The synergistic collaboration between regenerated cellulose and

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The synergistic collaboration between regenerated cellulose and surfactant to stabilize O/W emulsions for enhancing oil recovery Zhe Li, Baojun Bai, Derong Xu, Ziyu Meng, Tao Ma, Congbo Gou, Kai Gao, Renxian Sun, Hairong Wu, Jirui Hou, and Wanli Kang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02999 • Publication Date (Web): 21 Dec 2018 Downloaded from http://pubs.acs.org on December 22, 2018

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The synergistic collaboration between regenerated cellulose and surfactant

2

to stabilize O/W emulsions for enhancing oil recovery

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Zhe Lia, Baojun Baic,d,*, Derong Xua, Ziyu Menga, Tao Maa, Congbo Goua, Kai Gaoa,

4

Renxian Suna, Hairong Wua,*, Jirui Houa, Wanli Kanga,b,* a

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Research Institute of Enhanced Oil Recovery, China University of Petroleum

6

(Beijing), Beijing 102249, PR China b

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School of Petroleum Engineering, China University of Petroleum (East China),

8 9

Qingdao 266580, PR China c

China University of Petroleum-Beijing At Karamay, Karamay, Xinjiang 834000, PR

10 11

China d

Department of Geosciences and Geological and Petroleum Engineering, Missouri

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University of Science and Technology, Rolla, Missouri 65401, United States

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* E-mail: [email protected], [email protected], [email protected]

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Abstract

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A stable emulsion can play an important role in displacing oil or controlling

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reservoir conformance for enhanced oil recovery (EOR) projects. In this work, visual

17

inspection, multiple-light scattering, interfacial tension (IFT), and rheology were used

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to investigate the synergistic effects of regenerated cellulose and surfactant on

19

oil-in-water emulsions stability and their efficiency in EOR. The results show that

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adding regenerated cellulose can significantly increase the stability of a surfactant

21

emulsion, while decreasing the diameter, coalescence and floatation of oil droplets. 1

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This can be attributed to the synergistic interactions between cellulose and surfactant,

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which enable them to form a tighter interface layer and slightly reduce the O/W IFTs.

3

Moreover, in comparison with the surfactant-only systems, the surfactant-cellulose

4

systems exhibit higher viscoelasticity of the continuous phase, as well as better

5

shearing tolerance and self-recovery of emulsions. Ultimately, the microscopic oil

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displacement experiments demonstrate that the system can efficiently decrease the

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residual oil saturation after water flooding. These impressive performances make this

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blended system ideal for use in the chemical flooding process for EOR.

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Keywords: Regenerated cellulose; Alkyl polyglucoside; Synergistic interaction;

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Emulsion stability; Enhanced oil recovery

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1. Introduction

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As we all know, more than half of the reserved oil remains unproduced in lots of

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oilfields around the world at the end of natural flow (primary recovery) and water

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flooding (secondary recovery) methods.1 EOR (Enhanced oil recovery), can

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effectively improve the oil recovery by enhancing the microscopic displacement

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efficiency or the macroscopic sweep efficiency.2 Chemical flooding is an efficient

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EOR method, including surfactant, alkali, polymer, and their combination flooding,

18

etc.3-7

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Numerous laboratory studies and pilot applications have shown that EOR

20

efficiency can be improved with more stable emulsions in produced fluids,8-11 and

21

emulsions can increase the displacement efficiency and/or sweep efficiency through 2


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the transportation and/or entrapment mechanisms.12,

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model for simulating the physicochemical emulsion phenomena in ASP flooding, and

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the results showed that sufficient oil emulsification could significantly improve the

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in-situ oil displacement efficiency. Chen15 also found that the oil-washing ratio could

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be improved by enhancing the emulsification ability. Furthermore, French16 has used

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emulsions for mobility control during thermal recovery, elucidating that the formation

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of emulsions could block pores in steam flooding. Therefore, it is necessary to

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enhance the emulsification ability of an oil displacement system, as well as the

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stability of the emulsions, during the injection and migration processes underground.17

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Currently, Pickering emulsions are ubiquitous and have become common in

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applications due to their advantages in stability as compared to surfactant

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emulsions.18-22 The addition of particles, including oxides, silica, polymer lattices,

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clay, fat crystals, alumina and carbon,

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enhances their efficiency as stabilizers.

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improved via the synergistic effects between the surfactant solutions and particles at

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both the bulk phase and their interface.

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biomass on earth, cellulose derivatives have been found to exhibit an amphiphilic

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performance and subsequently form stable Pickering emulsions.23, 30-33 Additionally,

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Yin demonstrated that the synergism between cellulose and surfactant could

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significantly stabilize the foam by increasing the film thickness and the drainage of

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obstructed liquid.34 They consistently maintain respectable behaviors under high

23-25

13

Lei14 developed a numerical

to surfactant solutions, or vice versa,

26, 27

28, 29

The properties of the emulsions are

Surprisingly, as the most abundant

3


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temperature, salinity or pH conditions.35-38 Although native cellulose usually is not

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considered to be efficient emulsion stabilizer due to its highly crystalline structure and

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insolubility in water, many researchers have found that chemical modifications can

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produce cellulose derivatives for various applications, including films, microspheres,

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fibers, hydrogels and emulsions.39-41 Such derivatives have been applied widely in the

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packaging, separation, textile and biomedical fields.42-49 In some of the more recent

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studies, cellulose can be easily dissolved and regenerated for stabilizing the O/W

8

emulsions through the formation of cellulose II and amorphous cellulose.50 51

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Our previous work preliminarily verified the potential of regenerated cellulose in

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stabilizing O/W Pickering emulsions. Thus inspired, we now consider whether the

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addition of regenerated cellulose can efficiently increase the stability of the surfactant

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emulsions. To this purpose, the synergistic collaboration of surfactant and regenerated

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cellulose for emulsions stability are first investigated, and the droplet-sized variations

14

and migrations of the emulsions are subsequently characterized using the Turbiscan

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Lab Expert Stabilizer. Then, the interactions between commercially available

16

regenerated

17

viscoelasticity of the emulsions are separately explored through the interfacial tension

18

(IFT) and rheology methods. This study states a new prospect and idea for relevant

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works on surfactant emulsions, as well as guidance for EOR applications in

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reservoirs.

cellulose

and

alkyl

polyglucoside

surfactant

4


(APG1214)

and

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2. Materials and methods

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2.1. Materials

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The chemical structure of APG1214 (alkyl polyglucoside, effective content =

4

50%, Jiangsu Haian Chemical Co., Ltd) is shown in Fig. 1a (n=1.3-1.5, R=C12-14).

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And the chemical structure of regenerated cellulose (crystallinity index = 24.41%,

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Hangzhou Yeuha Technology Co., Ltd) is shown in Fig. 1b. The crude oil and

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formation water were supplied by the Changqing Oilfield (China). Tab. 1 and 2

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provide the properties of the crude oil and formation water, respectively. All aqueous

9

solutions were prepared by Milli-Q water.

10 11

(a)

12 13 14 15

(b) Fig. 1. Structures of (a) APG1214 and (b) regenerated cellulose. Tab. 1. Properties of the crude oil Items

Values

Saturate (%)

80.31

Aromatics (%)

15.43 5


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Resin (%)

4.25

Asphaltene (%)

0.01

Density at 30 °C (g/cm3)

0.845

Viscosity at 30 °C (mPa·s)

7.6

Acid value (KOH mg/g) 1

Tab. 2. Properties of the formation water Ion Concentration, mg/L

2

0.07

K+/Na+ Ca2+ Mg2+ SO42- CO32- HCO31519

29

27

7

100

2324

Cl-

Total

994

5000

2.2. Preparation of the emulsion

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First, 1% and 0.5% w/v regenerated cellulose solutions were prepared through

4

the dilution of 2.5% w/v solution as described in our previous work.52 APG1214 was

5

subsequently dissolved into the chemical solution and immediately transferred into a

6

plastic tube (0.4% w/v concentration was selected from previous work).53 Then, the

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emulsions were prepared at 45 ˚C with 7:3 of water/oil volume ratio using the IKA

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T18 homogenizer (IKA, Germany) for 3 min at 5000 rpm. After that, the dewatering

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rate and phase behavior of the emulsions were tested through the visual inspection

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over the course of 120 min at 45 ˚C.

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2.3. Visualization of emulsion droplets by optical microscopy

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XSJ-2 optical microscope (Chongqing Optical Instrument Corp., China) was

13

used to observe the visualization of emulsions droplets. Moreover, laser particle size

14

analyzer (Jinan Runzhi Technology Co., Ltd., China) was also used to measure size

15

distribution of the emulsions droplets at room temperature. 6


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2.4. Multiple-light scattering measurement

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Meanwhile, the size variations and migrations of the emulsion droplets were also

3

measured by a Turbiscan Lab Expert Stabilizer (Formulation, France) through

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backscattering (BS) at a temperature of 45 ˚C.52 Due to the opacity of emulsions and

5

absence of transmission light, the obtained spectra of BS light at different heights can

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reflect the characteristics of oil droplets for variation, migration or growth.

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2.5. FTIR analysis

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The chemical properties were studied using Fourier transform infrared

9

spectroscopy (FTIR). The lyophilized sample was put into a Nicolet Magna 560 FTIR

10

spectrophotometer (Thermo Fisher Scientific, USA) to obtain the FTIR spectrum with

11

a 0.35 cm-1 resolution and 4000-500 cm-1 wavenumbers. The ratio of 1/100

12

(sample/KBr) was applied in KBr disk method.

13

2.5. IFT measurement

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The TX-500C interfacial tensiometer (Bowing Industry Corp., USA) was used to

15

determine the IFT between chemical solution and crude oil at 45 ˚C.

16

2.6. Scanning electron microscopy (SEM)

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The microstructures of the regenerated cellulose were observed using a Hitachi

18

SU8010 SEM (Hitachi Corp., Japan) after the freeze-drying process for 48 h at -40 ˚C.

19

SEM images were taken at an accelerating voltage of 20 KV.

20

2.7. Rheology measurements

21

The rheological properties of the continuous phase were first measured using a 7


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Physica MCR301 Rheometer (Anton Paar, Austria) with the cone plate (diameter =

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49.959 mm). Moreover, the three-phase method was also used to measure the

3

rheological behaviors of the emulsions.4 The linear viscoelastic region was first

4

confirmed to carry out the following rheological tests.

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2.8. Microscopic oil displacement experiments

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An etched glass micromodel (8 cm× 8 cm×0.6 cm) was assembled and used in

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the microscopic displacement experiments, as shown in Fig. 2. The formation water

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and crude oil was first injected to saturate the micromodel. Then, water displacing

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was primarily used until the 98% water cut in 0.1 mL/min flow rate. The chemical

10

solutions were subsequently injected by 0.6 PV at the same rate (0.1 mL/min). The

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flow behaviors were characterized and analyzed using an imaging collection system.

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All experiments were conducted under ambient conditions.

13 14

Fig. 2. Schematic of the microscopic oil displacement experiment.

8


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3. Results and discussion

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3.1.

3

emulsions

Stability

of

the

regenerated

cellulose-surfactant

4

To identify the synergistic mechanisms of regenerated cellulose and surfactant,

5

the dewatering rate and appearance of the freshly prepared emulsions with various

6

concentrations of APG1214 and cellulose are first investigated and shown in Fig. 3. In

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surfactant-only and surfactant+0.25% cellulose emulsions, the freshly prepared

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emulsions almost broke down at 2 h after preparation. Adding the 0.5% concentration

9

cellulose decreased the dewatering rate (2 h) by more than half compared with the

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APG-only emulsion, and continuously decreased it to 17% at 1.0% regenerated

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cellulose. Moreover, the dewatering rate of 0.4% surfactant + 1.0% cellulose system

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is also lower than that of 1.0% cellulose-only system, which has been investigated in

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our previous study.52 These results suggest that the synergistic collaboration between

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regenerated cellulose and surfactant can significantly enhance the stability of

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emulsions. APG1214-cellulose solutions can efficiently emulsify the crude oil and

16

remain stable during the migration process underground via the synergism between

17

the regenerated cellulose and surfactant, eventually enhancing the oil recovery.

9


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1 2

Fig. 3. Dewatering rate, as a function of aging time and appearance (120 min), of

3

various emulsions.

4

3.2. Droplet size variation and migration of emulsions

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According to Stokes’ law, small droplet sizes can help to stabilize an emulsion;

6

therefore, droplet morphology and size distribution were characterized for further

7

investigation of the emulsion’s stability. Fig. 4 shows the optical images and droplet

8

size distributions of the crude oil emulsions stabilized by the APG1214 and

9

regenerated cellulose immediately after preparation. As shown in Fig. 4a, 4b and 4c, it

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can be found that the droplet size of the O/W emulsions decreased by adding

11

regenerated cellulose to the surfactant solution. Due to the increased time available

12

for droplet flocculation, aggregation and floatation, the emulsion with smaller droplets

13

exhibited higher stability.

14

Fig. 4 also depicts that both the average diameter and the property variations of

15

emulsion droplets decreased by adding regenerated cellulose. This decrease can be 10


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attributed to the fact that cellulose can construct the network structures, and APG1214

2

can also adsorb onto the cellulose particles via hydrogen bonds. Meanwhile, for two

3

droplets of similar size, the Ostwald ripening can weaken as the droplet size variation

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decreases. Then, the demulsification process and phase separation are relatively

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weakened, resulting in the higher stability of cellulose-surfactant Pickering O/W

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emulsions.

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Fig. 4. Optical images (insets a, b and c) and droplet size distributions of O/W

9

emulsions.

11


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1 2

Fig. 5. Backscattering spectra of emulsions stabilized by cellulose-APG1214 system

3

with various regenerated cellulose concentrations (a: 0%; b: 0.5%; c: 1.0%) and an

4

APG1214 concentration of 0.4% w/v.

5

As shown in Fig. 5, the ΔBS spectra were used to determine the dynamic 12


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stability for different emulsions. For the emulsion stabilized by 0.4% APG1214, a

2

dramatic change was observed within 2 h, and a decrease of the ΔBS intensity below

3

25 mm resulted in reaching 10% (Fig. 5a), indicating obvious droplet growth and

4

migration in the emulsion system. In the emulsion systems to which 0.5% and 1.0%

5

regenerated cellulose was added, the decrease of the ΔBS intensity was well deferred,

6

and its relevant range of height also decreased to 15 mm and 10 mm, respectively

7

(Fig. 5b and 5c), illustrating a significant weakening of the demulsification process.

8

Additionally, higher concentrations of cellulose can cause the ΔBS intensity in the

9

emulsion phase to increase even more significantly. This is attributed to the floatation

10

of droplets from the bottom phase and the decreased coalescence of droplets in the

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emulsion phase, which further indicates the stabilization of regenerated cellulose.

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3.3. Stability mechanism of regenerated cellulose-surfactant

13

emulsions

14

3.3.1 Oil-water interfacial tension

15

The surface of regenerated cellulose molecules possesses lots of free-hydroxyl,

16

and APG molecules also contain a certain amount of free-hydroxyl. Therefore, at a

17

proper concentration, regenerated cellulose can interact with APG and then form

18

hydrogen bonds in an aqueous solution, resulting in a higher adsorption of surfactant

19

and cellulose onto the O/W interface and a better stability of the emulsion. The IFT

20

spectrum between different cellulose-surfactant systems and crude oil is shown in Fig.

21

6. The IFT decreased and then increased slightly as the concentration of regenerated 13


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1

cellulose increased. Obviously, the increase in the IFT is due to competitive

2

adsorption between APG1214 and regenerated cellulose onto the O/W interface

3

occurring at a high concentration. In summary, the addition of cellulose can slightly

4

decrease the IFT to a certain value. Accordingly, it can be concluded that the low IFT

5

is not the key factor in stabilizing emulsions. Furthermore, an optimum concentration

6

of regenerated cellulose and a minimum IFT value should be established for different

7

kinds of crude oil.

8 9 10

Fig. 6. Oil/water IFTs for different concentrations of regenerated cellulose, at an APG1214 concentration of 0.4% w/v.

11

In order to further identify the hydrogen bonds between APG and cellulose, the

12

FTIR spectrum of a 0.4% APG1214+ 1.0% cellulose system is shown in Fig. 7. The

13

system exhibited obvious -OH and -CH2- stretching at 3450 cm-1 and 2900 cm-1 like

14

the other one.51 The C-H stretching and C-O-C bending were also found at 1050 cm-1 14


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and 1170-1082 cm-1, respectively. The bending of OH groups in the blended system

2

was moved to a low wavenumber from the range of 3650-3600 cm-1, which represents

3

the free-OH groups. This can reflect that surfactant molecules form the inter-OH

4

groups (hydrogen bonds) with cellulose molecules.

5 6

Fig. 7. FTIR spectrum of 0.4% APG1214+ 1.0% cellulose.

7

3.3.2 Rheology of the continuous phase

8

The continuous phase can decide the primary viscoelasticity of the O/W

9

emulsions; thus, the dynamic viscoelasticity of cellulose-surfactant solutions with

10

different concentrations of regenerated cellulose was analyzed and depicted in Fig. 8.

11

In surfactant-only solution, the system displayed a null G' and low G'' value at all

12

sweep frequencies, which suggests an obvious liquid-like behavior. However, adding

13

0.5% and 1.0% regenerated cellulose to surfactant solution signiﬁcantly increase the

14

viscoelasticity. At these two concentrations, an obvious solid-like behavior was 15


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1

observed because of the higher of G' than G" over the whole sweep range.

2 3

Fig. 8. Dynamic rheological curves for the different surfactant-cellulose solutions.

4 5

Fig. 9. Storage modulus (G') for different surfactant-cellulose solutions at 45 ˚C and 1

6

Hz. The insets are SEM images of solutions (a) 0.4% APG1214 and (b) 0.4%

7

APG1214+1.0% cellulose. 16


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In many cases, the storage modulus increased exponentially with the cellulose

2

concentration, and the higher order of equations represents a more efficient

3

aggregated capacity of cellulose.54,

4

concentration of regenerated cellulose at 45 ˚C and 1 Hz is plotted in Fig. 9, where the

5

insets are SEM images of 0.4% APG1214 and 0.4% APG1214+1.0% cellulose

6

dispersions, respectively. It can be calculated that G'=7.486C4.01, which corresponds

7

to previous data.56 This suggests that surfactant-cellulose systems can form tighter

8

three-dimensional aggregates as compared to that of surfactant-only in solutions, as

9

shown in Fig. 9 (inset).

10

55

The lgG' as a function of the exponential

3.3.3 Three-phase rheology of emulsions

11 12

Fig. 10. Three-phase rheological curves for surfactant-cellulose emulsions (strain =

13

1%, frequency = 1 Hz and shear rate = 100 s−1).

14

When the flooding agent for EOR is applied in reservoirs, the injected fluids can

15

flow continuously in the porous media. Thus, the rheological properties of the 17


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1

cellulose-surfactant O/W emulsions were investigated using the three-phase

2

rheological measurements depicted in Fig. 10. For the surfactant-only emulsions, G'

3

was negligible, while G'' values were visible in first oscillation-phase, indicating the

4

liquid-like property of APG emulsions. It could be attributed to the fact that the

5

continuous phase possessed a weak micelle structure after the emulsification process.

6

At the second shear-phase, the viscosity of emulsions decreased and subsequently

7

remained invariant under the shear rate of 100 s-1. The reduction is attributed to the

8

continuous shearing of the emulsions, while the invariability is because the oil

9

droplets have reached to its smallest diameter and then stabilized. At the third-phase

10

without shear, due to the effect of oscillation, the exhibited a weak stability G'' was

11

significantly greater than G', elucidating the weak stability of surfactant-only

12

emulsion.

13

Meanwhile, the three-phase behaviors of cellulose-surfactant emulsion were also

14

studied (Figure 10b, 10c). After adding the 0.5% concentration of regenerated

15

cellulose, at the first phase, the cellulose-APG1214 emulsion exhibited higher values

16

of both G' and G'' than APG1214 emulsion. This indicated that the emulsion’s

17

rheology had transitioned from viscosity dominant to elasticity dominant due to the

18

formation of three-dimensional structures and hydrogen bonds between the cellulose

19

and surfactant. Furthermore, the emulsion exhibited a similar reduction trend in

20

viscosity at the second shear-phase, though having a higher value due to the higher

21

bulk viscosity of the bending solution. At the third phase without shear, due to the 18


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effect of oscillation, the associated structures were partially recovered. Hence, the

2

value of G' surpassed that of G'', indicating the cellulose-surfactant emulsion’s higher

3

stability and self-recovery capability. Additionally, by increasing the concentration of

4

regenerated cellulose to 1.0%, the viscoelasticity of the emulsion increased, G'

5

remained higher than G'' throughout the double-oscillation phases, and the shearing

6

viscosity of the emulsion also increased.

7

Based on these results, the cellulose-surfactant emulsion displayed better

8

self-recovery capabilities and shearing resistance after shearing than that of

9

surfactant-only emulsion. Besides, its higher interfacial viscosity and more compact

10

O/W interfacial film inhibited surfactant to migrate from oil/water interface to water

11

solution. These results indicate that it may be able to retain the performance of the

12

emulsions for generation, stabilization and migration for the application of

13

cellulose-surfactant blended system in practical reservoirs.

14

3.4. Microscopic oil displacement comparisons after various

15

flooding stages

16

The dynamic oil displacement and micrographs after various flooding stages in

17

the microscopic flooding experiments are shown in Figs. 11 and 12, which illustrate

18

the displacing processes of 0.4% APG1214 flooding and 0.4% APG1214+ 1.0%

19

cellulose flooding, respectively. As depicted in Figs. 11a and 12a, the visual

20

micromodel was full of crude oil after oil saturation. As shown in Figs. 11b and 12b, a

21

large volume of the residual oil remained in the micromodel even after extensive 19


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Page 20 of 26

1

water flooding due to viscous fingering. Fig. 11c shows that surfactant flooding

2

decreased the oil saturation somewhat after 0.6 PV, and there was also a lot of oil

3

remaining in the micromodel. However, as shown in Fig. 12c, the micromodel

4

became almost transparent, suggesting that 0.6 PV (surfactant+cellulose) flooding has

5

displaced

6

surfactant-cellulose solution obviously increased the sweep efficiency and

7

displacement efficiency, not just in the main channels, but also from the injection inlet

8

to the outlet. This can be attributed to the superior emulsifiability and viscoelasticity

9

of the hybrid solution.

most

of

the

reserved

oil

in

micromodel.

Additionally,

the

10 11

Fig. 11. Micro-images after different displacing processes (a: oil saturation; b: water

12

displacing; c: 0.4% APG1214 displacing; d: localized close-up of one location after

13

APG1214 displacing). The solutions flow from right-top to left-bottom in the

14

micromodel. 20


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Energy & Fuels

1 2

Fig. 12. Micro-images after different displacing processes (a: oil saturation; b: water

3

displacing; c: 0.4% APG1214+ 1.0% cellulose displacing; d: localized close-up of one

4

location after APG1214 displacing). The solutions flow from right-top to left-bottom

5

in the micromodel.

6

A localized close-up of the micromodel after chemical flooding is also captured

7

in Figs. 11d and 12d. As compared with surfactant flooding, surfactant-cellulose

8

flooding can emulsify the residual oil, and the oil droplets can be stabilized and

9

displaced by the aggregated structures of the regenerated cellulose. This further

10

highlights the EOR efficiency and mechanism of the cellulose-surfactant system,

11

situating this system as a promising EOR system for oil production applications.

12

4. Conclusions

13

This work investigated the performance of surfactant and regenerated cellulose

14

solutions on emulsification, and their application in chemical flooding for EOR. By 21


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

adding regenerated cellulose to a surfactant system, the emulsions stability could be

2

well enhanced, while the phase separation could be deferred as the average droplet

3

size decreases. Moreover, the hydrogen bonds between cellulose and APG1214 can

4

slightly decrease the o/w IFT and increase both the three-dimensional aggregates and

5

viscoelasticity of the continuous phase. Accordingly, the three-phase rheological

6

properties indicate that surfactant-cellulose systems will display better shearing

7

tolerance and self-recovery capabilities than surfactant-only systems. Ultimately, as

8

compared to the surfactant-only system, the hybrid system can significantly increase

9

the oil production at the end of water flooding via mechanisms of more efficient

10

emulsification, stabilization and displacement of oil droplets.

11

Acknowledgments

12

The research was supported by the National Science and Technology Major

13

Project (2017ZX05009-004), the National Natural Science Foundation of China (No.

14

51774309), the Science Foundation of China University of Petroleum, Beijing (No.

15

2462015YJRC033) and at Karamay (No. RCYJ2017A-01-001).

16

References

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The synergistic collaboration between regenerated cellulose and

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