Scientia Iranica F (2014) 21(3), 1174{1178

Sharif University of TechnologyScientia Iranica

Transactions F: Nanotechnologywww.scientiairanica.com

Enhanced oil recovery performance and time-dependentrole of polymeric core-shell nanoemulsion

Y. Tamsiliana and A. Ramazani S.A.a,b;�

a. Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran, Iran.b. Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran.

Received 3 May 2014; received in revised form 25 May 2014; accepted 18 August 2014

KEYWORDSEnhanced oil recovery;Core-shellnanostructure;Wettability e�ects;Mobility ratio.

Abstract. Nano inverse emulsion polymerization has been used to synthesize highmolecular weight polyacrylamide nanoparticles with a hydrophobic nanoscale coatinglayer with low molecular weight. These core-shell nanoparticles modify the polymer ooding process, which can eliminate almost all problems of classical polymer oodingsuch as polymer solution high viscosity, polymer absorption and mechanical, thermaland biological degradations of the polymer. The nanostructure was characterized byDynamic Light Scattering (DLS) particle size analysis, thermal analysis (DSC), and UV-Vis spectroscopy that con�rm a core-shell nanostructure for the produced particles withconsiderable interaction of two polymers with narrow size distribution (90-140 nm). Also,micromodel and solubility experiments show that this method could considerably enhancethe performance of classical polymer ooding and reduce polymer usage during the polymer ooding process.c 2014 Sharif University of Technology. All rights reserved.

1. Introduction

There are many limitations within existing polymer ooding technology such as thermal, mechanical, shear,and biological degradation of polymer chains during theEnhanced Oil Recovery (EOR) process [1-4]. Recently,encapsulation and intelligent delivery studies have beenconsidered a sophisticated approach for the protectionand controlled release of precious materials in many�elds to overcome the above mentioned limitations inpolymer ooding with polyacrylamide solutions [5-7].

A novel core-shell nanostructure of polyacryl-amide and a hydrophobic polymer (such aspolystyrene) is designed and prepared to intellectuallycontrol the microscopic and macroscopic sweepe�ciency of polymer ooding in oil reservoirs.This nanostructure can release polyacrylamide atthe oil-water interface at reservoir temperature (�

*. Corresponding author. Tel.: +98 21 66166405E-mail address: ramazani@sharif.edu (A. Ramazani S.A.)

90�C), where water ooding should have maximumviscosity.

2. Materials and method

First, 60 ml of hexane solvent (Merk Chemical Co.)and 0.0035 ml of span 80 surfactant (Sigma-AldrichChemie GmbH Co.; C24H44O6) are mixed in a reactorwith three entries. After mixing these using a me-chanical mixer (3000 max rpm, Gri�n & George, GT.Britain) with a speed of around 2000 rpm, the waterphase including 5 g hydrophilic monomer of acrylamide(Merk Chemical Co.) and 20 ml of deionized water,is distributed to the previous solution. It should benoted that the distribution process of the water phaseis an important parameter a�ecting the size of coreparticles. So, the water phase is injected into themixed organic phase in the reactor via a microinjec-tion. This helps to make the emulsion of polymernanoparticles. After the water and organic mixingphases, the initiator system (redox), including ferrous

Y. Tamsilian and A. Ramazani S.A./Scientia Iranica, Transactions F: Nanotechnology 21 (2014) 1174{1178 1175

sulfate and potassium persulfate (Merk Chemical Co.),is injected (5:2 ratio) under temperature condition�15�C, by entering this material into the reactor. The�rst time period of polymerization is selected suchthat the reactor remains under the mentioned condi-tions for 30 minutes and, after that, is immediatelymoved to very low temperature conditions for 3 or4 days without mechanical mixing. After this time,nanoparticles of polyacrylamide with high molecularweight (> 10; 000; 000 Dalton) are produced and it istime to inject the second initiator and monomer of thenanolayer with hydrophobicity properties. Therefore,in the second step of the process, the redox initiatorunder low temperature conditions (�15�C) and styrenemonomer are injected for making the nanolayer. Itis interesting to point out that the initiator of thesecond step and the organic monomer must be injectedsimultaneously, and the initiator on the surface of thepolymer nanoparticle causes the making of a chain ofpolystyrene; this chain is propagated continuously. Asone of the goals is to make the smallest organic polymerlayer on the particles, the transfer of the chain mustbe done in speci�c time and an extra propagation ofthe polymer nanolayer chain is prevented. In thisway, by considering the short time for the secondpolymerization process (about 30 minutes), a thinlayer of polystyrene is made on the nanoparticles ofthe polyacrylamide and, after this time, the reactionprocess is terminated. The polystyrene nanolayer issolved in a hexane solvent, so this solvent must beremoved from the reactor at the end to prevent achange in particle size distribution and to preventtheir tenacity. This separation is done by removingthe materials of the reactor and centrifuging at aspeed of 5500 rpm for 30 minutes. After that, thematerial is divided into 3 phases. The bottom phaseconsists of pure hexane solvent with a dark colour,the middle phase from the mid solid particles iswith a white coating and the head phase consists ofwhite uids which are a mix of hexane and coatingparticles. The middle phase which is rich in coatednanoparticles is strewn into some water and remainsunder high speed mixing for 3 minutes. After that,the material is sprayed into a large amount of waterat high pressure. After centrifuging and separatingthe synthesized particles, the goal is to produce theparticles in powder form. Water must be removedfrom the suspension system and the particles becomeuseable as powder in the enhanced oil recovery. Thisprocess is done by freeze drying (Millrock TechnologyInc.). Finally, the synthesized powders have a core-shell nanostructure whose nanocore of polyacrylamideis 10 million Dalton (molecular weight), and whose sizeis 80 nanometres. Its shell is a nanolayer of polystyrenewith 40,000 Dalton (molecular weight) whose size is 10nanometres.

3. Results and discussion

Figure 1 shows the Dynamic Light Sattering (DLS) re-sults of polyacrylamide-polystyrene nanoparticles. Theaverage diameter of core-shell particles is in the rangeof 80 and 140 nm.

Di�erential Scanning Calorimetry (DSC) analysiswas carried out using samples of approximately 5-10 mg placed in closed aluminium crucibles. Theanalyses were performed under a nitrogen ow of15 mL.min�1 at a heating rate of 5�C.min�1 from 40to 250�C temperature. Two scans were obtained foreach sample and the data analyses were made using thecurve resulting from the second scan. Glass transitiontemperatures (Tg) of materials were obtained from the�rst derivative of DSC curves (Figure 2). Accordingto Figure 2, the polymeric nanostructure has two glasstransition temperatures in a range of 100-190�C, dueto the presence of a polystyrene shell (103�C) and apolyacrylamide core (109:5�C) in accordance with thesequential degradation process.

UV-Visible spectroscopy was carried out usingsamples of approximately 3-9 mg placed in closed

Figure 1. Size distribution of core-shell nanoparticles,obtained by DLS method.

Figure 2. Glass temperatures of core-shell nanoparticles,obtained by DSC method.

1176 Y. Tamsilian and A. Ramazani S.A./Scientia Iranica, Transactions F: Nanotechnology 21 (2014) 1174{1178

Figure 3. UV-Vis spectrum ofpolyacrylamide-polystyrene system.

Figure 4. Scheme of dissolution test.

quartz packs. According to Figure 3, there is an ab-sorbance peak for the core-shell sample at a wavelengthof 400 nm, which is similar to pure polystyrene, toverify complete coating of the hydrophilic polymer byhydrophobic polystyrene.

For investigating the behaviour of polyacrylamiderelease from its nanolayer coating and the e�ectson the rheological properties of the water phase inunderground reservoirs with a wettability variable, atest is planned as the coating particles remain on oil orxylene for a speci�c period of time. In this period, aftersampling, the viscosity of the water phase is measuredvia a dilute viscometer (Figure 4).

Under these conditions, in contacting the syn-thesized particles by the organic phase under thetemperature close to the underground oil reservoirs (90-100�C), the hydrophobic coating solves in the oil phasegradually, and the polyacrylamide molecules throughthe shell have an opportunity to di�use into the pushingphase (water). This case causes the controlled releaseof polyacrylamide and the increase of water viscosityto enhance sweep e�ciency. The molecular release ofpolyacrylamide, because of its high molecular weight,requires a long time, and one of the goals of this studyis that particles should move towards deep areas of oilreservoirs and remain in special fractures. Accordingto the special components of oil, these materials cause

Figure 5. Viscosity of pure polyacrylamide in waterphase vs. time.

Figure 6. Viscosity of core-shell nanoparticles in waterphase vs. time.

Table 1. Comprative results of water, pure polymer, andcore-shell ooding processes.

EOR method RF%

Water ooding 44.17381

Polymer ooding 61.02884

Core-shell ooding 59.40461

the in ation and dissolution of polystyrene in the oilphase and this causes the release of the inside materialsof the shell. As identi�ed in this test, for the timeof release, and for the polyacrylamide nanoparticleswhich are coated in the water phase, the dissolution ofpure polyacrylamide with 6 million Dolton (molecularweight) under the temperature 90-100�C takes 6 days(Figure 5), but the total release of the nanoparticles ofpolyacrylamide from the nanolayer of the polystyrenetakes 21 days to dissolve in the water phase undersimilar conditions (Figure 6).

The three methods of ooding, provided in the ex-perimental glass micromodel, are compared in Table 1to show the e�ects of the used agent in the enhanced

Y. Tamsilian and A. Ramazani S.A./Scientia Iranica, Transactions F: Nanotechnology 21 (2014) 1174{1178 1177

Figure 7. Oil recovery factor vs. pore volume injected inexperimental micromodel during core-shell ooding.

oil recovery process. According to the mechanism fortesting the percentage of oil recovery by the intelligent ooding process, it is found that, for core-shell polymer ooding, just in the volume of progress deployed by thepolymer, active polymer is used, and the percentage ofoil recovery is relatively similar to the ooding processof pure polymer (Figure 7). On the other hand, inthe ooding process with a new synthesized core-shellnanostructure, just 30% of the active polymer is usedcompared to that of classic polymer ooding.

4. Conclusions

In this research, through simultaneous inverse emulsionprocesses of polyacrylamide dilute solution and styrene,nanoparticles of polyacrylamide-polystyrene as core-shell multicomponent nanostructures were successfullysynthesized. The results reveal that polyacrylamideand polystyrene size ranges are 80-140 nm and 10-20 nm, respectively. They have the potential to blockfractures in oil reservoirs to enhanced immobile oilrecovery. Dissolution and micromodel polymer oodingexperiments reveal that the time and sweep e�ciency ofpolyacrylamide increase and energy consumption dur-ing the ooding process diminishes dramatically usingthe novel core-shell nanoparticles. Micromodel oodingexperiments show that using a core-shell structure canreduce usage of polymer by one-third of the initialvalue for obtaining the same recovery factor in classicalpolymer ooding.

References

1. Su, B., Dou, M., Gao, X., Shang, Y. and Gao, C.\Study on seawater nano�ltration softening technologyfor o�shore oil�eld water and polymer ooding", De-salination, 297(30), pp. 30-37 (2012).

2. Sheng, J.J. \Polymer ooding-fundamentals and �eldcases", Enhanced Oil Recovery Field Case Studies,

First Edition, Chapter 3, pp. 63-82, Gulf ProfessionalPublishing, USA (2013).

3. Wang, X., Wang, Zh., Zhou, Y., Xi, X., Li, W., Yang, L.and Wang, X. \Study of the contribution of the mainpollutants in the oil�eld polymer- ooding wastewaterto the critical ux", Desalination, 273(3), pp. 375-385(2011).

4. Jamaloei, B.Y., Kharrat, R. and Asghari, K. \Thein uence of salinity on the viscous instability in viscous-modi�ed low-interfacial tension ow during surfactant-polymer ooding in heavy oil reservoirs", Fuel, 97(174),pp. 174-185 (2012).

5. Zhou, X., Dong, M. and Maini, B. \The dominantmechanism of enhanced heavy oil recovery by chemical ooding in a two-dimensional physical model", Fuel,108(261), pp. 261-268 (2013).

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7. Lira, L.M., Martins, K.A. and Torresi, S.I. \Structuralparameters of polyacrylamide hydrogels obtained by theequilibrium swelling theory", Euro. Poly. J., 45(4), pp.1232-1238 (2009).

Biographies

Yousef Tamsilian is a PhD degree student of Chem-ical Engineering in the Institute of Nanoscience andNanotechnology at Sharif University of Technology,Tehran, Iran. His MS and PhD degree theses wereregarding the experimental and modeling study ofthe rheological behavior of polymeric core-shell nanos-tructures and smart nano uids during chemical EORprocesses. He has more than nine years of academicexperience in the university, and 5 years of professionalindustrial experience in the petroleum and chemicalindustries. He has published more than 30 papers in in-ternational and national journals and conferences, andthree books on the subjects of CFD, thermodynamics,and molecular dynamics. He has also registered twoUS patents and two Iranian patents with EOR prin-ciples. He has a very strong background in the �eldof nano-structured materials, enhanced oil recoveryusing polymer ooding, polymerization engineering,modeling of polymer and chemical processes by theCFD method (OpenFOAM Software) and hydrate for-mation and dissociation in underground porous media.His current research interests lie in the applicationof colloidal and interfacial phenomena to oil recovery,with applications in chemical EOR processes for smartpolymer ooding and surfactant-polymer ooding. Hisearly research work focused on the physico-chemicalinteractions between surfactants, interfaces and poly-mer nanoparticles within multi-phase porous media,and their applications in enhanced oil recovery andwell stimulation. Later, his work focused on the nano-dynamic behavior of multi-component mobility ratios,

1178 Y. Tamsilian and A. Ramazani S.A./Scientia Iranica, Transactions F: Nanotechnology 21 (2014) 1174{1178

wettability alteration, and IFT reduction in oil recoveryprocesses. From this background, his current researchinterests have evolved into two principal themes: 1-Continuum and molecular dynamic modeling and sim-ulation of core-shell nanostructure behavior, and 2-Experimental studies of smart polymer nanoparticlesin porous media.

Ahmad Ramazani S.A. graduated from the Chem-ical Engineering Department of Laval University,Canada, in 1999, and is currently Professor in theDepartment of Chemical and Petroleum Engineering atSharif University of Technology (SUT), Tehran, Iran.His PhD thesis was regarding the modeling of therheological behavior of short �ber �lled viscoelastic uids. He has published more than 300 papers ininternational and national journals and conferencesand has supervised more than 100 master and PhDdegree theses. He has also published three books onHeat Transfer, Rheology, and Numerical Mathematicsand authored several chapters of di�erent books. His

research work is in interdisciplinary subjects mostlyrelating to experimental and theoretical investigationof polymer relating processes and polymer properties,and the ow of polymeric and non-Newtonian uidsin di�erent engineering �elds, including biomedicaland petroleum engineering related media. From 2002-2003, he served as head of the biomedical group andfrom 2003-2008 as head of the polymer engineeringgroup at SUT. He was also executive chair of the 8thInternational Seminar on Polymer Science and Tech-nology held in 2007 and member of the organizing andscienti�c groups of several seminars and conferences.He acts as editorial guest of the Macromolecular Sym-posia Journal Volume, 274, published by Wiley-VCHand currently serves on the editorial board of severalinternational journals. He was invited professor at theEcole Polytechnique de Montreal in Canada in summer2009 where he presented some of his research work forthe second time as invited professor in CREPEC. Heis also chairman and organizer of the ICHEC14, whichwas held at SUT in 2012.