Synthesis of acryloylated starch-g-poly acrylates crosslinked polymer functionalized by emulsified vinyltrimethylsilane derivative as a novel EOR agent for severe polymer flooding strategy

Synthesis of acryloylated starch-g-poly acrylates crosslinked polymer functionalized by emulsified vinyltrimethylsilane derivative as a novel EOR agent for severe polymer flooding strategy

Accepted Manuscript Synthesis of acryloylated starch-g-poly acrylates crosslinked polymer functionalized by emulsified vinyltrimethylsilane derivative...

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Accepted Manuscript Synthesis of acryloylated starch-g-poly acrylates crosslinked polymer functionalized by emulsified vinyltrimethylsilane derivative as a novel EOR agent for severe polymer flooding strategy

A.N. El-hoshoudy PII: DOI: Reference:

S0141-8130(18)34649-X https://doi.org/10.1016/j.ijbiomac.2018.11.056 BIOMAC 10933

To appear in:

International Journal of Biological Macromolecules

Received date: Revised date: Accepted date:

1 September 2018 19 October 2018 11 November 2018

Please cite this article as: A.N. El-hoshoudy , Synthesis of acryloylated starch-g-poly acrylates crosslinked polymer functionalized by emulsified vinyltrimethylsilane derivative as a novel EOR agent for severe polymer flooding strategy. Biomac (2018), https://doi.org/ 10.1016/j.ijbiomac.2018.11.056

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ACCEPTED MANUSCRIPT Synthesis of acryloylated starch-g-poly acrylates crosslinked polymer functionalized by emulsified vinyltrimethylsilane derivative as a novel EOR agent for severe polymer flooding strategy A.N. El-hoshoudy a, b a

Production department, Egyptian Petroleum Research Institute, Naser City, Cairo, Egypt.

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Faculty of Energy and Environmental Engineering, British University in Egypt, Elshorouk City, Cairo, Egypt.

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Corresponding author: A.N. El-hoshoudy, Production department, Egyptian Petroleum Research Institute, Naser City, Cairo, Egypt; postal code 11727; Tel. +201143776927; Fax: (+202)22747433, e-mail address; [email protected] Abstract

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Starch is a natural polysaccharide with reasonable biodegradable properties, which grafted with vinyl monomers through different initiators to be applied in enhanced oil recovery (EOR) techniques.

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Several authors stated about starch modification through copolymerization and grafting of different monomers, however, these derivatives have some drawbacks related to bacterial biodegradation, ionic and thermal aging under severe reservoir conditions. The present study reported the preparation of grafted

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acryloylated starch with acrylamide/acrylic acid monomers and vinyltrimethylsilane through initiation

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copolymerization with the aid of quaternary ammonium-based surfmer. The chemical analysis generated by various spectroscopic analysis comprising IR, NMR, meanwhile particles distribution estimated through DLS. The embedded silica through a polymer matrix photographed by TEM, SEM and EDX

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elementary analysis, and the thermal effect determined by thermal gravimetric analysis. The rheological analysis estimated relative to shear degradation, ionic strength, and thermal aging at imitated reservoir

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environment. Flooding runs performed on linear non-consolidated sandstone model at nearly practical field conditions, where the displaced oil by polymer effect was recorded through the volumetric collector.

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The flooding tests designate that the synthesized starch-g-copolymer is prospering for chemical flooding applications under severe reservoir conditions, and achieve a recovery factor of 46% Sor.

Keywords: Biopolymers; acryloylated starch; chemical flooding. 1

ACCEPTED MANUSCRIPT 1. Introduction

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Starch is an abundant biological polysaccharide contain glucose units (glucose, amylose, and amylopectin) connected by α-D-glycosidic linkage[1]. Due to its low cost and eco-friendly environmental criteria[2], the starch used for many industrial purposes including pharmaceuticals, paper industry and chemical flooding in oil industry[1]. Nowadays, chemical displacement through porous media of petroleum reservoirs acquires incremental interest on the field scale owing to continued energy demand[3, 4]. Implementation of modified bio-polymers in chemical flooding will rise up and overcome that of hydrolyzed polyacrylamides due to higher thickening and viscosity of their solutions [5], resistance to thermal and acidic degradation, water shutoff ability, and their adsorption capability on reservoir rock[4], so it can block high permeable zones and control mobility ratio[6, 7]. These modifications as reported in the literature[4] comprise vinyl monomers copolymerization with the aid of crosslinkers and watersoluble initiators[8] to prepare three dimensional hydrogel with higher water absorption capacity [9, 10], which in turn can be utilized in oil field processing as a flooding and a profile modifying agents[11]. Different researchers stated about grafting of starch through initiation polymerization with different vinyl monomers including ethyl methacrylate, methacrylic acid, 1-vinyl-2-pyrrolidone, acrylic acid, acrylamide, acrylonitrile, 2-acrylamido-2-methyl-1-propane-sulfonic acid, and 2-hydroxy-3-methylacrylamide propyl trimethyl ammonium chloride and acrylamide as stated elsewhere[11]. Grafting of starch via vinyl monomers form crosslinked starch characterized by reduced biological degradation, improved shear strength of the solution and increased temperature resistance rather than virgin starch[12]. On an industrial scale, native starch, as well as its derivatives, have some limitations associated with thermal and biological degradation[11], which in turn adversely affect the flooding process in EOR operations. The current work deals with the synthesis of acryloylated starch to introduce vinyl double bond on the starch architecture [13], which then used for further grafting reaction with acrylamide/acrylic acid monomers in presence of vinyltrimethylsilane through typical initiation copolymerization. Starch grafting with acrylamide[14] and acrylic acid[15] enrich water absorption capacity [16] due to the presence of high content of carboxyl groups[17], moreover, dispersion of silica particles into polymer architecture boost system strengthening and salt tolerance due to their distinct properties[18, 19]. Flooding displacement generated via linear sandpacked design [3], and oil recovery calculated according to the discharged oil amount.

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2. Experimental 2.1 Materials

Marketable cornstarch; N,N-dimethyl acetamide, DMAc, ≥95%); LiCl, (ACS reagent); Pyridine (analytical grade); KOH spheres, reagent grade; methanol ultra-pure; acetone≥97% ; chloroform ≥97%; acryloyl chloride (97%,); Acrylamide (AM) (≥97%); Acrylic acid (AA, 99%); N,N-methylene-bis acrylamide ≥99.5%; vinyltrimethylsilane; Potassium persulfate (KPS ≥99 %). All chemicals purchased from Merck except starch. Acryloylated starch(As) synthesized according to Fang et al procedure [13]. The spectroscopic analysis and structure determination of AS are reported elsewhere[9, 13]; N, Ndimethyl-N-(4-vinyl benzyl) hexadecane-1-aminium chloride (DMVH) synthesized as reported in our previous literature[20] and act as a surfmer throughout the emulsion polymerization. 2.2 Characterization and Equipment

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Thermal stability measured on TGA-instrument SDT Q600 under nitrogen flooding at 50 cc/min. TEM photographing and EDX elementary analysis performed on Japanese JEOL HR-TEM microscope, the samples distributed in methyl alcohol and dipped on a copper grid. SEM analysis generated on Quanta 450-scanning electron microscope. 1H-NMR spectra generated with a Bruker EMX-420 MHz after collecting 32 scan cycle, using D2O as a solvent. IR peaks generated on American FTS-3000 spectrophotometer in the range of 400–4000 cm-1 using KBr tablets for sample mixing. Zetasizer 6.32 used for monitoring distribution of particles size at a scattering angle 90o and 25oC. viscoelastic and rheological properties measured on Brookfield cone-plate rheometer[21] provided with LVSC4-25 adapter spindle, cone/plate geometry (diameter=60 mm, angle=1o, plate-to-plate gap=0.104 mm) [20]. Solutions viscosity estimated relevant to the shearing action, ionic strength, and thermal effect [3]. Polymer aging assessed by keeping thin polymer films in an oven at aging temperatures of (50, 75, 100 °C) for seven days then analyzed by Raman spectroscopy.

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2.3 Synthesis of starch grafted copolymer: In a three-necked 250 ml Erlenmeyer flask furnished with a condenser, nitrogen source, and thermometer. 3.05g (DMVH) surfmer completely dissolved in 100 cc of distilled water. Add 6.2g acryloylated starch (AS) and stir at low rpm for 15 minutes until complete dissolution. To this mixture, add 0.15g of vinyltrimethylsilane with continuous stirring under nitrogen flooding environment. Add (15g AM / 15.2 g AA; 1:1 molar ratio) and adjust the temperature at 60°C, add 0.3 g of N, N-methylenebisacrylamide, 0.5 g of KPS initiator. The polymerization reaction continues for 4 hours. After reaction cooling, the formed gel precipitated by acetone (4×50ml) and subjected to Soxhlet extraction with chloroform for 36 hrs at 60°C, then grounded and kept on silica gel bed. Reaction steps are illustrated in scheme 1. The same batch prepared with the same amounts excluding the addition of acryloylated starch (AS).

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Scheme 1: Graft copolymerization steps

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2.4 Sandstone modeling and flooding

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A series of linear flooding processes were performed on linear sandpack assembly, where the flooding circumstances and model characteristics stated elsewhere[3]. Sand washed in compliance with the standard cleaning procedure [22] then saturated with brine for 24 hours followed by oil injection. After that, the brine was injected to displace the oil until 97 % water cut was reached[23, 24]. The starchg-copolymer solution with various slug concentrations was displaced at imitated reservoir temperature of 70oC, followed by brine displacing until discharged oil terminated in the discharge[25]. Oil recovery factor calculated based on displaced oil volume during polymer solution flooding. 3. Results and interpretations 3.1 Characterization of chemical structure IR bands and 1H-NMR of native starch and starch-g-copolymer as displayed in Figures 1-3 respectively.

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Starch-g-copolymer

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Figure 1: Infrared spectra of native starch and starch-g-copolymer

Figure 2: 1H-NMR of native starch

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Figure 3: 1H-NMR of starch-g-copolymer

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TGA-thermogram of the native starch as stated in the literature [7]shows triple decomposition regimes at 98, 254, and 354oC, where the residual mass reach 11.6% at 600oC[26]. TGA and DSC curve of the synthesized starch-g-copolymer as depicted in Figure 4, revealed three-thermal decomposition regions. The first regime at 22-250oC with 17% weight loss corresponding to the evaporation of hygroscopic moisture [27, 28]. The second stage at 250–420oC with 65% weight loss corresponding to degradation of the polymer chains and hydrophobic side chains decomposition [3, 29]. Above 420oC, occur complete degradation with 24% residual mass at 600oC. The displayed composite thermal stability relative to starch resorted to the diffusion of hydrophilic nano silica with the high surface area and high modulus into polymer architecture, which in turn enhance polymer strengthening properties [18, 19].

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Figure 4: TGA of starch-g-copolymer

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TEM graphing as signified in Figure 5 shows spherical starch capsules with the size of 10µm (Figure 5a). The synthesized starch-g-copolymer (Figure 5b) shows dark spots of nanosilica particles distributed in light-colored polymer architecture (i.e. core-shell structure). These silica particles diminish particles accumulation, which in turn condense the synthesized latex volume [30], in addition to improving polymer resistance to thermal and ionic degradation during the flooding process. (b) Starch-g-copolymer

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(a) Native Starch

Figure 5: TEM photographing Moreover, Energy dispersive X-ray analysis (EDX) and SEM analysis are provided in Figure 6a & b respectively. SEM analysis exhibit the morphology of starch particles with dark silica spots scattered in 7

ACCEPTED MANUSCRIPT starch-g-copolymer matrix. EDX analysis show silica and oxygen peaks, while peaks at 8-10 Kev resort to Cu and carbon of the grid. The silica load in this sample reach to 17.5 wt%. Both TEM, SEM, and EDX analyses prove that silica embedded through the prepared starch-g-copolymer.

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Figure 6: (a) EDX elementary analysis, (b) SEM analysis

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Dynamic light scattering (DLS) as shown in Figure 7 reveals that the size of starch particles reach 8000 nm, while the size of starch-g-copolymer reach 450-350 nm and concentrated around 400 nm. This condensing size behavior attributed to; 1)enclosure of highly reactive nanosilica with high surface area, so function as active sites for polymerization proceeding, which in turn reduce particles agglomeration and aggregation and delay macromolecules propagation in case of starch-g-copolymer rather than native starch due to nanoscale nucleation effect [3, 31-33]. Silica act as effective nanoscale nucleating agents which diminish the size of spherulites as reported by Li et al, 2018 [34]; 2)gelation effect during polymerization reaction as well as the introduction of charges on the surface of modified starch, since acrylic acid is highly negative charged; 3)the crosslinking agent considerably decreases the particles dimension and tapered the size distribution range[30]. The overall properties of modified starch and virgin starch can be summarized as indicated in Table 1.

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Figure 7: DLS of native starch and starch-g-copolymer

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(OH-) and (-CH) stretching [35, 36]

1670 cm-1

(CO) stretching

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stretching vibration of (OH-) &(C-O) groups of acrylic acid

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IR bands

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Table 1: Summary of the overall properties of native starch and starch-g-copolymer.

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(OH-) bending distortion [36]

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asymmetric , symmetric stretching vibrations (Si-O-Si) in the silica hybrid, respectively [3, 37] which designate the polymerization of

ACCEPTED MANUSCRIPT vinyltrimethylsilane through polymer backbone chains. Moreover, the absence of the distinguishing band of vinyl double bond reveals that polymerization generated fruitfully. Chemical shift (δ) ppm

Chemical shift (δ) ppm

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3.9-3.0 (m, 10H, -CHOH) anhydrous-glucose moieties [36]

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0.89 (t, 3H, -CH2-CH3-) terminal –CH3 group

4.8-4.2 (t, 7H, OH-CH- terminal OH-groups)

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0.62 (t, 2H,-CH2-CH2-Si(CH3)3)

6.72 (s, 2H, NH2-C=O) of acrylamide monomer

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3.8-3.9 (m, 4H, OH-CH2-CHterminal CH2-group pendant from glucose ring)

7.35(t, 2H, -NH-CH2-NH-) of N,Nmethylenebisacrylamide. The disappearance of the chemical shift at δ (ppm) = 7.1 which assigned to methylene double bond (-CH=CH2) indicates full monomers polymerization. Chemical shift at δ (ppm) = 3.52-4.25 assigned to starch peaks.

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3.2 Rheological and solution characteristics Crosslinked polymers swell in aqueous solutions as their solubility is pH-dependent [38]. At high PH, COOH- group of acrylic acid diffuse in the polymer matrix as COO- ions, so increase swelling [39]. In the

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ACCEPTED MANUSCRIPT present study, pH- adjusted at (13-14) by potassium hydroxide pellets to increase ionic shielding on the polymer chain and increase its solubility. 3.2.1 Viscoelastic properties

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Viscoelasticity carried out to measure the dynamic moduli (elastic moduli (G′) which estimate the reversibly stored deformation energy, while viscous moduli (G″) estimate the irreversibly dissipated energy through one cycle) ranged from 1 to 100 rad s-1 of the angular frequency (ω) at constant strain of 5% [21, 40], and temperature of 100 °C as shown in Figure 8. It is apparent that G′ modulus was higher than the G″ modulus, so the polymer exhibit a typical elastic gel-like performance [40]. This enhanced viscoelastic properties owing to the insertion of nanosilica particles, which act as a physical crosslinker and promote the strengthening of the copolymer hybrid network structure, so retard molecular chains disruption [21, 41]. This viscoelastic properties enhancement ascertains a strong bonding between silica nanoparticles and polymer molecular chains [21].

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Figure 8: Viscoelastic behavior, elastic modulus, G′, and viscous modulus, G″ versus angular frequency (ω)

3.2.2 Shear thinning effect[42]: shear stress evaluated as a function of shearing rate as displayed in Figure 9. The synthesized starch-g-copolymer obey behavior of the non-Newtonian fluid, since shear stress increase by shear rate increase, consequently preferred as a flooding candidate[43], and could be regarded as EOR nominees for chemical displacement objects [3], as it will mitigate forcing and pump action through the wellhead. This performance resort to the ongoing decline of a molecular tangling at an incremental shearing action[44]. Shear stress (  ,Pa) related to shear rate (γ,s-1) by the power law equation[45].

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ACCEPTED MANUSCRIPT   K n

(Eq.1)

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Where (k) is the flow consistency coefficient (Pa. s-n) and (n) is the flow behavior index [3]. For pseudoplastic solutions, (n) is lesser than or equal unity (n ≤1). After curve fitting, the calculated (n & K) values equal to 10.019 and 0.1083 respectively. This confirms that starch-g-copolymer is a pseudoplastic fluid, which is preferred for chemical flooding tasks [3, 43]. The non-fitted curve represents the actual measured data by viscometer, where the data non-smoothing may be explained on the basis of; during the rotation of the spindle especially at low shear rates, it may hit with an agglomerated moiety of the hydrogel which results in higher false readings, so we resort to curve fitting through the power law model.

Non-fitted curve Fitted curve

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Figure 9: Plot of shear rate versus shear stress

3.2.3 Salinity effect: salt effect assessed at different shearing rates and room temperature by monitoring viscosity of starch-g-copolymer solutions dissolved in different saline solutions. The ionic constituents of the saline solutions summarized in Table 2. It is observed that the viscosity decreases slightly with salt concentration increase from 50,000 ppm to 80,000 ppm, as shown in Figure 10. This reasonable salinity fighting behavior resort to; 1) increasing of hydrodynamic volumes of the prepared polymer by increasing ionic strength, consequently polymer chains resist deformation effect of divalent cations in the reservoir environment [3, 25]; 2) the presence of N+-atom in imidazolium ring enhances ionic interchangeability, so repel with divalent cations and mitigate its effect on polymer degradation [3, 20, 46]; 3) silica particles act as crosslinking agents which give rise to stiff dimensional network, so boost the solution viscosity [47].

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ACCEPTED MANUSCRIPT Table 2: concentration of ions used in salinity investigation. Solubilized ions

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Mg+2-ion (MgCl2.6H2O), mgL-1

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SO4-2-ion (Na2SO4), mgL-1

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Figure 10: Plot of viscosity versus different salinity conditions at room temperature and different shearing rates

3.2.4 Thermal tolerance: polymer displacement performed at harsh reservoir environment of high temperature and severe ionic strength, so thermal degradation appraised at various shearing rates and salinity of 80,000 ppm as exhibited in Figure 11. The viscosity continues to decreases with increasing temperature and shear effect. Despite these harsh circumstances, the viscosity decrease slightly. This behavior resort to; 1) gelation and solidification of the starch as well as improvement of intermolecular 13

ACCEPTED MANUSCRIPT hydrophobic association by increasing temperature, so solution viscosity increase[3, 42]; 2) insertion of nanosilica particles into polymer chains through copolymerization of trimethyl(vinyl)silane enhances polymer strengthening and thermal resistance owing to high moduli and reactivity [3, 18-20]. T=25oC T=50oC T=75oC

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Figure 11: Thermal effect relative to shearing action at salinity=80,000ppm

3.2.5 Polymer aging

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EOR polymers suffer from decomposition and degradation due to thermal aging at high reservoir temperature. In this section, polymer aging evaluated by Raman spectroscopy after long-term aging of

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polymer films as indicated in Figure 12. Different deformation modes can be obtained from C–H2, and C– H moieties using Raman spectroscopy. Therefore, it is possible to monitor the stability of the polymer after exposure to different temperatures (50, 75 and 100 °C) for 7 days. The Raman peak at 1329 cm–1

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resort to –C–CH in polyacrylamide which showed almost the same intensity for polymer aged at 50 and 75 °C. However, this band showed a relatively low intensity for polyacrylamide aged at 100 °C, suggesting low polymer conversion to unsaturated species. Due to the hydrophilic character and participation of the amide group in the hydrogen bonding since its vibration occurs near the bending mode of water, the amide group is strongly affected by aging. The Raman spectrum shows the peak at 1078 cm–1 owing to the rocking vibrations of –NH2 group, and indicates a little reduction in intensity for polymers aged at 100 °C compared to other temperatures [48].

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Figure 12: Raman spectra of polymer samples

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3.3 Displacement runs and recovery assessment

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Polymer flooding serves to control mobility ratio and improve swept competence [49]. Displacement tests generated on the unconsolidated sandpack prototype as stated in previous literature [3] at 70oC with different concentrations (0.5, 1.0, 1.5and 2.0 g L-1) of starch-g-copolymer and well-established polyacrylamide copolymer before grafting of acryloylated starch as shown in Figures 13 & 14 respectively. Table 3 summarize displacement conditions and characteristics of the sandpack model. Recovery factor demonstrated relative to residual oil saturation (Sor). The results show that the recovered oil amount increases by increasing polymer slug concentration and reaches 46% of residual oil at 1.5g/L slug concentration of starch-g-copolymer as shown in Figure 13. The nature significance of this enhanced oil recovery achieved through flooding with starch-g-copolymer resort to; 1) increased adsorbed amount of highly reactive hydrophilic nanosilica particles on the sandstone surface, so alter rock wetting criteria, improves mechanical and shearing properties, and improves sweeping effectiveness [3, 50, 51]; 2) gelling action of starch increases with dose increase so, viscosity of water phase increase and reduces mobility fraction, consequently improves sweeping effectiveness and increases the oil recovery factor. At concentration above 1.5g/L, recovered oil amount begins to decrease, this may resort to the formation of an emulsion by increasing of surfmer effect which hinders oil flow and resulting in high pressure drops across the packed model, consequently the relative permeability of sand to oil reduced significantly so, oil recovery decrease[3].

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Figure 13: Oil recovery factor in case of starch-g-copolymer

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In case of the base polyacrylamide copolymer, the recovered oil amount reaches its maximum value ~38% of residual oil saturation at slug concentration of 1.5g/L as shown in Figure 14, then begin to decrease. This behavior is in great compliance with that we previously reported in our previous literature[3], and resort to emulsifying of the oil by increasing concentration of surface active agent (surfmer) by dose increase, so recovered oil amount decrease after certain concentration.

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Figure 14: Oil recovery factor in case of base polyacrylamide copolymer

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It is apparent from figures 13 and 14 that the recovered oil amount in case of starch-g-copolymer is higher than that of base polyacrylamide, this behavior confirms that grafting of the starch on polyacrylamide improves oil recovery factor, due to starch gelling effect which boasts the sweeping efficiency of the aqueous phase, retard oil breakthrough so improves oil recovery.

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Table 3: Displacement and prototype criteria. Value 300 1368 21.9 200 33.3 16.6 66.6 70.0 1500.0 10.0 5.0

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Parameters Pore volume (PV), cc Bulk volume(Vb),cc Porosity (%) Injected oil volume, cc Initial water saturation(SWi), % Residual oil saturation (Sor), % Initial oil saturation (Soi), % Displacement temperature, °C Displacement Pressure, psi Brine injection rate, cc/h Oil phase injection rate, cc/h

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ACCEPTED MANUSCRIPT Conclusion

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Acryloylated starch successfully grafted on poly (acrylic-co-acrylamide) polymer using KPS initiator during typical emulsion polymerization technique in presence of the quaternary ammoniumbased surface-active agent and vinyltrimethylsilne derivative. The polymerization carried out through surfmer vicinity and on the silica surface, which reduces growing latex size and dimensions. Rheology of the displacing fluids relative to thermal and ionic response assessed at hard reservoir environment. The results prove the capability of the starch-g-copolymer to withstand reservoir environment. Displacement runs generated on linear sand packing using starch-g-copolymer and base polyacrylamide copolymer. The maximum recovery factor reaches 46% & 38%Sor in case of starch-g-copolymer and base polyacrylamide respectively, which is a flourishing trend in the utilization of modified starch derivatives as natural and low-cost biopolymers in chemical flooding projects. The prepared polymer is expected to modify sandstone wetness from oil-wet to water-wet owing to the occurrence of cationic nitrogen-group on surfmer which attracted to the negatively charged sand surface at pH= 6-9.

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