A novel α-aminophosphonic acid-modified acrylamide-based hydrophobic associating copolymer with superb water solubility for enhanced oil recovery

Article abstract of DOI:10.1039/c6ra11952b

As a non-renewable resource, the rational exploitation of oil has attracted a large amount of attention. Among many methods for enhanced oil recovery, polymer flooding is the most suitable method of chemical flooding for non-marine reservoirs and therefore various modified acrylamide-based copolymers have been studied. In this study, a novel α-aminophosphonic acid-modified hydrophobic associating copolymer was successfully synthesized by copolymerization of acrylamide, acrylic acid, N-allyldodecanamide and 1-(dimethylamino)allylphosphonic acid. The copolymer was characterized by FT-IR, ¹H NMR and thermogravimetry and exhibited superior water solubility and thickening capability. Subsequently, the shear resistance, temperature resistance and salt tolerance of the copolymer solution were investigated. The value of apparent viscosity retention of a 2000 mg L^-1 copolymer solution was as high as 58.55 mPa s at a shear rate of 170 s^-1 and remained at 40.20 mPa s at 120 °C. The values of apparent viscosity retention of 55.41 mPa s, 59.95 mPa s and 52.97 mPa s were observed in solutions of 10000 mg L^-1 NaCl, 1200 mg L^-1 MgCl₂, and 1200 mg L^-1 CaCl₂, respectively. These were better than those of partially hydrolyzed polyacrylamide under the same conditions. In addition, an increase of up to 14.52% in the oil recovery rate compared with that for water flooding could be achieved in a core flooding test using a 2000 mg L^-1 copolymer solution at 65 °C.

Full text of DOI:10.1039/c6ra11952b

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DOI: 10.1039/C6RA11952B
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ARTICLE
A novel α-aminophosphonic acid modified acrylamide-based
hydrophobic associating copolymer with superb water solubility
for enhanced oil recovery
Received 00th January 20xx,
Accepted 00th January 20xx
ab
b
c
b
b
a
Shaohua Gou,* Qin Zhang, Cheng Yang, Qing Li, Shuhui Xu, Yuanpeng Wu, and Qipeng
d
Guo*
DOI: 10.1039/x0xx00000x
As a nonrenewable resource, rational exploitation of oil attracted a large number of attentions. Among many methods for
enhanced oil recovery, polymer flooding is the most suitable chemical flooding for non-marine reservoirs, and thus various
modified acrylamide-based copolymers were studied. In this work, a novel α-aminophosphonic acid modified hydrophobic
associating copolymer was successfully synthesized by copolymerization of acrylamide, acrylic acid, N-allyldodecanamide
www.rsc.org/
1
and 1-(dimethylamino)allylphosphonic acid. The copolymer was characterized by FT-IR, H NMR and thermogravimetry, and
exhibited superior water solubility and thickening capability. Subsequently, the shear resistance, temperature resistance
and salt tolerance of the copolymer solution were investigated. The apparent viscosity retention value of 2000 mg/L
-
1
o
copolymer solution was as high as 58.55 mPa·s under the shear rate of 170 s , and remained 40.20 mPa·s at 120 C. The
apparent viscosity retention values of 55.41 mPa·s, 59.95 mPa·s and 52.97 mPa·s were kept in 10000 mg/L NaCl, 1200 mg/L
MgCl
2
, and 1200 mg/L CaCl solutions, respectively. They were better than partially hydrolyzed polyacrylamide under the
2
same conditions. In addition, up to 14.52% enhanced oil recovery rate than that of water flooding could be obtained by the
o
core flooding test using 2000 mg/L copolymer solution at 65 C.
oilfields.10,11 Polymer solution exhibited higher viscosity than water
so that it could enhance sweep efficiency through reducing water-oil
Introduction
Petroleum is one of the most important nonrenewable natural
resources for humans and cannot be substituted completely so far.
Therefore, we have to use it efficiently and exploit the residual oil as
12
mobility to reach the aim at enhancing oil recovery. Among many
polymers, polyacrylamide (PAM) and partially hydrolyzed
polyacrylamide (HPAM) were widely used due to good capacity for
13
EOR. However, the curl, hydrolysis, degradation and even
fragmentation of molecular chains in high temperature and high salt
1
much as possible from the reservoirs. As a traditional indispensable
research field, enhanced oil recovery (EOR) technologies such as gas
flooding, chemical flooding, thermal flooding and microbial flooding
have received considerable attention by researchers around the
14,15
formation would lead to a sharp decline of viscosity.
There were
numerous modified methods based on acrylamide copolymers were
studied accordingly. The water-soluble hydrophobic associating
polymers (HAWSP), which contained a small amount of hydrophobic
groups, showed favorable thickening properties, shear resistance,
2-5
world. Among them, chemical flooding, which contains alkaline
flooding, surfactant flooding, polymer flooding and alkaline-
surfactant-polymer (ASP) flooding, has been extensively studied
1
6-20
thermal stability and anti-polyelectrolyte behavior.
In aqueous
6-9
because of its promising performance and immediate effect.
solution, association was produced via hydrophobic groups in the
polymer chains tangled with each other, and it could increase
viscosity by means of increasing the hydrodynamic dimensions of the
Polymer flooding is the most suitable chemical flooding for non-
marine reservoirs mainly used in China, such as Daqing and Shengli
21,22
polymers.
Nevertheless, compared with conventional water-
soluble polymers, the associated action of hydrophobic associating
a.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,
polymers would give rise to greatly poor solubility with an increase
Southwest Petroleum University, Chengdu, Sichuan 610500, China.
E-mail: shaohuagou@swpu.edu.cn.
Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province, College of
Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu,
Sichuan 610500, China.
Drilling Fluids Branch, CNPC Greatwall Drilling Engineering Company Limited,
Panjin City, Liaoning 124010, China.
Polymers Research Group, Institute for Frontier Materials, Deakin University,
Locked Bag 2000, Geelong, Victoria 3220, Australia.
23-25
of hydrophobic content and hydrophobic chain length.
Several
b.
hours or even more than dozens of hours were needed when
dissolved it in water. Occasionally, the insoluble phenomenon would
happen, which led to difficult operation and higher cost, especially in
c.
26,27
offshore oilfields.
d.
To some extent, the solubility of HAWSP could be improved by
introducing ionic groups. These groups, which included carboxyl
groups, sulfonate groups, ammonium and others, dissolved in water
could form a layer of hydration film to improve the hydrophilicity of
E-mail: qguo@deakin.edu.au.
†
Electronic Supplementary Information (ESI) available: Optimum of
copolymerization conditions; Dissolution time of the copolymers. See
DOI: 10.1039/x0xx00000x
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the polymers.28 Heretofore, polymers contained phosphate groups chloride was dropwise added into a 250 mL round-bottom flask
View Article Online
2
9
DOI: 10.1039/C6RA11952B
3
have been widely studied and applied in tissue engineering, scale which had been added 2.22 g of allylamine, 3.14 g of Et
N and 50 mL
30
31
32
o
inhibitor, corrosion inhibitor, drilling fluid additives and other of dichloromethane at 0-5 C, maintained for 6 h. Then the reacted
33,34
applications for an oilfield
bioactivity and excellent water solubility,
introduced into the HAWSP for EOR. In fact, the phosphate- dried over Na
due to their thermal stability, mixture was washed with concentrated alkaline liquor, stood a while.
3
5,36
but they were rarely The solution separated two layers, took the upper organic phase,
SO , and filtered. The filtrate was evaporated under
2
4
containing monomer could also easily access a lipophilic compound reduced pressure, and the white powder with a yield of 85.3% was
1
to enhance their water solubility by dint of the ascending ionic produced. H NMR (400 MHz, CDCl
3
, δ): 0.91 (t, 3H, CH
), 1.64-1.67 (m, 2H, CH CH CH
CO), 3.89 (d, 2H, NHCH CH), 5.16(d, 2H, CH=CH
s, 1H, CONHCH ), 5.83-5.88 (m, 1H, CH CH=CH ).
2
CH
CO), 2.20
), 5.57
3
), 1.27-
37
character.
1.31 (m, 16H, CH
2
(CH
2
)
8
CH
3
2
2
2
(
(
t, 2H, CH
2
CH
2
2
2
Herein, a novel α-aminophosphonic acid modified acrylamide-
based hydrophobic associating copolymer was synthesized. This
2
2
2
copolymer, which named P(AM-AA-NAD-DMAAPA), was composed Synthesis of the copolymers
of acrylamide (AM), acrylic acid (AA), N-allyldodecanamide (NAD),
P(AM-AA-NAD-DMAAPA) was synthesized by following steps: AM,
AA, NAD, DMAAPA and a moderate amount of OP-10 were first
dissolved in deionized water according to a certain proportion. The
pH of the system was adjusted by NaOH. Maintained the mass of
monomers occupied 20% of total quality, and then the system was
transferred into a three-necked flask which was placed in a water
and 1-(dimethylamino)allylphosphonic acid (DMAAPA). Among them,
AM and AA acted as the backbone to ensure the viscosity, and NAD
was a functional monomer to improve the shear resistance and
thermal stability of the copolymer. DMAAPA was synthesized via
Mannich reaction and first introduced into HASWP for EOR. In our
previous work, we find that phosphate groups could reduce the salt
sensitivity of polymer, and now it also was used to improve the water
4 2 2 8 3
bath. (NH ) S O and NaHSO (molar ratio was 1:1) as initiator was
added into the solution when the temperature reached the set value
under nitrogen flow, and kept for 8 h. Then, the product was purified
with ethanol repeatedly and dried in a vacuum oven at least 24 h to
38
solubility. The structure of DMAAPA was analogous to amino acids,
39,40
and it is environmental friendliness and low toxicity.
Owing to
only tiny amounts of hydrophobic monomer and phosphate
monomer can dramatically improve some performance of polymer,
the cost and environmental injury of copolymer can be controlled at
a lower range. And a shorter dissolution time boosts a higher
production efficiency, so the copolymer has the high economic value
and further application prospect. To evaluate the potential of this
new copolymer for EOR application, the properties such as shear
resistance, temperature resistance, salt tolerance and oil
displacement efficiency of the copolymer solution were investigated
and compared with P(AM-AA-NAD) and HPAM, respectively.
1
obtain a kind of white powder, scilicet P(AM-AA-NAD-DMAAPA). H
NMR (400 MHz, D
2
O, δ): 0.93 (t, 3H, (CH
and CHCH CH), 1.99-2.23 (m, 12H, COCHCH
, N(CH and COCH CH ), 2.46 (d, 1H, –CHCHCO–), 3.39 (d,
CH), 7.66 (t, 1H, CONHCH ).
P(AA-AM-NAD) was synthesized using similar steps. Synthetic
2 9 3
) CH ), 1.27-1.64 (m, 26H,
CH
CH
3
(CH
2
)
9
CH
2
2
2
,
2
CHCH
2
3
)
2
2
2
2
H, NHCH
2
2
route of NAD, P(AM-AA-NAD) and P(AM-AA-NAD-DMAAPA) were
presented in Scheme 1.
Characterization
IR. The Fourier-transform infrared (FT-IR) spectra of NAD and
P(AM-AA-NAD-DMAAPA) with KBr pellets were scanned in the
Experimental
Materials
-1
wavelength range of 4000-500 cm by WQF-520 Fourier-transform
infrared spectrometer (Beijing Rayleigh Analytical Instrument
Corporation, China).
Acrylamide (AM), acrylic acid (AA), dodecanoic acid, thionyl chloride
(
SOCl
alkylphenol ethoxylates (OP-10), NaOH, (NH
MgCl ·6H O, CaCl and ethanol were analytical purity and used samples were dissolved in deuterated solvent (CDCl and D O).
2
), allylamine, dichloromethane, trimethylamine (Et
3
N),
1
H NMR. The H NMR spectra of NAD and P(AM-AA-NAD-DMAAPA)
1
4
)
2 2
S O
8
, NaHSO , NaCl, were detected using a 400 MHz Bruker NMR spectrometer after the
3
2
2
2
3
2
directly. The viscosity-average molecular weight of partially
hydrolyzed polyacrylamide (HPAM) was 8.0×10 and the hydrolysis
degree of it was 25%. All the chemicals were purchased from Kelong
Conversion rate determination. The conversion of each monomer
in copolymer was measured using high performance liquid
chromatography (HPLC; Shimadzu Co., Japan) with an ODS column
6
Chemical
dimethylamino)allylphosphonic acid (DMAAPA) was synthesized
according to the method reported in literature, the synthetic method
Reagent
Co.,
Ltd.,
Chengdu,
China.
1-
and a UV detector (mobile phase: CH
nm, column temperature: 40 C; flow rate: 1.0 mL/min). The sample
3
OH/H
2
O=9:1, wavelength: 210
(
o
used in the measurement was the ethanol which was used to purified
copolymer. The conversion was calculated with the following
41
was stated in supplementary material.
Synthesis of NAD
equation:
AC0
N-allyldodecanamide was prepared by the following procedure: 8.00
g of dodecanoic acid was dissolved in 30 mL of dichloromethane in a
ꢁ
-
×V
A0
ꢀ =
×100%
ꢁ
2
2
50 mL three-necked flask, and 4.84 g of SOCl was slowly dropped
Where α is the conversion rate, %; W is the total weight of monomer
in the reaction, g; A is the chromatographic peak area of the residual
monomer in ethanol; C (g/L) and A are the different concentration
0 0
of monomer standard solution and their chromatographic peak area,
respectively; V is the solution volume of ethanol.
into the flask at room temperature. Then the reaction temperature
o
was raised to 50 C and lasted about 1 h, cooled to room temperature.
2
The solvent and excessive SOCl was removed by rotary evaporation,
obtained dodecanoyl chloride. The freshly prepared dodecanoyl
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View Article Online
DOI: 10.1039/C6RA11952B
Scheme 1 The synthetic route of (a) NAD, (b) P(AM-AA-NAD-DMAAPA), (c) P(AM-AA-NAD).
Viscosity measurement. The intrinsic viscosity ([η]) of the was first investigated. Then a precise investigation was done using
copolymer was measured using an automatic Ubbelohde capillary pyrene fluorescence probe. The fluorescence intensities were
viscometer (0.6 mm, NCY, Shanghai Sikeda Scientific Instruments, measured by a pectrofluoro-photometer (Shimadzu RF-5301PC,
o
Inc., China) at 30 C; The apparent viscosity of the copolymer solution Japan). The emission spectra were in range of 350-550 nm; the
was measured by a Brookfield DV-III programmable rheometer excitation wavelength was 335 nm. Slit widths of both excitation and
(
Brookfield Co., America) with a 00# (6 rpm) or 61# (18.2 rpm) rotor. emission were fixed at 5 nm. The different concentrations of the
copolymer solutions with pyrene were prepared with deionized
water, and the concentration of pyrene was 5×10 mol/L. The ratios
between the strength of the first peak (I ) and the third peak (I ) were
1 3
calculated.
Gel permeation chromatography. Weight-average molecular
weight (M ) and number-average molecular weight (M ) were
w n
determined by gel permeation chromatography (GPC). The
-6
measurement was carried out on an Agilent 1100 apparatus with a
o
refractive index detector at 35 C. NaNO
3
aqueous solution (1.0 Rheological experiments
mol/L) as eluent and polyethylene oxide as standard were employed.
The flow rate of eluent was 1.0 mL/min, and the concentration of the
copolymer solution was 1000 mg/L.
Shear thinning behavior of 2000 mg/L copolymer solution was
investigated with a shear rate ranging from 7.34 s to 170 s at 25
-1
-1
o
C; Shear recovery behavior of 2000 mg/L copolymer solution was
-1
-1
Water solubility
measured when the shear rates increased from 170 s to 510 s and
then reduced again to 170 s at 25 C; Temperature resistance of
2
-1
o
Copolymer (40-45 meshes, 200 mg) was added into 100 mL of
o
o
000 mg/L copolymer solution was studied from 30 C to 120 C using
o
deionized water and stirred with a magnetic stirrer at 25 C. The
standard silicon oil as the heat transfer medium under the share rate
soluble state was originally observed by naked eye, and then the
change of conductivity was measured using a conductivity meter
-1
of 170 s . All of these properties were measured by a rotational
rheometer (Haake RheoStress 6000).
(
DSS-11A, Shanghai Rex Xinjing Instrument Co., Ltd.). The dissolution
time was recorded when the conductivity remains unchanged. Each Salt tolerance and aging test
experiment was repeated three times.
Salt tolerance was obtained by the change of apparent viscosity in
different concentration of NaCl, MgCl or CaCl solution at 25 C;
2 2
o
Thermogravimetry (TG)
Aging test was carried out via the apparent viscosity variation of the
copolymer solution. The sample had been kept in water bath for 240
h at 65 C and detected once every 24 h.
The thermal stability of 4.0452 mg of P(AM-AA-NAD-DMAAPA) was
tested by TGA/SDTA851e thermal gravimetric analyzer (METTLER
o
TOLEDO Co., Switzerland) from 25 to 800 °C in a nitrogen atmosphere
o
(
flow rate: 50 mL/min). The heating rate was 10 C/min. Then the TG Core Flooding Test
and DTG curves were obtained to analyze the thermal stability of the
copolymer.
EOR ability of 2000 mg/L of copolymer solution was investigated by
core flooding test. A stainless steel cylinder with a length of 250 mm
and an internal diameter of 25 mm was employed as the core
assembly. It was packed with strongly water-wet quartz sand (80
meshes) which was obtained from Shengli oil field in China. The sand
Pyrene Fluorescence Probe
To make sure the critical association concentration (CAC) of the
copolymer, the relationship between the viscosity and concentration
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Table 1 Optimum synthesis conditions for P(AM-AA-NAD-DMAAPA)
View Article Online
DOI: 10.1039/C6RA11952B
Mass ratio of monomer (%)
o
AM
0.0
AA
NAD
0.8
DMAAPA
0.2
Mass ratio of Initiator (%)
0.3
pH
7
Temperature ( C)
6
39.0
45
7
was washed by hydrochloric acid, and then soaked in plenty of water × C, AAA= 924454.32386 + 1.36313 × 10 ×C, ANAD= 241867.58691
6
until the pH reached neutral. The permeability (K
w
) and porosity of + 2.24428× 10 ×C, respectively. It follows that the conversion of
the core assembly were detected by injecting saline water with 3.0 AM, AA, and NAD are 99.43%, 98.10% and 83.96% separately.
mL/min of volume flow. Then the crude oil was injected into the core
assembly and aged for 48 h at 65 C. The density and apparent
IR. The FT-IR spectra of NAD and P(AM-AA-NAD-DMAAPA) were
o
viscosity of simulation crude oil (obtained from Shengli oil field) were
3
o
respectively 0.90 g/cm and 70.3 mPa·s at 65 C. The water flooding
was first carried out at 0.3 mL/min until the water content reached
9
5%. Then the copolymer, which was dissolved in mineralized water
+
(
the degree of mineralization was 5210 mg/L ([Na ] =1770 mg/L,
2+
2+
-
2-
[
Ca ] =102 mg/L, [Mg ] =17 mg/L, [Cl ] =2 270 mg/L, [CO
3
] =71
-
2-] =231 mg/L), was injected into the
mg/L, [HCO
3
] =749 mg/L, [SO
4
core assembly at 0.3 mL/min. Finally, the water flooding was carried
out again until the water content reached 95%. The EOR value was
calculated by the formula (1):
EOR = E
where EOR is the enhanced oil recovery, %; E
recovery, %; E is the water flooding recovery, %.
The residual resistance factor (RRF) was calculated with the
following formula:
1 2
- E (1)
1
is the polymer flooding
2
RFF = Kwb/Kwa (2)
Where Kwa is aqueous phase permeability in subsequent water
injection process, mD. Kwb is aqueous phase permeability in water
injection process before polymer flooding, mD.
Fig. 1 IR spectra of NAD and P(AM-AA-NAD-DMAAPA)
a
Results and discussion
Synthesis and Characterization
1
5
4
6
3
The effects of reaction conditions on apparent viscosity of P(AM-AA-
NAD-DMAAPA) were investigated via single variable method (for
details see Table S1 and Table S2 in supplementary material), and the
optimal synthesis conditions were listed in Table 1. The structure of
8
7
b
1
NAD and P(AM-AA-NAD-DMAAPA) were determined by H NMR
spectra (Fig. 2). The [η], M
w
, M
n
and apparent viscosity of P(AM-AA-
2
3
NAD-DMAAPA) were listed in Table 2.
4
1
5
6
Composition of copolymer. In order to make sure the content
of soluble fraction, the proportion of each component was calculated
by conversion rate. Both the feed ratio and calculated final monomer
.
.
.
.
.
.
.
.
.
9 0
8 0
7 0
6 0
δ5 0
ppm)
4 0
3 0
2 0
1 0
(
mass percentages of copolymers were listed in Table 3. The Fig. 2 The 1H NMR spectra of (a) NAD and (b) P(AM-AA-NAD-
7
calibration curves of monomers are AAM= 1638700 + 4.58547 ×10
Table 2 The [η], M
DMAAPA)
w
and M
n
of each copolymer
Copolymer
P(AM-AA-NAD-DMAAPA)
P(AM-AA-NAD)
M
w
(×106)
5.2
M
n
(×106)
2.9
M
w
/ M
n
[η] (mL/g)
1073.23
1006.80
Apparent viscosity (mPa·s)a
1.8
1.8
534.4
506.5
5.0
2.8
a
The concentration of each copolymer solution was 2000 mg/L.
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Tab le 3 Composition of P(AM-AA-NAD-DMAAPA)
View Article Online
DOI: 10.1039/C6RA11952B
Feed ratio/ wt %
NAD
Final composition/wt %a
Copolymer
P(AM-AA-NAD-
DMAAPA)
AM
0.0
AA
39.0
DMAAPA
0.2
AM
AA
NAD
0.68
DMAAPA
0.17
6
0.8
60.41
38.74
a
The mass of purified copolymer is 9.8750 g
shown in Fig. 1. For NAD, there were strong absorption peaks at 3298 introduction of cyclic structure. P(AM-AA-NAD-DMAAPA) merely
-1
-1
cm and 1645 cm because of the stretching vibration of N–H and required 0.75 h to dissolve, it was remarkably shorter than other
C=O. The characteristic absorption of C=C was present at 1557 copolymers due to introduce the hydrophilic group. The possible
-
1
-1
-1
cm . The peaks at 2916 cm and 2841 cm belonged to the dissolution process was shown in Fig.4, the interaction between
-
1
vibration of –CH
to the absorption peak of –(CH
AA-NAD-DMAAPA), the stretching absorption vibration of O–H, on the surface of phosphate group and gradually expanded in III;
N–H, and C=O severally appeared in 3417cm , 3198 cm and finally, the molecular chains evenly dispersed in water in IV. The
678 cm , which indicated that the structure of AA and AM are results proved that the phosphate group did vastly improve the
2
of allyl and –CH
3
, and at 716 cm is assigned phosphate group and water molecular was generated via hydrogen
–. For the spectrum of P(AM- bonds and ionic bonds in II; then a layer of hydrate film was formed
2 n
)
-
1
-1
-
1
1
already present in the copolymer. The peak of P=O presented at water solubility of the hydrophobic association polymer.
-
1
1
112 cm showed that the DMAAPA structure existed in the
molecule chain. It has been found the successful
copolymerization of AM, AA, NAD and DMAAPA.
Dissolution time
The dosage of hydrophobic groups can significantly affect the water
solubility of the copolymers. The dissolution time of the copolymers
containing different length of hydrophobic chain which had been
done before were hence compared to understand their water
solubility, the results were shown in Fig. 3 (the data were listed in
Table. S3 in supplementary material). It could be concluded that
these hydrophobic associating polymers spent a lot of time to
dissolve. The dissolution time of these copolymers generally
increased with the increase of hydrophobic chain and the
Fig. 4 Solubility behavior of P(AM-AA-NAD-DMAAPA)
Thermal stability
The thermal gravimetric curve of P(AM-AA-NAD-DMAAPA) was
shown in Fig. 5. It could be divided into three stages for weight loss.
o
The first stage occurred in the range of 25-199 C with a mass loss of
16.67%, which was due to the moisture evaporation from
intramolecular and intermolecular. The copolymer contained a
number of strong hydrophilic groups which could lead the sample to
20
o
take in water. The second stage occurred in 199-603 C, and lost
Fig. 3 Dissolution time of the copolymers
50.38% of weight. There were three peaks accordingly appeared at
o
o
o
a. NIMA was the abbreviation of 3-(2-(2-heptadec-8-enyl-4,5- 280 C, 331 C and 434 C in the DTG curve. The fracture between
42
dihydro-imidazol-1-yl)ethylcarbamoyl)acrylic acid; b. AP-P4 which carbon-hydrogen, carbon–oxygen and carbon-nitrogen bonds and
has been used in oilfields was the copolymerization of AM, AA and the decomposition of phosphate groups were happened during this
o
N-(2-(acryloyloxy)ethyl)-N,N-dimethylhexadecan-1-aminium
bromide; c. NAE was the abbreviation of N-allyloctadec-9-enamide;
process. The third stage was higher than 603 C, there was a mass
43
loss of 16.13%, and this could be attributed to the carbonization of
d.
DBDAP
was
the
abbreviation
of
N,N-Diallyl-2- the copolymer. The result indicated that P(AM-AA-NAD-DMAAPA)
4
4
dodecylbenzenesulfonamide .
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decrease sharply with the concentration increased from 400 mg/L to
View Article Online
DOI: 10.1039/C6RA11952B
2000 mg/L. An obvious decline of the I /I value meant that strongly
1 3
hydrophobic association has formed, and the pyrene molecules
4
5
transferred from water to the hydrophobic microdomains.
It could be concluded that the hydrophobic interaction would
visibly happen when the concentration of P(AM-AA-NAD-DMAAPA)
was above 370 mg/L. This result closed to the change tendency of
the viscosity-concentration curve in Fig. 6c. There was a catastrophe
point on this curve was so-called critical association concentration.
The reason for this phenomenon is the association of intramolecular
and intermolecular. The molecular chains will form supramolecular
network primarily base on intermolecular association when the
solution reach a certain concentration. The structure of network can
enhance the viscosity of copolymer solution via increasing
hydrodynamic volume.
Fig. 5 Thermal gravimetric and derivative thermogravimetric curves
of P(AM-AA-NAD-DMAAPA)
Effect of shear rate on apparent viscosity
had outstanding thermal stability, and it is not easy to degrade at Shear thinning behavior of the aqueous solution of the copolymers
higher temperature.
(2000 mg/L) was investigated, as illustrated in Fig. 7a. It could be
found that the copolymers showed non-Newtonian and a shear-
thinning behavior. The viscosity of the copolymer solutions dropped
obviously with the increase of the shear rate. P(AM-AA-NAD-
DMAAPA) and P(AM-AA-NAD) had a better viscosity retention value
Critical association concentration
Hydrophobic association is the most important characteristic for
hydrophobic associating polymers to enhance the viscosity of the
polymer solution. Therefore, it is a must to study the critical
association concentration (CAC) of P(AM-AA-NAD-DMAAPA) using
pyrene fluorescence probe. It was shown in Fig. 6a. There were five
absorption peaks separately located in 373, 379, 385, 395 and 410
nm need to be concerned. The ratio between the first peak intensity
(
58.55 and 52.43 mPa·s) than that of HPAM (37.86 mPa·s). It could
be attributed to the long hydrophobic chain was introduced into the
macromolecule, and the associated interactions of the aliphatic
chain between the intramolecular or intermolecular. Shear thinning,
in a manner, can contribute to the injectivity of the copolymer
solution, but it is very important to retain a certain viscosity after the
polymer solution is injected into formation. Therefore, shear
recovery behavior is an another significant property for polymer
flooding.
(
I
1
) and the third peak intensity (I
copolymer solutions could be depicted to estimate the breakpoint in
Fig. 6b. The values of I /I dropped slowly when the concentration of
the copolymer solution was less than 400 mg/L, and began to
3
) in different concentrations of the
1
3
Fig. 6 Hydrophobic associating behaviors of P(AM-AA-NAD-DMAAPA) solution: (a) fluorescence emission spectra in different concentrations
o
of the copolymer solutions at 25 C, (b) I
1
/I
3
of the pyrene emission in different concentrations of the copolymer solutions, and (c) apparent
-1
viscosity of various concentrations of the copolymer solutions at 7.34 s in deionized water
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Fig. 7 (a) Shear shinning behavior of the copolymers, (b) shear recovery of the copolymers
Shear recovery behavior is also called thixotropic, it means that downward tendency of apparent viscosity gradually became smooth
o
the viscosity of the polymer solution will decrease under the effect when the temperature was over 90 C. The viscosity retention value
o
of shear stress, and it will turn back into its original value when the of P(AM-AA-NAD-DMAAPA) could reach 40.20 mPa·s at 120 C, which
46
shear force is removed. The shear recovery behavior of P(AM-AA- was superior to that of P(AM-AA-NAD) (36.37 mPa·s) and HAPM (7.2
NAD-DMAAPA) was detected owing to the molecular structure of the mPa·s). This phenomenon was ascribed to lots of associating groups
polymer was readily destroyed by a long time shearing action when twisted together to form reversible and physical supermolecular
the displacing fluid was injected into the ground. As exhibited in Fig. structures by means of a certain intensity of van der Waal’s
7
b, the apparent viscosity of P(AM-AA-NAD- DMAAPA) and P(AM- interaction and the intertwist of molecular chains through hydrogen-
47
AA-NAD) did not drop severely when the shear rate increased from bond interactions in the solution.
-1
-1
-1
1
70 s to 510 s , and then returned again to 170 s . However, there
was an obvious decline on the viscosity of HPAM (viscosity loss of
1.9%) at the end of a round. Low viscosity loss of P(AM-AA-NAD-
Aging resistance is another important property for copolymer
solution, it shows the change of apparent viscosity of the copolymer
solution at reservoir temperature after a certain time. Good anti-
aging performance make the copolymer solution keep effective for a
long time in strata. As shown in Fig. 8b, the apparent viscosity of
P(AM-AA-NAD-DMAAPA) dramatically decreased when it was kept in
water bath for 24 h. Then the descent speed of the apparent viscosity
gradually became slow. Compared with HPAM, the viscosity
retention value of P(AM-AA-NAD-DMAAPA) could remain 173.4
mPa·s after 240 h were kept, it is much higher than that of HPAM. It
could be attributed to the present of the hydrophobic chain which
could prevent the molecular chains from hydrolyzing.
1
DMAAPA) and P(AM-AA-NAD) could be explained by the introduction
of NAD which could regain the reversible association via the
hydrogen bonding of the intramolecular or intermolecular. The
results indicated that P(AM-AA-NAD-DMAAPA) showed a preferable
performance of shear recovery ability which was beneficial for
enhancing recovery efficiency.
Effect of temperature on apparent viscosity
The influence of temperature on the viscosity of the copolymers was
investigated from 30 C to 120 C under 170 s , the change in trend
o
o
-1
was shown in Fig. 8a. It could be observed that the apparent viscosity Effect of salt solution on apparent viscosity
of all the copolymers decreased with the increasing temperature. In
the beginning, each curve decreased sharply, but the descending
speed of the apparent viscosity of HPAM was faster. Then the
Salt tolerance is another crucial property for copolymers as
chemical flooding agent. In an aqueous solution, the apparent
viscosity of copolymer was increased mainly through the
Fig. 8 (a) Temperature resistance and (b) aging resistance of the copolymers
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Fig. 9 NaCl, MgCl
2
and CaCl
2
tolerance of P(AM-AA-NAD-DMAAPA), P(AM-AA-NAD), and HPAM
electrostatic repulsive force, and this force was vastly weakened in AA-NAD) and HPAM was used in core flooding test. The injection
process was displayed in Fig. 10, and 0.4 PV (pore volume) of polymer
solution was injected. It could be found that flooding capacities of
the copolymer solutions were better than HPAM in Fig. 10a. P(AM-
AA-NAD-DMAAPA) solution enhanced 14.52% of oil recovery ratio
than water flooding, and 8.0% higher than HPAM solution. The
injection pressure of the polymer flooding rose obviously but
presented different levels in Fig. 10b. P(AM-AA-NAD-DMAAPA)
solution possessed higher value than others due to the higher
viscosity. Besides, P(AM-AA-NAD-DMAAPA) solution could establish
mineralized water due to screening effects. But the associating effect
of the hydrophobic association polymer can be strengthened with an
increase of solution polarity, thus retaining a higher viscosity.
Here, the salt tolerance of 2000 mg/L copolymer solution was
explored in various concentrations of salt solutions, and the results
were explained in Fig. 9. The viscosity retention values of P(AM-AA-
NAD-DMAAPA), P(AM-AA-NAD) and HPAM with 10000 mg/L NaCl
solution were 55.41 mPa·s, 42.33 mPa·s, and 16.86 mPa·s
48,49
respectively in Fig. 9a. In Fig. 9b, the copolymers with 1200 mg/L the highest residual resistance factor (2.32). All of the results were
MgCl
solution exhibited a lower apparent viscosity (P(AM-AA-NAD- summarized in Table 4. It showed that P(AM-AA-NAD-DMAAPA) had
2
DMAAPA): 59.95 mPa·s, P(AM-AA-NAD):45.11 mPa·s, HPAM: 17.4 outstanding ability for EOR because of its excellent performance.
mPa·s) than in the same concentration of NaCl solution due to
divalent metal ions had a greater screening effect. The similar
2
situation occurred in the copolymers with 1200 mg/L CaCl solution
in Fig. 9c. The viscosity retention values of P(AM-AA-NAD-DMAAPA),
P(AM-AA-NAD) and HPAM severally were 52.97 mPa·s, 40.81 mPa·s,
1
5.43 mPa·s.
Overall, after a period of rapid decline, the apparent viscosity of the
mixture kept nearly at a constant. However, P(AM-AA-NAD-DMAAPA)
had a higher viscosity retention value contrasted with P(AM-AA-NAD)
and HPAM. It could be attributed to the intermolecular or
intramolecular association, which enhanced the rigidity of the
macromolecules, could prevent the chains from curling in a certain
salinity conditions. Besides, the presence of a phosphate group in the
side chain might act as a sulfonate group to reduce the salt sensitivity
of the copolymer. Thus, it can be inferred that the salt tolerance of
P(AM-AA-NAD-DMAAPA) has been improved compared with HPAM.
Fig. 10 Recovery ratio of different solution systems
EOR ability
Core flooding tests were conducted to evaluate flooding capabilities.
The mineralized water respectively blended with 2000 mg/L P(AM-
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Table 4. Core-flooding conditions and the results of EOR
View Article Online
DOI: 10.1039/C6RA11952B
a
b
Porosity
%)
K
w
E
1
E
2
EOR
Entry
Sample
RRFc
(%)
(
(mD)
(%)
(%)
1
2
3
26.01
24.95
25.34
954.65
933.69
940.88
2000 mg/L HPAM
45.03
46.07
51.55
59.68
60.05
6.52
13.61
14.52
1.22
1.89
2.32
2000 mg/L P(AM-AA-NAD)
2000 mg/L P(AM-AA-NAD-DMAAPA) 45.53
aE
is the oil recovery ratio by water flooding; bE
is the total oil recovery ratio; RRF is the residual resistance factor.
c
1
2
2
016GZ0274.), the Opening Project of Oil & Gas Field Applied
Chemistry Key Laboratory of Sichuan Province (YQKF201404) and the
Open Extracurricular Experiment of Southwest Petroleum University
(
KSZ15066).
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This work was supported by the Foundation of Youth Science and
Technology Innovation Team of Sichuan Province (contract grant
number 2015TD0007), the Support Program of Science and
Technology of Sichuan Province (contract grant number
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DOI: 10.1039/C6RA11952B
A novel α-aminophosphonic acid modified acrylamide-based
hydrophobic associating copolymer with superb water solubility for
enhanced oil recovery
Shaohua Gou, Qin Zhang, Cheng Yang, Qing Li, Shuhui Xu, Yuanpeng Wu, and Qipeng Guo
Here we report a novel αꢀaminophosphonic acid modified acrylamideꢀbased hydrophobic associating
copolymer with possesses superb water solubility. The copolymer exhibits outstanding potential for
application in enhanced oil recovery, especially for highꢀtemperature and highꢀmineralization
oilfields.