Effect of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEO-PPO on the

Mar 5, 2014 - or PPO-PEO-ph-PEO-PPO (BEP) block polyether solutions are investigated ... HPAM, and HPAM/BEP system has a larger enhanced effect than ...
4 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/IECR

Effect of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEO-PPO on the Rheological and EOR Properties of Polymer Solutions Houjian Gong,† Long Xu,† Guiying Xu,*,‡ Mingzhe Dong,† and Yajun Li† †

College of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Shandong University, Jinan 250100, China

‡

S Supporting Information *

ABSTRACT: The rheological properties of partially hydrolyzed polyacrylamide (HPAM) and PEO-PPO-ph-PPO-PEO (BPE) or PPO-PEO-ph-PEO-PPO (BEP) block polyether solutions are investigated here. Another hydrophobically associating polymer (HMPAM) is chosen as a contrast. The rheological results show that the elastic modulus (G′) and viscous modulus (G″) of HPAM/BPE and HPAM/BEP solutions first increase then decrease, while the viscosities of HMPAM/BPE and HMPAM/BEP solutions decrease with the increase of block polyether concentration. The HPAM/BPE solution has a larger viscosity than HPAM/BEP, while the HMPAM/BPE solution has a lower viscosity than HMPAM/BEP. The polymer solutions containing BEP have larger G′ and G″ values than the solutions with BPE. Furthermore, the block polyethers reduce the sensitivity of viscosity to temperature. BEP is more effective to stabilize the viscoelastic property and improve the temperature resistance than BPE in HMPAM system. BEP has a better property to enhance the salt tolerance of the polymer solution than BPE. Moreover, the enhanced oil recovery (EOR) experiments show that HPAM/block polyether mixed solution has a larger oil recovery than HPAM, and HPAM/BEP system has a larger enhanced effect than HPAM/BPE solution.

1. INTRODUCTION Polymer flooding is currently one of the important methods in enhanced oil recovery (EOR).1 The water-soluble polymer with high molecular weight added into the injection water can increase the viscosity of water phase, simultaneously improve the mobility ratio, and enlarge the swept volume, to enhance the macroscopic recovery efficiency of crude oil.2−4 Partially hydrolyzed polyacrylamide (HPAM) is the most widely used polymer in tertiary oil recovery.3−5 However, the main problem of HPAM in the oilfield application is its poor performance in temperature tolerance and salt resistance. In recent years, a new type of water-soluble hydrophobically associating polymers for improved oil recovery has been of increasing interest. These polymers contain a small proportion of hydrophobic groups usually in the form of pendent side chains or terminal groups.6 In aqueous solution, the macromolecular network structure caused by intermolecular and intramolecular association of hydrophobic groups due to the hydrophobic effect increases the hydrodynamic volume, which shows a significant increase in viscosity, temperature-resistance, salt-resistance, and shear stability.7,8 The rheological properties of injected fluid have an important effect on oil-displacing efficiency in the chemical flooding. The EOR mechanism of viscoelastic polymer flooding is 2-fold. On the one hand, the additional increase of viscosity prohibits viscous fingering so that volumetric sweeping is expanded. On the other hand, the oil displacement efficiency is enhanced due to the deformation of long-chained molecular structure microscopically so that the residual oil can be hauled out in dead ends or pore throats and on the rock surface.9 The both factors are closely related to the viscous and elastic modulus. © 2014 American Chemical Society

The addition of surfactant can change the properties of polymer system, which is beneficial to its application in different fields.10−13 The polyacrylamide (PAM) molecules could form aggregates with sodium laurate (C11H23COONa) through hydrogen bonding in neutral and weak acid solutions. The formation of C11H23COONa/PAM aggregates could enlarge the amount of charges in the PAM main chain and make the PAM solution have the properties of polyelectrolyte. The electric-viscous effect was enhanced with the increase of C11H23COONa concentration.14 Meanwhile, the dipolar interaction between the sodium dodecyl sulfonate micelles and PAM would lead to the viscosity increase when the concentration of sodium dodecyl sulfonate was higher than its critical micellar concentration in the mixed solution. Li et al.15 studied the influence of the sodium dodecyl sulfate (SDS) on the rheological properties of PAM-poly(acrylic acid) (PAA) system. The results showed the rheological performance was dependent on the hydrophobic association between SDS and PAA molecules, and the interaction between SDS and PAA could promote the formation of network structure. Shashkina et al.16 investigated the effects of hydrophobic modified PAM on the rheological properties of the cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride (EHAC). The results showed the present of polymer could greatly improve the viscosity of EHAC system. It was mainly because the hydrophobic part of the polymer combined with EHAC micelles to form a network structure, which could enhance Received: Revised: Accepted: Published: 4544

December 15, 2013 February 28, 2014 March 5, 2014 March 5, 2014 dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

Figure 1. Structures of block polyethers and polymers.

Table 1. Characteristics of the Heavy Oil Sample compositions (%)

a

saturates

aromatics

pectin

asphaltene

density (g·cm−3)

viscositya (mPa·s, 50 °C)

acid number (mg of KOH/g of sample)

45.96

21.60

31.11

1.33

0.919

458

1.361

The viscosity of oil under the shear rate of 7 s−1.

Table 2. Components of the Formation Brine Ccation (mg·L−1) −1

+

total salinity (mg·L )

Na + K

8078

2798

+

Mg

2+

82

Canion (mg·L−1) Ca

2+

151

−

Cl

4415

SO4

2−

25

HCO3−

CO32−

559

48

the formation of a strong net-like structure.23 Therefore, the effects of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEOPPO on the rheological and EOR properties of HPAM and HMPAM solutions are investigated here. The aim is to investigate the effects of the interaction between polyether and HPAM or HMPAM on the rheological properties, temperature tolerance, salt resistance, and the relationship between EOR and rheological properties.

the temperature and salt resistance of the polymer/EHAC system. Our research group has studied the influence of anionic surfactant sodium oleic acid (C17H33COONa) and stearic acid sodium (C17H35COONa) on the rheological properties of HPAM and some factors such as temperature and pH on the rheological properties of HPAM/C17H35COONa.17−19 It was found that with the increase of C17H33COONa concentration, the viscosity of HPAM/C17H33COONa system first increased and then showed a decreasing trend. The high C17H33COONa concentration disrupted the network structure of HPAM, and the temperature tolerance and salt resistance of HPAM/ C17H35COONa solution was higher than HPAM system. Though there are so many researches about the interactions between polymer and surfactants with low molecular weight, the investigations on the interactions between polymer and macromolecular surfactants are less. The macromolecular surfactants have excellent properties and are paid more and more attentions.20 The block polyether PEO-PPO-PEO is one kind of macromolecules widely investigated in the theory and application areas. In our previous work, the aggregation behavior of PEO-PPO-ph-PPO-PEO block polyether and its application in dispersing carbon nanotube have been investigated.21,22 The PEO-PPO-ph-PPO-PEO block polyether has the hydrophobic groups of PPO, benzene ring and hydrophilic group of PEO. The benzene ring can increase the surface activity and change the aggregation behavior at the air/ water interface. The PEO-PPO-ph-PPO-PEO has better dispersion ability on carbon nanotube than PEO-PPO-PEO because of the strong hydrophobic interaction and π−π stacking interactions. Recently, we has found that the addition of a certain amount of PEO-PPO-PEO can improve the viscosity and viscoelasticity of hydrophobic modified polyacrylamide (HMPAM) solution in mineralized water because of

2. EXPERIMENTAL SECTION 2.1. Materials. The block polyethers PEO-PPO-ph-PPOPEO (BPE) and PPO-PEO-ph-PEO-PPO (BEP) were synthesized in the laboratory.21,22 The molecular weights of BPE and BEP molecules were 3720 and 4070, respectively. Polymers were supplied by the State Key Laboratory of Offshore Oil Exploitation, CNOOC Research Institute. The intrinsic viscosities of HPAM and HMPAM were 2359 and 1452 mL·g−1 at 25 °C determined by the Ubbelohde viscometer, and their degrees hydrolysis were 25.2% and 24.2%, respectively. The structures of BPE, BEP, HPAM, and HMPAM are displayed in Figure 1. The heavy oil sample used in this study has been already divested of water and gas, and the characteristics are shown in Table 1. The formation brine used were prepared with the inorganic salt of NaCl, KCl, CaCl2, NaHCO3, Na2CO3, Na2SO4, and MgCl2·6H2O in laboratory. The ionic concentrations of the inorganic salt are listed in Table 2. The total salinity is the sum of the ionic concentrations. The other low salinity is gotten by diluting the formation brine. 2.2. Rheological Measurements. The solutions of polymer and polyether were prepared by mechanical stirring at the ambient temperature (25 °C). The rheological measurements were carried out on a Haake RS75 Rheometer (Germany) with a coaxial cylinder sensor system Z41-Ti. The 4545

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

Figure 2. Viscosity of polymer and block polyether solutions as a function of shear rate: (A) HPAM/BPE; (B) HPAM/BEP; (C) HMPAM/BPE; (D) HMPAM/BEP.

maximum allowable temperature deviation was ±0.1 °C. Samples were kept stationary more than 24 h before measuring to guarantee that there were no bubbles in them. Rate control mode (CR) was chosen in the steady-state shearing experiment. The range of shear rates was from 0.01 to 1000 s−1. The stress sweep was carried out with the stress range from 0.01 to 20.00 Pa at the fixed frequency, 1.00 Hz. Then, the oscillatory frequency sweep measurements were carried out during the frequency of 0.01−10.00 Hz in the oscillation mode (OSC). 2.3. Sandpacking Procedure. The displacement tests were performed by using sandpack holders measuring 15.0 cm in length and 3.8 cm in diameter. Both ends of the sandpack holders were equipped with fluid distributors, on which a 200 mesh stainless steel screen was spot-welded to prevent fine sand from flowing out and to provide a more even distribution of injected fluid. The sandpack flood tests were conducted at 50 °C in the temperature control box. For each test, the fresh sand of 80−120 mesh was packed in the sandpack holders with the use of a mechanical hydraulic pump. The hydraulic pump was pressed while the fresh sand was poured into the sandpack holder. Different absolute permeability can be obtained by adjusting the mesh of the sand and the applied pressure. The pore volume of the porous media was measured using the method by subtracting the volume of the sand in the core holder from the volume of the sandpack holder. The weight of the sand loaded into the sandpack holder was recorded and the volume of the material was determined accurately for each experiment. Therefore, the porosity is the ratio of the pore volume with the volume of the sandpack holder. The absolute permeability of the porous medium was measured by using injecting brine through the sandpack holder with sand at different flow rates, and the injection pressure was

measured with a pressure transducer. Then, the absolute permeability was calculated using Darcy’s Law. In experiments, the pore volume was about 67 mL, and the porosity of the sandpacks was approximately 38%. The absolute permeability of the sandpacks varied between 1.3−1.7 darcy. The displacement tests were conducted horizontally. The sandpacks were saturated first with the brine, and then saturated with the oil. The oil was injected continuously until water cut was less than 2.0%. The sandpacks underwent initial water flooding with oil recovery of about 40% OOIP. Then, different chemical solutions were injected until oil cut was less than 2.0%, and an extended water flooding was continued until the oil production became negligible. In the entire displacement process, the injection rate of the displacing fluids was controlled at 0.5 mL/min. The increment of oil recovery by polymer slug and extended water flooding was adopted to evaluate the efficiency of different polymers. The pressure drop across the sandpack during the displacement was monitored using a digital pressure gauge.

3. RESULTS AND DISCUSSION 3.1. Effect of Block Polyethers on the Rheological Behavior of HPAM and HMPAM Solutions. We first investigate the effect of the block polyether BPE and BEP at different concentration on the rheological behavior of 0.12 wt % polymer aqueous solution at 25 °C, respectively. The results are shown in Figure 2. It can be seen from Figure 2A and B that as the shear rate increases, the viscosity of the HPAM solution greatly reduces. When the shear rate increases from 0.5 s−1 to 1000 s−1, the viscosity of 0.12 wt % HPAM decreases from 1500 mPa·s down to 10 mPa·s. When BPE or BEP with different concentrations are present in the solution, the viscosities of the complex systems increase in different degrees. 4546

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

polyether and amide protons in HPAM, thereby enhancing the network structure, and then increase the viscosity of the solution. With the further increase of concentration, the aggregate of polyether molecules begin to form. The polyether molecules around the HPAM chain transfer to participate in the formation of micelles resulting in the destruction of the network structure and the decrease of viscosity. Figure 3 also shows that the viscosity of HPAM/BPE system is higher than that of HPAM/BEP. We has found that BPE is more easily than BEP to form micelles in the previous study.21 When the BPE micelles are formed by the hydrophobic PO chains as the core and the hydrophilic EO chains surrounding in the outer layer, the micelles could interact with more HPAM molecules due to the large hydrophilic micellar shell, which is conducive to the formation of the network structure. Because the hydrophobic PO chain and the benzene ring are divided into three parts by hydrophilic EO chains in BEP molecules, whether BEP molecules exist as mono molecule or micelle in the system, BEP has a weaker hydrogen-bonding interaction with HPAM than BPE. There is an interesting phenomenon that the viscosity the HMPAM/BEP solution is higher than that of HMPAM/BPE. The critical micellar concentration (cmc) values of BPE and BEP are 0.01 wt % and 0.2 wt %, respectively.21 When the concentration of block polyether is less than 0.2 wt %, the BPE can form micelles in the solution, while BEP exists in molecular state. The hydrophobic interactions between BPE micelles and HMPAM molecules are stronger than that between BEP and HMPAM molecules so that HMPAM/BPE solution has a lower viscosity than HMPAM/BEP system. When the concentration of polyether is larger than 0.2 wt %, both BPE and BEP molecules can form micelles in the solution, the influence of hydrophobic interactions between BPE micelles and HMPAM is almost the same as that between BEP micelle and HMAPM. Therefore, the viscosity of HMPAM/BPE is almost the same as that of HMPAM/BEP when the polyether concentration is larger than 0.2 wt %. The viscoelastic properties of the system can greatly influence the oil displacement efficiency. The viscoelastic polymer solution could reduce every type of residual oil in different extent. The greater the viscoelasticity of the system, the stronger the capability of the polymer solution carrying out the residue oil.30 Therefore, the study on the effect of different structural block polyether on the viscoelasticity of HPAM and HMPAM solution is very important, which will advance the application of the polymer/block polyether complex system in oil field. The relationship between the viscoelasticity of different polymer/block polyether and frequency is shown in Figure 4. The storage modulus (also known as the elastic modulus) G′ and loss modulus (also known as the viscous modulus) G″ of the different polymers/block polyether system gradually increase with the increase of frequency, which is accordance with HPAM/C17H33COONa and other polymer system.31−33 Moreover, G′ and G″ of HPAM solution are higher than those of HMPAM, and G′ is greater than G″ in HPAM solution, but G′ of HMPAM solution is less than G″. HPAM molecules can form a stronger network than HMPAM so that the HPAM system exhibits stronger elastic behavior than HMPAM. In order to accurately reflecting the effect of the polyether structure on the viscoelasticity of HPAM and HMPAM systems, we get the curves of G′ and G″ at the frequency of 0.1 Hz vs block polyether concentration, which is showed in Figure 5. The variations of G′ and G″ are significantly different

Parts C and D of Figure 2 show the effect of block polyethers on the viscosity of HMPAM solution. HMPAM solution has a significantly lower viscosity than HPAM system. With the shear rate increasing, the decrease of viscosity is also lower than that of HPAM solution. For instance, when the shear rate is 0.5 s−1, the viscosities of 0.12 wt % HMPAM and HPAM solutions are 160 and 1430 mPa·s, respectively. When the shear rate increases to 1000 s−1, their viscosities are 7.4 and 26.5 mPa·s, respectively. The adding of BPE or BEP causes the viscosity of HMPAM solution decrease, which is opposite to the effects of the polyethers on HPAM solution. Usually, the intermolecular hydrogen bonds and hydrophobic interaction are considered the main reason causing the formation of network structure. When the shear rate increases, shear action would destroy the network structure of the system to cause a sharp decrease of the viscosity.15,24−27 When adding BPE or BEP, a large number of oxygen atoms in polyether molecule can act as proton acceptor, which can make intermolecular hydrogen bonds interact with the protons in acylamino groups of HPAM, thus enhance the network of polymer system.28 Meanwhile, the formation of aggregate through hydrophobic interactions between hydrophobic groups of HMPAM and the PO groups in BPE or BEP can result in the destruction of macromolecular network structure and the reduction of the viscosity.15,29 In order to better analysis the effect of different structure of polyether on polymer viscosity, Figure 3 shows the viscosity

Figure 3. Viscosity of polymer and block polyether mixed solution at 7 s−1.

changes with different polyether concentration in different polymer/block polyether solutions at the shear rate of 7 s−1. As the concentration of block polyether increases, the viscosity of HPAM/block polyether increases rapidly, then decreases slowly. The viscosity variations of HPAM/block polyether solutions with the polyether concentration is similar with that of polymer/sodium oleate system.17 The presence of sodium oleate would enhance the ionic strength of the solution. The strong hydration of Na+ not only captures the hydration layer surrounding HPAM molecules but also compresses the electric double layer around the polar head of HPAM, which can make the HPAM molecular chain contract and hydrodynamic volume decrease, to cause the viscosity reduce. However, the presence of nonionic block polyether cannot change the ionic strength of the solution. Numerous hydrogen bonding interactions will occur between a large number of ether oxygen atoms in block 4547

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

Figure 4. Viscoelasitcity of different polymer/block polyether solutions as a function of frequency: (A) HPAM/BPE; (B) HPAM/BEP; (C) HMPAM/BPE; (D) HMPAM/BEP.

Figure 5. G ′ (A) and G″ (B) values of different polymer/polyether solutions at 0.1 Hz as a function of polyether concentration.

in the presence of BPE or BEP molecules. G ′ and G ″ are strengthened by BPE or BEP in HPAM system, while G′ and G″ are reduced in HMPAM system in the presence of BPE or BEP molecules. It is consistent with the variation of the viscosity of different polymer/block polyether with the shear rate. It is proved once again that there are interactions of hydrogen bonding occurring between HPAM and block polyether, which can enhance the network structure of the system, so the G′ and G″ are increased.16 Because of the hydrophobic interaction between HMPAM and block polyether, the network structure of HMPAM can be destroyed by the added block polyether. Therefore, the G′ and G″ are reduced. With the increase of BPE or BEP concentration, G′ and G″ change little, illustrating that the effect of the block

polyether concentration on the viscoelasticity of polymer/ polyether systems is very small. Furthermore, whether the polymer is HPAM or HMPAM, BEP/polymer solutions have larger G′ and G″ values than BPE/polymer mixed system, which is different from the viscosity variation of the different polymer/block polyether with the polyether concentration mentioned above. Here, it is probably because BEP molecules have stronger interactions with HPAM or HMPAM than BPE, so that the viscoelasticity of the system is enhanced. 3.2. Effect of Temperature on the Rheological Properties of Polymer/Polyether Solutions. With the development of oil exploration, the petroleum reservoir in high temperature and salinity conditions is paid more and more attention. The temperature is an important factor affecting the 4548

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

Figure 6. (A and B) Viscosity of polymer/polyether solutions at 7 s−1 as a function of temperature; (C and D) relationship between ln η and ln(1/ T).

Figure 7. G ′ and G″ values of polymer/polyether solutions at 0.1 Hz as a function of temperature.

nature of the polymer flooding system. It is considered the effect of temperature on rheological property of the block polyether and polymer system is important to the practical application.34 The viscosity variation of different polymers/ block polyether system with temperature are investigated and shown in Figure 6. As the temperature increases, the viscosities of HPAM and HMPAM solution all decrease. When the BPE or BEP is added into the solution of polymer, the viscosity of the mixed system has the similar variation with the increase of temperature. When the temperature rises, the water molecules move faster and damage the winding structure of HPAM or HMPAM chain to cause the decrease of viscosity. Though the hydrogen bond and hydrophobically associating interactions between the polyether and polymer molecules can influence the viscosity of the mixed solution, the interaction cannot change

the viscosity variation with temperature. When the temperature rises from 25 to 65 °C, the viscosity retention ratios of HPAM, HPAM/BPE and HPAM/BEP solutions are 91.7%, 93.4%, and 94.7%, respectively. Meanwhile, the viscosity retention ratios of HMPAM, HMPMA/BPE and HMPAM/BEP solutions are 47%, 53.9%, and 54.6%, respectively. The results show that the addition of BPE or BEP obviously enhances the viscosity retention ratios of HPAM and HMPAM system, and the temperature resistance is improved. The influence of temperature on the viscosity of polymers solution has been described by an Arrehenius equation, as shown in eq 1. 4549

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

Figure 8. Viscosity of polymer/polyether solutions at 7 s−1 as a function of salinity.

⎛ ΔEη ⎞ η = A ·exp⎜ ⎟ ⎝ RT ⎠

stabilize the viscoelastic property of HMPAM system and to improve the temperature resistance than BPE. 3.3. Effect of Salinity on the Rheological Properties of Polymer/Polyether Systems. In addition to temperature, the inorganic salt is also an important factor affecting the enhanced oil recovery of polymer flooding system. In the actual reservoir environment, the brine often contains a variety of inorganic salts, which has a significant impact on the viscosity of the polymer flooding system.34,37,38 Here, the polymer and polyether concentrations are 0.12 wt % and 0.2 wt %, respectively. The viscosities of different polymer/polyether systems are measured under different degree of salinity, as shown in Figure 8. The viscosities of HPAM and HMPAM system are significantly reduced with the increase of salinity. The decreasing trend of viscosity of HPAM system begins to slow down when the salinity increases to 4000 mg·L−1, while the decreasing trend of viscosity of HMPAM system begins to slow down when the salinity increases to 2000 mg·L−1. The BPE/ HPAM mixed solution has a lower viscosity than HPAM and the viscosity decreases with the increase of salinity, while BEP/ HPAM mixed solution has a higher viscosity than HPAM. The viscosities of the mixed HMPAM/polyether systems are lower than single HMPAM system, but when the salinity is higher than 2000 mg·L−1, with the further increase of salinity, the reduce trend of the viscosity is slowing down. Besides, the viscosity of the HMPAM/BEP mixed system is slightly higher than that of HMPAM/BPE system. The addition of salt can make the ionic strength increase. The strong hydration of inorganic ions can take away the hydration shell around HPAM molecules. This effect can cause the end-to-end distance of molecular chain decrease and the polymer molecular chain curling. At the same time, the inorganic ions, especially Ca2+ and Mg2+, can shield the negative charge of HPAM chain, cause the macromolecular chain curling up, and lead to the decrease of the viscosity. Meanwhile, the hydrophilic micellar shell formed by EO groups can bind Ca2+, which can make the micelles positively charged.39 The hydrogen-bonding interactions between EO groups in BPE and acylamino groups in HPAM can be destroyed. BEP has a weaker hydrogen-bonding interaction with HPAM than BPE, the influence of inorganic salt on the interactions between BEP and HPAM can be ignored. Therefore, HPAM/BPE system has a lower viscosity than HPAM solution, while HPAM/BEP system has a larger viscosity than HPAM solution in the presence of inorganic salt.

(1)

where the parameter A is a constant determined by polymer style, molecular weight, and rigidity of molecular chain. R is gas constant. ΔEη is viscous-flow activation energy. The sensitivity of the viscosity to the temperature is proportional to the value of ΔEη. We can get the curve of ln η vs ln(1/T) from the relationship of η and T. The value of ΔEη can be gotten from the slope of the line in the curves shown in Figure 6C and D. The ΔEη values of HPAM, HPAM/BPE, and HPAM/BEP solutions are 218.9, 163.5, and 129.7 kJ·mol−1. Meanwhile, the ΔEη values of HMPAM, HMPAM/BPE, and HMPAM/BEP solutions are 1878, 1605, and 1501 kJ·mol−1, respectively. Generally, the magnitude of energy of activation determines the sensitivity of solutions toward temperature and reflects the influence of the temperature on the intermolecular interaction of the macromolecules in the solvent.35 The higher the activation energy is, the weaker the heat resistance of polymer is.36 Hence, the results suggest that the heat-resistant property of HPAM is better than that of HMPAM. In other words, the viscosity of HMPAM is more sensitive to temperature than that of HPAM. The viscous-flow activation energy of HPAM or HMPAM system is decreased when the polyether BPE or BEP is present in the solution. Therefore, the block polyether can reduce the sensitivity of viscosity to temperature, which is significant for the practical application of the polymer systems in the oil field. The dependences of loss and storage modulus of the different polymer/polyether systems on the temperature variation from 25 to 65 °C have been investigated. Figure 7 shows that G′ and G″ of HPAM and HMPAM system decrease with the increase of temperature. Obviously, in the presence of block polyether, the G′ and G″ of HPAM system are not decreased significantly, while the decreasing trend of the both G′ and G″ of HMPAM system is becoming slower with the increase of temperature. For example, when the temperature increases from 25 to 65 °C, the reduced degrees of G′ in HPAM, HPMA/BPE and HPAM/BEP system are 19.7%, 4.4% and 3.0%, respectively, and the reduced degrees of G′ in HMPAM, HMPMA/BPE and HMPAM/BEP system are 90.2%, 99.0% and 90.0%, respectively. The results show that BPE or BEP could interact with HPAM, which could still maintain the viscoelastic property of system and decrease the effect of temperature. It is shown that BEP is more effective to 4550

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

Figure 9. Variation of G′ and G″ at 0.1 Hz as a function of salinity.

Figure 10. Cumulative oil recovery (A) and pressure change (B) of different systems as a function of pore volumes injected.

EOR property is investigated. The cumulative oil recovery of different systems as a function of the injected pore volumes is shown in Figure 10A. It can be found that the final water flooding of 5 PV has an oil recovery of about 49% of OOIP (original oil in place). To be more specific, the final oil recovery for HMPAM flooding is just a little higher than that of brine. During the HMPAM flooding, the pressure is not obviously increased. For HPAM, the oil recovery increases from 49% to 58.1% after 1.0 PV polymer flooding. The pressure has an obviously increase during the polymer flooding. When the brine is first flooded, the heavy oil could be displaced by the brine. Because the heavy oil has a much larger viscosity than brine, the higher pressure is needed to drive the heavy oil. The heavy oil in the channel with high permeability could be first displaced. Once the brine channel is formed, the brine will flow along the channel. It can be seen from Figure 10B that the pressure begins to decrease only after brine flooding of 0.1 PV. When the pressure reduces to the minimum, there is no heavy oil displaced. Then, the polymer solution is flooded and can increase the viscosity of aqueous phase to enhance the sweep volume. The viscosity of HMPAM solution in the salinity of 8074 mg·L−1 is almost near to that of brine, while the viscosity of HPAM solution with the same salinity is almost 10 times of brine as shown in Figure 8. Therefore, the lower the viscosity of HMPAM is the main reason that the HMPAM flooding cannot further enhance the heavy oil recovery. The effects of BPE and BEP on the enhanced oil recovery of HPAM solution are also investigated and shown in Figure 10. The final oil recoveries of HPAM/BPE and HPAM/BEP are 67.3% and 69.0% OOIP, with tertiary oil recovery of 26.3% and 29.0% OOIP, respectively. Viscoelastic behaviors inevitably occur during HPAM solution flushing through the oil

In order to investigate quantificationally the impact of block polyether on the salt tolerance of the polymer system, we calculate the viscosity retention ratio. The viscosity retention ratios of HPAM, HPMA/BPE and HPAM/BEP system are 65.8%, 37.5% and 78.7%, respectively, as the salinity increases from 0 to 8074 mg·L−1; while the viscosity retention ratios of HMPAM, HMPMA/BPE and HMPAM/BEP are 17.7%, 4.0% and 7.5%, respectively. Therefore, BEP has a better property to enhance the salt tolerance of the polymer solution than BPE. The viscoelasticity of the polymer/polyether solution at different salinity is also investigated and shown in Figure 9. The impact of salinity on the viscoelasticity of the system is obvious. As the salinity increases, the G′ and G″of HPAM and HMPAM system first decrease and then change little. G′ of HPAM solution is larger than G ″ in pure water, but G″ is larger than G′ in brine. It is because inorganic ions in the brine have strong hydration and electrostatic interaction, which can take away the hydration water around HPAM molecules. The loss of hydration water can made the coil end-to-end distance of the macromolecule decrease, and the polymer chains come to curl. In this way, the effect of inorganic ions can destroy the network structure of the system, and then the elastic modulus is lower than the viscous modulus.18 The G′ and G″ of the HPAM/BPE or BEP solutions vary similarly with that of the HPAM solution. The G′ and G″ of HPAM/BEP are higher than those of HPAM, while the G′ and G″ of HPAM/BPE are lower than those of HPAM. G″ of the HMPAM systems is always higher than G′ whether in pure water or brine. 3.4. Effect of Polyethers on EOR Property of Polymer Solutions. According to the above investigation, the BPE and BEP can influence the viscosity and viscoelasticity of HPAM and HMPAM solutions. Here, the effect of the polyether on the 4551

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research formation and can play an important role in oil recovery.40,41 The oil recovery order of HPAM, HPAM/BPE, and HPAM/ BEP is HPAM/BEP > HPAM/BPE > HPAM, while the order of G′ and G″ values is HPAM/BEP > HPAM > HPAM/BPE (shown in Figures 8 and 9). It is clear that the oil recovery order is not consistent with that of the G′ and G″ values. Therefore, the viscoelasticity is an important but not the only impact factor on the EOR. Furthermore, the emulsification of surfactant is also an important impact factor for the displacement of heavy oil.42 The experimental results show that both BPE and BEP at the concentration of 0.2 wt % have strong emulsification ability (shown in Figure S1 in the Supporting Information). Though the viscosity and viscoelasticity of HPAM is higher than HPAM/BPE at the salinity of 8074 mg·L−1, the emulsification effect of BPE can make the viscous heavy oil form oil in water (O/W) emulsions. Therefore, the HPAM/BPE solution has a larger oil recovery than HPAM though the G′ and G″ values of HPAM/BPE are lower than those of HPAM system. Both BPE and BEP can emulsify the heavy oil, and the interfacial tensions between the both polyether and heavy oil are all about 0.1 mN/m. Therefore, the high values of G′ and G″ are the main reason that the BEP/HPAM solution has a higher oil recovery than BPE/HPAM system.

■

REFERENCES

(1) Li, G.; Zhai, L.; Xu, G.; Shen, Q.; Mao, H.; Pei, M. Current tertiary oil recovery in China. J. Dispersion Sci. Technol. 2000, 21 (4), 367−408. (2) Chang, H. L.; Zhang, Z. Q.; Wang, Q. M.; Xu, Z. S.; Guo, Z. D.; Sun, H. Q.; Cao, X. L.; Qiao, Q. Advances in polymer flooding and alkaline/surfactant/polymer processes as developed and applied in the People’s Republic of China. J. Petrol. Tech. 2006, 58 (2), 84−89. (3) Wang, W.; Liu, Y.; Gu, Y. Application of a novel polymer system in chemical enhanced oil recovery (EOR). Colloid Polym. Sci. 2003, 281 (11), 1046−1054. (4) Wang, W.; Gu, Y.; Liu, Y., Applications of weak gel for in-depth profile modification and oil displacement. J. Can. Pet. Technol. 2003, 42 (6). (5) Mothé, C. G.; Correia, D. Z.; de Fran a, F. P.; Riga, A. T. Thermal and rheological study of polysaccharides for enhanced oil recovery. J. Therm. Anal. Calorim. 2006, 85 (1), 31−36. (6) Evani, S.; Rose, G. D. Water soluble hydrophobe association polymers. Polym. Mater. Sci. Eng. 1987, 57, 477−481. (7) Feng, Y.; Zheng, Y.; Luo, P. Aqueous solution properties of hydrophobically associating polyacrylamide. Chem. Res. Appl. 2000, 12 (001), 70−73. (8) Klucker, R.; Munch, J. P.; Schosseler, F. Combined static and dynamic light scattering study of associating random block copolymers in solution. Macromolecules 1997, 30 (13), 3839−3848. (9) Zhang, Z.; Li, J.; Zhou, J. Microscopic Roles of “Viscoelasticity” in HPMA polymer flooding for EOR. Transp. Porous Media 2011, 86 (1), 199−214. (10) Majumdar, T.; Mandal, H. K.; Kamila, P.; Mahapatra, A. Influence of polymer-surfactant interactions on the reactivity of the coIII-feII redox couple. J. Colloid Interface Sci. 2010, 350 (1), 212−219. (11) Petrovic, L. B.; Sovilj, V. J.; Katona, J. M.; Milanovic, J. L. Influence of polymer-surfactant interactions on o/w emulsion properties and microcapsule formation. J. Colloid Interface Sci. 2010, 342 (2), 333−339. (12) Katona, J. M.; Sovilj, V. J.; Petrovic, L. B. Microencapsulation of oil by polymer mixture-ionic surfactant interaction induced coacervation. Carbohydr. Polym. 2010, 79 (3), 563−570. (13) Beheshti, N.; Kj niksen, A. L.; Zhu, K.; Knudsen, K. D.; Nystro m, B. Viscosification in polymer−surfactant mixtures at low temperatures. J. Phys. Chem. B 2010, 114 (19), 6273−6280. (14) Cao, X.; Jiang, S.; Sun, H.; Jiang, X.; Li, F. On the interaction between polyacrylamide and anionic surfactants. Chin. J. Appl. Chem. 2002, 19 (9), 866−869. (15) Li, Y.; Kwak, J. C. T. Rheology of hydrophobically modified polyacrylamide-co-poly (acrylic acid) on addition of surfactant and variation of solution pH. Langmuir 2004, 20 (12), 4859−4866. (16) Shashkina, J. A.; Philippova, O. E.; Zaroslov, Y. D.; Khokhlov, A. R.; Pryakhina, T. A.; Blagodatskikh, I. V. Rheology of viscoelastic solutions of cationic surfactant. Effect of added associating polymer. Langmuir 2005, 21 (4), 1524−1530. (17) Xin, X.; Xu, G.; Gong, H.; Bai, Y.; Tan, Y. Interaction between sodium oleate and partially hydrolyzed polyacrylamide: A rheological study. Colloids Surf., A 2008, 326 (1−2), 1−9. (18) Xin, X.; Xu, G.; Wu, D.; Li, Y.; Cao, X. The effect of CaCl2 on the interaction between hydrolyzed polyacrylamide and sodium stearate: Rheological property study. Colloids Surf., A 2007, 305 (1− 3), 138−144.

ASSOCIATED CONTENT

S Supporting Information *

Pictures of emulsification test for heavy oil and brine with the addition of BPE (A) and BEP (B). This material is available free of charge via the Internet at http://pubs.acs.org.

■

ACKNOWLEDGMENTS

We gratefully acknowledge financial support from the Natural Science Foundation of China (Grant No. 51204197), the Fundamental Research Funds for the Central Universities (13CX02046A), Program for Changjiang Scholars and Innovative Research Team in University (IRT1294), and the Special Program for Major Research of the Science and Technology, China (Grant No. 2011ZX05024-004-08).

4. CONCLUSIONS The rheological and EOR properties of polymer (HPAM and HMPAM) and block polyether (BPE and BEP) solutions are investigated. The rheological results show the block polyether can interact with HPAM molecules by the hydrogen bonds formed between the EO groups of block polyether and the amide groups in the HPAM molecular chain. The interactions can enhance the polymer molecular network and increase the viscosity and viscoelasticity. Meanwhile, the hydrophobic interactions between HMPAM and block polyether can cause the decrease of viscosity and viscoelasticity. Furthermore, the block polyether can reduce the sensitivity of viscosity to temperature. BEP is more effective to stabilize the viscoelastic property and to improve the temperature resistance than BPE in HMPAM solution. Moreover, BEP has a better property to enhance the salt tolerance of the polymer solution than BPE. The displacement experiments show that the sufficiently high viscosity of the polymer solution is necessary to displace the heavy oil. Meanwhile, the emulsification of block polyether has significance on the EOR properties of polymer solutions. In brief, the block polyether cannot only influence the rheological behavior of polymer solutions but also enhance the heavy oil recovery of polymer flooding.

■

■

Article

AUTHOR INFORMATION

Corresponding Author

*Phone: +86-531-88365436. Fax: +86-531-88564750. E-mail: [email protected]. Notes

The authors declare no competing financial interest. 4552

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553

Industrial & Engineering Chemistry Research

Article

non-hydrolyzed polymers in pure water and brine. Polymer 2005, 46 (22), 9283−9295. (39) Chen, Y.; Xu, G. Improvement of Ca2+-tolerance by the introduction of EO groups for the anionic surfactants: Molecular dynamics simulation. Colloids Surf., A 2013, 424 (0), 26−32. (40) Han, X.; Wang, W.; Xu, Y. The viscoelastic behavior of HPAM solutions in porous media and its effects on displacement efficiency. International Meeting on Petroleum Engineering 1995, DOI: 10.2118/ 30013-MS. (41) Lee, S.; Kim, D.; Huh, C.; Pope, G. Development of a comprehensive rheological property database for EOR polymers. SPE Annual Technical Conference and Exhibition 2009, DOI: 10.2118/ 124798-MS. (42) Ge, J.; Wang, D.; Zhang, G.; Jiang, P.; Haitao. The effect of emulsifying power and interfacial tension on displacement characteristics for displacement systems of heavy crude oil. Acta Pet. Sin. 2009, 25 (5), 690−696.

(19) Gong, H.; Xin, X.; Xu, G.; Wang, Y. The dynamic interfacial tension between HPAM/C17H33COONa mixed solution and crude oil in the presence of sodium halide. Colloids Surf., A 2008, 317 (1−3), 522−527. (20) Zana, R. Dimeric and oligomeric surfactants. Behavior at interfaces and in aqueous solution: A review. Adv. Colloid Interface Sci. 2002, 97 (1), 205−253. (21) Gong, H.; Xu, G.; Liu, T.; Xu, L.; Zhai, X.; Zhang, J.; Lv, X. Aggregation behaviors of PEO-PPO-ph-PPO-PEO and PPO-PEO-phPEO-PPO at an air/water interface: Experimental study and molecular dynamics simulation. Langmuir 2012, 28 (38), 13590−13600. (22) Gong, H.; Xu, G.; Liu, T.; Pang, J.; Dou, W.; Xin, X. Synthesis of block polyethers with various structures and their application in dispersing single-walled carbon nanotubes. Colloid Polym. Sci. 2011, 289 (8), 933−942. (23) Han, T.; Xu, G.; Chen, Y.; Zhou, T.; Tan, Y.; Lv, X.; Zhang, J. Improving performances of hydrophobically modified polyacrylamide in mineralized water by block polyether with branched structure. J. Dispersion Sci. Technol. 2012, 33 (5), 697−703. (24) Kopperud, H. M.; Hansen, F. K.; Nystr m, B. Effect of surfactant and temperature on the rheological properties of aqueous solutions of unmodified and hydrophobically modified polyacrylamide. Macromol. Chem. Phys. 1998, 199 (11), 2385−2394. (25) Regalado, E. J.; Selb, J.; Candau, F. Viscoelastic behavior of semidilute solutions of multisticker polymer chains. Macromolecules 1999, 32 (25), 8580−8588. (26) Jiménez-Regalado, E.; Selb, J.; Candau, F. Effect of surfactant on the viscoelastic behavior of semidilute solutions of multisticker associating polyacrylamides. Langmuir 2000, 16 (23), 8611−8621. (27) Li, Y.; Kwak, J. C. T. Rheology and binding studies in aqueous systems of hydrophobically modified acrylamide and acrylic acid copolymers and surfactants. Colloids Surf., A 2003, 225 (1−3), 169− 180. (28) Li, Y.; Hou, W. G.; Zhu, W. Q. Adsorption of cationic starch on aluminum magnesium hydrotalcite-like compound. Colloids Surf., A 2007, 303 (3), 166−172. (29) Feng, Y.; Grassl, B.; Billon, L.; Khoukh, A.; Fran ois, J. Effects of NaCl on steady rheological behaviour in aqueous solutions of hydrophobically modified polyacrylamide and its partially hydrolyzed analogues prepared by post-modification. Polym. Int. 2002, 51 (10), 939−947. (30) Xia, H.; Wang, D.; Wang, G.; Fanshun Kong, Elastic behavior of polymer solution to residual oil at dead-end. Acta Pet. Sin. 2006, 27 (2). (31) Hou, J.; Liu, Z.; Zhang, S.; Yue, X.; Yang, J. The role of viscoelasticity of alkali/surfactant/polymer solutions in enhanced oil recovery. J. Petrol. Sci. Eng. 2005, 47 (3−4), 219−235. (32) Yu, W.; Zhou, W.; Zhou, C. Linear viscoelasticity of polymer blends with co-continuous morphology. Polymer 2010, 51 (9), 2091− 2098. (33) Colby, R. H. Structure and linear viscoelasticity of flexible polymer solutions: comparison of polyelectrolyte and neutral polymer solutions. Rheol. Acta 2010, 49 (5), 425−442. (34) Saadatabadi, A. R.; Nourani, M.; Emadi, M. A. Rheological behavior and hydrodynamic diameter of high molecular weight, partially hydrolyzed poly(acrylamide) in high salinity and temperature conditions. Iran. Polym. J. 2010, 19 (2), 105−113. (35) Lewandowska, K. Comparative studies of rheological properties of polyacrylamide and partially hydrolyzed polyacrylamide solutions. J. Appl. Polym. Sci. 2007, 103 (4), 2235−2241. (36) Zhou, C.; Yang, W.; Yu, Z.; Zhou, W.; Xia, Y.; Han, Z.; Wu, Q. Synthesis and solution properties of novel comb-shaped acrylamide copolymers. Polym. Bull. 2011, 66 (3), 407−417. (37) Rashidi, M.; Blokhus, A. M.; Skauge, A. Viscosity study of salt tolerant polymers. J. Appl. Polym. Sci. 2010, 117 (3), 1551−1557. (38) Feng, Y.; Billon, L.; Grassl, B.; Bastiat, G.; Borisov, O.; François, J. Hydrophobically associating polyacrylamides and their partially hydrolyzed derivatives prepared by post-modification. 2. Properties of 4553

dx.doi.org/10.1021/ie404236r | Ind. Eng. Chem. Res. 2014, 53, 4544−4553