Thesis Final

Studies on the Characterization, Interfacial Tension and

Rheology of a Novel Polymeric Surfactant Derived from

Castor Oil for Enhanced Oil Recovery

Dissertation submitted in partial fulfillment of

requirements for the award of the degree of

Master of Technology

In

PETROLEUM ENGINEERING

By

NILANJAN PAL (Admission no. 2013MT0087)

Under the guidance of

Dr. AJAY MANDAL Associate Professor

Department of Petroleum Engineering

DEPARTMENT OF PETROLEUM ENGINEERING

INDIAN SCHOOL OF MINES, DHANBAD

April 2015

DEPARTMENT OF PETROLEUM ENGINEERING INDIAN SCHOOL OF MINES UNIVERSITY

Dhanbad-826004, Jharkhand (India)

________________________Address for Communication_______________________

Dept. of Petroleum Engg., Indian School of Mines University, Dhanbad-826004, Jharkhand

Tel. : +91-326-2296632, 2235280, Fax : +91-326-2296632/2296563

E-mail: [email protected] Website : www.ismdhanbad.ac.in

CERTIFICATE

This is to certify that the dissertation entitled “Studies on the Characterization, Interfacial

Tension and Rheology of a Novel Polymeric Surfactant Derived from Castor Oil for Enhanced

Oil Recovery” carried out by Nilanjan Pal (Admission No. 2013MT0087) in the Department of

Petroleum Engineering, Indian School of Mines, Dhanbad in partial fulfillment of the

requirements for the award of the degree of Master of Technology in Petroleum Engineering is

a record of bonafide research work carried out by him under my supervision and guidance. His

dissertation, in my opinion, is worthy of consideration for the award of the degree of Master of

Technology in accordance with regulations of the institute.

To the best of my knowledge, the results embodied in this dissertation have not been

submitted anywhere else for the award of degree certificate.

Dr. Ajay Mandal

Associate Professor

Department of Petroleum Engineering

Indian School of Mines

Dhanbad-826004

mailto:[email protected]

Dedicated to my beloved parents

Page | II

I

It is a privilege to lay earnest thanks to my guide Dr. Ajay Mandal, Associate Professor,

Department of Petroleum Engineering, Indian School of Mines Dhanbad, for his excellent

guidance, caring, patience, and providing me with an motivating atmosphere for doing the

dissertation. His expertise was motivation for me from the inception of this dissertation till the

writing of this project report. I could not have imagined having a better advisor and mentor for

my project.

I am thankful to Prof. V. P. Sharma, Head of Department and distinguished faculty members

of the Department of Petroleum Engineering, Indian School of Mines, Dhanbad for valuable

support to help the completion of my research work in the department which has admirable

facilities from every aspect as required by any researcher.

It was a great time working with PhD research students, Mr. Keshak Babu, Mr. Shranish Kar

and Mr. Sunil Kumar who have been helpful at the very ground level during the various stages

of experiments that were undertaken for the completion of my project (thesis) work.

NILANJAN PAL

Admission No. 2013MT0087


Petroleum Engineering

ACKNOWLEDGEMENT

Page | III

II

1. "Synthesis and Characterization of new Polymeric Surfactant for

Chemical Enhanced Oil Recovery", Ajay Mandal, Keshak Babu,

Nilanjan Pal, V. K. Saxena.

2. “Surface Tension, Dynamic Light Scattering and Rheological

studies of a new Polymeric Surfactant for application in enhanced

oil recovery”, Nilanjan Pal, Keshak Babu, Ajay Mandal.

3. “Studies on Interfacial Tension and Contact Angle of Synthesized

surfactant and Polymeric from Castor Oil for Enhanced Oil

Recovery”, Keshak Babu, Nilanjan Pal, Achinta Bera, V.K. Saxena,

Ajay Mandal.

COMMUNICATED PAPERS

Page | IV

III

Various experimental studies were carried out on a novel polymeric surfactant synthesized

from castor oil. FTIR analysis of polymeric surfactants with varying acrylamide-to-sulfonate

weight ratios revealed similar chemical composition and bonding arrangement with different

transmittance percentages. Dynamic Light Scattering (DLS) experiments were performed on

all polymeric surfactants to show that hydrodynamic particle diameter generally increased with

concentration due to aggregation of molecules. Addition of NaCl resulted in decrease in

particle size. The effects of concentration and salt addition on interfacial studies and rheology

were investigated. IFT values decreased with concentration upto a certain limit called Critical

Micelle Concentration after which the IFT value increased. Addition of salt saw the same trend

with the lowest IFT value obtained at optimal salinity of the salt-polymeric mixture. The values

of CMC and optimal salinity were identified along with their corresponding IFT values to aid

in the formulation of desired mixtures for achieving ultralow IFT. Viscosity was found to

increase with increase with PMES concentration. However, reduction in viscosity was

observed with temperature rise and salt addition. Analysis of rheological data showed that

polymeric surfactant behaved ideally up to a critical shear rate of 50 s-1 but exhibited shear-

thinning or pseudoplastic behavior at higher shear rates. Determination of viscoelastic

properties were carried out by dynamic mechanical analysis in oscillatory mode. Storage

modulus G' and loss modulus G'' increased with increasing PMES concentration. Specific

frequency (SF) indicated by the crossing point between G' and G'' on the viscoelastic curve

represents the point of transition between elastic and viscous phases of the polymeric surfactant

system.

Keywords: Polymeric Surfactant; Castor Oil; Fourier Transform Infrared Spectroscopy;

Dynamic Light Scattering; Interfacial Tension; Viscosity; Shear Stress; Viscoelasticity

ABSTRACT

Page | V

IV

1. Investigate the effects of concentration and salt addition on the particle size profile of

polymeric surfactant in aqueous solution by DLS Analysis.

2. Analyze and compare the effects of concentration, acrylamide-to-sulfonate ratio and

salt addition on the interfacial tension measurements for polymeric surfactant and

SMES.

3. Study the rheological properties, including viscosity, shear stress and viscoelastic

properties of polymeric surfactant solutions in aqueous solution and under the effect

of salt.

NILANJAN PAL

Admission No. 2013MT0087


Petroleum Engineering

OBJECTIVES OF THE EXPERIMENTAL STUDY

Page | VI

V

DESCRIPTION Page

No.

ACKNOWLEDGEMENT

COMMUNICATED PAPERS

ABSTRACT

OBJECTIVES OF THE EXPERIMENTAL STUDY

CONTENTS

II

III

IV

V

VI

LIST OF FIGURES VIII

1. INTRODUCTION 2-4

2. LITERATURE REVIEW 5-10

2.1. Current Demand for oil and need for EOR 5

2.2. Prospects of Chemical flooding for EOR 6

2.3. Prominence in ASP Flooding 8

2.4. Chemical EOR challenges 9

2.5. Potential possibilities in the synthesis of a new polymeric surfactant 9

3. WORK OVERVIEW 11-12

3.1. Previous and Relevant Works 11

3.2. Focus of the Present Study 12

4. DLS CHARACTERIZATION 13-20

4.1. Principle of DLS Analysis 13

4.2. Experimental Section 14

4.2.1. Material(s) Required 14

4.2.2. Apparatus Description 14

4.2.3. Measurable Quantities 15

4.2.4. Technical Features 15

4.2.5. Zetasizer Nano S90 Specifications 16

4.2.6. Experimental Procedure 17

4.3. Results and Discussions 18

4.3.1. Effect of PMES concentration on particle size distribution profile 18

4.3.2. Effect of salt addition on particle size distribution profile 19

CONTENTS

Page | VII

5. INTERFACIAL TENSION STUDIES 21-40

5.1. Principle of IFT measurement by Spinning Drop Method 21






5.2.5. SVT-15 Tensiometer Specifications 27

5.2.6. Capillary Tube Specifications 28



5.3.1. Effect of surfactant concentration on interfacial tension

measurements for SMES solution

31

5.3.2. Effect of NaCl addition on interfacial tension measurements for

SMES solution

33

5.3.3. Effect of concentration on IFT of polymeric surfactant (PMES)

solutions with different acrylamide-to-surfactant ratios

34

5.3.4. Effect of NaCl addition on the most effective polymeric

surfactant solution

38

5.3.5. Effect of Acrylamide-to-Sulfonate Ratios on salt-polymeric

surfactant mixture with lowest IFT value

39

6. RHEOLOGICAL STUDIES 41-56

6.1. Principle of rheometry 41






6.2.5. Bohlin Gemini 2 Rheometer Specifications 44



6.3.1. Effect of Temperature on PMES viscosity 47

6.3.2. Effect of PMES concentration and acrylamide-to-sulfonate ratio

on viscosity and shear Stress

49

6.3.3. Effect of addition of salt on PMES viscosity 53

6.3.4. Effect of concentration on dynamic viscoelasticity

55

7. SUMMARY AND CONCLUSIONS 57-59

REFERENCES 60

Page | VIII

VI

Figure no.

Description Page no.

Fig 3.1 Infrared spectrum of polymeric methyl ester sulfonate 11

Fig 4.1 ZETASIZER (Nano-S90, Malvern) apparatus for DLS

analysis 14

Fig 4.2 Polarizer Tube for storing sample solution during DLS

Analysis 17

Fig 4.3 Effect of PMES concentration on hydrodynamic diameter

of molecules in polymer ethyl ester sulfonate solution 18


of PMES solution containing 1% NaCl 19





Fig 5.1 Spinning Drop in a Spinning Drop Tensiometer along the

Spinning Axis 21

Fig 5.2 Spinning Drop Tensiometer SVT 15N Assembly 24

Fig 5.3 High Temperature Capillary Tube FEC 622/400-HT 25

Fig 5.4 Spinning Drop Video Tensiometer SVT 15N 27

Fig 5.5 A typical Spinning Drop (Crude Oil) in Capillary Tube in

SVT 15N Tensiometer 29

Fig 5.6 Variation of interfacial tension with surfactant

concentration for SMES solution at 298 K

31

Fig 5.7 Snapshot of spinning drop (crude oil) at CMC value (5500

ppm) for SMES solution

32

Fig 5.8 Variation of interfacial tension with NaCl salt

concentration for 5500 ppm SMES solution at 298 K

33

Fig 5.9 Snapshot of spinning drop (crude oil) at optimal salinity

(3.5%) at CMC (5500 ppm) for SMES solution

33

Fig 5.10 Variation of IFT with PMES concentration at different

acrylamide-to-sulfonate ratios at 298 K

35


ppm) for P1 solution

35



36

LIST

OF

FIGURES

Page | IX



36



37



37

Fig 5.16 Effect of NaCl addition on interfacial tension values for P5

sample (acrylamide-to-sulfonate ratio 1:1) at 4500 ppm

aqueous solution at 298 K

38


(4.5%) at CMC (4500ppm) for P5 solution

39

Fig 5.18 Effect of variation of acrylamide-to-sulfonate ratios on the

IFT values at 4500 ppm PMES solution containing 4.5%

NaCl at 298 K

39


(4.5%) at CMC (4500 ppm) for salt-P4 (acrylamide-to-

surfactant ratio 0.8:1) polymeric surfactant mixture

40

Fig 6.1 Bohlin Gemini 2 Rheometer Assembly 43

Fig 6.2 Variation of Dynamic Viscosity of Polymeric Surfactant

(PMES) with acrylamide to sulfonate ratio for 2500 ppm PMES

Solution at different temperatures

47




48




48

Fig 6.5 Experimental Steady shear viscosity profile of P1 solution (with

acrylamide-to-sulfonate ratio 0.4: 1) at 298 K at varying

concentrations

50



concentrations

50



concentrations

51



concentrations

51


acrylamide-to-sulfonate ratio 1: 1) at 298 K at varying

concentrations

52

Fig 6.10 Experimental Shear stress profile of P5 solution (with

acrylamide-to-sulfonate ratio 1: 1) at 298 K at varying

concentrations

52

Fig 6.11 Effect of addition of NaCl on the viscosity profile of 6000 ppm

P5 solution (with acrylamide-to-sulfonate ratio 1: 1) at 298 K at

varying concentrations

54

Page | X

Fig 6.12 Effect of addition of CaCl2 on the viscosity profile of 6000 ppm

P5 solution (with acrylamide-to-sulfonate ratio 1: 1) at 298 K at

varying concentrations

54

Fig 6.13 Effect of addition of NaCl and CaCl2 on zero-shear stress curve

of 6000 ppm P5 solution (with acrylamide-to-sulfonate ratio 1:

1) at 298 K at varying concentrations

55

Fig 6.14 Dynamic viscoelasticity curves showing the effect of angular

frequency on storage and loss moduli for P5 solution (with

Sulfonate-to-acrylamide ratio 1: 1) at 298 K at varying

concentrations

56

Page | 2

Chapter 1

Introduction

Traditional oil extraction methods by primary and secondary recovery processes generally

produce about 20 to 40% of the reservoir’s Original Oil in Place (OOIP) during its mature

lifetime. The remaining oil is still trapped in porous media due to the viscous forces, surface

and interfacial forces, and reservoir heterogeneities which results in poor displacement

efficiency [1]. This revelation has led to the application and development of many Enhanced

Oil Recovery methods.

Chemical enhanced oil recovery methods are field proven techniques that improve efficiency

and effectiveness of oil recovery. EOR processes involve a wide variety of mechanisms,

including use of polymers and surfactants that alter or improve the properties of reservoir fluids

to make it more conducive to extraction. Injection of water-soluble polymers is widely

employed in EOR due to its ability to improve sweep efficiency [1] by reducing the mobility

of displacing medium [2]. Surfactant flooding can significantly reduce the oil-water interfacial

tension, lower capillary forces and facilitate wettability alteration to improve oil recovery

[3,4,5]. The application of both polymer and surfactant may prove to be economically effective,

though complications involving proper formulation and design may arise. Improper mixing of

polymer and surfactant may lead to undesirable phase separation.

Lately, studies have been reported on the synthesis and applications of polymeric surfactants

in enhanced oil recovery [6,7]. Although polymeric surfactants are undoubtedly less well-

defined than surfactants, they have created greater interest in terms of flexibility, functionality

and diversity [8]. Polymeric surfactant, synthesized by appropriate mixing of polymer and

surfactant, encompasses the beneficial effects of both polymer and surfactant flooding. Besides

cost-effective, polymeric surfactants allow good mobility control and decrease interfacial

tension, thereby improving oil recovery by increase of fractional flow of oil [9]. The polymeric

methyl ester sulfonate (PMES) can improve the oil recovery rate under standard reservoir

conditions [10].

Various synthetic methods may be employed to introduce graft chains onto the polymer surface

[11] or onto the polymer backbone [12]. The polymeric surfactant investigated in the present

study was synthesized by attaching the sulfonate group of surfactant to the hydrophobic group

Page | 3

of an acrylamide monomer backbone by polymerization process [13]. The process was

designed to graft the sulfonate group to the polymer backbone as a one component system.

Infrared spectroscopy is crucial for elucidating the chemical structure and bonding arrangement

of polymeric materials at a molecular level [14]. The chemical structure and bonding

arrangement of the polymeric surfactant is characterized by FTIR (Fourier Transform Infrared)

spectroscopy analysis with reference to the Spectroscopic identification of organic compounds

by Silverstein et.al. 2005 [15]. This is accomplished by determination of components or groups

of atoms that absorb at specific frequencies in the infrared region [16,17]. FTIR studies on the

synthesized polymeric surfactant (derived from castor oil) is focused in this study. A similar

investigation was carried out on the infrared (IR) spectrum of polymeric surfactant derived

from Jatropha oil [18].

Dynamic Light Scattering is an important characterization technique to determine the size

distribution profile of particles in polymeric solutions. Investigation of hydrodynamic radii

obtained by DLS is very important in understanding the interfacial activity of polymeric

surfactants. The hydrodynamic particle size may be disaggregated by action of alkali [7].

Previous studies revealed that CMC segments roll up aqueous salt systems, altering particle

conformation from rod-like spherical structures and the particle size becomes smaller [19].

The fundamental requirement of many recovery processes is to produce low or ultra-low IFT.

Polymeric surfactants help in reducing the interfacial tension between oil and the displacing

phase, consequently mobilizing residual oil to improve overall oil efficiency. Increase in

capillary number as a consequence of IFT reduction is of practical importance in EOR

processes [20]. Interfacial activity is affected by temperature, concentration, addition of alkali,

salts, etc [21,22]. Investigations were earlier performed to study the interfacial tension

measurements between crude oil and aqueous solutions of SMES and PMES derived from

Jatropha oil [18].

Polymeric surfactant flooding improves the viscosity of the displacing fluid in the reservoir,

thereby increasing the areal and vertical sweep (displacement) efficiency. The effectiveness

and economic feasibility of EOR by flooding is related to the injectivity or injection rate, which

in turn is dependent on the viscosity of the injected fluid [23]. Viscosity is controlled by a

number of factors such as temperature, concentration, presence of salts, etc [24,25]. Normally,

pseudo plastic behavior exhibited by polymer systems is considered beneficial at higher shear

rates since viscosity near the injection well is lowered, which provides improved injectivity

Page | 4

[26]. However, higher viscosities are desired once the injected polymeric surfactant moves far

into the reservoir to achieve desired mobility ratio [9,26]. Recent studies indicate that

viscoelasticity is also an important property of polymer systems that contributes to sweeping

residual oil in pore ends and oil film in pore or pore throats, thereby aiding in improved sweep

efficiency [27]. Hence, both viscometric and viscoelasticity measurements provide important

data about the flow behavior of polymeric surfactants.

This thesis includes studies on the characterization, interfacial activity and rheology of a novel

polymeric surfactant synthesized from castor oil methyl ester. Characterization of the

synthesized polymeric surfactants was performed by FTIR and DLS experiments. FTIR

spectroscopy was useful in characterizing the chemical constitution and bonding nature of the

sample. DLS experiments were performed to understand the particle size profile in the absence

and presence of salts. The results of studies were analyzed to understand flow behavior and

chemical composition of the polymeric surfactant. Attention is primarily focused on achieving

low IFT and high mobility control for polymeric surfactants with different acrylamide-to-

sulfonate ratios at different concentrations. Interfacial tension readings was obtained for both

SMES and PMES solutions with crude oil sample using a Spinning Drop Tensiometer. Effect

of sodium chloride addition on IFT reduction was also studied. Extensive studies were made

with the help of an Advanced Air Bearing Rheometer to study the effect of temperature,

concentration and salt addition (NaCl and CaCl2) on viscosity, shear stress and viscoelastic

properties to determine the justifiability of the polymeric surfactant as an effectual chemical

flooding agent.

Page | 5

Chapter 2

Literature Review

2.1. Current Demand for Oil & Need for EOR

Crude oil makes a major contribution to the world economy today. The provision of heat, light,

and transportation depends on oil and there has not been yet a single energy source to replace

crude oil that is widely integrated. Moreover, the global economy currently depends on the

ability to acquire the energy required and it is indisputable that oil is the main contributor to

this demand. Currently, there is no an energy source available that could compete with oil,

making the world, and mainly the high energy consumers to rely on countries with large

reserves (Energy Information Administration, 2003).

Traditionally oil production strategies have followed primary depletion, secondary recovery,

and tertiary recovery processes. Primary depletion uses the natural reservoir energy to

accomplish the displacement of oil from the porous rocks to the producing wells (Craft et al.,

1991). An average of 10 to 20 percent of original oil in place (OOIP) can be recovered through

primary recovery. Secondary recovery methods are processes in which the oil is subjected to

immiscible displacement with injected fluids such as water or gas. It is estimated that about

thirty to fifty percent of the OOIP can be produced through the entire life of a mature reservoir

that has been developed under primary and secondary recovery methods (Green & Willhite,

1998). The remaining oil is still trapped in the porous media. This is attributed to surface and

interfacial forces (capillary forces), viscosity forces, and reservoir heterogeneities which results

in poor displacement efficiency (Green & Willhite, 1998). Recognition of these facts has led

to the development and use of many enhanced oil recovery (EOR) methods. EOR methods hold

promise for recovering a significant portion of the remaining oil after conventional methods.

Planning for improving or enhancing oil production strategies through EOR methods is one of

the most critical challenges facing the industry today. EOR not only will extend the life of this

important non-renewable resource, but it will also delay a world production decline and

shortage in the energy supply. Realizing the significant potential of EOR, most of oil

companies embarked on a massive journey to advance EOR processes. Various modifications

of EOR methods have been developed to recover at least a portion of the remaining oil. Thermal

Page | 6

processes are the most common type of EOR, where a hot invading phase, such as steam, hot

water or a combustible gas, is injected in order to increase the temperature of oil and gas in the

reservoir and facilitate their flow to the production wells (Green & Willhite, 1998). Another

type of EOR process consists of injecting a miscible phase with the oil and gas into the reservoir

to eliminate the interfacial tension effects. The miscible phase can be a hydrocarbon solvent,

CO2 or an inert gas (N2). Another common EOR technique is chemical flooding which includes

alkalis, surfactants, and polymers, or combinations thereof. The injected alkali and surfactant

agents can lower interfacial tension (IFT) between oil and water, thereby mobilize the residual

oil. Polymers are used to increase the viscosity of the aqueous solution for mobility control

(Green & Willhite, 1998).

2.2. Prospects of Chemical flooding for EOR

Chemical flooding, which has been developed since the early 1950s, is an important method

for enhanced oil recovery that includes alkaline flooding, alkali-surfactant flooding, and alkali-

surfactant-polymer flooding. Surfactant flooding and its variants are EOR processes that have

been employed to recover the residual oil after primary and secondary recovery process.

The efficiency of the chemical EOR is a function of liquid viscosity, relative permeability,

interfacial tensions, wettability, and capillary pressures (Liu, 2008). Even if all the oil is

contacted by the injected chemicals, some oil would still remain in the reservoir. This is due to

the trapping of oil droplets by capillary forces due to high interfacial tension (IFT) between

water and oil (Liu, 2008). Capillary number must be increased in order to reduce the residual

oil saturation. The most logical way to increase the capillary number is to reduce the IFT

(Berger & Lee, 2006; Liu, 2008). Therefore, the principal objective of the chemical process is

to lower the interfacial tension so that the recovery performance will be improved.

The concept of recovering oil by surfactant flooding dates back to 1929 when De Groot was

granted a patent claiming water-soluble surfactants as an aid to improve oil recovery. The

surfactant could reduce the interfacial tension between the brine and residual oil. The use of

proper surfactant can effectively lower the IFT resulting in a corresponding increase in the

capillary number (Berger & Lee, 2006). The success of surfactant flooding depends on many

factors such as formulation, cost of surfactants, availability of chemicals, and oil prices in the

market. In enhanced oil recovery, surfactants could be used in several formulations to enhance

Page | 7

oil production. Some of these formulations are surfactant-alkali flooding, surfactant-polymer

flooding, and alkali-surfactant-polymer flooding. The idea of combining surfactants and alkalis

was first proposed by Reisberg and Doscher in 1956. They added non-ionic surfactants to the

alkali solution to improve oil recovery at laboratory scale. Recent work has shown that the

addition of alkali to the surfactant solution would not only decrease the IFT, but also reduces

the surfactant adsorption on the negatively charged sand surface (Touhami et al., 2001). An

inexpensive alkali could be used with expensive surfactants to achieve both a technically

successful and economically feasible flood.

In order to design an effective surfactant-alkali flooding formulation, it is important to utilize

the synergistic effect between the surfactant and alkali. Surfactants tend to accumulate at the

oil and water interface where the hydrophilic and hydrophobic ends of the molecules can be in

a minimal energy state. This increases the surface pressure and decreases both the interfacial

energy and the IFT. Rudin & Wasan (1992) concluded that the dominant mechanism of the

synergistic effect is the formation of mixed micelles of the surfactants and the generated in situ

surfactant. The mixed micelles cause the IFT to drop significantly (Nelson et al., 1984). At the

same time, surfactant adsorption on sand is reduced by the presence of alkali. The sand surface

will become increasingly negatively charged with an increase in pH and will thereby retard the

adsorption of the anionic surfactant.

A number of alkali-surfactant flooding field tests have been described in the literature (Mayer

et al., 1983; McCafferty and McClaflin, 1992). Success of these processes in an actual reservoir

will depend on how well and for how long the internally-generated surfactant and the

externally-added surfactant work together as intended. Mayer et al., (1983) summarized based

on known field tests the amount of alkali injected and the performance results for early alkaline

flooding processes. Most of the projects were not as profitable as expected. Falls et al., (1992)

reported successful field tests using alkaline-surfactant flooding in recovering water-flood

residual oil from sandstone reservoirs in the White Castle Field, USA. The process recovered

at least 38% of the residual oil after water-flooding.

Alkali-surfactant flooding is a promising method for enhanced oil recovery. With the

combination of alkali and a small amount of surfactant, oil-water IFT can be reduced much

more than with either alkali or surfactant alone. However, the recovery factor of this process is

usually insufficient due to the unfavorable mobility ratio. Hence, a polymer is added to the

surfactant solution to improve the sweep efficiency.

Page | 8

2.3. Prominence in Alkali-Surfactant-Polymer (ASP) Flooding

Alkali-surfactant-polymer (ASP) is considered to be one of the major EOR techniques that can

be successfully used in producing light and medium oils. The advantage of ASP flooding over

conventional alkaline flooding is that ASP can be used for low acid number crudes while

alkaline flooding can only be applied for medium to high acid number crudes. In the ASP

process, alkali reacts with acidic oils to form in-situ surfactant and increases the pH to lower

surfactant adsorption on the porous media. Surfactants are used to lower the IFT between oil

and water while polymer is used to improve the sweep efficiency by providing mobility control

(Elraies et al., 2010). ASP flooding has been extensively evaluated in the laboratory and widely

used in field applications with great success. In recent years, many ASP field pilot tests have

been conducted in USA, India, Venezuela, and China (Pitts et al 2006; Pratap & Gauma, 2004;

Clara et al 2001; Wang et al., 1999). The ASP process uses the benefits of the three flooding

methods, and oil recovery is greatly enhanced by decreasing interfacial tension (IFT),

increasing the capillary number, enhancing microscopic displacing efficiency, and improving

the mobility ratio (Pingping et al., 2009). However, even with these advantages and the success

of ASP projects, the process is not without some disadvantages.

The application of alkali-surfactant polymer in the Daqing oil field in China is an example of

successful field trials. However, because of the high cost of surfactants, this process has not

been expanded (Wang et al., 1997). In order to reduce the cost of the surfactant and to enlarge

the swept volume, this technology was upgraded to alkali-surfactant-polymer flooding. The

combination of alkali surfactant-polymer is expected to cause the residual oil to be

economically recovered from the reservoir.

An earlier paper written by Hou and co-workers (2001) addresses the corrosion and scale

problems that occurred during the ASP flood in Daqing field. The strong alkali had detrimental

effects on polymer performance and in many cases additional polymer was required to achieve

the desired viscosity (Wang et al., 2006). Nasr-El-Din et al., (1992) conducted an experimental

study to examine the effectiveness of alkali concentration in ASP performance. Their

experiments confirmed an exponential decrease in viscosity of the combined ASP slug with

the increase in alkali concentration. The selection of proper surfactants is one of the key factors

for chemical EOR application. Surfactant should be stable under reservoir conditions resulting

in an ultralow interfacial tension. Wangqi & Dave, (2004) conducted screening studied by

interfacial tension experiments using different types of surfactants and validated by core flood

Page | 9

tests. The IFT results showed wide range of IFT reduction, depends on the surfactant

concentration and type. Core flood results indicated that 11.2% OOIP could be recovered when

the selected surfactant concentration and type are combined with alkali and polymer. Flaaten

et al., 2008 performed the screening and optimization of surfactant formulations by

microemulsion phase behavior using various combinations of surfactants, co-solvents, and

alkalis. Branched alcohol propoxy sulfates and internal olefin sulfonates demonstrated a

superior performance when mixed with conventional alkali. The recovery performance

indicated that nearly 100% of residual oil was recovered with very low surfactant adsorption.

2.4. Chemical EOR challenges

Most pilot tests reported in the 2000s accomplished a higher oil recovery than those in the

1970s and 1980s. Improvements in the functionality of the chemicals and a better

understanding of the process mechanisms are the causes for these successes. These field tests

indicate that surfactant flooding and its variants can be technically successful. However, the

main downside for these chemical EOR applications was still the high manufacture cost of

surfactants and the cost of raw materials. The recovered oil by this process was not economical

or the economical and technical risk was too high compared with the oil price (Austad & Milter,

2000). Therefore, a lot of work has been recently conducted to develop an economical

surfactant when the crude oil prices remained high. To reduce the cost of surfactant production,

much attention is focused toward agriculturally derived oleo-chemicals as alternative

feedstocks (Gregorio, 2005). Many surfactants have been produced from natural oils to satisfy

EOR requirements (Wuest et al., 1994; Li et al., 2000). Soybean and coconut oils are the most

popular raw materials used to derive oleo-chemical feedstocks such as fatty alcohol and esters

(Hill, 2000).

2.5. Potential possibilities in the synthesis of a new polymeric

surfactant

This section of the chapter is focused on the description of the development of a new polymeric

surfactant with the aim to overcome some of the existing problems associated with

conventional ASP flooding. The goal is to produce a new surfactant that will be both

Page | 10

economical and effective for interfacial tension reduction and viscosity control. The basic idea

was to attach the sulfonate group to a hydrophobic group of an associative polymer chain. A

hydrophobically modified polymer is one class of water soluble associative polymer that

contains a small number of hydrophobic groups (Abdala, 2002). Hydrophobically modified

polymers have either a telechelic structure in which the chains are end-capped with the

hydrophobic groups, or more complicated comb-like structures in which the hydrophobic

groups are randomly grafted to the polymer backbone. The backbone has a polyelectrolyte

feature and is composed of a polymer of acrylamide or acrylic acid, and ethyl acrylate. Upon

neutralization, the polymer backbone adopts a more extended conformation allowing the

hydrophobic groups to associate forming a transient network structure (Abdala, 2002).

Herein, a single step route that is similar to the method reported by Ye et al., (2004) was used

to produce a new polymeric surfactant via the polymerization process. This surfactant was

designed to graft the sulfonated group to the polymer backbone as one component system for

interfacial tension reduction and viscosity control. Therefore, the polymerization was

conducted with an excess of different surfactant to acrylamide ratios. Sodium methyl ester

sulfonate (SMES) was used as a surfactant feedstock in the polymerization process. Because

the goal was to design a cost effective surfactant, the SMES was synthesized from castor oil as

the raw material. Additionally, it is not a petroleum derivative and has limited food and

medicinal applications.

Page | 11

Chapter 3

Work Overview

3.1. Previous and Relevant Works

The synthesis of polymeric surfactant from castor oil methyl ester was earlier carried out by

our fellow researcher Mr. Keshak Babu under the guidance of Dr. Ajay Mandal in the

Department of Petroleum Engineering. It basically involved two stages of manufacture. First,

sodium methyl ester sulfonate (SMES) was extracted from castor oil. Finally, polymerization

was performed in order to synthesize polymer methyl ester sulfonate (PMES) from SMES.

Characterization of the polymeric surfactant was also studied earlier by Mr. Keshak Babu

(PhD) in terms of chemical composition in finely powdered form in aqueous solution. The

FTIR spectrophotometer (Perkin Elmer-Spectrum Two) was used to determine the chemical

functional groups present in the synthesized polymeric surfactant. Infrared adsorption bands in

FTIR spectroscopy are investigated with reference to the Spectroscopic identification of

organic compounds by Silverstein et.al. 2005 [15]. Fourier Transform Infrared (FTIR)

Spectroscopy analyzed the presence of esters, sulfonate, amide, methyl and acrylamide groups

by careful examination of absorption peaks in the infrared region. The infrared spectrum of a

typical polymer methyl ester sulfonate sample is illustrated, as shown in Figure 3.1.

3500 3000 2500 2000 1500 1000

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Abso

rba

nce

Wavenumber (cm-1)

3434

29261666

1452

11811789

Fig 3.1. Infrared spectrum of polymeric methyl ester sulfonate

Page | 12

3.2. Focus of the Present Study

This thesis encompasses the study of a novel polymeric surfactant derived from castor oil via

the polymerization of sodium methyl ester sulfonate. Since this is a newly synthesized

polymeric surfactant, no prior work was done in this particular topic. I have focused my

research work on particle size characterization, interfacial studies and flow behavior of the

synthesized polymeric surfactant (PMES).

The particle size analysis of the synthesized polymeric surfactant in aqueous solution was

determined at 30 ±0.1°C using ZETASIZER (Nano-S90, Nano series Malvern). The laser

wavelength and the scattering angle were 633 nm and 90° respectively. The refractive index

(1.332) of each solution was measured with the help of a portable refractometer (Refracto 30PX

model). This data would support useful correlation with interfacial tension measurements.

Interfacial tensions between different polymeric surfactant and SMES solutions with crude oil

were measured with the help of spinning drop method. Model SVT 15 spinning drop

tensiometer equipped with video camera was used to determine the IFT at 298 K. SMES or

PMES in aqueous solution was introduced into a high-temperature capillary tube with desirable

specifications.

Rheological measurements were carried out using a Bohlin Gemini 2 Rheometer, manufactured

by M/S Malvern Instruments Limited, UK. It is a model of an ‘Advanced Air Bearing

Rheometer’. Ewart Mooney Geometry was used to obtain data in both viscometry and

oscillatory mode measurements. The viscosity and shear rate measurements in both modes

were carried out using cup and bob (coaxial cylinder) measuring system. This experiment is

useful in the determination of viscosity, shear stress and viscoelastic properties, if any, for flow

behavior analysis.

The polymeric surfactant PMES with different acrylamide-to-sulfonate weight ratios is

introduced and labelled in the table below.

Acrylamide-to-sulfonate Ratio 0.4:1 0.5:1 0.6:1 0.8:1 1:1

Notation P1 P2 P3 P4 P5

Page | 13

Chapter 4

DLS Characterization

4.1. Principle of DLS Analysis

Dynamic Light Scattering or DLS (also referred to as Photon Correlation Spectroscopy or

Quasi-Elastic Light Scattering) is one of the most techniques employed for the determination

of particle size profile in solutions. It allows particle sizing down to 1 nm diameter.

Dynamic Light Scattering (DLS) works by measuring the intensity of light scattered by the

molecules in the sample as a function of time. When light is scattered by a molecule some of

the incident light is scattered. If the molecule was stationary then the amount of light scattered

would be constant. But, as all molecules in solution diffuse with Brownian motion in relation

to the detector, interference (constructive or destructive) occurs causing a change in light

intensity. By measuring the time scale of light intensity fluctuations, DLS provides information

regarding the average size, size distribution, and poly-dispersity of molecules in solution.

The faster the particles diffuse, the faster the intensity will change (if the light was bright

enough this would be seen as a twinkling effect). The speed of these changes is thus directly

related to the motion of the molecule. The diffusion of the molecules is essentially controlled

by the following factors:

Temperature – the higher the temperature, the faster the molecules will move.

Viscosity of the Solvent – the more viscous the solvent, the slower the molecules will

move.

The size of the molecules – the bigger the molecules, the slower the molecules will

move.

If the temperature and solvent are constant and known, the variation in the intensity of the

scattered light is directly related to the “size” of the molecule. This number is referred to as

the hydrodynamic diameter (Dh). The hydrodynamic diameter represents the sphere, which

is defined by the molecule rotating in all directions plus the hydration layer, modified by how

Page | 14

easy it is to pass the solvent through that volume. It is actually a measure of how easy it is to

move the molecule through the solvent.

4.2. Experimental Section

4.2.1. Material(s) Required

The material used in FTIR experiment was polymeric methyl ester sulfonate (PMES) in

powdered form. The acrylamide-to-sulfonate ratio in the polymeric surfactant PMES was

essentially varied on a comparative basis. Sodium chloride (NaCl) was also added at 1%, 2%

and 3% to the solutions to study its effect on particle size distribution.

4.2.2. Apparatus Description

Fig 4.1. ZETASIZER (Nano-S90, Malvern) apparatus for DLS analysis

The particle size analysis of the synthesized polymeric surfactant in aqueous solution was

determined at 30 ±0.1°C using ZETASIZER (Nano-S90, Nano series Malvern). The laser

wavelength and the scattering angle were 633 nm and 90° respectively. The refractive index

(1.332) of each solution was measured with the help of a portable refractometer (Refracto 30PX

model). All samples of the polymeric surfactant were prepared in distilled water and filtered

using a 0.2 µm pore size membrane in order to remove possible dust particles from the solution.

Page | 15

The absorbance of PMES solutions were measured using an UV-1800 (UV- VIS

spectrophotometer Shimadzu, Japan) at a wavelength of 217 nm. The value of absorbance was

obtained at a value of 2.33.

4.2.3. Measurable quantities

Particle size distribution profile in terms of a curve representing relationship between

hydrodynamic diameter and concentration in aqueous solution (using DLS apparatus)

Refractive Index (using refractometer)

Absorbance (using spectrophotometer)

4.2.4. Technical Features

The Zetasizer Nano S90 consists of the below mentioned technical features: Size measurement from 0.3nm (diameter) to 5 microns using 90 degree scattering

optics.

Molecular weight measurement down to 9,800Da.

A ‘Quality Factor’ and ‘Expert Advice System’ gives the confidence of having an

expert at your shoulder.

21CFR part 11 software option enables compliance with ER/ES.

Research software option gives access to further features and analysis algorithms for

the light scattering specialist.

Automation of measurements using an autotitrator option.

Alternative laser, 50mW at 532nm for samples incompatible with the standard 633nm

laser fitted.

Optical filter option to improve measurements with fluorescent sample.

Temperature range extension option to 120°C.

Systems can be upgraded to add zeta potential at a later date.

Page | 16

4.2.5. Zetasizer Nano S90 Specifications

1. Particle size and molecular size

Measurement range: 0.3nm – 5.0 microns* (diameter).

Measurement principle: Dynamic Light Scattering.

Minimum sample volume: 20µL.

Accuracy: Better than +/-2% on NIST traceable latex standards.

Precision / Repeatability: Better than +/-2% on NIST traceable latex standards.

Sensitivity: 10mg/mL (Lysozyme)

2. Molecular weight.

Measurement range: Molecular weight

Measurement principle: Static Light Scattering using Debye plot.

Minimum sample volume: 20µL (3-5 sample concentrations required).

Accuracy: +/- 10% typical

Temperature control range: 0°C - 90°C +/-0.1**, 120°C option.

Light source: He-Ne laser 633nm, Max 4mW.

Laser safety: Class 1.

Power: 100VA.

3. Weight and dimensions:

Dimensions: 320mm, 600mm, 260mm (W,D,H).

Weight: 21 (kg)

4. Operating environment:

Temperature range: 10°C – 35°C.

Humidity: 35% - 80% non-condensing.

Page | 17

4.2.6. Experimental Procedure

1. First, a small amount of PMES sample was poured in a glass tubette. I ensured that no

fingerprints/ impurities were found on the outer or the inner surface of the polarizer

glass tube by cleaning it with a tissue paper.

Fig 4.2. Polarizer Tubette for storing sample solution during DLS Analysis

2. Then I pressed the ‘OPEN’ button on the analyzer and placed the polarizer (glass

tubette) in the compartment.

3. I pressed the button again to seal off the compartment and quickly opened the CFR

software (Materials Management Software).

4. I clicked on the Start button on software interface and waited for about 2 minutes for

the reading to generate.

5. During these 2 minutes, the apparatus measured the diffusion of particles moving under

Brownian motion, and converts this to size and a size distribution using the Stokes-

Einstein relationship.

6. The software interface generated the value of hydrodynamic diameter of particles in the

solution indicated by Z (Average) value.

7. Increase or decrease in the value of hydrodynamic diameter is a measure of aggregation

or disaggregation of molecules in solution as a result of concentration or salinity

change.

Page | 18

8. This procedure was repeated for other samples with/ without NaCl (sodium chloride)

addition.

9. After proper examination of samples, I cleaned the polarizer/ tubette to prevent

incorrect analysis by light scattering technique.

10. Finally, I switched off the analyzer assembly and saved the data in pdf format for further

examination.

4.3. Results and Discussions

4.3.1. Effect of PMES concentration on particle size distribution profile

Figure 4.3 shows that the hydrodynamic diameter generally increases with increasing PMES

concentration. It is quite simply observed that the increase of hydrodynamic diameter is due to

the aggregation of the molecules. The movement of the particles gives rise to diffusion in

various polymeric surfactant solutions, where the rate of diffusion is more rapid for small

particles thereby contributing to faster diffusion [31]. As a result, with the increase in PMES

surfactant concentration, the particle size increases simultaneously.

Fig 4.3. Effect of PMES concentration on hydrodynamic diameter of molecules in polymer ethyl ester

sulfonate solution

0

500

1000

1500

2000

2500

3000

3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500

Hyd

rod

ynam

ic D

iam

eter

(n

m)

PMES Concentration (ppm)

P1 P2 P3 P4 P5

Page | 19

4.3.2. Effect of salt addition on particle size distribution profile

Fig 4.4. Effect of PMES concentration on hydrodynamic diameter of PMES solution containing 1%

NaCl


NaCl

0

200

400

600

800

1000

1200

1400

1600

3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500

Hyd

rod

ynam

ic D

iam

eter

(n

m)


P1 (1% NaCl) P2 (1% NaCl) P3 (1% NaCl) P4 (1% NaCl) P5 (1% NaCl)

0

200

400

600

800

1000

1200

1400

1600

3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500

Hyd

rod

ynam

ic D

iam

eter

(n

m)



Page | 20


NaCl

The effect of sodium chloride 1%, 2% and 3% (mass %) on DLS experiment also plays an

important role for enhanced oil recovery as shown in Figure 4.4, 4.5 and 4.6. Hydrodynamic

diameter was generally found to decrease with increase in salt (concentration) addition since

micelles may disaggregate to smaller size and may even break down to polymer chains. This

may be due to rolling up of CMC segments in aqueous salt solutions, thereby changing particle

structure from rod-like to spherical shape. As a result, the size of micelles becomes smaller.

This could help decrease the surface tension and interfacial tension [7].

0

200

400

600

800

1000

1200

1400

1600

3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500

Hyd

rod

ynam

ic D

iam

eter

(n

m)



Page | 21

Chapter 5

Interfacial Tension Studies

5.1 Principle of IFT measurement by Spinning Drop Method

In this method, a droplet of crude oil (lower density liquid) is injected into a surfactant solution

(higher density liquid) contained inside a rotating horizontal glass tube. For individual speeds

of rotation applied in the method, the drop attains an equilibrium shape, which is determined

by the balance between interfacial tension and pressure difference at interface due to centrifugal

force and density difference between the surfactant and crude oil. The drop attains a stable

shape when the above forces are balanced. Flow is assumed to be Newtonian.

Since the rotation of the horizontal tube creates a centrifugal force towards the tube walls, the

liquid drop will start to deform into an elongated shape; this elongation stops when the

interfacial tension and centrifugal forces are balanced. The surface tension between the two

liquids (for bubbles: between the fluid and the gas) can then be derived from the shape of the

drop at this equilibrium point. A device used for such measurements is called a spinning drop

tensiometer.

An approximate theory was developed by Bernard Vonnegut in 1942, to measure the surface

tension of the fluids, which is based on the principle that the interfacial tension and centrifugal

forces are balanced at mechanical equilibrium. This theory assumes that the droplet's length L

is much greater than its radius R, so that it may be approximated as a straight circular cylinder.

Fig 5.1. Spinning Drop in a Spinning Drop Tensiometer along the Spinning Axis

Page | 22

The relation between the surface tension and angular velocity of a droplet can be obtained in

different ways. One of them involves considering the total mechanical energy of the droplet as

the summation of its kinetic energy and its surface energy:

The kinetic energy of a cylinder of length L and radius R rotating about its central axis is

given by

in which

is the moment of inertia of a cylinder rotating about its central axis and ω is its angular velocity.

The surface energy of the droplet is given by

in which V is the constant volume of the droplet and σ is the interfacial tension. Then the total

mechanical energy of the droplet is

in which Δρ is the difference between the densities of the droplet and of the surrounding fluid.

At mechanical equilibrium, the mechanical energy is minimized, and thus

Substituting in

for a cylinder and then solving this relation for interfacial tension yields

http://en.wikipedia.org/wiki/Angular_velocity

http://en.wikipedia.org/wiki/Kinetic_energy

http://en.wikipedia.org/wiki/Moment_of_inertia

Page | 23

This equation is known as Vonnegut’s expression. Interfacial tension of any liquid that gives a

shape very close to a cylinder at steady state, can be estimated using this equation. The straight

cylindrical shape will always develop for sufficiently high ω; this typically happens for L/R >

4. Once this shape has developed, further increasing ω will decrease R while

increasing L keeping LR2 fixed to meet conservation of volume.


5.2.1. Materials Required

Crude oil used in the study was acquired from ONGC, Ankleshwar Asset. The crude oil is light

and its API index is found to be 38.2° at 15°C by using a pycnometer. The surfactant used in

the experiment was Sodium methyl ester sulfonate (SMES). Acrylamide monomer and

potassium persulfate were also obtained as important constituents in the polymeric surfactant.

Acetone was used as an extracting agent. The acrylamide-to-sulfonate ratio in the polymeric

surfactant PMES was essentially varied on a comparative basis. Sodium chloride (NaCl) was

also added in varying concentrations to SMES and polymeric methyl ester sulfonate (PMES)

for interfacial measurements.


Interfacial tensions between different polymeric surfactant and SMES solutions with crude oil

were measured with the help of spinning drop method. Model SVT 15 spinning drop

tensiometer equipped with video camera was used to determine the IFT at 298 K. In this

equipment, a horizontally arranged capillary glass tube filled with a bulk phase and a

specifically lighter drop phase is set in rotation. The diameter of the drop which is elongated

by centrifugal force correlates with the interfacial tension.

For each sample, SMES or PMES in aqueous solution was introduced into the high-temperature

capillary tube. The tube was first filled with the desired solution and then closed with Teflon

Page | 24

cap fitted with rubber gasket and washer. A small drop of the crude oil was injected into the

tube through the rubber spectrum using a syringe. Appropriate rotation speed was adjusted, so

that the crude oil droplet can be suitably elongated. Finally, the IFT between the two fluids

were calculated using a built in software system. The spinning drop tensiometer apparatus and

high-temperature capillary tube are shown in Figure 5.2 and 5.3 respectively.


Static and time dependent interfacial tension between two not completely miscible

liquids

Two and three dimensional extensional relaxation of viscoelastic liquids and liquid

droplets encapsulated or enclosed in membranes (only SVT 20)

Yield stress of liquid crystalline materials (only SVT 20)

Thermal expansion coefficients of liquids

Fig 5.2. Spinning Drop Tensiometer SVT 15N Assembly

Page | 25


The SVT 15N consists of the basic instrument with the following technical features:

Capillary system with electronically commutated, highly dynamic and vibration free

D.C. motor.

Software controlled speed; the SVT 20 also realizes stepwise and sinusoidal variations

of the rotational speed for the measurement of relaxational effects.

Intensity adjustable, stroboscopic and permanent LED-lighting with build-in triggering

of the video system for the observation of droplets in different orientations relative to

the CCD-camera system.

Fig 5.3. High Temperature Capillary Tube FEC 622/400-HT

Page | 26

SVT 20 with touch screen for real-time observation of temperature and other variables

of state; additional manual control of rotational speed, capillary tilt angle, stroboscopic

view angle and intensity of illumination.

Measuring capillaries with a diameter of 12 or 6.25mm, made of borosilicate glass;

optionally made of fused silica for UV light polymerization experiments

(encapsulation) of droplets.

Capillary block with software controlled tilt mechanism.

Automatic, software controlled positioning of the optical zoom lens for an easy

centering of the droplet along the optical axis.

High-performance six-fold power zoom lens with an integrated continuous fine focus

Video system with CCD-camera.

High-performance video digitizing board (frame grabber) for the PC.

Serial RS 232C interface with PC connecting cable, in the SVT 20 with additional

interface for the optional liquid dosing unit LDU and other accessories.

Automatic Calibration tool for scaling of droplet sizes for the video system.

Page | 27

Fig 5.4. Spinning Drop Video Tensiometer SVT 15N

5.2.5. SVT-15 Tensiometer Specifications

1. Measuring range- Interfacial tension: 1·10-6… 2·103 mN/m

2. Speed range- 0 ... 20000 rpm (0 ... 10000 rpm SVT 15)

3. Resolution- ± 0.001 rpm, long term stability of the absolute rotational speed: ± 0.5 rpm,

maximum speed step in relaxation tests: max. ± 2000 rpm/s (SVT 20)

4. Oscillation frequency- 0.01 … 200 Hz at a minimum speed of 3000 rpm (SVT 20)

5. Tilt angle of the capillary block- ± 10°, resolution: 0.0023°

6. Optics- Six-fold zoom lens (0.7 ... 4.5-fold magnification) with integrated fine focus

(± 6 mm) and high light transmitting capacity

7. CCD-camera- with a resolution of max. 768 x 576 pixels,

8. Field of view (FOV)- 1.9 x 1.4 to 12.1 x 9.1 mm

9. Optical distortion- < 0.05 %

Page | 28

10. Video system- High-performance image processing system with 132 MBytes/s data

transfer rate (compatible to European standard CCIR and US standard RS-170),

Up to 50 images/s digitizing speed

11. Measuring methods- Spinning Drop-Method

12. Diameter of capillary- outer 12 mm, inner 8 mm (optional: outer6.25 mm, inner 2.45

mm)

13. Temperature measurement and range- 2x Pt100 input for -60° … 450° C (Pt100

optional), 0.1 K resolution; 1/3 DIN IEC 751 (± 0.03 %), class B; Temperature range:

-10 ... 130 °C

14. Dimensions (L x W x H)- 390 x 390 x 400 mm

15. Weight- 25 kg (base unit SVT: 25 kg, power supply module: 10 kg)

16. Power supply- 100- 240 VAC; 50 … 60 Hz; 450 VA

17. Alternative/Supplementary units and accessories- Fitting/Capillary-Set for small

amounts of liquids; Precision-dosing systems; Control and Analysis Software

SCA20/SVT + SCA25/SVT; complete PC systems

5.2.6. Capillary Tube Specifications

1. Specification- FEC 622/400-HT

2. Type- Fast Exchange Capillary for High Temperature

3. Part no. 2000792

4. Material- Borosilicate Glass

5. Temperature Range- 30- 180° C

6. Outer diameter- 6.22 mm

7. Inner diameter- 4.00 mm

8. Visible Length- 50 mm

Page | 29


1. I make samples of desired concentrations ( above, below and on the CMC values)

2. I clean the capillary glass tube with water, acetone and/ or tetrachloro-ethylene.

3. I filled the capillary tube with the desired surfactant solution (SMES and PMES

solutions) with varying concentrations.

4. I ensured that the water supply to the tensiometer motor assembly is maintained, so as

to prevent heating.

5. I inserted the tube containing surfactant and polymeric surfactant solutions into the

capillary block and tightened the connections.

6. The tensiometer was in “OPEN” condition.

7. I rotated the tube at about 200-400 rpm speed by using the SVT software interface.

8. I injected a pint-sized amount of crude oil into the capillary tube during low-speed

rotation. I ensured that there were no air droplets in the tube, especially in the injected

crude sample.

Fig 5.5. A typical Spinning Drop (Crude Oil) in Capillary Tube in SVT 15N Tensiometer

9. I adjusted the rotational speed (~3000rpm).

10. I adjusted the camera position to view the specified drop on the screen.

11. I adjusted the tilt angle via SVT interface to stop/ hold the drop.

12. Timed Measurement (Using Profile Fit)

Page | 30

Move fitting box (frame) over the drop.

Select Profile Fit/ Fast Fit.

Extract Profile button.

Verify that the profile is detected correctly.

Set time interval (~ 5 seconds). Ensure the time-interval must be long enogh to

carry out finding of profile.

Open a “New Result Window” to save measuring values.

Click the “L” (Tracking/ Timed Measurement) button to start IFT

measurements at 5- second interval.

During the measurement, a graph between IFT (Mn/m) along Y-axis vs Time

stamp (s) along X- axis.

After a satisfactory number of measurements for a specified sample is obtained,

I clicked the “L” button to stop IFT measurement.

13. I saved the reading data in graph and table formats (as pdf/ xps format).

14. After a considerable number of readings, I repeated the procedure from 2 to 13 for

samples of other concentrations.

15. The value where IFT value is lowest is the modified CMC value.

16. At this CMC value, I varied Nacl concentrations (10%) to test the samples and repeat

the procedure from 2 to 13 and find the optimum salinity at CMC.

17. I cleaned the equipment and tube with acetone/ water after the testing of samples is

complete.

18. I switched off the SVT system, tensiometer and refrigerated water circulator. I covered

the tensiometer and capillary block with foam.

Page | 31


5.3.1. Effect of surfactant concentration on interfacial tension measurements

for SMES solution

The Interfacial Tension (IFT) of a surfactant- crude oil system depends on the adsorption of

the surfactant at the crude oil/ water interface. Surfactant type, concentration of surfactant,

temperature and other factors affect the adsorption of surfactants at the crude oil- water

interface. Surfactant concentration influences the IFT variation between crude oil and the water

system.

Fig 5.6. Variation of interfacial tension with surfactant concentration for SMES solution at 298 K

0

0.03

0.06

0.09

0.12

0.15

0 1000 2000 3000 4000 5000 6000 7000 8000

Inte

rfac

ial T

ensi

on

(m

N/m

)

Surfactant Concentration (ppm)

Page | 32

Fig 5.7. Snapshot of spinning drop (crude oil) at CMC value (5500 ppm) for SMES solution

Figure 5.6 shows the variation of interfacial tension values with SMES concentration in

aqueous solution at 298 K. Using spinning drop method, minimum values of IFT were obtained

for SMES solution at 500 ppm, 1500 ppm, 3500 ppm, 4500 ppm, 5500 ppm, 6500 ppm and

7500 ppm concentrations. It was observed that IFT initially decreases with surfactant

concentration. However after a particular limit, the value of IFT increases slightly. This value

of surfactant concentration at which interfacial tension is found to be minimum is called

‘Critical Micelle Concentration’. This behavior is observed because the surfactant molecule

starts to aggregate and form micelle in concentration at the interfaces, thereby restricting or

minimizing interfacial activity. As a result, IFT value after CMC either increases or remains

constant.

In IFT data measurements for SMES, the value of CMC was found to be 5500 ppm. The

corresponding minimum value of IFT was 0.0344 mN/m.

Page | 33

5.3.2. Effect of NaCl addition on interfacial tension measurements for SMES

solution

Fig 5.8. Variation of interfacial tension with NaCl salt concentration for 5500 ppm SMES solution at

298 K

Fig 5.9. Snapshot of spinning drop (crude oil) at optimal salinity (3.5%) at CMC (5500 ppm) for

SMES solution

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 1 2 3 4 5 6

Inte

rfac

ial T

ensi

on

(m

N/m

)

NaCl Concentration (%)

Page | 34

IFT was found to decrease drastically with salt addition as shown in Figure 5.8. It was observed

from the above figure that at 298 K, with increase in NaCl concentration in SMES solution,

interfacial tension initially decreases and then increases at a particular concentration of NaCl

salt. This is referred to as optimal salinity. Beyond optimal salinity, further addition of salt has

no or detrimental effects on interfacial activity.

The IFT was found to decrease upto a magnitude of the order of 0.05 on salt addition. The

lowest obtained value of IFT was 0.00197 mN/m at an optimal salinity of 3.5% NaCl. This

combined effect of salt and surfactant in crude oil/ water systems is often referred to as the

synergistic effect of salt-surfactant mixture on the IFT.

5.3.3. Effect of concentration on IFT of polymeric surfactant (PMES)

solutions with different acrylamide-to-surfactant ratios

IFT studies were carried out on polymeric surfactant solutions with varying acrylamide-to-

sulfonate ratios at 3500 ppm, 4500 ppm, 5500 ppm, 6500 ppm and 7500 ppm at 298 K. The

IFT values were found to decrease with increase in concentration and after that particular

concentration, it begins to increase slightly. The CMC values of various polymer methyl ester

sulfonate samples were obtained in this experiment. Figure 5.10 shows that the CMC values of

P1, P2, P3, P4 and P5 polymeric surfactants in aqueous solutions were 6500 ppm, 5500 ppm,

5500 ppm, 4500 ppm and 4500 ppm in descending order. The minimum IFT values at CMC

for P1, P2, P3, P4 and P5 were observed to be 0.0854, 0.0647, 0.0612, 0.0493 and 0.0352

mN/m respectively. It is hence clear from the interfacial data that P5 solution is best suited for

interfacial tension reduction. Another advantage is that P5 achieves low IFT value at lower

concentration (4500 ppm) than other polymeric surfactant solutions. The spinning drop

snapshots at the above mentioned IFT values are shown in Figure 5.11, 5.12, 5.13, 5.14 and

5.15.

Page | 35

Fig 5.10. Variation of IFT with PMES concentration at different acrylamide-to-sulfonate ratios at

298K

Fig 5.11. Snapshot of spinning drop (crude oil) at CMC value (6500 ppm) for P1 solution

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000

Inte

rfac

ial T

ensi

on

(m

N/m

)

Acrylamide-to-Sulfonate Ratio

P1 (0.4:1) P2 (0.5:1) P3 (0.6:1) P4 (0.8:1) P5 (1:1)

Page | 36



Page | 37



Page | 38

5.3.4. Effect of NaCl addition on the most effective polymeric surfactant

solution

Sodium chloride (NaCl) was varied at 0.5%, 1.5%, 2.5%, 3.5%, 4.5% and 5.5% to investigate

the effect of salt addition on IFT of the polymeric surfactant best suited for IFT reduction to

allow good mobility control. The interfacial tension decreased initially with increase in salt

concentration and then increased slightly for P5 polymeric surfactant (acrylamide-to-sulfonate

ratio 1:1) at 4500 ppm at 298 K. From Figure 5.16, it is evident that optimal salinity was

measured at 4.5% with interfacial tension value of 0.00432 mN/m. The spinning drop image is

shown in Figure 5.17.

Fig 5.16. Effect of NaCl addition on interfacial tension values for P5 sample (acrylamide-to-sulfonate

ratio 1:1) at 4500 ppm aqueous solution at 298 K

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 1 2 3 4 5 6

Inte

rfac

ial T

ensi

on

(m

N/m

)

NaCl Concentration (%)

Page | 39

Fig 5.17. Snapshot of spinning drop (crude oil) at optimal salinity (4.5%) at CMC (4500ppm) for P5

solution

5.3.5. Effect of Acrylamide-to-Sulfonate Ratios on salt-polymeric surfactant

mixture with lowest IFT value

Figure 5.18. Effect of variation of acrylamide-to-sulfonate ratios on the IFT values at 4500 ppm

PMES solution containing 4.5% NaCl at 298 K

0.003

0.0035

0.004

0.0045

0.005

0.0055

0.006

0.0065

0.007

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Inte

rfac

ial T

ensi

on

(m

N/m

)


Page | 40

Figure 5.19. Snapshot of spinning drop (crude oil) at optimal salinity (4.5%) at CMC (4500 ppm) for

salt-P4 (acrylamide-to-surfactant ratio 0.8:1) polymeric surfactant mixture

The most effective salt-polymeric surfactant mixture in terms of interfacial was obtained at

4500 ppm with 4.5% NaCl content. The acrylamide-to-surfactant ratios were varied to study

its relative effect on IFT measurements. It was evident from Figure 5.18 that P4 (acrylamide-

to-surfactant ratio 0.8:1) is more effectual than other polymeric surfactants to lower IFT to

ultra-low value than polymeric surfactants at combined conditions of CMC and optimal

salinity. This data is relevant in formulating potent salt-polymeric surfactant mixtures for

improved oil recovery by mechanism of interfacial tension reduction and desired mobility

control.

Page | 41

Chapter 6

Rheological Studies

6.1. Principle of rheometry

Rheometry is a powerful technique for the measurement of complex shear rheology across all

material types – sensitive enough to measure the viscosity of dilute polymer solutions, and yet

robust enough to measure the viscoelasticity of high modulus polymers or composites.

Rotational rheometry is ideal for discerning structural and compositional changes of materials,

which can be critical controlling factors in flow and deformation properties, and ultimately

product stability and performance.

The basic principle of rheometry is to perform simple experiments where the flow

characteristics such as the shear stress distribution and the velocity profile are known in

advance and can be imposed. Under these conditions, it is possible to infer the flow curve, that

is, the variation of the shear stress as a function of the shear rate, from measurements of flow

quantities such as torque and the rotational velocity for a rotational viscometer.

A rheometer is usually an instrument, which can exert a torque/force on a material and

accurately measures its response with time (or conversely, it can impose a strain and measures

the resulting torque).

The basics of the rotational rheometry technique are as follows:

The sample is loaded into the gap of a measuring system, or geometry – such as a cone and

plate or a concentric cylinder system – specifically designed to impose simple shear flow when

rotated.

The measuring system is supported by a virtually frictionless air-bearing, and driven by an

ultra-low inertia motor, coupled to an ultra-high precision position encoder. The sample and

measuring system are also temperature controlled.

Various rheological characteristics of the sample can be determined by rotating, oscillating or

applying a step function to the measuring system – either by controlling motor torque (stress

controlled rheometry) or position change (strain controlled rheometry).

Page | 42

Common test modes are rotational (or flow) to measure shear viscosity, and oscillation to

measure dynamic material properties such as viscoelastic modulus and phase angle.

Rotational rheometry also enables other rheological properties to be evaluated, including

yield stress, thixotropy, creep and recovery and stress relaxation.


6.2.1. Material(s) Required

Polymeric methyl ester sulfonate (PMES) solutions at different concentrations were

experimented for rheological data. Salts, namely sodium chloride (NaCl) and calcium

chloride (CaCl2) were also added at different concentrations to study their individual

effects on viscosity.


Rheological measurements were carried out using a Bohlin Gemini 2 Rheometer, shown in

Figure 6.1 manufactured by M/S Malvern Instruments Limited, UK. This rheometer is a model

of an ‘Advanced Air Bearing Rheometer’. It uses air as the lubricating medium, thereby

allowing virtually friction-free application of torque.

Ewart Mooney Geometry was used to obtain data in both viscometry and oscillatory mode

measurements. The viscosity and shear rate measurements in viscometry mode were carried

out using cup and bob (coaxial cylinder) measuring system. A small amount of the fluid was

filled in a test cell referred to as the cup. A flat-faced bob was pressed into the cylindrical cup

containing the fluid such that the vertical gap between the bob and the base of the cup

containing the fluid is 0.5 µm. The bob in contact with the fluid in the cup was then rotated at

varying specified speeds (strain rates). The force exerted by the fluid sample (in the narrow

vertical gap between the bob and the base of the cup) on the cylinder is indicated by the value

of the shear stress. The viscosity was measured due to the drag created by the fluid on the

cylindrical surface due to rotation of the bob.

The range of shear rate for viscometry mode for this experiment was varied in the range

from 1 to 1000 s-1, and the corresponding values of viscosity and shear rate were measured

corresponding to the varying shear rates. The viscometry readings were carried out at 298

Page | 43

K, 313 K and 333 K and their varying effects were compared at a speed of 80 s-1 as shown

in the figures, for different concentrations of the polymeric surfactant solutions. The

readings in the oscillatory mode were obtained using angular frequency between the values

of 0.1 and 150 rad/s. In oscillatory mode, amplitude sweep and frequency sweep

measurements were carried out on a small amount of the polymeric surfactant samples to

determine their viscoelastic properties. The oscillatory readings were obtained at 298 K.

Figure 6.1. Bohlin Gemini 2 Rheometer Assembly


Discernment of shear-thinning or shear-thickening behavior

Outlining a flow curve between shear stress and shear rate

Zero shear stress to determine Newtonian behavior, if any, at low shear rates

Yield stress data from critical shear rate

Viscoelastic properties

Page | 44


The Bohlin Gemini 2 Rheometer consists of the below mentioned technical features:

Rotonetic 2 Drive, patented, adaptive control technology which is optimized for both

strain controlled and stress controlled operation.

High resolution torque mapping system to allow low torques to be set very accurately.

Enabled testing in all conventional strain and stress controlled modes including stress

relaxation, creep and viscometric modes

Full range of EasySwap™ temperature controllers which include fully integrated peltier

devices, a forced gas oven with optional liquid nitrogen cooling and electrical heating.

Quick and easy configureuration to allow testing on a wide range of materials and

applications including polymer melts, composites, fluids and semi-solids.

6.2.5. Bohlin Gemini 2 Rheometer Specifications

1. Torque range: 0.05µNm …. 200mNm Controlled stress/rate viscometry. Controlled

stress/strain oscillation.

2. Torque resolution: Better than 1 nNm Position resolution: 50 nano radians

3. Frequency range: 1 micro Hz …. 150Hz

4. Controlled speed range (CR mode): 0.01 milli rad/sec …. 600 rad/sec

5. Measurable speed range (CS mode): 10 nano rad/sec …. 600 rad/sec

6. Normal force NI measurement range: 0.001 …. 20N (50N option)

7. Step change in strain: <10ms.

8. Temperature range (dependent on control used): -150°C …. 550°C

9. Temperature Controls:

Fluids Circulator: -40°C …. 250°C

ETO (Extended Temperature Option): -15°C …. 300°C

Melts Oven: ambient …. 450°C

Peltier Plate: -30°C …. 200°C

Peltier Cylinder: -20°C …. 180°C

Universal Peltier Option- Coaxial Cylinder or Cone-Plate Geometries

ETC (Extended Temperature Cell): ambient …. 550°C

Page | 45

ETC with optimal LTU (Low Temperature Unit): -150°C …. 550°C

10. Nominal operating voltage: 110V, 220V

11. Size (with Peltier plate): 52 cm (H) * 33 cm (W) * 37 cm (D)

12. Weight (with Peltier plate): 28 kg

13. Optional equipment(s)

Measuring Systems

Vacuum Disposable Plates: Peltier Plate, Melts Oven or ETO

High Pressure (Sealed Cell): 40 bar pressure, 30°C …. 150°C

High Pressure/ High Temperature Cell: 300 bar pressure, ambient …. 300°C

Optical UV Curing Cell

Optical Analysis Cell

Immobilisation Cell

Electro-rheology Cell: DC Voltage upto 10 Kv


1. I utilized the cup and bob (concentric cylinder) measuring system in order to

generate rheological data.

2. The cup, referred to as Mooney cell, is first cleaned thoroughly to remove any

impurities present.

3. I filled the cup with PMES samples upto the brim of the cup, and then placed the

bob at the center of the cup.

4. It is then ensured that a small amount of fluid is present in the narrow vertical gap

between cup and bob.

5. The assembly is then to for a stationary position.

6. The rheometer is then switched ‘ON’ and Gemini software is then opened.

7. First the experiment is conducted in viscometry mode at 298 K, 313 K and 333 K

for viscosity and shear stress measurements.

The range of values for shear rate and number of samplings is calibrated. In

our experiment, the shear rate is between 1 and 250 s-1 with 31 sample

points.

Page | 46

Then, we start the experiment to obtain 31 sample readings for both

viscosity and shear stress at equal intervals (linear/ logarithmic) of shear

rates between 1 and 250 s-1.

The viscosity and shear stress profile is obtained and saved in .xls format.

8. The above procedure is the repeated for PMES solutions containing salts (NaCl and

CaCl2) to obtain viscosity and flow curves for further analysis.

9. After the viscometric readings are completed, I started the oscillatory mode for

viscoelastic measurements at 298 K.

First, amplitude sweep experiments are conducted to study and decide the

frequency range for LVR (Linear Viscoelastic Condition) to achieve the

range for stability.

Frequency sweep measurements are then performed for LVR range of

angular frequencies, say 0.1 to 150 rad/s and predetermined number of

sample points, say 31.

The viscoelastic curves depicting the values of storage and loss moduli at

31 different frequency reading are obtained.

The curve is then copied and saved in .xls formal for further analysis.

10. The rheometer is then switched ‘OFF’ by plugging off the motor assembly and the

cylindrical assembly is the disassembled.

11. After repeating the viscometric and oscillatory measurement procedure explained

earlier, the values are separately plotted and checked for any discrepancies.

12. The viscosity and shear stress curve depicts the flow behavior of the PMES samples

and determines if it has shear thinning or shear thickening characteristics.

13. The shear stress curves depict the zero shear viscosity for each sample, portraying

the Newtonian flow region at low shear rates.

14. The viscoelastic curves portrayed in oscillatory mode shows the relationship of

dynamic moduli with angular frequency. Further analysis shows a crossover point

between storage modulus and loss modulus curves to determine the specific

frequency.

15. The value of SF obtained from all sample measurements represents the transition

point between the elastic and viscous phases.

Page | 47


6.3.1. Effect of Temperature on PMES viscosity

Variation of viscosity of PMES as a function of weight ratios of acrylamide monomer and

SMES present in polymeric surfactant has been studied. The flow curves for 2500 ppm, 5000

ppm and 7500 ppm PMES solutions at different acrylamide-to-sulfonate ratios at 80 s-1 shear

rate are shown in Figure 6.2, 6.3 and 6.4 respectively. The experiments were conducted at 298

K, 313 K and 333 K.

From the temperature dependence of viscosities, it is evident that at various ratios of PMES

solutions examined, the viscosities decreased with rise in temperature as expected [32]. This is

due to the fact that with temperature increase, the time period of contact between the

neighboring molecules reduces and the intermolecular interactions. In other words, cohesive

forces between the molecules decrease as an effect of the increased velocities of individual

molecules. It was found that with temperature rise, solution P5 having acrylamide-to-sulfonate

ratio 1:1 has higher viscosities than other solutions due to longer chain length of acrylamide

polymer.

Fig 6.2. Variation of Dynamic Viscosity of Polymeric Surfactant (PMES) with acrylamide to

sulfonate ratio for 2500 ppm PMES Solution at different temperatures

0

0.005

0.01

0.015

0.02

0.025

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

Vis

cosi

ty (

Pa.

s)

Acrylamide-to-Surfactant Ratio

298 K

313 K

333 K

ν= 80 s-1

Page | 48





0

0.005

0.01

0.015

0.02

0.025

0.03

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

Vis

cosi

ty (

Pa.

s)

Acrylamide-to-Surfactant Ratio

298 K

313 K

333 K

ν= 80 s-1

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

Vis

cosi

ty (

Pa.

s)


298 K

313 K

333 K

ν= 80 s-1

Page | 49

6.3.2. Effect of PMES concentration and acrylamide-to-sulfonate ratio on

viscosity and shear Stress

PMES concentrations in different acrylamide-to-sulfonate ratios were varied at 1500 ppm,

3000 ppm, 4500 ppm and 6000 ppm at 298 K. For viscometric analysis, the shear rate was

varied between 1 s-1 and 250 s-1. Solution viscosities increased with increasing concentration

for each PMES solution. As expected, viscosity was found to increase with concentration of

the polymeric surfactant. The viscosity profiles of polymeric surfactant solutions with varying

arylamide-to-sulfonate ratio at different concentrations, as found experimentally, have been

depicted in Figure 6.5, 6.6, 6.7, 6.8 and 6.9 as shown. It was observed that P5 recorded higher

viscosity than other solutions at low shear rates. Shear stress was expectedly found to increase

with concentration. As P5 yeilds best rheological data, the shear stress profile for P5 polymeric

surfactant is depicted in Figure 6.10. Consequently, P5 permits better mobility control and

greater sweep efficiency than other polymeric surfactants during displacement and recovery

processes [9]. Furthermore, viscosities of solutions were found to increase with increasing

acrylamide-to-sulfonate ratios. Increased viscosity may be attributed to their increased

hydrodynamic volume which has the twin effect of blocking the motion of solvent molecules

and retarding their motion by binding [33]. Shear stress profile depicted from experimental

results also showed increase with acrylamide-to-sulfonate ratio, shown in Figure 6.10.

Page | 50

Fig 6.5. Experimental Steady shear viscosity profile of P1 solution (with acrylamide-to-sulfonate ratio

0.4: 1) at 298 K at varying concentrations



0.001

0.01

0.1

1 10 100 1000

Vis

cosi

ty (

Pa.

s)

Shear rate (1/s)

1500 ppm 3000 ppm 4500 ppm 6000 ppm

0.001

0.01

0.1

1 10 100 1000

Vis

cosi

ty (

Pa.

s)

Shear rate (1/s)

1500 ppm 3000 ppm 4500 ppm 6000 ppm

Page | 51





0.001

0.01

0.1

1 10 100 1000

Vis

cosi

ty (

Pa.

s)

Shear rate (1/s)

1500 ppm 3000 ppm 4500 ppm 6000 ppm

0.001

0.01

0.1

1 10 100 1000

Vis

cosi

ty (

Pa.

s)

Shear rate (1/s)

1500 ppm 3000 ppm 4500 ppm 6000 ppm

Page | 52


1: 1) at 298 K at varying concentrations

Fig 6.10. Experimental Shear stress profile of P5 solution (with acrylamide-to-sulfonate ratio 1: 1) at

298 K at varying concentrations

0.001

0.01

0.1

1 10 100 1000

Vis

cosi

ty (

Pa.

s)

Shear rate (1/s)

1500 ppm 3000 ppm 4500 ppm 6000 ppm

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 50 100 150 200 250 300

Shea

r St

ress

(P

a)

Shear Rate (1/s)

1500 ppm

3000 ppm

4500 ppm

6000 ppm

Page | 53

Interestingly, it was observed that polymeric surfactant showed dual flow behavior at different

strain rates. It was observed from experimental results that all the solutions follow Newtonian

behavior upto a shear rate (or strain rate) of 50 s-1. This value of shear rate (50 s-1) which marks

the transition from Newtonian to non-Newtonian behavior is referred to as the critical shear

rate. Beyond 50 s-1 the solutions were found to exhibit non-Newtonian behavior. Critical shear

rate remained constant for polymeric surfactants of all concentrations and acrylamide-to-

sulfonate ratios. This indicates that the viscosity of fluids is independent of the shear stress and

shear stress increases linearly with strain rate upto a strain rate of 50 s-1. Reduction in viscosity

with shear rate is primarily related to the orientation of macromolecules along the flow

streamline and to the disentanglement of macromolecules with increase in shear force [34].

Shear-thinning behavior of polymeric surfactants at high shear rates may prove to be favorable

during injection process, due to viscosity decrease at higher shear rates, increasing injectivity

[19]. Furthermore, high consistent viscosity values are desirable when polymeric surfactant

moves deep into the reservoir at low shear rates, thereby improving mobility control and

recovery efficiency [9].

6.3.3. Effect of addition of salt on PMES viscosity

On the basis of rheological experiments, it was found that viscosity of polymeric surfactant

increased with concentration. Analysis of polymeric surfactant P5 at different concentrations

resulted in higher mobility control than surfactants with other acrylamide-to-sulfonate ratios.

The effects of addition of 1.5% and 2% sodium chloride (NaCl) and calcium chloride (CaCl2)

on the viscosity of 6000 ppm P5 solution were studied at 298 K. Viscosity was observed to

decrease with NaCl and CaCl2 addition as shown in figure 6.11 and 6.12.

Analysis of flow curves obtained from addition of salt showed Newtonian behavior at low

shear rates. At any specified shear rate, the apparent viscosity was diminished as concentration

of salts increased. The critical shear rate 50 s-1 at which a transition from Newtonian to

pseudoplastic behavior remained constant with increasing salt concentration. This decrease in

viscosity of polymeric surfactant in the presence of salts is mainly attributed to change in

conformation of molecules, which reduces the hydrodynamic diameter and diminishes the

degree of molecule chain entanglement [34]. Both NaCl and CaCl2 were observed to suppress

the viscosity of the polymer surfactant solution. However, CaCl2 reduces the viscosity to a

greater extent because of the doubly charged cations. Moreover, Ca2+ may act as a cross-linking

Page | 54

agent to interconnect the molecule chains and further influence the conformation and flow

behavior of the polymeric surfactant in aqueous solution.

Fig 6.11. Effect of addition of NaCl on the viscosity profile of 6000 ppm P5 solution (with

acrylamide-to-sulfonate ratio 1: 1) at 298 K at varying concentrations

Fig 6.12. Effect of addition of CaCl2 on the viscosity profile of 6000 ppm P5 solution (with

acrylamide-to-sulfonate ratio 1: 1) at 298 K at varying concentrations

0.001

0.01

0.1

1 10 100 1000

Vis

cosi

ty (

Pa.

s)

Shear Rate (1/s)

No NaCl

1.5% NaCl

2% NaCl

0.001

0.01

0.1

1 10 100 1000

Vis

cosi

ty (

Pa.

s)

Shear Rate (1/s)

No CaCl2

1.5% CaCl2

2% CaCl2

Page | 55

Fig 6.13. Effect of addition of NaCl and CaCl2 on zero-shear stress curve of 6000 ppm P5 solution

(with acrylamide-to-sulfonate ratio 1: 1) at 298 K at varying concentrations

At low shear rates, the polymer surfactant exhibited Newtonian behavior. Viscosity in the

Newtonian regime is referred to as zero shear viscosity [35]. The value of zero shear viscosity

is very important in understanding the microstructure of the polymeric surfactant. The effect

of addition of NaCl and CaCl2 (at 40 s-1 shear rate) on zero shear viscosity of polymeric

surfactant P5 at 6000 ppm is depicted in Figure 6.13. The zero shear viscosity was found to

decrease with increase in salt concentration in the polymeric surfactant solution. This is

explained by alteration in the conformity of molecules, that diminishes the degree of

entanglement or aggregation of molecule chains.

6.3.4. Effect of concentration on dynamic viscoelasticity

Determination of dynamic modulus is instrumental in determining both elastic and viscous

characteristics when undergoing deformation. Figure 6.14 shows the dynamic viscoelasticity

curves of PMES between dynamic modulus and angular frequency at 298 K. Angular

0

0.005

0.01

0.015

0.02

0.025

0 0.5 1 1.5 2 2.5

Vis

cosi

ty (

Pa.

s)

Salt Concentration (%)

NaCl

CaCl2

Page | 56

frequency readings were varied between 0.1 and 150 radians/second. Oscillatory experiments

were conducted for P5 polymeric surfactant (allowing for maximum mobility control) at

concentrations of 1500, 3000, 4500 and 6000 ppm.

Fig 6.14. Dynamic viscoelasticity curves showing the effect of angular frequency on storage and loss

moduli for P5 solution (with Sulfonate-to-acrylamide ratio 1: 1) at 298 K at varying concentrations

It was observed that the polymeric surfactant exhibited viscoelastic properties. Both storage

modulus G' and loss modulus G'' increased with increasing PMES concentration. A crossover

point was found for G' and G'' of each polymer surfactant solution. This crossing point

determines the specific frequency (SF). In experimental results illustrated in Figure 6.14, the

value of specific frequency was found to decrease with increased PMES concentration. The

value of specific frequency is instrumental in signifying the point of transition between the

elastic phase and viscous phase of the sample [36]. The loss modulus G'' was higher than the

storage modulus G' when angular frequency was less than SF, showing that the viscous

component dominated the viscoelastic properties of PMES solutions. But, when the angular

velocity was greater than the SF value, elasticity component (or storage component) was the

controlling factor and was more effective than the viscous component.

0.0001

0.001

0.01

0.1

1

10

100

0.1 1 10 100 1000

G' &

G''

(Pa)

Angular Frequency (rad/s)

G' 1500 ppm G'' 1500 ppm G' 3000 ppm G'' 3000 ppm G' 4500 ppm G'' 4500 ppm G' 6000 ppm G'' 6000 ppm

Page | 57

Chapter 7

Summary and Conclusions

Numerous experimental studies have been carried out to understand the characterization and

flow properties of a novel polymeric surfactant synthesized from castor oil methyl ester.

Primary focus was stressed upon the investigation of particle size distribution (DLS analysis),

interfacial tension (spinning drop tensiometer) and rheological data (rheometer).

Careful examination of particle size distribution profile for polymeric surfactant revealed that

hydrodynamic diameter generally increases with increasing PMES concentration due to the

aggregation of the molecules. With increase in salt (concentration) addition, hydrodynamic

diameter was generally found to decrease since micelles may disaggregate to smaller size and

may even break down to polymer chains. This may be due to rolling up of CMC segments in

aqueous salt solutions, thereby changing particle structure from rod-like to spherical shape. As

a result, the size of micelles becomes smaller. This knowledge is particularly important for

correlating data to reduce surface tension and interfacial tension, aimed at improved oil

recovery.

Interfacial data was obtained to compare results and corresponding effects of both SMES and

polymer methyl ester sulfonate (PMES). It was observed that IFT initially decreases with

surfactant and PMES concentration. However after a particular limit, the value of IFT increases

slightly. This value of surfactant concentration at which interfacial tension is found to be

minimum is called ‘Critical Micelle Concentration’. This behavior is observed because the

surfactant/ polymeric surfactant molecule starts to aggregate at this CMC value and form

micelle in concentration at the interfaces, thereby restricting or minimizing interfacial activity.

As a result, IFT value after CMC either increases or remains constant. In IFT data

measurements for SMES, the value of CMC was found to be 5500 ppm and its corresponding

minimum IFT value was 0.0344 mN/m. Furthermore for polymeric surfactants in aqueous

solutions, the minimum IFT values for P1, P2, P3, P4 and P5 were observed to be 0.0854,

0.0647, 0.0612, 0.0493 and 0.0352 mN/m at CMC values of 6500 ppm, 5500 ppm, 5500 ppm,

4500 ppm and 4500 ppm respectively.

IFT was found to decrease drastically with salt addition. At 298 K, with increase in NaCl

concentration in SMES and PMES solutions, interfacial tension initially decreases and then

Page | 58

increases at a particular concentration of NaCl salt. This is referred to as optimal salinity.

Beyond optimal salinity, further addition of salt has no or detrimental effects on interfacial

activity. The lowest obtained value of IFT for SMES solution was 0.00197 mN/m at an optimal

salinity of 3.5% NaCl. This combined effect of salt and surfactant in crude oil/ water systems

is often referred to as the synergistic effect of salt-surfactant mixture on the IFT. The interfacial

tension decreased initially with increase in salt concentration and then increased slightly for P5

polymeric surfactant (acrylamide-to-sulfonate ratio 1:1) at 4500 ppm at 298 K. optimal salinity

was measured at 4.5% with interfacial tension value of 0.00432 mN/m. The most effective salt-

polymeric surfactant mixture in terms of interfacial was obtained at 4500 ppm with 4.5% NaCl

content. P4 (acrylamide-to-surfactant ratio 0.8:1) is more effectual than other polymeric

surfactants to lower IFT to ultra-low value than polymeric surfactants at combined conditions

of CMC and optimal salinity.

An extensive study was made to study the rheological (flow) behavior of polymeric surfactants

to determine proper formulations/ mixtures for improved mobility control. From the

temperature dependence of viscosities, it is evident that at various ratios of PMES solutions

examined, the viscosities decreased with rise in temperature as expected. This is due to the fact

that cohesive forces between the molecules decrease as an effect of the increased velocities of

individual molecules. It was found that with temperature rise, solution P5 having acrylamide-

to-sulfonate ratio 1:1 has higher viscosities than other solutions due to longer chain length of

acrylamide polymer. Viscosity was found to increase with concentration of the polymeric

surfactant. It was observed that P5 recorded higher viscosity than other solutions at low shear

rates. Shear stress was expectedly found to increase with concentration. Furthermore,

viscosities of solutions were found to increase with increasing acrylamide-to-sulfonate ratios.

Increased viscosity may be attributed to their increased hydrodynamic volume which has the

twin effect of blocking the motion of solvent molecules and retarding their motion by binding

with them. Interestingly, it was observed that polymeric surfactant showed dual flow behavior

at different strain rates. It was observed from experimental results that all the solutions follow

Newtonian behavior upto a shear rate (or strain rate) of 50 s-1. This value of shear rate (50 s-1)

which marks the transition from Newtonian to non-Newtonian behavior is referred to as the

critical shear rate. Beyond 50 s-1 the solutions were found to exhibit pseudoplastic or shear-

thinning characteristics. Reduction in viscosity with shear rate is primarily related to the

orientation of macromolecules along the flow streamline and to the disentanglement of

macromolecules with increase in shear force. Shear-thinning behavior of polymeric surfactants

Page | 59

at high shear rates may prove to be favorable during injection process, due to viscosity decrease

at higher shear rates, increasing injectivity. Furthermore, high consistent viscosity values are

desirable when polymeric surfactant moves deep into the reservoir at low shear rates, thereby

improving mobility control and recovery efficiency. Both NaCl and CaCl2 were observed to

suppress the viscosity of the polymer surfactant solution. However, CaCl2 reduces the viscosity

to a greater extent because of the doubly charged cations. This decrease in viscosity of

polymeric surfactant in the presence of salts is mainly attributed to change in conformation of

molecules, which reduces the hydrodynamic diameter and diminishes the degree of molecule

chain entanglement. Moreover, Ca2+ may act as a cross-linking agent to interconnect the

molecule chains and further influence the conformation and flow behavior of the polymeric

surfactant in aqueous solution. The zero shear viscosity was found to decrease with increase in

salt concentration in the polymeric surfactant solution. This is explained by alteration in the

conformity of molecules, that diminishes the degree of entanglement or aggregation of

molecule chains. It was observed that the polymeric surfactant exhibited viscoelastic

properties. Both storage modulus G' and loss modulus G'' increased with increasing PMES

concentration. A crossover point was found for G' and G'' of each polymer surfactant solution.

This crossing point determines the specific frequency (SF). The value of specific frequency is

instrumental in signifying the point of transition between the elastic phase and viscous phase

of the sample.

The above investigated data from DLS, IFT and rheological experiments is very useful for the

formulation of effective salt-polymeric surfactant mixtures for improved oil recovery by

mechanism of interfacial tension reduction and desired mobility control. It is also a major factor

controlling the selection of proper polymeric surfactants (with/ without salt) with cost-

effectiveness in desired applications

Page | 60

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