.1% and 10.2%) in comparison with similar concentration partially
hydrolyzed polyacrylamide (HPAM). The temperature resistance of the AM/AA/NDS/NIMA solution was
also remarkably improved and the viscosity retention rate reached 54.8% under 110 1C. According to the
Accepted 7th July 2015
DOI: 10.1039/c5nj01153a
ꢀ1
core flooding tests, oil recovery could be enhanced by up to 15.46% by 2000 mg L of the AM/AA/
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NDS/NIMA brine solution at 80 1C.
Recently, hydrophobically associating polymers (HAPAM),
where PAM is modified with a small number of various hydro-
Introduction
With the developments in exploring complicated geologic reservoirs, phobic groups, have been proposed for use as oil-field chemical
1
3–16
increasing attention has been paid to maximizing the residual additives by many researchers,
which can somewhat
oil obtained, which was retained in the formation after water improve linear flexible chains as a means to preferably resist
1
,2
flooding. Generally, polyacrylamide (PAM) and/or partially harsh formation conditions. Numerous research efforts have
hydrolyzed polyacrylamide (HPAM), as the most commonly confirmed that hydrophobic moieties incorporated directly into
utilized water-soluble polymers in commercial chemical EOR the backbone of polymers are associated in the aqueous phase
3–6
applications, impair the viscosity in high-salinity environments by intra and intermolecular interactions once above the critical
7–9
17–19
and deform extremely at high-temperature. Furthermore, the micelle concentration.
Owing to the reversible dissociation
thickening power is greatly reduced at an elevated shear rate and process of physical links, those proved the distinct shear
shear stress, which is associated with the irreversible shear thinning and thixotropy in aqueous solutions under shear rate
1
0–12
degradation of their linear flexible chains.
and shear time. Additionally, the high surface and interfacial
activities exhibited by most hydrophobic moieties on function-
alized polymers were found to be related to the presence of
a
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,
Southwest Petroleum University, Chengdu, Sichuan 610500, China.
E-mail: shaohuagou@swpu.edu.cn
2
0–22
hydrophobic groups.
Commercially, given particular rheo-
logical properties, high surface and interfacial activities, the
potential of those polymers in EOR applications has been of
great interest in chemical technology for use in surfactant
b
Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province,
College of Chemistry and Chemical Engineering, Southwest Petroleum University,
Chengdu, Sichuan 610500, China
c
16
15
23,24
Polymers Research Group, Institute for Frontier Materials, Deakin University,
Locked Bag 20000, Geelong, Victoria 3220, Australia. E-mail: qguo@deakin.edu.au
chemistry, flocculation, profile modification,
and as
2
5
industrial thickeners, etc.
†
Electronic supplementary information (ESI) available: Synthesis routes, and
The solubility of hydrophobically associating polymers in
aqueous phase, one of the most considerable requirements in
the process of oil exploration, therefore, has been given increasing
attention. However, HAPAM implemented in many oil applications,
1
their initial H NMR spectrogram analysis of NDS and NIMA; solution prepara-
tion and characterization; fluorescence spectra of different concentrations of
copolymer solutions; the composition of synthesized brine for dissolving polymer
particle samples in the rheological experiments. See DOI: 10.1039/c5nj01153a
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even in laboratory study, has been demonstrated to incompletely
26–28
disperse in aqueous phase.
Compared with conventional
water-soluble polymers, HAPAM presents poor dissolving capacity
29–32
with the increase in hydrophobic moieties.
In parallel with the
ongoing discussions on the contribution of hydrophobic long
chains to the relative poor solubility of HAPAM, other acrylamide-
based polymers functionalized with efficient comonomers have
been extensively reported in the literature in a bid to improve their
water solubility and oilfield chemical applications; for instance,
3
3–35
the combination of acrylamide with sulfonamide groups,
sulfonic acid groups,
36,37
38
39,40
phosphate groups, zwitterion groups
and others exhibited a more preferable hydrolysis ability in the
application process for EOR.
In this article, we had hierarchically synthesized the monomer,
namely, 3-(2-(2-heptadec-8-enyl-4,5-dihydro-imidazol-1-yl)ethyl-
carbamoyl)acrylic acid (NIMA) with an imidazoline ring structure
in conjunction with a long aliphatic chain hydrophobic moiety,
and the other one, denoted as 3-(diallyl-amino)-2-hydroxypropyl
sulfonate (NDS) with a sulfonate group. Then, the novel water-
soluble polymers (named as AM/AA/NIMA and AM/AA/NDS/
NIMA, respectively), found to be composed of acrylamide (AM),
acrylic acid (AA), NIMA and/or NDS, were synthesised via a simple
free-radical co-polymerization strategy. Infrared spectroscopy
Scheme 1 Synthesis routes of (a) AM/AA/NIMA and (b) AM/AA/NDS/
NIMA.
1
1
(IR), H nuclear magnetic resonance ( H NMR), thermogravi-
metry (TG), differential thermogravimetry (DTG), viscosimetry,
and the use of a pyrene fluorescence probe were conducted to
characterize the morphologies for the obtained polymers. The
Synthesis of copolymers AM/AA/NIMA and AM/AA/NDS/
polymers were placed in aqueous solution or brine, whereupon NIMA. The indicated amounts of raw materials AM, AA, NIMA
we further focused our research of the influence of their environ- and/or NDS were added into a flask with mechanical stirring in
ments on their unique properties for EOR, such as thickening deionized water under an inert nitrogen atmosphere. NaOH
ability, dissolving capacity, thermal stability, anti-shear degradation, solution was utilized to regulate the pH to a given value with
rheological behavior, salt tolerance, resistance factor, residual magnetic stirring for 10–15 min. Copolymerization was allowed
resistance factor, and EOR value.
4 2 2 8 3
to initiate by the addition of (NH ) S O and NaHSO (molar
ratio 1 : 1) at a stated temperature for a minimum of 6 h. The
white granular copolymers, after being purified repeatedly
through ethanol, were dried at 45–55 1C under vacuum for approxi-
mately 8–12 h. The synthesis routes were shown in Scheme 1.
Experimental section
Materials
Acrylamide (AM), acrylic acid (AA), sodium bisulfite (NaHSO
ethanol, sodium hydroxide, ammonium persulfate ((NH ) S O
4 2 2 8
3
),
),
Pyrene fluorescence probe
The fluorescence intensities were measured with a Shimadzu
RF-5301PC spectrofluorophotometer with excitation at 335 nm.
A slit width of excitation and emission was fixed at 5 nm and a
spectral range was scanned at 350–580 nm with a temperature
of 25 1C. The different concentration copolymer solutions were
prepared with the saturated aqueous solution of pyrene; the
maleic anhydride (MA), oleic acid, diethylenetriamine, epichloro-
hydrin, and diallyl amine were all of analytical reagent grade and
were used directly without further purification treatment. The
above chemicals were purchased from Kelong Chemical Reagent
Factory (Chengdu, China). The partially hydrolyzed polyacryl-
amide (HPAM) had a 20–30% degree of hydrolysis, Mw = 5 ꢁ
ꢀ
6
ꢀ1 41
6
concentration of pyrene was about 2 ꢁ 10 mol L
.
The
1
0 . The resevoir-simulating brine used in this paper was pre-
ratios between the strength of the first peak (I ) and the third
pared with the inorganic salt on the basis of most formation
reservoirs, such as NaCl, KCl, CaCl , NaHCO , Na SO , and
MgCl O, etc.
ꢂ6H
1
peak (I ) in the fluorescence spectra were calculated.
3
2
3
2
4
2
2
Water solubility test
Synthesis
The solution conductivity was measured by using a DDS-11A
Preparation of functionalized comonomers. See the ESI† conductivity meter (Shanghai Rex Xinjing Instrument Co., Ltd,
for the detailed synthesis procedure and synthesis routes of China). Polymer particle samples (16–20 meshes) were dis-
the comonomers NIMA and NDS. Furthermore, the detailed persed and dissolved in deionized water performing at the
characterization of NIMA and NDS are given in the ESI.†
ambient temperature (about 25 1C). The water solubility curves
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were obtained using the dissolution time, which is defined as Results and discussion
the time from initially adding the polymer to the solution
conductivity stabilizing.
The AM/AA/NIMA and AM/AA/NDS/NIMA acrylamide-based
polymers were prepared via redox free-radical polymerization
of AM, AA, NIMA and/or NDS in the presence of (NH
4 2 2 8
) S O –
Rheological characterization
NaHSO . After purification and drying, the viscosities of the
3
polymer solutions with the desired concentrations were measured
under different conditions.
The rheological behaviors were measured with an advanced
polymer analyzer (Haake RheoStress 6000 rotational rheometer)
from Germany. Shear-tolerance measurements were investigated
ꢀ
1
Optimal synthesis conditions of copolymerization
with a shear rate ranging from 7.34 to 1000 s under a constant
temperature of 30 1C. Shear recovery performance measurements The variation in the apparent viscosity of the copolymer solutions
ꢀ
1
ꢀ1
were carried out using an alternate shear rate between 170 s
(1000 mg L ) with different synthesis conditions was identified
ꢀ1
and 510 s at a desired concentration at 30 ꢃ 1 1C. Temperature- by a single variable method, which was measured by a Brookfield
resistance tests were conducted by varying the temperature from DV-III+Pro Viscometer at room temperature (30 1C), as shown in
5 1C to 120 1C under a shear rate of 170 s . The total salinity Fig. 1a–e. It was found that the optimal synthesis conditions for
ꢀ
1
2
of the synthetic brine across the rheological tests was about the copolymer AM/AA/NIMA were as follows: the initiator concen-
ꢀ1
3
500 mg L (see Table S1, ESI†). The polymer solutions were tration was 0.5 wt%; pH value of the solution was 7; the reaction
kept stationary to temperature equilibrate for a minimum of temperature was 40 1C; the ratio of AM and AA in weight was
5 min before characterisations were carried out to guarantee 70 : 30; loading of NIMA was 1.5 wt%. Then the results of the
that the experiments are mainly accurate. The viscoelastic copolymer AM/AA/NDS/NIMA solution revealed that the maxi-
1
ꢀ1
measurement was carried out with the oscillatory frequency mum apparent viscosity was 379.2 mPa s at 1000 mg L , in the
ranging from 0.01 to 10.00 Hz at the steady-state stress under following conditions: the initiator concentration was 0.5 wt%, pH
3
0 1C.
value of the solution was 7, the reaction temperature was 35 1C,
the ratio of AM and AA in weight was 65 : 35, the concentrations of
monomer NDS and NIMA were 2.0 wt% and 1.5 wt%, respectively.
The thickening abilities of the obtained polymers were
confirmed under different magnifications at around 30 1C in
comparison to HPAM. The apparent viscosity increased in
stages along with a strong increase in copolymer concentration
Core flooding test
A series of one-dimensional sand-packed models were utilized
to test the effect of the copolymers on enhanced oil recovery by
the combination of saturated brine/polymer flooding at 80 1C.
The simulated oil (67.4 mPa s at 80 1C) was prepared as the oil
phase in the core flooding experiments. The water-flooding
across the core plugs was prepared in advance by dissolving
different salts in deionized water so that the total salinity was
about 7200 mg L (see Table 1). To eliminate capillary side
effects, all flooding experiments were performed at an original
flow rate of 0.2 mL min , afterwards elevated to 0.5 mL min
ꢀ
1
in the range of 100–5000 mg L in aqueous phase. The result
demonstrated that the copolymers exert a better thickening
property than HPAM (Fig. 1(f)). From the curves of viscosity
variation of the copolymers AM/AA/NIMA and AM/AA/NDS/
NIMA, a dramatic increase was detected beyond the concen-
ꢀ
1
ꢀ
1
ꢀ1
tration of 800 mg L and 1000 mg L , respectively. This
revealed that the catastrophe points of the obtained polymers
are lower than that of HPAM. This phenomenon could be
induced by the strong interchain association and lead to the
formation of large aggregates as the polymer concentration
increased and surpassed its critical level. The high-effect thick-
ening behavior of these associative polymers contributed
significantly to the network structures of the polymer chains.
ꢀ1
ꢀ1
.
The experiment involved following steps: (1) the simulated
crude oil was placed so as to infuse the prepared core assembly,
wherein the sand was dry for a minimum of 24 hours before
ꢀ1
performing the experiment; (2) at a flow rate of 0.5 mL min
,
saline solution was injected to substitute the simulated crude
oil until no more oil was produced and the water content
was about 95%, wherein the permeability and porosity of the
core plugs were estimated by the procedure of replacing the Characteristic analysis
simulated oil; (3) the predissolved copolymer or HPAM solutions
IR analysis. The structures of the obtained monomers and
were injected to displace the saline water until the pressure
difference across the cores was stabilized and no more oil was
produced; (4) the subsequent flooding water was eventually
injected to replace the above mentioned polymer solution samples
until no more oil was produced and the pressure difference for the
cores was primarily steady-going.
copolymers were investigated using an infrared spectrometer,
as described in Fig. 2. The copolymers’ IR spectra show that the
monomers NIMA and/or NDS were successfully introduced into
the backbone of the PAM molecular chains on account of
ꢀ1
ꢀ1
ꢀ1
the characteristic peaks at 3423 cm , 1633 cm , 1540 cm
,
ꢀ1
ꢀ1
1
496 cm , and 1401 cm in the AM/AA/NIMA IR spectrum
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
and 3431 cm , 1673 cm , 1559 cm , 1458 cm , 1400 cm
,
ꢀ
1
ꢀ1
1172 cm , and 1118 cm in the IR spectrum of polymer
Table 1 Composition of synthetic water flooding
AM/AA/NDS/NIMA. Obviously, the new absorption peaks at
around 1172 cm and 1118 cm in the AM/AA/NDS/NIMA
IR spectrum were attributable to the stretching vibration of
+
+
2+
2+
ꢀ
3ꢀ
42ꢀ
Total
Ion
Na
K
Ca Mg Cl
HCO SO
549 7225
ꢀ1
ꢀ1
ꢀ1
Concentration (mg L ) 2231 70 95 226 4026 28
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Fig. 1 Effect of (a) initiator concentration, (b) pH, (c) temperature, (d) AM/AA and (e) NIMA or NDS on apparent viscosity for the polymers; (f) the
thickening abilities of polymer solutions.
Fig. 2 IR of obtained monomers and copolymers.
3ꢀ
ꢀ1
–
1
SO groups, which belong to the bands at 1179 cm and
ꢀ
1
ꢀ
3
225 cm of –SO
groups in the NDS IR spectrum.
1
1
H NMR analysis. From the H NMR spectrum of copolymer
AM/AA/NIMA in Fig. 3(a), the chemical shift value observed at
.66 ppm is assigned to the NH protons of [CONHCH –]. The
chemical shift value owing to the NH protons of [CONH ] is
7
2
2
observed at 6.84 ppm. The chemical shift value at 5.71–5.73 ppm
is attributed to –NCH – of [(CH )NCH CH NQ] of the heterocycle
2
2
2
2
2
of NIMA. The characteristic peak due to –CH NQof the imidazo-
line ring was detected at 3.52–3.71 ppm. The chemical shift value
around 5.53–5.56 ppm is the protons of the aliphatic –CHQCH–
of [–CO(CH
copolymerisation of the NIMA monomer. The chemical shift
value at about 1.06–1.07 ppm was attributed to the –CH
2 7 2 7 3
) CHQCH(CH ) CH ], indicating the successful
1
3
proton Fig. 3 H NMR of copolymers (a) AM/AA/NIMA and (b) AM/AA/NDS/NIMA.
of the aliphatic chain. The protons of the aliphatic –CH2–
and polymeric chain appeared at 1.52 ppm, and the signals
of the –CH– protons of the polymeric chain were observed at characteristics to AM/AA/NIMA. The extra peak at 2.82 ppm
1
.98–2.34 ppm.
2 2 3
representing the –CH– protons of [–CH CH(OH)CH SO Na],
1
Depicted in Fig. 3(b) is the H NMR spectrum of copolymer obviously suggests that the monomer NDS (see Fig. S1 for
1
AM/AA/NDS/NIMA, which revealed similar morphological the H NMR spectrum, ESI†) was successfully polymerized.
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Owing to the synthesis method using NaOH solution to adjust
the pH value across the polymerisation reaction, the –OH
protons of [–COOH] could not be detected.
Critical association concentration
The ratios (I /I ) of the intensities of the first and the third
1
3
peaks in the pyrene probe fluorescence spectrum (called the
‘polarity scale’’) were employed to characterize the critical
‘
association concentration (CAC) of the two copolymers, which
is defined as the concentration at which the intramolecular
42
Fig. 5 Curves of conductivity changes in the dissolution process of the
copolymers.
association begins to transfer into intermolecular association.
The values of I /I dependent on concentrations of the copolymers
1
3
in the fluorescence spectra (see Fig. S2, ESI†) are given in Fig. 4.
For the curves of I /I , the I /I values decreased abruptly when the
1
3
1 3
declining tendency of solubility of the associating polymers.
Compared with AM/AA/NIMA, furthermore, the copolymer
AM/AA/NDS/NIMA exerted preferable water solubility owing to
the extra introduction of a sulfonate group in the polymer
molecular chain.
concentrations of polymers AM/AA/NIMA and AM/AA/NDS/NIMA
ꢀ
1
ꢀ1
surpassed 0.8 g L and 1.0 g L , respectively. This indicated the
formation of a strongly hydrophobic microdomain due to the
intermolecular association, and pyrene molecules transferred into
the hydrophobic microdomains, giving rise to the abrupt decrease
of I /I values owing to the weakening polarity of the microenvir- Intrinsic viscosity [g]
1
3
onment around the pyrene molecule. The results also obviously
reveal the relationship curves between the viscosity and polymer
concentrations in Fig. 1(f).
The intrinsic viscosities [Z] of the copolymers AM/AA/NIMA
and AM/AA/NDS/NIMA were measured, which can express the
molecular weight and the expanding extent of the molecular
chain of copolymer. As expected, it can be readily derived that
the intrinsic viscosity of the copolymers AM/AA/NIMA and
Water solubility
ꢀ
1
ꢀ1
The displacement system, generally, is prepared by injecting
water into the oil reservoir in many oilfield applications. The
solubility of the water-soluble hydrophobic associating polymer
may decline with the increase in hydrophobic moieties however,
to restrict the application benefit and formation damage.
HAPAM, reported in many articles and numerous experimental
studies, can increase significantly the viscosity and weaken the
solubility of a polymer, especially at high overall hydrophobic
concentrations. Thereby, the solubility of polymers, a crucial
factor, should be of concern in the displacement system for EOR.
Presented in Fig. 5 are the conductivity changes in the
dissolution process. The solubility of the obtained polymers
was more prominent than the common hydrophobic associating
polymer, and AM/AA/NDS/NIMA required 63 min to dissolve
which was shorter than that of AM/AA/NIMA (92 min). Through
an attempt with the water-soluble polymers functionalized on
AM/AA/NDS/NIMA were 1149.6 mL g and 1021.8 mL g
respectively.
,
Thermal stability
The mass loss and thermal gravimetric curves of AM/AA/NIMA
and AM/AA/NDS/NIMA are depicted in Fig. 6. It was evident that
the polymers had three stages of mass loss as the curves
delineated. The first step of mass loss of AM/AA/NIMA appeared
ꢀ
the monomer NIMA with –COO and/or the sulfonate group of
NDS, we found that the presence of these groups could slow the
Fig. 6 Mass loss and thermal gravimetric curves of (a) AM/AA/NIMA and
Fig. 4 Effect of different concentrations of copolymers on the I
1
/I
3
value.
(b) AM/AA/NDS/NIMA.
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ꢀ
1
in the range of 25–176 1C with a weight loss of 7.66 wt% owing solutions (2000 mg L ) in synthetic brine (see Table S1, ESI†)
to the evaporation of intra and intermolecular moisture, which at 30 1C. Both of the apparent viscosity curves exhibited a small
took place in the range of 25–178 1C with a mass loss of rise initially at low shear rates, but then shear thinning was
6.06 wt% for AM/AA/NDS/NIMA. The second one of AM/AA/ observed at a high shear rate. The phenomena might be
NIMA occurred in the temperature range of 176–517 1C with a attributed to the balance of intra and intermolecular associa-
mass loss of 61.74%, which could be associated with the imine tions which could slightly increase the viscosity at a low shear
reaction of the amide group, and the thermolysis of the hydro- rate, then the disruption and breakage of the network junction
4
3,44
phobic long chain and imidazoline ring, while that of AM/AA/ followed by the further increase in shear rate.
It could be
NDS/NIMA appeared in the range of 178–484 1C with a weight concluded that the copolymers exhibited a characteristic of
loss of 64.31 wt%. The final stage of mass loss of AM/AA/NIMA shear-thinning behaviour, which was attributed to the physical
4
5,46
appeared above 517 1C with the mass loss corresponding to the reversibility of the association framework.
carbonization, whereas that of AM/AA/NDS/NIMA occurred For polymers AM/AA/NIMA and AM/AA/NDS/NIMA in the
ꢀ
1
beyond 484 1C with a mass loss of 10.49 wt%. Obviously, an aqueous phase (2000 mg L ), the results of an extremely
excess weight loss peak of the DTG curve of AM/AA/NDS/NIMA abrupt change in the shear rate after a permanent shear rate
at the second stage (446 1C) was detected in comparison with was applied for 5 min are shown in Fig. 7(c). It was discovered
AM/AA/NIMA which can be attributed to decomposition of the that the apparent viscosity of the polymer solutions practically
sulfonate group of NDS. Furthermore, it could be observed that underwent a flipping back and forth with the shear rate ranging
ꢀ1
ꢀ1
ꢀ1
the mass loss rate and weight loss of AM/AA/NDS/NIMA were from 170 s to 510 s , then back again to 170 s . Although a
less than those of AM/AA/NIMA comparing the DTG curves of slight decline in viscosity occurred at a higher shear rate on
the obtained polymers. The thermal gravimetric data indicated account of the part disruption of the network structure, the
that the copolymers had excellent thermal stability.
obtained polymers exhibited satisfying shear stability. As the
shear rate and shear stress increased however, the three-
dimensional network structures of the polymer chains formed
Rheological behavior
Shear resistance. The conventional water-soluble polymer is due to the intermolecular association effect are more likely to
sensitive to the shear degradation of viscosity at a high pressure give rise to high-shear resistance.
and high flow rate, which would affect immensely its oilfield
application for EOR. Depicted in Fig. 7 are the dependencies of 2000 mg L in the aqueous phase, an almost temperature
the shear rate on the apparent viscosity of the obtained polymers dependent viscosity was observed at a constant shear rate, as
Temperature tolerance. For a polymer concentration of
ꢀ1
and HPAM solutions at a range of certain conditions.
shown in Fig. 8(a). At low temperature, an inconspicuous
The results of the study of the shear stability of the synthe- decrease in viscosity was initially observed, which can be
ꢀ1
sized copolymers in deionized water (2000 mg L ) are delineated attributed to the intermolecular assemblies of the polymers
in Fig. 7(a). Although a sharp decrease in viscosity accompanied modified with hydrophobic groups. With the temperature rising,
the shear rate rising, the trend of the decline in the apparent the progressive rupture of the intermolecular aggregation of the
viscosity of the obtained polymers decreased gradually under network structure would affect the molecular weight of the
high shear stress in comparison to HPAM. The results for the polymer, and hence lead to a decrease in solution viscosity.
copolymers AM/AA/NIMA and AM/AA/NDS/NIMA demonstrated The AM/AA/NIMA and AM/AA/NDS/NIMA solutions displayed
their excellent anti-shear degradation. The obtained higher high temperature tolerance at 110 1C compared with that at
ꢀ
1
viscosity retention rates were about 5.02% and 7.65% at 1000 s
,
25 1C, and had viscosity retention rates of 40.5% and 54.8%,
respectively, compared to the HPAM solution which lost most respectively. This could be explained by the hydrophobic effect of
of the viscosity, while the addition of functional monomers was NIMA and the stiff microstructure of the imidazoline ring, and/
4
7
maintained at an ultralow value.
or the ability of NDS to undergo strong hydrogen-bonding,
To gain further insight into the anti-shear behavior, shown which could sustain a higher viscosity retention rate under high-
4
8
in Fig. 7(b) are the shear rheological results of the polymer temperature.
Fig. 7 Effect of shear rate on apparent viscosity in (a) aqueous phase and (b) synthetic brine; (c) shear recovery at different shear rates.
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Fig. 8 Effect of temperature on the apparent viscosity in (a) the aqueous phase and (b) synthetic brine; (c) temperature tolerance at different shear rates.
Fig. 8(b) is shown to gain further insight into the tempera- Salt resistance
ꢀ
1
ture resistance of the obtained polymer solutions (2000 mg L
)
Fig. 9(a) shows the stability of the obtained copolymers at
ꢀ
1
in synthetic brine (see Table S1, ESI†) at 170 s . It could be
observed that the apparent viscosity of both the synthesized
polymer solutions was almost stable initially, but then
decreased gradually with the temperature rising. However, a
distinct difference could be easily observed when comparing
the two curves, where AM/AA/NDS/NIMA presented a better
viscosity retention rate (about 23.7%) than AM/AA/NIMA (about
ꢀ1
+
1
000 mg L against Na , and the tests of resistance against
2+
2+
Ca or Mg are shown in Fig. 9(b). The viscosity residual rate
for the copolymer AM/AA/NIMA and AM/AA/NDS/NIMA solu-
tions could be up to 17.1% and 10.2% in 10 000 mg L of NaCl
solution, and then up to 12.1% and 9.3% in 2000 mg L CaCl
and 16.3% and 12.4% in 2000 mg L MgCl
ꢀ1
ꢀ1
2
,
ꢀ1
2
, respectively.
Compared with HPAM, the copolymers present remarkable salt
tolerance owing to the interaction of the long carbon chain of
NIMA and the enhanced internal rotation resistance relating to
1
6.9%) under the temperature of 90 1C. The phenomena can be
explained with the fact that incorporating electronic charges
and hydrophobic groups into a water-soluble polymer can
control the interaction of the intra and intermolecular inter-
actions between the polymer chains and increase their stability
in brine, which makes the apparent viscosity of the corresponding
solutions less sensitive to the external temperature.
The influence of the temperature on the copolymer solutions
2000 mg L ) in deionized water was investigated at range of The viscoelastic properties as a function of the oscillation
51
the sulfonate groups. Additionally, these results also demon-
strated that the copolymers have preferable salt-resistance to
monovalent salt than divalent salt.
49
Viscoelasticity
ꢀ
1
(
ꢀ1
ꢀ1
2
3
5–120 1C at three different shear rates (170 s , 270 s and frequency for copolymer AM/AA/NIMA and AM/AA/NDS/NIMA
70 s , respectively), as shown in Fig. 8(c). As expected, it can be solutions (2000 mg L ) were researched using a Haake
ꢀ
1
ꢀ1
observed that the apparent viscosity gradually decreased with the RheoStress 6000 rotational rheometer. The variation of the
increase in shear rate and temperature from those curves for the dynamic system was curved by the slope of the storage modulus
0
00
polymer solutions. Besides, the influence of the temperature was G , the loss modulus G and the crossing point G , which were
c
more prominent at a higher shear rate where the disruption of the dependent on frequency (see Fig. 10). As indicated in Fig. 10,
0
intermolecular association effect is more pronounced compared thereby, a viscous behavior was observed when G was less than
0
0
0
00
to that at a low shear rate. The phenomena can be explained G in the course of the low-frequency region. Then G and G
by the weakening of the hydrophobic effect at high tempera- increased gradually accompanying the rise in the oscillation
0
ture, which can lead to the increased mobility of the polymer frequency, and the elastic behavior predominated once the G
0
0
chain and the loss of interchain interactions as the tempera- value surpassed the G value, namely, was above the frequency
5
0
ture increases.
at which the curves cross each other, G . This shows great
c
2 2
Fig. 9 Variation of the apparent viscosities of copolymer solutions with different (a) NaCl and (b) CaCl /MgCl concentrations.
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Fig. 10 Variation of viscoelastic properties with the oscillation frequency
Fig. 12 Results of the core-flooding experiments.
for copolymer solutions.
into the porous medium as the flooding pressure and injection
pressure differential was constantly elevated. Obviously, the
profile control abilities of the obtained polymers were more
prominent than those of HPAM, which was elucidated by the
curves of flooding pressure as a function of injected volume.
Shown in Table 2 are the characteristic parameters for the
polymer solution samples deduced by the core flooding experi-
ments, such as initial flooding pressure, breakthrough pressure,
stable pressure, resistance factor (RF), and residual resistance
factor (RRF). Apparently, it can be observed that the two copolymers
containing hydrophobic side chains exhibited superior profile
control capability, whereby AM/AA/NDS/NIMA had preferable
potential in the profile controlled application for enhanced oil
recovery, which was associated with its higher stable flooding
pressure region in comparison to AM/AA/NIMA and HPAM
solutions.
Fig. 11 Effect of injected volume on the flooding pressure.
potential for enhanced oil recovery in EOR applications attributed
to the typical viscoelastic behaviour of the HAPAM solutions.
52
Enhanced oil recovery. The results for the AM/AA/NDS/NIMA
solution in the core flooding tests were investigated under the
simulated salinity oil reservoir environment, as shown in
Core flooding analysis
Profile control ability. Depicted in Fig. 11 is the flooding
pressure profile as function of the injected volume (PV) for
ꢀ1
Fig. 12. Compared with HPAM (EOR of 1000 mg L solution =
ꢀ1
2
000 mg L copolymer solutions and post water flooding.
3
.29%), the values of the obtained polymer solutions for EOR were
From the curves, it can be observed that the climbing flooding
pressure presented three types of change trend, thereof the
pressure increased along with the increased flooding pressure
differential during the injection of polymer solutions. The
flooding pressure was raised gradually at the onset of polymer
flooding after 5 PV of water flooding. It can be recognized that
the pressure was further increased, whereas it declined rapidly
to a platform value in the wake of the injection of post water
flooding. Polymer particles try to enter larger porous channels
associated with their physical selection and afterwards further
migrate and start to accumulate which gives rise to the injec-
ꢀ1
ꢀ1
up to 7.04% (1000 mg L ) and 11.52% (1500 mg L ), respec-
tively. It was conspicuous that the value of about 15.46% more oil
recovery could be obtained by the AM/AA/NDS/NIMA solution
ꢀ1
(
2000 mg L ) after water flooding. Furthermore, it was obviously
discovered that the EOR effect of AM/AA/NDS/NIMA was much
better than that of AM/AA/NIMA at the same concentration in the
water phase.
Conclusions
tion pressure elevation and the facilitating of the post water Novel imidazoline derivatives with/without sulfonate have been
flooding diversion. Moreover, resistance to restrain their successfully synthesized and introduced into polyacrylamide
motion would occur, while more polymer solution migrated chains via simple free-radical co-polymerization. The critical
Table 2 Characteristic parameters in core-flooding experiments
Core parameter
Pressure parameter/MPa
Residual
Resistance resistance
Core
Diameter/ Length/ Permeability/
Polymer solution
Porosity/% samples
Initial
Breakthrough Stable
ꢀ
2
2
samples cm
cm
10 mm
pressure pressure
pressure factor
factor
1
2
3
2.501
2.498
2.503
50.04
50.02
49.98
7.840
7.838
7.841
23.60
23.59
23.62
AM/AA/NIMA
AM/AA/NDS/NIMA 0.0199
HPAM 0.0201
0.0185
0.2411
0.2723
0.0705
0.0773
0.0956
0.0263
13.03
13.68
3.51
4.18
4.80
1.31
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Paper
association concentrations of the synthetic polymers due to the 15 G. O. Yahaya, A. A. Ahdab, S. A. Ali, B. F. Abu-Sharkh and
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ꢀ1
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