An anti-biodegradable hydrophobic sulfonate-based acrylamide copolymer containing 2,4-dichlorophenoxy for enhanced oil recovery

Article abstract of DOI:10.1039/c5nj01821h

We report here a novel anti-biodegradable hydrophobic acrylamide copolymer that was prepared from acrylamide, acrylic acid, sodium 3-(allyloxy)-2-hydroxypropane-1-sulfonate and N-allyl-2-(2,4-dichlorophenoxy) acetamide using the 2,2'-azobis(2-methylpropionamide) dihydrochloride initiation system. Subsequently, the copolymer was characterized by FT-IR, ¹H NMR, TG-DTG and water-solubility. And the biodegradability test indicated that the copolymer was not deemed to be readily biodegradable via a closed bottle test established by the Organization for Economic Co-operation and Development (OECD 301 D). Meanwhile the copolymer could significantly enhance the viscosity of the aqueous solution in comparison with partially hydrolyzed polyacrylamide. A viscosity retention of 51.9% indicated the result of a dramatic improvement of temperature tolerance. And then the excellent salt resistance, shear resistance, viscoelasticity, long-term stability of the copolymer could be obtained, which provides a good theoretical foundation for the application in enhanced oil recovery. In addition, this copolymer exerted stronger mobility control ability with a resistance factor of 22.1 and a residual resistance factor of 5.0, and superior ability for enhanced oil recovery of 12.9%. Hence, the copolymer has potential application for enhanced oil recovery in high-temperature and high-salinity reservoirs.

Full text of DOI:10.1039/c5nj01821h

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An anti-biodegradable hydrophobic sulfonate-
based acrylamide copolymer containing
Cite this:DOI: 10.1039/c5nj01821h
2,4-dichlorophenoxy for enhanced oil recovery†
Shaohua Gou,*ab Yang He,b Lihua Zhou,c Peng Zhao,b Qin Zhang,b Shiwei Lib and
Qipeng Guo*d
We report here a novel anti-biodegradable hydrophobic acrylamide copolymer that was prepared
from acrylamide, acrylic acid, sodium 3-(allyloxy)-2-hydroxypropane-1-sulfonate and N-allyl-2-(2,4-
dichlorophenoxy) acetamide using the 2,20-azobis(2-methylpropionamide) dihydrochloride initiation
system. Subsequently, the copolymer was characterized by FT-IR, 1H NMR, TG-DTG and water-
solubility. And the biodegradability test indicated that the copolymer was not deemed to be readily
biodegradable via a closed bottle test established by the Organization for Economic Co-operation and
Development (OECD 301 D). Meanwhile the copolymer could significantly enhance the viscosity of the
aqueous solution in comparison with partially hydrolyzed polyacrylamide. A viscosity retention of 51.9%
indicated the result of a dramatic improvement of temperature tolerance. And then the excellent salt
resistance, shear resistance, viscoelasticity, long-term stability of the copolymer could be obtained,
which provides a good theoretical foundation for the application in enhanced oil recovery. In addition,
this copolymer exerted stronger mobility control ability with a resistance factor of 22.1 and a residual
resistance factor of 5.0, and superior ability for enhanced oil recovery of 12.9%. Hence, the copolymer
has potential application for enhanced oil recovery in high-temperature and high-salinity reservoirs.
Received (in Montpellier, France)
13th July 2015,
Accepted 15th September 2015
DOI: 10.1039/c5nj01821h
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important indexes but also two key factors of polymer flooding
effectiveness, because polymer flooding technology is mainly to
Introduction
As an important global energy, petroleum holds a significant enhance oil recovery by increasing the swept volume and oil
position in the development of national economy.1 Many displacement efficiency of displacing fluid.8–11 However, the
countries around the world, such as America, Russia, and Arab commonly used EOR chemicals, partially hydrolyzed polyacryl-
countries, are rich in oil. However, many oil fields in China amide (HPAM) and xanthan gum, are difficult to completely
have entered the development phase of high water cut. Thereby, meet the factor at high-temperature and under high-salinity
a set of perfect enhanced oil recovery (EOR) technologies has conditions due to the hydrolysis, biodegradation, poor ability of
been formed due to the enormous petroleum consumption.2,3 increasing viscosity, and others.12,13 Therefore, the development
Among these, the application of polymer flooding has achieved of some new HPAM substitutes has played an important role in
approving results.4–7 For polymer flooding, the viscosity and the research of the polymer flooding.4,14
long-term stability of displacing fluid are not only two of the
Considerable research studies have focused on the ways to
improve the resistance of the polymers to the harsh conditions,
such as increasing the rigidity of the polymer, and strengthening
intermolecular forces.15–19 McCormick and Bock et al. synthe-
sized hydrophobically associating polyacrylamides and exam-
ined the effect of temperature and salt on the viscosity of the
polymers.20,21 Additionally, the polymers containing hydrophobic
and rigid ring groups exhibit obvious thickening ability, and
temperature-thickening properties.22,23 Therefore, a number of
hydrophobically associating polymers have been studied as
candidates for enhanced oil recovery. However, the poor dis-
solubility has become the limit for their wide application in oil
exploration. As we know, strong hydrate groups, such as sulfonic
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
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 State Key Laboratory of Biotherapy, West China Hospital of Sichuan University,
Chengdu, Sichuan 610041, China
d Polymers Research Group, Institute for Frontier Materials, Deakin University,
Locked Bag 20000, Geelong, Victoria 3220, Australia. E-mail: qguo@deakin.edu.au
† Electronic supplementary information (ESI) available: Optimum copolymerization
conditions; intrinsic viscosity of copolymers. See DOI: 10.1039/c5nj01821h
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and hydroxyl groups, can significantly improve the water-solubility 30 min. The reaction was carried out under reflux at 55 1C for
of the polymers.24,25 In this paper, sodium 3-(allyloxy)-2- 4 h. Then the mixture was cooled to room temperature. The
hydroxypropane-1-sulfonate (APS) as a functional monomer was solvent and excessive thionyl chloride were removed by rotary
introduced into the polymer chain to enhance the water solubility. evaporation, 2-(2,4-dichlorophenoxy) acetyl chloride (2b) was
In addition, because a number of bacteria survive in the obtained. All of 1c was dissolved in a 50 mL round bottom flask
formation water, commonly used acrylamide copolymers and with 15 mL CH2Cl2. In an ice bath, allylamine (0.11 mol) and
xanthan gum are vulnerable to be degraded by natural micro- triethylamine (0.15 mol) dissolved in 10 mL CH2Cl2 were slowly
organisms. The excellent result for EOR is hard to be obtained added with intense stirring for 5 h. Then the mixture was
when using ordinary polymers. Bao et al. found that the HPAM successively washed by deionized water, dilute hydrochloric
removal efficiency of 36.3% was obtained within the 7 d period acid, and saturated salt solution, dried using anhydrous sodium
when HPAM served as a sole nitrogen source.26 It was reported sulfate, evaporated. Then light yellow solid N-allyl-2-(2,4-
that chlorobenzene derivatives were relatively difficult to be dichlorophenoxy)acetamide (DCAP, 83.4% yield) was obtained.
1
degraded by general microorganisms and they can be degraded The H NMR and 13C NMR spectra of DCAP were displayed in
by only a handful of microorganisms, such as Pseudommonas Fig. S1 (see ESI†). DCAP: 1H NMR (400 MHz, CDCl3, d, ppm): 4.0
sp. and Flavobacterium. Wang et al. reported that an average (s, 2H, –CH2–NH–), 4.5 (s, 2H, –C(O)–CH2–O–), 5.2–5.3 (dd, J1 =
degradation of 5.5% of 1,3-dichlorobenzene by adapting bacterium 17.3 Hz, J2 = 10.4 Hz, 2H, CH2–HC = CH2), 5.9 (m, 1H, H2C = CH–
PF-11 was monitored every day.27–30 And the introduction of CH2–), 6.9 (t, J1 = 4.9 Hz, J2 = 2.8 Hz, 2H, Ar-50-H, Ar-60-H),
chlorobenzene groups into copolymers could improve their 7.2 (dd, J1 = 2.8 Hz, J2 = 4.0 Hz, 1H, Ar-30-H), 7.4 (s, 1H, N–H);
thermal stability and enhance the rigidity of the copolymers.31–34 13C NMR (100 MHz, CDCl3, d, ppm): 41.3, 68.4, 114.7, 116.6,
In this work, N-allyl-2-(2,4-dichlorophenoxy) acetamide (DCAP) as a 123.8, 127.5, 128.0, 130.2, 133.5, 151.6, 166.9.
functionalized hydrophobic monomer was copolymerized with
Synthesis of AM/AA/APS and AM/AA/APS/DCAP
sodium 3-(allyloxy)-2-hydroxypropane-1-sulfonate (APS), acryla-
mide (AM) and acrylic acid (AA). This water-soluble hydrophobic AM/AA/APS and AM/AA/APS/DCAP were prepared by AM, AA,
copolymer was investigated systematically on several aspects APS and DCAP using a V-50 initiator system (for details, see
such as water solubility, biodegradability, thickening properties, ESI†), as shown in Scheme 1. Briefly, all the monomers with
salt resistance, rheological properties, and EOR ability, which appropriate composition were dissolved in deionized water.
provides a theoretical basis for its potential application as a new Additionally, for AM/AA/APS/DCAP, OP-10 was added as a
EOR chemical.
solubilizing agent. The pH of the reaction system was adjusted
by NaOH solution. The initiator V-50 was added into reaction
system under a nitrogen atmosphere at indicated temperature.
After reacting for 8 h, the copolymer gels were washed
with ethanol, and then dried at 40 1C in a vacuum for 24 h
to obtain the corresponding copolymers, AM/AA/APS and AM/
AA/APS/DCAP.
Experimental
Materials
The chemicals, acrylamide (AM), acrylic acid (AA), 2,20-azobis-
(2-methylpropionamide) dihydrochloride (V-50), alkylphenol ethoxy-
lates (OP-10), 2-(2,4-dichlorophenoxy) acetic acid, triethylamine,
thionyl chloride, CH2Cl2, NaOH, NaCl, MgCl2ꢀ6H2O, CaCl2, NaSO3,
were of analytical purity and purchased from Chengdu Kelong
Chemical Reagent Factory Co. (Sichuan, China). Allylamine was
purchased from Nanjing Forward Chemical Reagent Factory Co.
(Nanjing, China). 1-Allyloxy-2,3-epoxy propane was supplied by
Qufu Huarong New Chemical Materials Co., Ltd (Shandong,
China). HPAM (Mn = 6.5 ꢁ 106) was obtained from Daqing
Refining and Chemical Company. Other chemicals were commer-
cially available and used directly without further purification.
Characterization
Gel permeation chromatography (GPC). The molecular
weights of AM/AA/APS and AM/AA/APS/DCAP with a concen-
tration of 100 mg Lꢂ1 were measured using Waters E2695 Gel
Permeation Chromatography (Waters, America) at 30 1C using
NaNO3 aqueous solution (1.0 M) as an eluent. The flow rate was
1.0 mL minꢂ1
.
Elemental analysis. The elemental analysis of AM/AA/APS
and AM/AA/APS/DCAP was carried out using a Vario EL-III
elemental analyzer (Elementar, Germany).
Fourier transform infrared (FT-IR) spectroscopy. The FT-IR
spectra of AM/AA/APS and AM/AA/APS/DCAP were obtained
Synthesis of APS and DCAP
Sodium 3-(allyloxy)-2-hydroxypropane-1-sulfonate (APS) was using a WQF-520A Flourier Transform Infrared spectrophotometer
synthesized according to the method reported by the literature, (Beijing Beifen-Ruili Analytical Instrument Co., Ltd, China) with
and the synthesis route was shown in Scheme S1a (see ESI†).35 KBr pellets by averaging 32 scans at room temperature.
N-allyl-2-(2,4-dichlorophenoxy) acetamide (DCAP) was obtained
1H nuclear magnetic resonance (1H NMR) spectroscopy. The
using 2-(2,4-dichlorophenoxy) acetic acid, thionyl chloride and 1H NMR spectra of AM/AA/APS and AM/AA/APS/DCAP were
allylamine as raw materials, as shown in Scheme S1b (see ESI†). recorded on a Bruker AVANCE III 400 MHz NMR spectrometer
2-(2,4-dichlorophenoxy) acetic acid (2a) (0.10 mol) was completely (Bruker, Switzerland) in D2O.
dissolved with 30 mL CH2Cl2 in a 250 mL round bottom flask,
Intrinsic viscosity measurements. The flux time of copolymer
and then thionyl chloride (0.12 mol) was slowly added within solution of different concentrations with 1 mol Lꢂ1 NaCl was
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Scheme 1 (a) The synthesis route of AM/AA/APS, (b) the synthesis route of AM/AA/APS/DCAP.
measured using an Ubbelohde viscometer at 30 1C. The specific bottles. All the bottles were maintained in full and then incu-
viscosity (Zsp) and intrinsic viscosity [Z] were calculated using the bated in dark at 20 1C for 28 days. The dissolved oxygen of each
following eqn (1) and (2).36
BOD bottles was measured using a DO-200 dissolved oxygen
analyzer (Nanjing Zhuoma electromechanical Co. Ltd, China),
and then the remaining BOD bottles continued to be cultured
under the same conditions. The COD was determined using the
potassium dichromate reflux method. The degradation rate (Dt)
is obtained at frequent intervals over a 28 d period by the
following eqn (3).
t ꢂ t0
Zsp
¼
(1)
(2)
t0
ꢀ
½Zꢃ ¼ lim Zsp
C
C!0
in which Zsp is the specific viscosity of the copolymer; t0 is the flux
time of 1 mol Lꢂ1 NaCl solution, s; and t is the flux time of
copolymer brine solution, s.
BODðO2 mg=test substance mgÞ
Dtð%Þ ¼
ꢁ 100
(3)
CODðO2 mg=test substance mgÞ
As shown in Fig. S4 (see ESI†), the results revealed that [Z]
of AM/AA/APS and AM/AA/APS/DCAP was 1326 mL gꢂ1 and
1317 mL gꢂ1, respectively.
Thermogravimetry and derivative thermogravimetry (TG-DTG).
In a nitrogen atmosphere (flow rate: 50 mL minꢂ1), 7.0305 mg
AM/AA/APS and 7.1900 mg AM/AA/APS/DCAP were tested using
a TGA/SDTA851e Thermogravimetric and Differential Thermal
Analyzer (METTLER TOLEDO Co., Switzerland) from 25 to
800 1C at 10 1C minꢂ1, and then the TG and DTG curves were
obtained to analyze the thermal stability of the copolymers.
Tackifying and salt tolerance
Tackifying of copolymers was investigated by measuring the
apparent viscosity of different concentration of the copolymer
solutions. Copolymer solutions with a salt tolerance of 2000 mg Lꢂ1
were investigated at different concentrations of small molecule
electrolytes, such as NaCl, MgCl2, and CaCl2. The apparent
viscosities of the copolymer solutions were determined using
a Brookfield DV-III Programmable Rheometer (Brookfield Co.,
America) with a 00# (6 rpm) or 62# (18.8 rpm) rotor.
Water solubility
Rheological measurements
Temperature resistance of the copolymer solution with 2000 mg Lꢂ1
was measured using a HAAKE MARS III rheometer (HAAKE,
Copolymer particles (40–45 meshes, 2000 mg) were dissolved
in 1000 mL deionized water, recording solution conductivity.
The solution conductivity was measured by using a DDS-11A
conductivity meter (Shanghai Rex Xinjing Instrument Co., Ltd,
China). Dissolution time is defined as the time from adding the
copolymer to solution conductivity stabilizing.37
Germany) from 20 to 120 1C at 7.34 sꢂ1
.
Shear thinning behavior of the copolymer solution with
2000 mg Lꢂ1 was investigated on a HAAKE MARS III rheometer
(HAAKE, Germany) from 7.34 to 1000 sꢂ1 at 25 1C.
Shear resistance of the copolymer solution with 2000 mg Lꢂ1
was studied on a HAAKE MARS III rheometer (HAAKE, Germany)
Biodegradability test
Biodegradability of AM/AA/APS, AM/AA/APS/DCAP, HPAM and at 25 1C. The copolymer solution was measured at 7.34 sꢂ1
,
xanthan gum was obtained from biochemical oxygen demand 1000 sꢂ1, and 7.34 sꢂ1 for 30 min, respectively.
(BOD) and chemical oxygen demand (COD) using the closed
Viscoelasticity of the copolymer solution with 2000 mg Lꢂ1
bottle test (OECD 301 D).38–40 Briefly, the mixture of the was obtained by measuring the elastic modulus and viscous
copolymer (3.0 mg Lꢂ1), as a sole carbon source, and the modulus of the copolymer solution in the frequency scanning
secondary effluent was, respectively, added into the same BOD range, 0.01–10 Hz.
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Table 1 Composition and content of the total dissolved solid in the
simulated formation water
pore volume (PV) was injected. The EOR value was obtained by
the following eqn (6).
Na+ Mg2+ Ca2+ Clꢂ
SO4 HCO3 CO3 TDS
2ꢂ
ꢂ
2ꢂ
Inorganic ions
EOR = Ht ꢂ Hw
(6)
Content (mg Lꢂ1) 6588 348 435 10 883 1004 126
205
19 589
in which EOR is the enhanced oil recovery, %; Ht is the oil
recovery of the whole displacement process, %; and Hw is the
oil recovery of water flooding, %.
Long-term stability
2000 mg copolymers with long-term stability dissolved in 1.0 L
simulated formation water were investigated by measuring the
apparent viscosity of the solution at different times at 80 1C for
60 days on a Brookfield DV-III Programmable Rheometer
(Brookfield Co., America) with a 00# (6 rpm) or 62# (18.8 rpm)
rotor. And the content and composition of the total dissolved
solid (TDS) in simulated formation water were listed in Table 1.
Results and discussion
Synthesis of AM/AA/APS and AM/AA/APS/DCAP copolymers
The copolymers AM/AA/APS and AM/AA/APS/DCAP were synthe-
sized through copolymerization of AM, AA, APS and DCAP.
The compositions of copolymers AM/AA/APS were obtained by
elemental analysis. And the composition of AM/AA/APS/DCAP
Mobility control analysis
1
was determined by H NMR and elemental analysis (see ESI†).
Mobility control ability of the copolymer solutions with 2000 mg Lꢂ1
was characterized by the resistance factor (RF) and the residual
resistance factor (RRF).41,42 The core barrel with a length
of 250 mm and an internal diameter of 25 mm was packed
with quartz sand which was washed by hydrochloric acid and
distilled water several times. The copolymers were dissolved in
simulated formation water (Table 1). Core flow experiments
were carried out at 80 1C in an incubator. The injection pressure
was recorded using a pressure sensor. The infection rate of
water saturation, copolymer solution and water flooding was
2.0 mL minꢂ1 measured using an ISCO 260D syringe pump. The
RF and RRF were calculated by the following eqn (4) and (5).
The molecular weights of AM/AA/APS and AM/AA/APS/DCAP
were measured by GPC. The results are listed in Table 2.
Fig. 1a shows the FT-IR spectra of AM/AA/APS and AM/AA/
APS/DCAP copolymers. For AM/AA/APS, the peaks at 3406 cmꢂ1
and 3181 cmꢂ1 were the stretching vibration peaks of N–H. The
stretching vibration peak of C–H was at 2928 cmꢂ1. The peak at
1674 cmꢂ1 was assigned to the characteristic peak of CQO. The
peaks at 1197 cmꢂ1 and 1042 cmꢂ1 were the characteristic
absorption peaks of –SO3Na. The stretching vibration of C–O–C
was the peak at 1114 cmꢂ1. The result indicated that AM, AA,
and APS were copolymerized to the chain of the copolymer. For
the FT-IR spectra of AM/AA/APS/DCAP, the characteristic
absorption peaks of N–H, C–H, CQO, C–O–C, and –SO3Na
groups existed in the corresponding location that were similar
to the FT-IR spectra of AM/AA/APS. Additionally, two weak
absorption peaks at 879 cmꢂ1 and 816 cmꢂ1 could be observed,
which were attributed to the characteristic peaks of 1,2,4-
trisubstituted benzene groups. It has been found the successful
copolymerization of AM, AA, APS, and DCAP.
ꢁ
Pp Qp
RF ¼
(4)
(5)
Pws=Qws
Pwf =Qwf
Pws=Qws
RRF ¼
1
in which Pp is the stable pressure when injecting copolymer
solution, MPa; Qp is the injecting rate when injecting the copolymer
solution, mL minꢂ1; Pws is the stable pressure when saturating
water, MPa; and Qws is the injecting rate when saturating water, mL
minꢂ1; Pwf is the stable pressure when water flooding, MPa; and
The H NMR spectrum of AM/AA/APS/DCAP was shown in
Fig. 1b. It was obvious that the protons of the aliphatic –CH2–
group of the main copolymer chain appeared at 1.59–1.71 ppm.
The chemical shift value at 2.15–2.26 ppm was related to the
protons of –CH– in the main copolymer chain. The signal of
protons at 2.37 ppm showed the existence of –CH2–NH–CO–
groups. The signal of protons at 2.50 ppm was due to –CH2–O–
CH2–CH(OH)– groups. The characteristic peak at 3.12 ppm was
Qwf is the injecting rate when water flooding, mL minꢂ1
.
Enhanced oil recovery analysis
EOR ability of the copolymer solutions with 2000 mg Lꢂ1 was assigned to the protons of [–O–CH2–CH(OH)–CH2–] groups. The
investigated via core flooding experiments at 80 1C. The core signal of protons was observed at 3.47 ppm due to–CH2– of
was saturated and aged with crude oil for 2 days. The core was [–CH(OH)–CH2–SO3Na] groups. The signal of protons of –CH2–
flooded with simulated formation water at 0.2 mL minꢂ1 until CH(OH)–CH2– appeared at 3.76 ppm. The chemical shift at
the water cut was up to 95%; the copolymer solution of 0.3 time 3.84 ppm was assigned to the protons of –NH–CO–CH2–O– groups.
Table 2 Compositions and molecular weights of AM/AA/APS and AM/AA/APS/DCAP copolymers
Molar ratio of reactants (%)
AM AA APS DCAP
AM/AA/APS/DCAP 82.55 15.46 1.70 0.29
Elements mass ratio (%)
Molar composition of copolymer (%)
Copolymer
C
N
S
AM
AA
APS
DCAP
Mw (ꢁ106) Mw/Mn
47.26
47.21
14.59
15.00
0.65
0.69
80.93
83.06
17.25
15.26
1.57
1.68
0.25
—
6.51
6.69
2.12
2.03
AM/AA/APS
82.79 15.50 1.71
—
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Fig. 1 (a) IR spectra of AM/AA/APS and AM/AA/APS/DCAP, (b) 1H NMRR spectra of AM/AA/APS and AM/AA/APS/DCAP.
And the signal of protons at 6.92 ppm and 7.71 ppm exhibited dissolubility of AM/AA/APS with a short dissolution time of
the presence of the protons in the benzene ring.
73 min. The hydrophobic copolymer AM/AA/APS/DCAP had
excellent water solubility as expected.
Water solubility
Biodegradability
The introduction of hydrophobic monomers can significantly
affect water solubility of the copolymer. Therefore, the dissolution
time of AM/AA/APS, AM/AA/APS/DCAP and HPAM was deter-
mined to investigate the water solubility of the copolymers, as
shown in Fig. 2a. It was found that the dissolubility curves of
three copolymers displayed a similar trend. The results indi-
cated that the complete dissolution of AM/AA/APS/DCAP just
needed an extra 15 min compared with HPAM (84 min). The
dissolubility of hydrophobic copolymers was significantly
improved by introducing strong hydrate groups, sulfonic and
hydroxyl groups, which could be found from the result of the
Biodegradability of AM/AA/APS/DCAP, AM/AA/APS, HPAM and
xanthan gum was analysed via a degradation rate (Dt), as
displayed in Fig. 2b. From the comparative degradation study,
it has been observed that xanthan gum, AM/AA/APS and HPAM
showed rapid degradation within a 16 d period, and then
reached a plateau. It was obvious that xanthan gum, AM/AA/
APS and HPAM exhibited an accelerated rate of degradation
than AM/AA/APS/DCAP. Refer to the standard 301 established
by the Organization for Economic Co-operation and Development
(OECD), the degradation which reaches the pass level of 60%
is considered to be as ‘‘ready biodegradability’’. As shown in
Fig. 2b, the degradation of xanthan gum, AM/AA/APS and HPAM
had been reached 60% within the 28 d period of the test. The
degradation rate of AM/AA/APS/DCAP was far less than 60%,
which indicated that the degradation could be minimized by the
incorporation of 2,4-dichlorophenoxy and AM/AA/APS/DCAP
was less susceptible to biodegradability.
Effects of concentration on the apparent viscosity
Tackifying, as one of the most important copolymer properties,
was investigated by measuring the apparent viscosity of AM/AA/
APS, AM/AA/APS/DCAP, and HPAM solution at concentration,
100–3000 mg Lꢂ1. It was clear from Fig. 3 that the apparent
viscosity of AM/AA/APS and HPAM solution displayed a linear
growth with an increase of the copolymer concentration. Unlike
AM/AA/APS and HPAM, a slow increase in apparent viscosity
at a concentration from 100 to 800 mg Lꢂ1 was observed for
AM/AA/APS/DCAP, which might be explained by the coil of
the polymer chain as the result of intramolecular association
of 2,4-dichlorophenoxy groups at low copolymer concentration.
However, AM/AA/APS/DCAP displayed a rapid growth in apparent
viscosity above 800 mg Lꢂ1 copolymer solution. With an increase
of the solution concentration, the three-dimensional network
formed due to hydrophobic association among the polymer chain
Fig. 2 (a) Dissolution time curves of HPAM, AM/AA/APS and AM/AA/APS/
DCAP, (b) biodegradability of HPAM, AM/AA/APS, AM/AA/APS/DCAP and
xanthan gum.
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As shown in Fig. 4a, the viscosity rate of AM/AA/APS/DCAP,
AM/AA/APS, and HPAM solution with 20 000 mg Lꢂ1 NaCl was
17.6%, 11.8%, and 3.2%, respectively. And the copolymers with
2000 mg Lꢂ1 CaCl2 exhibited a slightly low viscosity retention
rate (AM/AA/APS/DCAP: 16.7%, AM/AA/APS: 10.1%, and HPAM:
4.1%) as shown in Fig. 4b. A similar change tendency of the
apparent viscosity of the copolymers with 2000 mg Lꢂ1 MgCl2
was observed in Fig. 4c, which showed that the viscosity
retention rate of AM/AA/APS/DCAP, AM/AA/APS, and HPAM
was 15.2%, 9.3% and 3.1%, respectively.
Fig. 3 Tackifying of HPAM, AM/AA/APS and AM/AA/APS/DCAP.
Thermal stability
The thermal stability of the copolymers, AM/AA/APS and AM/
AA/APS/DCAP, was investigated as shown in Fig. 5. It was found
that the TG curve of AM/AA/APS displayed three stages in
Fig. 5a. The copolymer lost 8.18% of its mass in the range of
25–176 1C, which was due to the loss of free water and bound
water present in the copolymer sample. The second process
occurred in the range of 176–431 1C, with a mass loss of
50.64%. Meanwhile, there were three peaks of the weight loss
rate appearing at 205, 225 and 323 1C in the DTG curve. At this
stage, the reduction of the copolymer’s mass was mainly due to
breaking up of the polar bonds (C–O, C–H and C–N bonds) and
decomposition of sulfonate groups in the side chains. The third
step took place beyond 431 1C with the mass loss of 33.53%,
which was believed to be associated with the breakage of the
C–C bonds in the AM/AA/APS chain.46,47
As shown in Fig. 5b, the TG curve of AM/AA/APS/DCAP
exhibited three similar stages with AM/AA/APS of a mass loss
of 5.79% at 25–176 1C, a mass loss of 64.01% in the range of
176–482 1C and a mass loss of 19.90% beyond 482 1C. What is
more, the position and strength of the weight loss rate peaks in
the DTG curve of AM/AA/APS/DCAP at the second stage were
essentially identical to AM/AA/APS. An additional peak at 445 1C
was observed in the DTG curve of AM/AA/APS/DCAP, which
might be the extraction of 2,4-dichlorophenoxy groups. The
residual mass of AM/AA/APS/DCAP (10.30%) at 800 1C was more
than that of AM/AA/APS (7.65%). The result indicated that the
AM/AA/APS/DCAP copolymer had excellent thermal stability.
can contribute to the rapid increase in apparent viscosity.43
Therefore, from 800 to 900 mg Lꢂ1, AM/AA/APS/DCAP exhibited a
sharp increase in apparent viscosity of copolymer solution. As
shown in Fig. 3, AM/AA/APS/DCAP exhibited a higher apparent
viscosity of 410.5 mPa s than that of AM/AA/APS (386.7 mPa s) and
HPAM (349.4 mPa s) at a concentration of 2000 mg Lꢂ1, which
revealed that AM/AA/APS/DCAP possessed better thickening ability.
Effects of salt on the apparent viscosity
Salt tolerance, as another important performance, was investi-
gated because of the existence of various inorganic ions in the
formation water. The apparent viscosity as a function of NaCl,
CaCl2, and MgCl2 was usually studied to obtain salt tolerance of
the copolymer.44 The results are shown in Fig. 4. For three
copolymers, a first decrease, and then a stationary trend in
apparent viscosity were observed when adding NaCl, CaCl2, and
MgCl2 into the copolymer solution. In deionized water, an
extended state of the polymer chain contributes to the high
apparent viscosity due to the electrostatic repulsion of –COOꢂ.
Adding a small molecule electrolyte can lead to the coil of
the polymer chain because of the electrostatic shielding, which
showed relatively low apparent viscosity. However, in comparison
with HPAM solution, the stable viscosity of AM/AA/APS was higher
than HPAM because of the introduction of a strong hydrate group
and a sulfonate group. In addition, AM/AA/APS/DCAP had a higher
value of apparent viscosity than AM/AA/APS and HPAM, which was
ascribed to hydrophobic 2,4-dichlorophenoxy and sulfonate
groups.45 It has also been found that the effect of divalent cations
Effects of temperature on the apparent viscosity
on apparent viscosity of the copolymer solution was greater than The thermal stability of AM/AA/APS, AM/AA/APS/DCAP, and
that of monovalent cations. HPAM solution was investigated by measuring the change of
Fig. 4 NaCl, CaCl2 and MgCl2 tolerance of AM/AA/APS, AM/AA/APS/DCAP and HPAM solution.
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Fig. 5 TG-DTG curves of (a) AM/AA/APS/DCAP and (b) AM/AA/APS.
Fig. 6 (a) Temperature resistance of the copolymers, (b) shear shinning behavior of the copolymers, (c) shear recovery of the copolymers.
the apparent viscosity from 20 1C to 120 1C. The change in trend
Shear recovery behavior. The shear recovery behavior was
was displayed in Fig. 6a. A significant decrease in apparent investigated because a long time interaction of high shear is
viscosity was observed as the temperature increased, and the easy to destroy the molecular structure of the polymer when
viscosity retention rate of 21.5% at 120 1C was relatively low displacing fluid was injected into the formation. As exhibited
compared to that at 25 1C for HPAM solution. The apparent in Fig. 6c, it was evident that the apparent viscosity of AM/AA/
viscosity of AM/AA/APS/DCAP and AM/AA/APS showed a slight APS/DCAP returned to the initial value after 30 min shear at
variation at low temperature and then a large reduction at high 1000 sꢂ1. For AM/AA/APS, a low viscosity loss, 3.0%, was
temperature. However, the apparent viscosity of AM/AA/APS/DCAP observed under 1000 sꢂ1. However, the apparent viscosity of
decreased significantly from 85 1C, and the temperature at which HPAM decreased obviously after 30 min shear at 1000 sꢂ1, and
the apparent viscosity of the copolymer solution began to reduce exhibited a loss of 12.9%. The results indicated that AM/AA/
sharply was distinctly higher than that of AM/AA/APS. The high APS/DCAP possessed fantastic shear resistance due to the
viscosity retention obtained, 51.9%, indicated the extraordinary introduction of rigid groups.
temperature resistance at 120 1C, which was ascribed to the strong
hydration ability of sulfonate groups and the strong interaction
Viscoelasticity
among hydrophobic groups within the temperature range.48,49
The viscoelasticity of AM/AA/APS/DCAP, AM/AA/APS, and HPAM
solutions was researched by the obtained viscous modulus (G00)
and elastic modulus (G0), as shown in Fig. 7a. It could be seen
Effects of shear on the apparent viscosity
Shear thinning behavior. The effect of shear rate on the from Fig. 7a that both G00 and G0 increased gradually within the
apparent viscosity of the copolymers was studied, as illustrated oscillation frequency range. Both G00 and G0 of AM/AA/APS/
in Fig. 6b. It was found that AM/AA/APS/DCAP, AM/AA/APS DCAP and AM/AA/APS were significantly higher than those of
and HPAM solutions revealed non-Newtonian shear-thinning HPAM. As shown in Fig. 7a, G0 of HPAM surpassed its G00 at a
behavior. As the shear rate increased from 7.34 to 100 sꢂ1, the high frequency (41.0 Hz), which indicated that HPAM exerted
viscosity of copolymer solutions dropped obviously, and then the elastic properties. The elasticity of AM/AA/APS was greater
the viscosity maintained a small decreasing trend within the than viscidity at a low frequency of 0.2 Hz. While AM/AA/APS/
shear rate range. However, because of the introduction of rigid DCAP showed distinct elastic behavior within the scan frequency
groups, 2,4-dichlorophenoxy, the higher viscosity retention range, which was mainly due to enhanced rigidity of the
value of AM/AA/APS/DCAP, 9.4%, could be obtained as the copolymer.50 The excellent viscoelasticity, especially elasticity,
shear rate changed from 7.34 to 1000 sꢂ1 in comparison with might contribute to improving the swept area of displacing fluid
AM/AA/APS (6.0%) and HPAM (4.7%).
to enhance oil recovery in a porous medium.51
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Fig. 8 (a) Mobility control ability of AM/AA/APS/DCAP, AM/AA/APS and
HPAM, (b) enhanced oil recovery ability of AM/AA/APS/DCAP, AM/AA/APS
and HPAM.
Fig. 7 (a) Viscoelastic behavior of the copolymers, (b) long-term stability
of the copolymers.
Long-term stability
promote the steady flow for the polymers with big hydro-
dynamic volume. In the process of injecting sequent water, the
polymer content in the core became less and less with the more
formation water injecting into the core. It was recognized that the
pressure declined sharply when injecting sequent water.
As listed in Table 3, all the injection pressure was recorded
and the resistance factor (RF) and the residual resistance factor
(RRF) were obtained by eqn (4) and (5). It was found the AM/AA/
APS/DCAP solution could establish much higher RF of 22.1 and
RRF of 5.0 than that of AM/AA/APS (RF: 11.5, RRF: 2.5) and
HPAM (RF: 8.9, RRF: 1.3) under the same conditions, which
indicated that AM/AA/APS/DCAP solution had stronger mobility
control ability that was favourable to enhance oil recovery.
The long-term stability is significantly important for displacing
fluid that flows in formation for a long time. As shown in
Fig. 7b, the apparent viscosity as a function of time was
investigated under the condition of seal. All the copolymers
exhibited a slight reduction in apparent viscosity, and the loss
in apparent viscosity of HPAM, 38.2%, was larger than that of
AM/AA/APS/DCAP and AM/AA/APS. Little viscosity loss was
observed for AM/AA/APS/DCAP after sealing for 60 days at
80 1C. The results showed that AM/AA/APS/DCAP possessed
remarkable long-term stability.
Mobility control ability
The flow characteristic behavior of AM/AA/APS/DCAP, AM/AA/
APS, and HPAM solutions in porous media was studied via core
flooding experiments. As seen in Fig. 8a, three evident stages
for three copolymers were visible in the injection pressure
curves. It was clear that the injection pressure of water saturation
Enhanced oil recovery
EOR ability of AM/AA/APS/DCAP, AM/AA/APS and HPAM was
investigated on the basis of water flooding, as displayed in
was gradually stable until injecting 2.4 PV simulated formation Fig. 8b. The polymer solution of 0.3 PV was injected into the
water. Then the injection pressure rose to a large extent along core to achieve a high recovery ratio after gaining steady recovery,
with the increase of injection volume of the copolymer solutions. 42.5%, under the condition of water flooding of 2.4 PV. It was
And the injecting pressure has become relatively stable within the found that AM/AA/APS solution could enhance additional recovery
injection volume range from about 5.0 to 8.0 PV. However, the of 9.3% compared with HPAM (3.7%). However, the extra recovery
stable pressure of injecting different polymer solution varied
enormously on account of various polymers possessing hydro-
Table 3 RF and RRF of AM/AA/APS/DCAP, AM/AA/APS and HPAM
dynamic volume. It could be observed that AM/AA/APS/DCAP
Water
saturation solution
pressure pressure
Polymer
Water
flooding
pressure
exhibited the greatest injection pressure, 0.2427 MPa, in com-
parison with AM/AA/APS and HPAM. The introduction of hydro-
phobic 2,4-dichlorophenoxy and sulfonate groups led to the
increase of hydrodynamic volume, which made potentially
detrimental flow of the copolymers in porous media. Thereby,
Polymer
(10ꢂ3 MPa) (10ꢂ3 MPa) (10ꢂ3 MPa) RF
RRF
AM/AA/APS/DCAP 11.0
242.7
137.4
93.5
55.4
30.0
13.6
22.1 5.0
11.5 2.5
8.9 1.3
AM/AA/APS
11.9
10.5
the greater pressure and larger volume might be needed to HPAM
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ratio of 12.9% could be obtained when flooding with AM/AA/
APS/DCAP solution. The results of core flooding experiments
showed that AM/AA/APS/DCAP had superior ability to enhance
oil recovery, which was supported by the excellent performance
achieved in the previous research studies.
Conclusions
In conclusion, a hydrophobic acrylamide copolymer was prepared
successfully by acrylamide, acrylic acid, sodium 3-(allyloxy)-2-
hydroxypropane-1-sulfonate and N-allyl-2-(2,4-dichlorophenoxy)
acetamide using the 2,20-azobis(2-methyl propionamide) dihydro-
chloride system for enhanced oil recovery. The copolymer
exhibited excellent performances on water solubility, resistance
to biodegradability, and tackifying. It has also been found that
the copolymer possessed remarkable salt resistance with a viscosity
retention rate of 17.6% under the condition of 20 000 mg Lꢂ1 NaCl,
16.7% under the condition of 2000 mg Lꢂ1 CaCl2, and 15.2% under
the condition of 2000 mg Lꢂ1 MgCl2. And the better temperature
tolerance, shear resistance, viscoelasticity, and long-term stability
could be obtained compared with partially hydrolyzed polyacry-
lamide. It was also shown that the copolymer displacing
solution had stronger mobility control ability with an RF of
22.1 and an RRF of 5.0, and superior ability to enhance oil
recovery of 12.9%. And the further research on the microstructure
of the copolymer solution, displacement efficiency under various
conditions, and applications of other similar copolymers for EOR
chemical is in progress.
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Acknowledgements
This work was supported by the Scientific Research Starting
Project of Southwest Petroleum University (contract grant
numbers 2014PYZ008 & 2014SJZ759), the Key Programs of
Educational Commission of Sichuan Province of China (Natural
Science, contract grant number 15ZA0051), the Foundation of
Youth Science and Technology Innovation Team of Sichuan
Province (contract grant number 2015TD0007).
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