Rheological behavior of hydrolyzed polyacrylamide solution flowing through a molecular weight adjusting device with porous medium☆

Lühong Zhang ,Jiangtao Wang ,2,Yuqi Zhang ,Bin Jiang ,3,Xiaoming Xiao ,2,*,Li Hao

1 School of Chemical Engineering and Technology,Tianjin University,Tianjin 300072,China

2 Collaborative Innovation Center of Chemical Science and Engineering,Tianjin 300072,China

3 National Engineering Research Center for Distillation Technology,Tianjin 300072,China

☆Supported by the Program for Yangtse River Scholars and Innovative Research Terms in Universities(IRT0936),the National Basic Research Program of China(2009CB219905,2009CB219907),and the Daqing Oil field Co.,Ltd.

*Corresponding author.

E-mail address:xmxiao@tju.edu.cn(X.Xiao).

A B S T R A C T The separate-layer injection in different interlayers and the injection of the same-molecular-weight polymer solution in a layer are necessary in the polymer flooding process because of heterogeneous multilayer sandstone reservoirs in EOR projects.To alleviate the matching problems between the layer permeability and the injected polymer molecular weight,a molecular weight adjusting device with porous medium was designed on the basis of mechanical degradation principle.In terms of four variables(polymer concentration,pore diameter,length of shear component and flowrate),the rheological behavior of hydrolyzed polyacrylamide(HPAM)solution flowing through the device was investigated in detail.The change of these variables is able to control the shear rate of HPAM solutions through ceramic foam,and achieve the desired degree of shear degradation and the final rheological parameters—viscosity loss,viscoelasticity and pressure drop.Therefore,a linear relationship between viscosity loss and shearing rate was established so as to obtain the targeted viscosity easily.Field tests in the Daqing Oil Field showed that the polymer molecular weight could drop 20%to 50%.In a word,the results could guide the industrial application of the novel device and the further study of polymer degradation flowing through the porous medium.

?2015 The Chemical Industry and Engineering Society of China,and Chemical Industry Press.All rights reserved.

1.Introduction

With the recent surge of interest in enhanced oil recovery(EOR),improved polymer flooding[1]has been applied in the Daqing Oil Field in northern China on a large scale basis.As is known,Chinese oil fields are characterized by heterogeneous multilayer sandstone reservoirs which need partially hydrolyzed polyacrylamide(HPAM)solutions with appropriate molecular weight.This indicates that the viscosity and size of the emulsion formed in the reservoir are of great importance.If the size is too large and viscosity is high,it can plug the pore spaces thus reducing the overall recovery;if the size is too small and viscosity is very low,the desirable sweep efficiency will not be achieved,also causing reduction in recovery[2,3].Therefore,combining separate-layer injection technology during polymer flooding with the same-molecular-weight polymer injection in the similar layer,the challenge of interlayer differences could be resolved effectively and expediently.Liang et al.[4]developed different-molecular-weight polymer injection technology which achieved the designed requirements of controlling both separate-layer injection rate and molecular weight,but it can lead to the blockage of sandstone because the polymer in the interlayers is prone to cause detention problem and the speed of injection is limited.Consequently,how to obtain different molecular weights and viscosities going with the changed zone permeability[5]whenever and wherever possible is of great importance.Except for several special injection technologies depending on correspondent relation ship between molecular weight and reservoir under study and application in the Daqing Oil Field,there is no further research and application of polymer molecule weight regulating mechanisms or devices at home and abroad.Hence,we designed a small-scale polymer molecular weight adjusting device to realize the separate-layer injection into different interlayers.

As a kind of water soluble polyelectrolyte with negative charges along its chain,HPAM[6]is widely used as mobility control agents in polymer injection chemical EOR applications[7].HPAM is particularly sensitive to shear degradation[8]for its fragile molecular chains so that the viscosity and molecular weight can decrease at different degrees under powerful shear force.Based on the earlier literature evidences and observations[9],HPAM solution exhibited the non-Newtonian behavior with shear-thickening areas.Combined with its viscosity property,the use of HPAM could improve the sweep of the oil bypassed due to reservoir heterogeneity.Zhang et al.[10]declared the mechanistic features of polymer solution through porous medium.Zhang et al.[11]also concerned the viscoelastic behavior of HPAM solution in porous medium and its effects on displacement efficiency.Morris and Jackson[12]explained the degree of mechanical shear degradation of polymer solutions derived from polymer molecular weight,polymer concentration,core permeability,and flowrate,and they also indicated that the pressure drop on both ends of the porous medium cannot be too large.Therefore,many researchers paid more attention to the viscoelastic effects of the polymer solution flowing through porous medium,especially the relationship between pressure drop and flowrate[13,14].In this study we mainly focus on and analyze the rheological change of HPAM solution and the press drop through porous medium in order to get the polymer solution with different targeted viscosities and the design of the novel device.

Polymer rheology[15]not only affects the polymer injectivity but also dominates the oil production rate and the final oil recovery during the chemical-enhanced EOR process[16].Thus,the exhaustive research on rheological behavior is not only a very important part in the polymer flooding technology[17],but also the foundation of polymer flooding reservoir engineering and guideline for field experiment.Considering effects of variable factors on polymer flow through the porous medium,rheological models were established to predict the experimental results effectively and easily[18],and Liberatore et al.[19]has researched the effect of mechanical degradation on molecular weight distribution.Though many researches were focused on the rheological behavior of HPAM solution flow and the HPAM solution related device,few studies have discussed the case HPAM flows through separate-layer injection device made of porous medium.

In view of mechanical degradation of HPAM solutions and the pressure drop across porous medium,we designed a device with ceramic foams aiming at adjusting the viscosity or molecular weight of polymer with small pressure drop.Ceramic foam is a promising porous material as the key shearing component because its light weight,high porosity,good mechanical strength,and complex geometry channels,plus the good chemical stability could keep the polymer solution clean all the time.These excellent properties made it different from the traditional packed bed layer[20],and capable of getting a better shearing effect with a smaller pressure drop.By changing the pore diameter and volume fraction of these microporous materials,the polymer molecular weight and viscosity can be degraded in different degrees.At the same time,compared to other similar equipment[4],the biggest advantage of the new equipment is that the non-Newtonian fluid is subjected to a uniform shearing force when flowing through the component,which is in line with the requirements of homogeneous injection.Moreover,the onetime investment cost of the equipment is low and the operation is simple,and more importantly,the ground equipment and pipe network in the oil field needn't be changed.

In this paper the rheological characterization of HPAM solutions was studied before and after polymer solutions flow through the designed molecular weight adjusting device.The theoretical basis for the field application of the new polymer molecule weight adjusting device was also explored via the experiment.Finally,the field tests were conducted in the Daqing Oil Field after we succeeded in the lab-scale application.

2.Experimental

2.1.Materials

Hydrolyzed polyacrylamide used in the experimentis provided by the Daqing Oil Field.Its average relative molecular mass is 2.5×107g·mol-1,hydrolyzation is 25%-30%,and solid content is 90%.

2.2.The preparation of HPAM solution

HPAM solutions at three concentrations(1000 mg·L-1,2000 mg·L-1,and 3000 mg·L-1)were prepared by adding polymer powders into the vortex of distilled water(pH=6-7)under magnetic stirring.Gentle stirring was maintained for 5 h at room temperature(25°C-30°C)to avoid mechanical degradation of polymer.The polymer solutions were left standing for aging time to 24 h.

2.3.Experimental apparatus

The main components of the experimental setup include:a molecular weight adjusting element made of ceramic foam,a buffer tank for the prepared polymer solution,a metering pump to drive the stream through the shearing device,a pulse damper and a back pressure valve to make sure the stream with steady flow velocity,several pressure transducers and a computer with data collection board installed for accurate records of the pressure drop,and a storage tank for collecting effluents.The apparent porosity of porous SiC foam is provided by Shenyang Institute of Metals,CAS(prepared by sintering according to[21]).The porosity of the ceramic foam ranges from 70%to 90%,while the pore size varies from 2 to 4 mm.A schematic diagram of experimental setup is shown in Fig.1.

Fig.1.Schematic diagram of the experimental setup.

On the basis of mechanical degradation principle,a stainless steel pipe(diameter:15 mm)packed with dry ceramic foams(total length:50 mm,pore diameter:φ2 mm,φ3 mm,φ4 mm,porosity:75%)was designed as the key component of molecular weight adjusting device.The shear degradation of polymer solutions is mainly determined by the pore diameter of the ceramic foam.The smaller the pore diameter is,the higher the shear degradation.Through adjusting the valve opening,changing the pore diameter,and allocating appropriate number of ceramic foam components,this device can control the degradation degree and polymer molecular weight[22].

2.4.Analysis and test

Viscosity measurements were always performed by a DV-II+PRO viscometer(Brook field,USA)at 6 r·min-1and the temperature of(20±0.1)°C.Viscoelasticity measurements were carried out by a HAAKE rheometer with a cone and plate geometry at(20±0.1)°C.Oscillation tests were conducted to measure the storage modulus G′,loss modulus G″at a constant stress of 0.03 Pa and frequency range of 0.1-10 Hz.These ranges of frequency and strain were chosen to provide a stress of reasonable magnitude for purpose of sensitivity.

3.Results and Discussions

In addition to viscosity,elasticity also plays an important role in the polymer flooding process.The effect of shear degradation is evaluated by four key parameters:apparent viscosity,viscoelasticity,pressure drop and the length of shear components.From a series of experiential results,the effects of these parameters on the rheological behaviors of HPAM solution for the control of corresponding molecular weight or viscosity with different sandstone reservoirs could be revealed.

3.1.Apparent viscosity

As one of the most important factors to polymer flooding,the viscosity of polymer solution can regulate the ratio of oil and water mobility(polymer solution)to change the size of sweeping volume.From Fig.2,we can see that the apparent viscosity of HPAM solution decreases with the increasing shear rate under given shearing condition.Consequently,the HPAM solutions exhibits shear-thinning characteristic which indicates that the HPAM solution is non-Newtonian,the relationship of shear rate versus viscosity is not linear.When fluid stress increases during the mechanical degradation or flowrate becomes large enough to break the polymer molecular chains,the mechanical degradation of polymer solution occurs to result in the change of molecular viscosity.Therefore,viscosity loss can be used to characterize the degree of polymer degradation[12].

Fig.2.Viscosity changes with shear rate of HPAM solution at 25°C.

Fig.3 shows the apparent viscosity loss versus flowrate at different polymer concentrations ranging from1000 to 3000 mg·L-1with different pore diameters ranging from 2 mm to 4 mm.It can be seen that shear degradation induces a progressive loss in viscosity,meanwhile the viscosity losses have similar changing trends under different experiment conditions.From the graph it is clear that the greatest viscosity loss of 24.7%was obtained at the highest polymer concentration of 3000 mg·L-1under the largest flowrate of 180 L·h-1for the smallest pore diameter of Φ2 mm.

For a given viscosity,the shear rate should be defined in advance,which is related to the permeability,the porosity of porous medium and actual fluid velocity.It is necessary to choose an appropriate model to calculate the interstitial shear rate in the porous medium.Christopher and Middleman[23]suggested the following equation to estimate shear rates in a porous medium:

where(3n+1)/4n is a non-Newtonian correction factor for power-law fluids;Q is flowrate,cm3·s-1;A is the cross sectional area of pore,cm2;γ˙ the shear rate,s-1;K is permeability,cm2;and Φ is the porosity.

Moreover,the empirical formula of permeability for the silicon carbide porous medium was derived as follows[22,23]:

where τ is the tortuosity factor.The pore diameters are 2 mm,3 mm and 4 mm respectively in the study,the length is 50 mm and porosity Φ is 75%.n is the rheological index of power-law fluids.By fitting of steady-state rheological curve,the values of the required parameters in this study can be calculated,as listed in Table 1.

To further determine the impact of concentration,pore size,and flowrate on the viscosity loss,the shear rates in ceramic foam for each experimental case were calculated via Eqs.(1)-(2)[24].The plot correlating the viscosity loss and shear rate was obtained as in Fig.4.It is found that all the experimental points approximately lie in the same line, fluctuating in about 3%,which could be accepted in engineering applications.The linear fitting formula is obtained as y=0.00978x+0.05855,where y is the viscosity loss and x is the shear rate.The coefficient of determination(R)of the linear fitting curve is 0.99331,which illustrates that the viscosity loss and shear rate has a good linear relationship.Such a near-linear relationship provides a simple and effective theoretical basis to predict the viscosity loss of polymer solution through the molecule weight adjusting device.In the industrial application we can get the targeted molecular weight according to the sandstone interlayers.Then the relationship between viscosity loss and shear rate can guide to obtain the value of shear rate.In other words,the designed shear rate could be obtained by the set of variable values according to Eq.(1).

3.2.Viscoelasticity

As a non-Newtonian fluid,polymer solution exhibits both viscous and elastic properties.With the increase in viscoelasticity,the ability of expanding the sweep volume is greater and the oil displacement effect is better.The viscoelasticity of polymer solution includes the loss modulus(G″)and the storage modulus(G′)which were measured by a HAAKE rheometer with a cone and plate geometry.

3.2.1.The loss modulus(G″)

In Fig.5,experimental data for the loss modulus(G″)of original and sheared HPAM solutions under the flowrate of 180 L·h-1at three different HPAM concentrations as a function of frequency are presented.From the data,we can find that the greater the concentration of original polymer solution,the larger the initial value of G″.The reduction of loss modulus increases with the increase of polymer concentration,which is similar with the aforementioned changing trend of viscosity.The results demonstrate that the loss modulus is representative of the viscosity characteristics of polymer solution in dynamic oscillation experiments,as reported by Mason et al.[25].According to the characteristics of shear degradation,under given external conditions the polymer gradually degrades to a certain extent and then remains unchanged.From Fig.5,there is only a small decline for G″of HPAM between the fourth and fifth shearings.Although high concentration leads to a substantial degradation,the value is still bigger than the case of low concentration.

3.2.2.The storage modulus G′

Fig.3.Effect of flowrate on viscosity loss under different HPAM concentrations and pore diameters.

Table 1 Model parameters to calculate shear rate in ceramic foam of HPAM

Compared with the loss modulus,the storage modulus G′,as the representatives of elastic part[26],has received more extensive attentions of researchers in recent years,researchers discovered that the elasticity also plays a key role in polymer flooding in addition to high viscosity.From Fig.6,similar to loss modulus,G′increases with the increase of polymer concentration.For HPAM of 1000 mg·L-1,G′keeps decreasing in the repeated shearing processes,and for HPAM of 2000 mg·L-1and 3000 mg·L-1,G′increases after the first shearing and then decreases in the following shearing.The reason for this abnormal difference is that the viscoelastic property of polymer solution is dominated by both polymer molecular weight and viscosity.When polymer solution passes through the molecule weight adjusting device for the first time,only a portion of larger molecules are broken down into smaller ones as the ceramic foam channel is very short,coupled with the newly generated small molecular,the average molecular weight becomes smaller,but the molecule weight distribution broadens[27].For 1000 mg·L-1with little degradation,the molecule weight distribution changed a little while the molecule weight obviously declines,which results in the steady decrease of G′.For 2000 mg·L-1,the molecule weight distribution has a stronger influence,so G′increases after first shearing,and is not less than the initial value until the third shearing.For 3000 mg·L-1,G′drops below the initial value after second shearing.Consequently,to get an appropriate shearing result,the concentration needs to be moderated and there are some limits for the storage modulus.

Fig.4.The relationship between viscosity loss and shear rate under different pore diameters and flowrates(porous medium 50 mm long).

In addition to the concentration, flowrate is also an important factor.Fig.7 shows the storage modulus G′(Pa)versus frequency(Hz)for the original and the sheared HPAM polymer solution of 2000 mg·L-1at flowrate of 36 L·h-1,108 L·h-1and 180 L·h-1.If the flowrate is too small,the storage modulus keeps constant.As the flowrate increases,the storage modulus increases after the first shearing and then decreases in the following processes.For moderate flowrate(108 L·h-1),the increased storage modulus decreases very slowly,after five shearings the storage modulus returns to the original value.

3.3.Pressure drop

In addition to the viscosity loss,the pressure drop across the shear device is another evaluation parameter about the shear degradation effect.The big pressure drop results from the large viscosity and the special viscoelasticity when the solution flows through the device.If the pressure drop exceeds the range of the device,the shear degradation effect will be influenced greatly.

Fig.8 shows the relationship between the pressure drop and the flowrate for the shearing of HPAM(concentration is 1000,2000,3000 mg·L-1)in molecule weight adjusting device with different ceramic foams(2 mm,3 mm,4 mm).Many strong experimental evidences have indicated that the flow of viscoelastic fluids through porous medium or packed beds can exhibit the sharp increasing pressure drop,which may result from the extensional nature of viscoelastic flow field in the pores caused by successive expansions and contractions in the complex pore space.From Fig.8 we can see that with the increase of flowrate,the pressure drop slightly rises at first,and then the growth rate slows down.The transition point is related to the pore size and concentration.There are two possible reasons:one is the buffering effect of mechanical degradation on pressure drop,Kozicki[28]not only considered the viscous flow and extensional flow,but also took account polymer degradation in the formula,which made the calculated value more accurate;the other explanation is that the structure of ceramic foam performs high porosity.In Fig.8,the maximum pressure drop of HPAM flowing through the porous medium is 370 kPa,while the loss of viscosity reaches 24.7%.It can be seen that the new molecule weight adjusting device is effective to adjust the viscosity of polymer solution with relatively lower pressure drop.

Fig.5.Loss modulus before and after shearing for HPAM versus frequency under different HPAM concentrations(porous medium 50 mm long).

3.4.Length of shear component

In order to examine the effect of shear component length on shear degradation,the HPAM solutions at 2000 mg·L-1were injected into the molecular weight adjusting device with different total lengths(50,100,150,200,250 mm),the pore diameters for all devices are φ2 mm.The effect of total length on the apparent viscosity loss is shown in Fig.9.

From Fig.9,we can see that the viscosity loss increases with the total length generally.Under the small flowrate,the viscosity loss is almost unchanged among different total lengths,and under the big flowrate,the viscosity loss increases when the total length rises evidently from 50 mm to 150 mm,and changes little with the continual growth of the total length to 200 mm and 250 mm.This is because for the given polymer with big molecule weight,the viscosity loss has its limitation,and the mechanical degradation approach more easily reaches its limitation,compared with the biological degradation approach and chemical degradation approach.

Fig.6.Storage modulus before and after shearing for HPAM versus frequency under different HPAM concentrations(porous medium 50 mm long).

Fig.7.Storage modulus before and after shearing for HPAM versus frequency under different flowrates(porous medium 50 mm long).

Fig.8.Effect of flowrate on pressure drop with different HPAM concentrations,pore.

Fig.9.The viscosity loss of the HPAM solution after different shearings(porous medium φ2 mm).

3.5.Field tests

The novel molecule weight adjusting equipment was applied on ZD22-5E47 well and ZD22-E53 wells in the Daqing Oil Field(pipeline inserted with a piece of dry ceramic foam:total length 32 mm,pore diameter φ2 mm).By detecting and analyzing,both wells show different heterogeneous multilayer sandstones which need different HPAM solutions.As shown in Fig.10,the test device was equipped with sampling bottles(S1,S2)and pressure gauges(P1,P2)at both inlet and outlet.The viscosity and molecular weight before and after the molecular weight adjusting equipment were obtained by measuring the hydrolyzed polyacrylamide solution samples from sampling bottles(S1,S2).Pressure drop was calculated with the pressure gauges(P1,P2).Different molecular weight polymer solutions with the concentration of 2000 mg·L-1were injected into the novel molecular weight adjusting device by a metering pump.Through the comparison of molecular weight data before and after the shearing device(Table 2),we can see that the greater the flowrate,the greater the molecular weight loss.The trend is consistent with the tests in laboratory experiments.Under the same flowrate,the larger the molecular weight,the greater the molecular weight loss.For both wells,the molecular weight loss rate are basically identical under the same conditions,which indicated that this molecular weight adjusting device is simple to install and has a wide adaptability.

Fig.10.Photo of the field test device in the Daqing Oil Field.

Table 2 Comparison of HPAM molecule weight data in field tests

4.Conclusions

In conclusion,the novel molecular weight adjusting device with ceramic foams in accordance with the mechanical degradation principle is a competitive solution for matching problems between layer permeability and polymer molecular weight.The novel device has shown a good future application in the EOR progress.

(1)After the rheological tests conducted on HPAM samples before and after this novel device,the largest viscosity loss rate is 24.7%,and the pressure drop corresponding to the maximum viscosity loss is only 370 kPa.The polymer molecular weight degrade is in a reasonable range and the pressure loss is relatively small compared to other devices and traditional packed bed.

(2)Viscosity loss seems to be dependent only on the shear rate in the device and the residence time.According to the liner relationship between viscosity loss and shear rate,the desired viscosity can be precisely and easily achieved.

(3)The effect of viscosity and elasticity of the polymer solution flowing through the shearing device is presented by the measurement of loss modulus(G″)and storage modulus(G′).Via the reasonable increase of shear rate,polymer viscosity can degrade,whereas the elasticity of the polymer will increase or remain unchanged.

(4)Field tests in the Daqing Oil Field showed that the polymer molecular weight could degrade 20%to 50%,which demonstrated that the control of molecular weight can be achieved.

[1]B.S.Shaker,A.Skauge,Enhanced oil recovery(EOR)by combined low salinity water/polymer flooding,Energy Fuel 27(3)(2013)1223-1235.

[2]Z.H.Wang,X.P.Le,Y.G.Feng,C.X.Zhang,The role of matching relationship between polymer injection parameters and reservoirs in enhanced oil recovery,J.Pet.Sci.Eng.111(2013)139-143.

[3]Y.Q.Li,J.X.Gao,D.D.Yin,J.J.Li,H.L.Liu,Study on the matching relationship between polymer hydrodynamic characteristic size and pore throat radius of target block s based on the microporous membrane filtration method,J.Chem.2014(2014),http://dx.doi.org/10.1155/2014/569126(ID 569126(7 pp.)).

[4]Y.N.Liang,S.C.Zhang,X.H.Pei,H.Duan,Practice and understanding of separate-layer polymer injection in Daqing Oil Field,SPE Prod.Oper.26(3)(2011)224-228.

[5]G.Z.Zhou,M.H.Xie,M.Liu,H.X.Wu,X.L.Long,Dissolution characteristics of hydrophobically associating polyacrylamide in stirred tanks,Chin.J.Chem.Eng.18(1)(2010)170-174.

[6]N.J.Lai,W.Dong,Ye,J.Dong,X.P.Qin,W.L.Chen,K.Chen,A water-soluble acrylamide hydrophobically associating polymer:Synthesis,characterization,and properties as EOR chemical,J.Appl.Polym.Sci.129(4)(2013)1888-1896.

[7]B.Wei,L.Romero-Zerón,D.Rodrigue,Mechanical properties and flow behavior of polymers for enhanced oil recovery,J.Macromol.Sci.B 53(4)(2014)625-644.

[8]R.S.Seright,T.Fan,K.Wavrik,R.Balaban,New insights into polymer rheology in porous media,SPE J.16(01)(2011)35-42.

[9]D.A.Z.Wever,L.M.Polgar,M.C.A.Stuart,F.Picchioni,A.A.Broekhuis,Polymer molecular architecture as a tool for controlling the rheological properties of aqueous polyacrylamide solutions for enhanced oil recovery,Ind.Eng.Chem.Res.52(47)(2013)16993-17005.

[10]R.Zhang,Z.B.Ye,L.Peng,N.Qin,Z.Shu,P.Y.Luo,The shearing effect on hydrophobically associative water-soluble polymer and partially hydrolyzed polyacrylamide passing through wellbore simulation device,J.Appl.Polym.Sci.127(1)(2013)682-689.

[11]Z.Zhang,J.Li,J.Zhou,Microscopic roles of‘viscoelasticity’in HPMA polymer flooding for EOR,Transp.Porous Media 86(1)(2011)199-214.

[12]C.W.Morris,K.M.Jackson,Mechanical degradation of polyacrylamide solutions in porous media,SPE symposium on improved methods of oil recovery,Soc.Petrol.Eng,1978.

[13]J.C.Slattery,Flow of viscoelastic fluids through porous media,AIChE J.13(6)(1967)1066-1071.

[14]T.Sochi,Flow of non-Newtonian fluids in porous media,J.Polym.Sci.Polym.Phys.48(23)(2010)2437-2767.

[15]K.Ren,G.Y.Jiang,C.M.Xu,M.Q.Lin,Synthesis and solution properties of hydrophobic associating polymers,Chin.J.Chem.Eng.13(2)(2005)266-270.

[16]S.Wu,Shear and elongational rheology of partially hydrolyzed polyacrylamide used for enhanced oil recovery,Appl.Rheol.23(2013)280-286.

[17]J.C.Jung,K.Zhang,B.H.Chon,H.J.Choi,Rheology and polymer flooding characteristics of partially hydrolyzed polyacrylamide for enhanced heavy oil recovery,J.Appl.Polym.Sci.127(6)(2013)4833-4839.

[18]A.Stavland,H.Jonsbroten,A.Lohne,A.Moen,N.Giske,Polymer flooding- flow properties in porous media versus rheological parameters,SPE 72nd EAGE Conference&Exhibition,2010.

[19]M.W.Liberatore,S.Baik,A.J.McHugh,T.J.Hanratty,Turbulent drag reduction of polyacrylamide solutions:Effect of degradation on molecular weight distribution,J.Non-Newtonian Fluid 123(2)(2004)175-183.

[20]D.H.Kim,S.H.Kim,J.Y.Byun,A microreactor with metallic catalyst support for hydrogen production by partial oxidation of dimethyl ether,Chem.Eng.J.280(2015)468-474.

[21]L.H.Zhang,X.K.Liu,X.G.Li,X.Gao,H.Sui,J.S.Zhang,A novel SiC foam valve tray for distillation columns,Chin.J.Chem.Eng.21(8)(2013)821-826.

[22]L.H.Zhang,Y.L.Sun,B.Jiang,X.G.Li,J.Zhang,N.Yang,A microporous polymer molecular weight adjusting deviceCN 103277076A 2013(in Chinese).

[23]R.H.Christopher,S.Middleman,Power-law flow through a packed tube,Ind.Eng.Chem.Fundam.4(4)(1965)422-426.

[24]W.Littmann,Polymer flooding,Elsevier,New York,1988.

[25]T.G.Mason,D.A.Weitz,Optical measurements of frequency-dependent linear viscoelastic moduli of complex fluids,Phys.Rev.Lett.74(7)(1995)1250-1253.

[26]C.Wilkes,B.Gampert,Experimental investigations on the influence of the concentration of polyacrylamide solutions on elongational flow behavior,Chem.Eng.Technol.28(5)(2005)561-565.

[27]A.Zaitoun,P.Makakou,N.Blin,R.S.Al-maamari,A.R.AL-Hashmi,M.Abdel-Goad,H.H.Al-Sharji,Shear stability of EOR polymers,SPE J.17(2)(2012)335-339.

[28]W.Kozicki,Viscoelastic flow in packed beds or porous media,Can.J.Chem.Eng.79(1)(2001)124-131.