Title: Surface properties and flow behavior of foams in relation to fluid displacement in porous media /
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Title: Surface properties and flow behavior of foams in relation to fluid displacement in porous media /
Physical Description: xviii, 255 leaves : ill. ; 28 cm.
Language: English
Creator: Ling, Tien-Feng Tyrone, 1954-
Publication Date: 1987
Copyright Date: 1987
 Subjects
Subject: Foam   ( lcsh )
Porous materials   ( lcsh )
Fluid dynamics   ( lcsh )
Chemical Engineering thesis Ph. D
Dissertations, Academic -- Chemical Engineering -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
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Thesis: Thesis (Ph. D.)--University of Florida, 1987.
Bibliography: Bibliography: leaves 247-254.
Statement of Responsibility: by Tien-Feng Tyrone Ling.
General Note: Typescript.
General Note: Vita.
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Bibliographic ID: UF00098258
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 001076285
oclc - 19045232
notis - AFG1044

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SURFACIEI ,,$ OPiRTIES AND FLOW BEHAVIOR OF FOAMS
IN RELATION TO FLUID DISPLACEMENT IN POROUS MEDIA









By

TIEN-VNG TYRONE LING

















SDTI PRESENTED TO THE GRADUATE SCHOOL
UNIVERSITY OF FLORIDA IN
L FULFILLMENT OF THE REQUIREMENTS
F E DEGREE OF DOCTOR OF PHILOSOPHY



UNIVERSITY OF FLORIDA


1987
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To

my parents and my wife












ACKNOWLEDGEMENTS


I wish to express my sincere appreciation to Professor

Dinesh O. Shah, thesis advisor and chairman of the

supervisory committee, for his excellent guidance and

continuous encouragement. I also would like to convey my

deep appreciation and thanks to Professor Birdwell

Finlayson for his advice and concern as well as generous

support. Special thanks also go to the members of the

supervisory committee, Professors J.P. O'Connell, R.

Narayanan, G. Westermann-Clark, G. Lyberatos, and B.M.

Moudgil for their time, advice, and interest in my research

activities.

I thank my colleagues in Professor Shah's group for

the many hours spent in fruitful conversation and

encouragement. Thanks are gratefully extended to Charles

Brown, Heike Charest, Tracy Lambert, Ronald Baxley, Shirley

Kelly, and Nancy Krell for their assistance and

cooperation. My gratitude also extends to Thomas M.

Dunthorn, Alison Jessup, and Patricia Brown for their

assistance of proof reading during the preparation of this

manuscript.

Above all, I wish to express my most sincere thanks to

my parents, Mr. and Mrs. Kung-Po Ling, and my wife,

Ling-Jean, for their many years of love, patience, and


iii







support without which this work could not have been

accomplished. I thank, too, my son, Vincent, who has given

me much joy in my life.














TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ........................................ iii

LIST OF TABLES...................... ................. vii

LIST OF FIGURES........ .... .. ........................ viii

ABSTRACT..... ......................................... xvi

CHAPTER

I INTRODUCTION................................. 1

II SURFACE PROPERTIES OF FOAMING AGENTS AND
FOAM STABILITY............................ 9

2.1 Introduction........................... 9
2.2 Materials and Methods .................. 12
2.3 Theory .................................. 21
2.4 Results and Discussion.................. 31
2.5 Conclusions ............................ 74

III FLUID DISPLACEMENT IN POROUS MEDIA BY
IN-SITU FOAM .............................. 78

3.1 Introduction............................ 78
3.2 Materials and Methods................... 79
3.3 Effective Mobility of Air in the
Presence of Foam..................... 82
3.4 Results and Discussion.................. 85
3.5 Conclusions ............................ 117

IV MODELING OF FOAM FLOW IN POROUS MEDIUM...... 121

4.1 Introduction. ........................... 121
4.2 Theory....... ...... ................... 123
4.3 Results and Discussion ................. 135
4.4 Conclusions ............................ 154

V STABILITY OF THIN FILMS ... ................. 156

5.1 Introduction ........................... 156
5.2 DLVO Theory............................. 157
5.3 Derivation. ............................ 160
5.4 Numerical Method........................ 166








5.5 Results and Discussion ................. 172
5.6 Conclusions ............................ 177

VI EFFECTS OF ADDING POLYMER ON THE FOAM....... 178

6.1 Introduction. ........................... 178
6.2 Theory................................. 180
6.3 Results and Discussion.................. 182
6.4 Conclusions ............................ 205

VII APPLICATIONS OF FLUID FLOW THROUGH POROUS
MEDIA.. .................................... 209

7.1 Heavy Oil Recovery by Foam Flooding.... 209
7.2 Transport Mechanism of Viscoelastic
Gels in Porous Media.................. 221

VIII CONCLUSIONS AND RECOMMENDATIONS............. 237

8.1 Conclusions ............................ 237
8.2 Recommendations ........................ 240

APPENDIX A............................................ 244

APPENDIX B............................................ 246

REFERENCES..... ....... ............................... 247

BIOGRAPHY............................................ 255















LIST OF TABLES


Table Page

3.1 Summary of the Surface Properties of the Mixed
Foaming Agents of SDS with Different Alkyl
Alcohols. ........................................ 99

4.1 Average Time-dependent Z Function for Mixed
Foaming Agents of Stepanflo Surfactants......... 137

4.2 Average Time-dependent Z Function for Mixed
Foaming Agents of SDS + C OH + NaCl............. 138

4.3 Average Time-dependent Z Function for Mixed
Foaming Agents of Stepanflo 40 + CnOH + NaCl .... 139

4.4 Predictions of Pressure and Velocity at L/4
for a Foam Compressibility of 0.01.............. 145

4.5 Predictions of Pressure and Velocity at L/4
for a Foam Compressibility of 0.001............. 146

4.6 Predictions of Pressure and Velocity at L/4
for a Foam Compressibility of 0.0001............ 147


vii













LIST OF FIGURES


Figure Page

1.1 Schematic Illustration of the Effects of Foam on
Transport of Steam or Gas in Porous Media.......... 3

2.1 Apparatus for the Measurement of Foam Quality..... 16

2.2 Apparatus for the Measurement of Apparent Foam
Viscosity. ....................................... 18

2.3 Schematic Diagram of Apparatus for Foam Flow
through a Micromodel .............................. 20

2.4 Plateau Border in a Foam........................... 28

2.5 Variation in Surface Tension as a Function of the
Concentration of Suntech IV Surfactants........... 32

2.6 Variation in Surface Tension as a Function of the
Concentration of Stepanflo Surfactants............ 33

2.7 Surface Tension for Solutions of SDS and Alkyl
Alcohols. ........................................ 34

2.8 Surface Tension for Solutions of SDS + Alkyl
Alcohols with and without Salt.................... 36

2.9 Surface Tension of Mixture of SDS + Alkyl Alcohols
in 0.5% Brine as a Function of the Concentration
of SDS............................................ 37

2.10 Effect of Surfactants with Different Alkyl
Alcohols on Surface Tension........................ 39

2.11 Variation in Surface Viscosity as a Function of
the Concentration of Suntech IV Surfactants....... 40

2.12 Effect of the Concentration of Suntech IV
Surfactants on Foaminess........................... 42

2.13 Variation in Foaminess for Stepanflo Surfactants.. 43

2.14 Effect of Surfactants with Different Alkyl
Alcohols on Foaminess ............................. 44


viii








2.15 Variation in Foam Quality for Stepanflo
Surfactants ....................................... 46

2.16 Variation in Foam Quality as a Function of the
Concentration of Stepanflo 40..................... 48

2.17 Variation in Foam Quality as a Function of SDS
with Different Alkyl Alcohols...................... 49

2.18 Variation in Foam Quality as a Function of
Stepanflo 40 with Different Alkyl Alcohols........ 50

2.19 Variation in Apparent Foam Viscosity for
Stepanflo Surfactants............................. 51

2.20 Apparent Foam Viscosity for Mixed Foaming Agents
of Stepanflo 40 and Alkyl Alcohols................ 53

2.21 Apparent Foam Viscosity for Mixed Foaming Agents
of SDS and Alkyl Alcohols.......................... 54

2.22 Apparent Foam Viscosity as a Function of Foam
Quality........................................... 56

2.23 Rate of Drainage for Mixed Foaming Agents of SDS
and Alkyl Alcohols................................. 58

2.24 Rate of Drainage for Mixed Foaming Agents of
Stepanflo 40 and Alkyl Alcohols................... 59

2.25 Rate Constants of Drainage Process for Mixed
Foaming Agents of SDS and Alkyl Alcohols.......... 62

2.26 Rate Constants of Drainage Process for Mixed
Foaming Agents of Stepanflo 40 and Alkyl
Alcohols ...........................................63

2.27 Photographs of Suntech IV Foams at Various Time
Intervals after the Foams Were Produced............ 64

2.28 Photographs of Foams for Mixture of SDS with
Alkyl Alcohols at Various Time Intervals after
the Foams Were Produced........................... 65

2.29 Photographs of Foams for Mixture of SDS with
Alkyl Alcohols at Various Time Intervals after
the Foams Were Produced............................ 66

2.30 Photographs of Foams for Mixture of Stepanflo 40
with Alkyl Alcohols at 24 Hours after the Foams
Were Produced. ................................... 67







2.31 Histograms of Bubble Size Distribution for
Suntech IVA Foam at 60 Minutes after the Foam
Was Produced. ..................................... 68

2.32 Histograms of Bubble Size Distribution for
Suntech IVB Foam at 60 Minutes after the Foam
Was Produced. ..................................... 69

2.33 Histograms of Bubble Size Distribution for
Suntech IVC Foam at 60 Minutes after the Foam
Was Produced. ..................................... 70

2.34 Photomicrograph of Foams in Micromodel............ 73

2.35 Two Mechanisms of Gas Flow in Porous Media Filled
with Surfactant Solution........................... 75

3.1 Schematic Diagram of the Experimental Set Up for
Flow through Porous Media Studies................. 81

3.2 Schematic Diagram of the Heterogeneous Porous
Media for Fluid Displacement Experiments with
and without Foam................................... 83

3.3 Effect of the Concentration of Suntech IV
Surfactants on Fluid Displacement Efficiency....... 86

3.4 Variation in Breakthrough Time as a Function of
the Concentration of Suntech IV Surfactants........ 87

3.5 Effect of the Concentration of Suntech IV
Surfactants on Effective Air Mobility............. 89

3.6 Fluid Displacement Efficiency and Breakthrough
Time Produced by Stepanflo Surfactants............ 90

3.7 Effect of SDS with Different Alkyl Alcohols on
Fluid Displacement Efficiency and Breakthrough
Time............................................... 92

3.8 Effect of Stepanflo 40 with Different Alkyl
Alcohols on Fluid Displacement Efficiency and
Breakthrough Time.................................. 93

3.9 Effect of Suntech IVA with Different Alkyl
Alcohols on Fluid Displacement Efficiency and
Breakthrough Time.................................. 94

3.10 Effect of Surfactants with Different Alkyl
Alcohols on Effective Air Mobility................ 95

3.11 Comparison of Fluid Displacement Efficiency Using
SDS(5mM)+CnOH(0.5mM) with Sharma's Results......... 98








3.12 Fluid Recovery from Berea Core in Heterogeneous
porous media versus Concentration of Suntech IVA..102

3.13 Fluid Recovery from Berea Core in Heterogeneous
porous media as a Function of SDS Concentration
Mixed with Alkyl Alcohols and Salt................ 104

3.14 Effect of SDS with Different Alkyl Alcohols on
Fluid Displacement Efficiency in Various Porous
Media.............................................106

3.15 Effect of SDS with Different Alkyl Alcohols on
Breakthrough Time in Various Porous Media..........107

3.16 Effect of SDS with Different Alkyl Alcohols on
Effective Air Mobility in Various Porous Media....108

3.17 Variation in Fluid Displacement Efficiency as a
Function of the Volume of Surfactant Solution
Injected into Various Porous Media................ 109

3.18 Variation in Breakthrough Time as a Function of
the Volume of Surfactant Solution Injected into
Various Porous Media ..............................111

3.19 Fluid Recovery from Berea Core as a Function of
the Volume of Surfactant Solution Injected into
Heterogeneous Porous Media......................... 112

3.20 Schematic Illustration of the Pressure
Distribution in Porous Media during the Foam
Flooding Process...................................113

3.21 A typical Pressure Distribution Measured at
Several Fixed Points during the Foam Flooding
Process...........................................115

3.22 Pressure Drops at Breakthrough Time between Two
Fixed Points along Various Porous Media............116

3.23 Variation in Fluid Displacement Efficiency as a
Function of the Pressure Drops at Breakthrough
Time...............................................118

4.1 Cylindrical Coordinates System.................... 130

4.2 Pressure Distributions Measured at Several Fixed
Points during the Foam Flooding Process........... 141

4.3 Pressure Distributions Predicted by the Model at
Several Fixed Points along a Porous Medium ........142







4.4 Comparison of Velocity Profiles at Several Fixed
Points Predicted by the Model with Experimental
Data Measured at the Outlet....................... 144

4.5 Prediction of Velocity Profile as a Function of
Foam Viscosity.....................................149

4.6 Prediction of Velocity Profile as a Function of
Radius for Various Porous Media.....................151

4.7 Effect of Foam Viscosity on Velocity Profile
Predicted by the Model ............................152

4.8 Prediction of Volume Flow Rate as a Function of
Foam Viscosity for Various Porous Media........... 153

5.1 Potential Energy as a Function of Separation
Distance ......................................... 158

5.2 Bispherical Coordinates System. n = ln(r2/r1 ),
where Q1 and Q, are Limit Points at co, -o,
Respectvely........................................ 162

5.3 Bispherical Coordinates System and Symbols Used
to Determine the Bispherical Coordinates..........164

5.4 A Mapping of Bispherical Coordinates onto
x-y Space .........................................167

5.5 Flow Chart of a Numerical Method for Solving the
Generalized Poisson-Boltzmann Equation in
Bispherical Coordinates............................ 171

5.6 Repulsive Interaction Energy as a Function of
Separation Distance................................ 173

5.7 Repulsive Interaction Energy as a Function of
Ionic Strength.....................................175

5.8 Effect of Number of Grids on Repulsive
Interaction Energy.................................176

6.1 Surface Tension of Mixture of SDS + C OH + NaC1
as a Function of the Concentration of Decyl
Alcohol.............................................. 184

6.2 Surface Tension of Mixture of Stepanflo 40
+ C OH + NaCl as a Function of the Concentratiion
of bDecyl Alcohol .................................. 185

6.3 Effect of SDS with Different Concentrations of
Decyl Alcohol on Fluid Displacement Efficiency.... 186


xii








6.4 Effect of SDS with Different Concentrations of
Decyl Alcohol on Breakthrough Time and Effective
Air Mobility...................................... 187

6.5 Effect of Stepanflo 40 with Different
Concentrations of Decyl Alcohol on Fluid
Displacement Efficiency...........................188

6.6 Effect of Stepanflo 40 with Different
Concentrations of Decyl Alcohol on Breakthrough
Time and Effective Air Mobility................... 189

6.7 Effect on Surface Tension of Adding Xanthan to
SDS Solution, with and without Decyl Alcohol...... 191

6.8 Effect on Surface Tension of Adding Xanthan to
Stepanflo 40 Solution, with and without Decyl
Alcohol. .......................................... 192

6.9 Variation in Foam Quality for Mixed Foaming
Agents of SDS + CIoOH with Different Xanthan
Concentrations...................................... 194


6.10 Variation in Foam Quality for Mixed Foaming
Agents of Stepanflo 40 + C, OH with Different
Xanthan Concentrations.......................

6.11 Foam Quality of Various Mixed Foaming Agents
as a Function of Time........................

6.12 Foam Quality of various Mixed Foaming Agents
as a Function of Time........................

6.13 Rate of Drainage for Mixed Foaming Agents of
SDS + C OH with Different Concentrations of
Xanthan ......................................

6.14 Rate of Drainage for Mixed Foaming Agents of
Stepanflo 40 + C OH with Different
Concentrations o Xanthan....................

6.15 Effect of Adding Xanthan on Apparent Foam
Viscosity....................................


.....195


.....197


.....198



.....199



.....200


.....202


6.16 Bubble Size for Foams of Mixture of SDS + C OH
with Different Xanthan Concentrations at
16 Hours after the Foams Were Produced............203


6.17 Bubble Size for Foams of Mixture of Stepanflo 40
+ C OH with Different Xanthan Concentrations
at i% Hours after the Foams Were Produced.......


..204


xiii







6.18 Mean Radii of Mixed Foaming Agents as a Function
of Xanthan Concentrations..........................206

7.1 Tertiary Oil Recovery by Foam and Polymer
Flooding Methods with the Same Foaming Solutions
Containing Xanthan ................................215

7.2 Histogram of Oil Production by Polymer Flooding...217

7.3 Histogram of Oil Production by Foam Flooding......219

7.4 Schematic Diagram of the Surfactant-Polymer-Foam
Flooding in Comparison with the Surfactant-
Polymer Flooding.................................. 220

7.5 Comparison of Tertiary Oil Recovery by
Surfactant-Polymer Flooding and Surfactant-
Polymer-Foam Flooding .............................222

7.6 Histogram of Oil Production by Surfactant-Polymer
Flooding........................................... 223

7.7 Histogram of Oil Production by Surfactant-
Polymer-Foam Flooding .............................224

7.8 Reproducibility of the Wash-out Kinetics Method...227

7.9 Pressure Drops of Various Biopolymers
(50% vol./vol.) as a Function of the Volume of
Balanced Salt Solution Injected into Porous
Media................................................ 229

7.10 Pressure Drops of Various Biopolymers
(75% vol./vol.) as a Function of the Volume of
Balanced Salt Solution Injected into Porous
Media .............................................230

7.11 Pressure Drops of Various Biopolymers
(No Dilution) as a Function of the Volume of
Balanced Salt Solution Injected into Porous
Media .............................................231

7.12 Effect of Polymer Concentration on the Maximum
Pressure Drop Developed at Breakthrough...........232

7.13 Pressure Drops of Sodium Hyaluronate and
Chondroitin Sulfate as a Function of Balanced
Salt Solution Injected into Porous Media..........233


xiV








7.14 Effect of Interaction between Sodium Hyaluronate
and Chondroitin Sulfate on Pressure Developed in
Porous Media...................................... 234

7.15 Effect of Interaction between Sodium Hyaluronate
and Chondroitin Sulfate on the Maximum Pressure
Drop Developed at Breakthrough....................235











Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy



SURFACE PROPERTIES AND FLOW BEHAVIOR OF FOAMS
IN RELATION TO FLUID DISPLACEMENT IN POROUS MEDIA




By

TIEN-FENG TYRONE LING

December, 1987



Chairman: Dinesh 0. Shah
Major Department: Chemical Engineering Department


Surface properties such as surface tension, surface

viscosity, foaminess, foam quality, apparent foam viscosity,

rate of drainage, bubble size distribution, etc., were

investigated and correlated with fluid displacement in

porous media. The effect of chain length compatibility,

i.e., similarity, on surface properties of foaming

solutions and fluid displacement in porous media were also

studied. The foam behavior in porous media was well

correlated to the surface properties of the foaming agent.

The presence of long chain alcohols in the foaming agent

improved fluid displacement compared to results obtained by

the foaming agent alone. However, the effect of chain

length compatibility was only partially observed for the


xvi








fluid displacement experiments.

Two mathematical models for foam flow through porous

media were developed which can be used to predict foam

viscosity and foam behavior in porous media. To better

understand the foam stability, a numerical solution of the

Poisson-Boltzmann equation in two dimensional bispherical

coordinates was obtained and used to calculate the

potential energy of interaction between two spherical

bubbles. The method is completely general because neither

the simplified equation (e.g., the first few terms of an

expansion of the Boltzmann equation with restrictions on

potential magnitude) nor other restrictive conditions

(e.g., infinite flat plate model, small surface potential,

univalent-salt condition, etc.) are required. Predicted

potential energies were consistent with results from other

models.

The effect of polymer on foam properties was also

studied. The improvement of surface activity of the

surfactants was due mainly to the effect of the excluded

polymer volume and electrical double layers. The change of

the surface properties of the polymer containing foam was

dependent on the counterbalance of the theology of the

liquid films and the water content in the liquid films.

These studies have been successfully applied to

enhanced oil recovery and to characterization of biological

polymers. A concept of surfactant-polymer-foam flooding is

proposed, including the use of nonionic surfactants to form


xvii







alcohol-free microemulsions and the injection of foam for

the mobility control in heavy oil recovery. A wash-out

mechanism in porous media was applied to characterize the

physical properties of intraocular biological polymers.


xviii














CHAPTER I


INTRODUCTION



Foams are aggregates of gas bubbles dispersed in a

relatively small amount of liquid. Bubbles separated from

each other by thin liquid films vary in size from several

microns to several millimeters. Foams are both unusual and

intriguing in their physical properties, and have been

studied by many researchers [1-9]. There is little doubt

that at least some foams behave like non-Newtonian fluids,

and have apparent viscosities considerably higher than

those of either the gas or liquid phase [10]. Foam

properties are determined by numerous factors such as the

surface tension of the liquid, surface viscosity, bubble

size distribution, interbubble gas diffusion, Gibbs

elasticity, drainage of liquid from lamellae, adsorption/

desorption of surfactant molecules at the liquid/gas

interface, rheology of the adsorbed layer, external

pressure, and temperature [11-15]. For the flow of foam

through a porous medium, the permeability of the porous

medium, the pore size, and the surface properties of the

matrix, etc., must be considered as the factors related to

theological properties of foams.








Foam has been successfully used as a fracturing fluid

for several years [16]. It is a very powerful tool for

fluid leakoff control [17,18]. Montman [19] reported that

foam cement could be used to seal underground storage

caverns, insulate wellbores, and perform remedial squeeze

jobs. In the meantime, CO2 foam has been employed in gas

and oil wells, high- and low-temperature reservoirs, and

deep and shallow holes even though there are some

limitations. A successful field application of CO -foam

fracturing fluids in the Arkansas-Louisiana-Texas region

was reported by Warnock et al. [20].

One technique for thermal oil recovery involves the

injection of steam into a reservior to reduce the oil

viscosity and make the oil more mobile. Foam has been

suggested as a "blocking agent" in steam injection to

reduce gravity override and channeling effects (Figure

1.1). The mobility of injected steam can be controlled by

the generation of foam in a porous medium and the reduction

of mobility is proportionately higher in the more permeable

sands. The process is highly efficient since the foam first

finds its way into the largest pores, in which it tends to

block further flow. The smaller pores are thus invaded

next, and so on until the entire permeable section has been

filled with the foam. Laboratory experiments have shown

that vertical sweep efficiency is much improved by the

injection of foam [211. Despite the great potential of the

foam flooding process, the mechanism of the foam/oil













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displacement is still not fully understood. The basic

principles of foam flooding have been studied for the past

25 years by many investigators [22-26]. A number of

research papers have been published on foam behavior in

porous media [27-31].

Sharma and coworkers [32] proposed that the molecular

properties of foaming agents can influence the microscopic

characteristics of the foam which in turn can affect its

flow behavior in porous media and ultimately the oil

recovery efficiency. However, Sharma's work gives rise to

certain questions since (1) the generality of the result

was questionable because only one surfactant, sodium

dodecyl sulfate, with different alkyl alcohols was selected

and used to study several surface properties of foaming

solutions; some important foam properties such as foam

quality, apparent foam viscosity, rate of drainage, etc.,

were not investigated, and (2) several experimental results

obtained in this work were different from Sharma's.

Therefore, further study of foam properties and their

relationship to foam behavior in porous media was necessary

for the use of foam in enhanced oil recovery. Chapters II

and III present the results of laboratory studies designed

to correlate the relationship between the surface

properties and microscopic characteristics of foaming

agents and fluid displacement in porous media. Pure (e.g.,

sodium dodecyl sulfate) as well as commercial surfactants

(e.g., Stepanflo 40 and Suntech IVA) were selected and the




5


concept of chain length compatibility was applied to both

systems. The foam-promoting additives (i.e., co-surfactants)

used in experiments were straight, long-chain alcohols,

CH 17OH, CIoH 2OH, C12H25OH, C14 H2OH, and C 1H33OH. The

condensed notation, C OH (n = 8, 10, 12, 14, and 16), will

be used through this work. Various surface properties such

as surface tension, surface viscosity, foaminess, foam

quality, apparent foam viscosity, rate of drainage, bubble

size distribution, and observations of microscopic foam

behavior in micromodels, were studied and are reported in

these chapters. Some interesting phenomena which differed

from previous studies [32-33] are discussed. The results

may provide part of the answers to the following questions:

(1) Are all the surface properties of the foam consistent

with the theory of chain length compatibility?

(2) Does the foam behavior in porous media correspond to

the effects of chain length compatibility?

(3) Can we predict the foam behavior in porous media by

only observing the surface properties of the foam

outside the porous media?

(4) Is there any rule which can correlate the surface

properties of the foam with the foam displacement

processes?

To better understand and explain foam behavior in

porous media, two mathematical models based on the Darcy's

law, a modified equation of continuity, and the equation of

state of the foam are developed in Chapter IV. These models








can be very important in the prediction of pressure

distribution, velocity profile, and volume flow rate during

foam flooding. The effects of foam viscosity, permeability

of porous media, and compressibility of foam on the foam

flow through porous media were studied.

Chapter V focuses on the stability of foam bubbles.

The understanding of foam stability and foam breaking

requires an understanding of interactions between two thin

films. Two major forces, namely, the London-van der waals

force and the electrostatic repulsive force, are considered

for the interactions between two films. The DLVO theory was

introduced and the general Poisson-Boltzmann equation has

been developed in bispherical coordinates. A general

numerical solution of the Poisson-Boltzmann equation was

obtained and compared with other models' results. The

solution was then used to calculate the potential energy of

interaction between two spherical bubbles.

It is well known [14] that the elasticity and

viscosity of the foam can be improved by the addition of a

proper polymer. Almost all of the cited references [34-39]

deal with anionic surfactant-cationic polymer interactions

in relation to the physical properties of the aqueous

solutions. Little attention has been devoted to the effect

of anionic surfactant-anionic polymer interactions on foam

properties. In Chapter VI, the effects of adding anionic

polymer on the surface properties of the foam containing an

anionic surfactant were studied. Various surface properties








of mixed surfactant + polymer systems such as surface

tension, foam quality, apparent foam viscosity, rate of

drainage, and bubble size distribution were investigated.

Interactions between similarly charged surfactant and

polymer were also studied and the results support the

mechanism proposed by Desai [40]. The improvement of

surface activity of an anionic surfactant is due mainly to

the effects of the excluded polymer volume and the

electrical double layers.

The flow of fluid in porous media is encountered

frequently in chemistry, biology, and engineering. It is

also of interest in petroleum engineering, especially the

displacement of oil with gas, water, or polymer solutions.

Chapter VII gives two applications of fluid flow through

porous media. One is heavy oil recovery by foam flooding,

and the other is the transport mechanism of viscoelastic

gels in porous media. Several methods for tertiary oil

recovery such as foam flooding, polymer flooding,

surfactant-polymer flooding, and surfactant-polymer-foam

flooding were examined. It has been demonstrated that foam

can be used as a mobility control buffer instead of using a

large amount of polymer. A viscoelastic polymeric gel

(Viscoat ) has been used in the intraocular surgery. To

better understand the flow behavior of Viscoat in

trabecular meshwork, which is a porous channel, a wash-out

kinetics model is proposed. The results are compared with

other viscoelastic gels (e.g., Healon hyaluronic acid,





8


etc.) and are used to explain a rise in the postoperative

intraocular pressure.

Finally, Chapter VIII summarizes the results of the

entire study and provides recommendations for future

research in this area.














CHAPTER II


SURFACE PROPERTIES OF FOAMING AGENTS
AND FOAM STABILITY


2.1 Introduction



It is essential to study the surface properties of

foaming agents to understand the behavior of foam. Foam

properties are determined by numerous factors such as

surface tension of the solution, surface viscosity, bubble

size distribution, interbubble gas diffusion, Gibbs

elasticity, drainage of liquid from lamellae, adsorption/

desorption of surfactant molecules at the liquid/gas

interface, theology of the adsorbed layer, external

pressure, and temperature [11-15]. Several external

properties exhibited by foam are foaminess, foam quality,

apparent foam viscosity, foam compressibility, rate of

drainage, bubble size distribution, etc. These external

properties often correlate with each other and determine a

foam's behavior [14,41].

The indicators of foam stability [42] are (1) time

required to rupture, (2) gas diffusion rate, (3) loss of

interfacial area, (4) change of bubble size distribution,

and (5) drainage of interstitial liquid out of the








lamellae. The stability of a foam is directly dependent on

the ability of the surfactant molecules to adsorb at the

liquid/gas interface. Reduction of the surface area, and

the consequent to rupture of the lamellae, requires that

the adsorbed solute be returned to the bulk solution. The

more strongly adsorbed the solute, the larger is the free

energy contribution to the stability of the lamellae.

Therefore, a slower rate of loss of interfacial area

corresponds to higher foam stability. A measurement of the

time required to decrease the initial foam volume by 50% is

called the half-life of the foam. Since the reproducibility

of this parameter is poor, this method is not employed

here. The bubble size distribution and the rate of drainage

are the relevant properties most readily accessible and

were used in this work to study foam stability.

Measurements of gas diffusion rate and loss of interfacial

area require specialized equipment and hence they are not

considered in this work.

Schick and Fowkes [43] showed that polar additives can

lower the critical micelle concentration (CMC) of anionic

surfactants and stabilize the foam. The effectiveness of

the additives in reducing the CMC of sulfate- and

sulfonate-type surfactants is due to the hydrogen-bonding

between the additive and the surfactant molecules. Most of

these additives contain hydroxyl, primary or secondary

amine, carboxyl, sulfonyl groups, or combinations of these

groups. They also showed that the maximum lowering of the








CMC occurs when the surfactant and the additive possess the

same length of the straight hydrocarbon chain. Klevens [44]

reported that an additive present in the surface film

resulted in tighter packing of surfactant molecules and

lower surface tension. These factors stabilize a foam by

conferring high surface viscosity and low gas permeability.

Moreover, an additive which can bind to surfactants in

films can lead to slow-drainage or rigid interfacial films

[45]. Therefore, the stability of a foam is enhanced by

adding foam-promoting additives.

Although previous studies [33,46] give some evidence

of the effect of chain length compatibility on foams, we

raise the following questions:

(1) Do all surface properties of a foam correspond to the

theory of chain length compatibility?

(2) Does foam behavior in porous media reflect the effects

of the chain length compatibility on foam properties?

(3) Can we predict foam behavior in porous media by only

observing the properties of the foam outside porous

medium?

In this chapter the effect of chain length

compatibility on the surface properties of foaming agents

as well as foam stability are discussed. Furthermore,

results are related later to foam behavior in a porous

medium (Chapter III). Surfactants used in the experiments

included sodium dodecyl sulfate (SDS) and a series of

commercial surfactants, Stepanflo and Suntech IV. The polar








additives, also called co-surfactants, were alkyl alcohols,

CSOH, C0 OH, C12OH, C14OH, and C16OH.



2.2 Materials and Methods



2.2.1 Materials

Several different commercial and pure surfactants were

used in experiments. Stepanflo surfactants and Suntech IV

were supplied by Stepan Company, Illinois, and by Sun

Refining and Marketing Company, Pennsylvania, respectively.

Sodium dodecyl sulfate was purchased from Research Organic

Inc., Ohio. Long chain alkyl alcohols, C OH (n = 8, 10, 12,

14, and 16), were purchased from Sigma Chemical Company,

St. Louis, Missouri. All foaming agents were used as such

without further treatment. The purity of SDS and alkyl

alcohols was tested using NMR and showed 99% purity. Sodium

chloride was obtained from Fisher Scientific Company, New

Jersey. Distilled water was used throughout experiments.



2.2.2 Methods



2.2.2.1 Surface tension

The Wilhelmy plate method [47] was used for the

measurement of the static surface tension of surfactant

soultions. A surfactant solution (25ml) was poured in a

petri dish, and sufficient time (about two hours) was

allowed for the surfactant molecules to diffuse into the








surface layer. The platinum blade was always cleaned in

distilled water, then heated to a red color with a Bunsen

burner before using. All measurements were carried out at

room temperature and the results reported are the average

values.



2.2.2.2 Surface viscosity

The surface viscosity of the surfactant solution was

measured using a single knife-edge rotational viscometer

[13]. Surfactant solution (20ml) was injected into the cup

(diameter 5cm and depth 1cm) which was placed at the center

of a turntable. About two hours were allowed for the

surfactant molecules to reach equilibrium at the liquid/air

interface. The bob was then slowly lowered until it was

just touching the liquid surface. The angular deflections

were recorded at various rotational speeds by viewing

through a telescope. The rotational speeds were adjusted

continuously and smoothly to the desired speed from zero to

ten rpm. The equipment was enclosed in a plexiglas box and

could be leveled with three adjustable screws. The surface

viscosity was calculated by employing the modification of

the Reiner equation [13]. Three readings were taken for

each solution and the results reported are the average

values. It should be noted that surface viscosity has the

dimensions mass x time-', rather than mass x length-' x

time-1 as for the three dimensional or bulk viscosity, and

the unit gm/sec is usually called the surface poise.










2.2.2.3 Foaminess

A glass cylinder with 2cm diameter and 118 cm length

was used for the measurement of foaminess of the foaming

agents. The cylinder contained a sieve 25-50 pm in size at

the bottom and had an outer jacket for water circulation to

keep the temperature constant. A definite volume (50 ml) of

surfactant solution was carefully injected into the

cylinder along the glass wall in order to prevent the

surfactant solution from foaming. The foams were produced

by the injection of air at constant pressure from a

compressed air cylinder. The pressure applied at the inlet

of the foam generator was strictly controlled because the

foaminess was very sensitive to the pressure.

Foam volumes were recorded at various time intervals.

The results were reproducible within 10%. After a foam was

produced an attempt was made to measure its decay.

Theoretically, this would allow us to evaluate the

half-life of a foam. However, it was difficult to determine

the exact foam volume left in the cylinder after a certain

time, the collapse often occurred in the middle of foam

column, and the resulting shape was irregular. Due to the

poor reproducibility of the experimental results, the

half-life of foams was not studied here.








2.2.2.4 Foam quality

A home-made glass cylinder (2.7cm ID x 14.5cm L) with

two slits and two valves at both ends was used for the

measurement of the specific conductivity of the foam

(Figure 2.1). Two electrodes were placed vertically in the

two slits and were connected to a digital multimeter (model

8050A, John Fluke MFG. Co. Inc., Everett, WA.). Foam was

produced in a foam generator (see Foaminess) and was pushed

into the cylinder from one end while leaving the valve at

the other end open. Once the foam filled up the cylinder,

both valves were closed and the electrical resistance (Rf)

of the foam at different time intervals was recorded. The

initial time was counted as the foam was generated. During

measurements, the liquid drained from the bubbles was

drained out by carefully opening and closing the valve. The

conductance L, of a foam with a resistance R, is

Lf = 1/Rf

The specific conductivity Kf of a foam is

Lf = K (A/h)

where A is the cross-sectional area of the cylinder and h

is the distance between two electrodes.

The same technique was used for the measurement of the

specific conductivity of surfactant solutions. A solution

was injected directly into the cylinder using a syringe.

Figure 2.1 shows the apparatus which was used for measuring

foam quality as defined in section 2.3.4.













































Figure 2.1. Apparatus for the Measurement of Foam
Quality.








2.2.2.5 Apparent foam viscosity

The apparatus used for measuring the apparent foam

viscosity is shown in Figure 2.2. The pressure drop across

the capillary tube and the average volume flow rate were

measured. The apparent viscosity was calculated with the

Hagen-Poiseuille equation. Due to the drainage of liquid

from the foam, the time elapsed for each experiment was

also recorded. The initial time was counted as soon as the

foam was produced. A capillary tube with 0.378 cm diameter

and 125 cm length was used in the experiments.

Theoretically, the smaller the diameter of the tube, the

more accurate the results. In practice, foam was easy to

break down (i.e., discontinuous) in a smaller diameter

tube. A proper tube diameter had to be selected by

trial-and-error.



2.2.2.6 Rate of drainage

A definite volume (30ml) of surfactant solution was

injected into a graduated cylinder (100ml). Foam was

produced by shaking the cylinder vigorously for three

minutes. To keep all experiments under the same conditions,

the liquid volumes were recorded at various time intervals

after the liquid volume in the cylinder had reached 20ml.

The initial time during which 20ml fluid accumulated was

not counted. The kinetics of drainage were measured for

solution collected beyond 20ml.
























*
.ij
.,-I
U4
O
0

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O
0

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c)
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fo
























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4-)





k f


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r(








2.2.2.7 Bubble size distribution

A rectangular plexiglas cell (2.75"x2.75"x0.5") was

used for measurements of bubble size. Ten milliliters of a

surfactant solution were injected into the cell. The foam

was generated by vigorously shaking the cell for three

minutes. The foam was then photographed at various time

intervals. The photographs were analyzed using a digital

image analysis system consisting of an Image Technology

model 5000 processor, an IBM personal computer, and a Sony

video camera, to determine the average bubble size and

bubble size distribution.



2.2.2.8 Microscopic view of foam flow in porous medium

The general foam behavior at the microscopic level was

investigated using a micromodel. The experimental apparatus

was designed to achieve the following major objectives:

(1) Find the mechanisms of gas flow in porous media in the

presence of mixed surfactant solutions.

(2) Visually observe and study the flowing foam.

A schematic diagram of the apparatus is shown in Figure

2.3. The apparatus included a camera control unit (Sony,

Model DXC-1850), video cassette recorder (Panasonic, Model

NV-8950), time data generator (Panasonic, Model WJ-810),

video monitor (Panasonic, Model CT-1330M), and video camera

(Sony, Model DXC-1850). The micromodel had a pore neck of

50 pm and pore diameter of 100 pm. The micromodel was

saturated with surfactant solution followed by air flow to








generate in-situ foam. The photographs of foam generated

inside the micromodel were taken directly using the

television camera attached to the microscope.



2.3 Theory



2.3.1 Surface Tension

Surface tension is a measure of the work required to

increase the surface by unit area, at constant temperature,

pressure, and composition [48]. It is also a measure of the

attraction between molecules. In general, the surface

tension decreases with increasing temperature or pressure.

As the temperature is increased, the kinetic energy of

liquid molecules increases, and the attractive forces

between molecules are easily overcome, which in turn

reduces the surface tension of the liquid. An increase in

the pressure over the liquid surface will cause more

gaseous molecules to come in contact with the surface. The

attractions between liquid molecules and gaseous molecules

neutralize part of the inward attractions of the liquid

molecules. The net effect is a decrease in surface tension

with increasing pressure.

At constant temperature and pressure, the surface

tension of a surfactant solution decreases as the

concentration of the surfactant increases until the CMC is

reached. There is little effect on surface tension when the

concentration is above the CMC. Therefore, the CMC of a































Constant Pressure
Air Supply


Syringe Pump Dra


Figure 2.3.


Camera Time Date
Control Unit Generator





Television
Camera
a..... Video Cassette
S_ J Video Monitor Recorder


Microscope

Bubble Flowmeter
M---icromodel ----- -----


in U Liquid
Collector
Pressure
Transducers


II
Chart
Indicatorecorder
Recorder
.... I


Vacuum
Pump


Schematic Diagram of Apparatus for Foam
Flow through a Micromodel.








surfactant can be determined from the measurement of the

surface tension. The CMC is an important physical property

for a surfactant because it is related to many other

surface properties of the surfactant.



2.3.2 Surface Viscosity

Surface viscosity is a measure of molecular

interactions in monomolecular films at the interface. The

study of surface viscosity is useful in connection with

foam stability. Shah [49,50] has shown that the surfactant

solution with high surface viscosity produces a stable film

due to tight packing of the surfactant molecules. For some

commercial surfactants, a similar trend was observed in the

variation of surface viscosity with increasing surfactant

concentration [4]. These results suggest that a high

surface viscosity leads to a retardation of bulk liquid

flow near the surfaces, which in turn reduces the rate of

thinning of the liquid films and, consequently increases

the foam stability. Surface viscosity can also damp out

fluctuations that might lead to rupture of the film.

Bikerman [51] pointed out that the surface viscosity may

affect the foam life through its effect on foam formation

if the foam is produced by the beating method.



2.3.3 Foaminess

Foaminess is a measure of the capability of a foaming

agent to produce foam. The method of determination is








dynamic. If one takes a cylinder filled with surfactant

solution and shakes it vigorously, then the work done on

the system mainly goes into expanding the interfacial area.

The work done in expanding an interface is given by ydA,

where y is the interfacial tension and dA is the increase

in interfacial area. Therefore, one would expect the

largest interfacial area in the system which has the

minimum interfacial tension at the liquid/air interface.

One might also expect that large foam volume corresponds to

low interfacial tension. Actually this is not true. For

instance, n-octyl alcohol does not produce much foam even

though its surface tension, 27.53 dynes/cm at 200C, is very

low [52]. This implies that not only surface tension but

also foam stability has to be considered for foaminess. The

processes of foam generation and foam collapse, as well as

their combined effects, determine the capability of a

foaming agent to produce the foam. For a given foaming

agent, in the pre-CMC region, foaminess generally increases

with increasing surfactant concentration. The maximum foam

volume is observed when the concentration is around or

slightly above CMC. Further increases in surfactant

concentration does not improve foaminess.



2.3.4 Foam Quality

The volumetric gas content of a foam is called foam

quality and is expressed by the relationship:

foam quality (gaseous volume)/(total foam volume)








Lemlich [3] reported that the volume fraction of liquid in

the foam can be determined by measuring the specific

conductivity of foam:

+i = 3Kf/KS (2.1)

where 3. = the volume fraction of liquid in the foam

K = the specific conductivity of foam

K = the specific conductivity of solution.

The foam quality is equal to 1
conductivity is based on the view of foam as a network of

interconnected films whose liquid content has the same

specific conductance as the bulk solution.

Foams with a quality higher than 0.8 are termed "dry"

while those with a quality lower than 0.7 are termed "wet."

Raza and Marsden [53] have shown that a minimum of about 4%

liquid is required to produce foams. This implies that the

maximum foam quality which can be achieved is around 0.96.

Any "foam" with a quality higher than 0.96 must be like a

chain of bubbles separated from each other by a thin liquid

film (i.e., lamella). Usually, liquid drains off very fast

from wet foams; further drainage may be retarded due to the

Marangoni-Gibbs effect [54]. There is an optimum range of

quality in which foams exhibit uniform dispersion of the

two phases and are more stable. Laboratory experiments have

shown that foams may remain stable for more than a month at

rest, and even longer when flowing in a low permeability

porous medium (k < ImD) [55]. On the other hand, the

apparent viscosity of a dry foam is higher than that of a








wet foam [56]. Hence, dry foam is preferred in applications

to enhanced oil recovery.



2.3.5 Apparent Foam Viscosity

It is well known that the apparent viscosity of a foam

is considerably higher than that of either constituent

phase. Also, foam is the only known compressible

non-Newtonian fluid with both variable density and

viscosity. There is almost no way to measure the foam

viscosity as foam flows through a porous medium. A classical

conceptual model for the fluid flow through porous media

was the bundle of capillary tubes model. Therefore, an

approximate method may be employed to determine the

apparent foam viscosity when foam is treated as a single

fluid flowing through a capillary tube. The relationship

between the flow rate and pressure drop in a capillary is

described by the Hagen-Poiseuille law [57]:

Q = (nR4 P)/(8pL) (2.2)

where R = the radius of the capillary tube

=P = the pressure drop across the tube

Q = the average volume rate of flow

L = the length of the tube

p = the viscosity of the fluid

The assumptions that are implied in the development of the

Hagen-Poiseuille law are:

(1) the flow is laminar (Reynolds number < 2100)

(2) the density of the fluid is constant








(3) the flow is at steady state

(4) the fluid is Newtonian

(5) end effects are neglected

(6) the fluid behaves as a continuum

(7) there is no slip at the tube wall.

Based on these assumptions, it is clear that the foam flow

in a capillary cannot be described by Equation (2.2).

Princen [58] suggested that when the equivalent bubble

radius is small compared to the capillary radius, foam

exists as bulk foam instead of as a chain of bubbles. Also,

if the pressure drop is small then it has little effect on

the foam density. The velocity of the foam is slow at this

low pressure so that it may be viewed as an incompressible,

Newtonian fluid. In consequence, Equation (2.2) is

appropriate for the measurement of foam viscosity in a

certain low pressure range.

The liquid content of foam dominates foam density. The

less liquid contained in the foam, the higher foam

viscosity. On the other hand, the liquid content determines

foam quality. So, the higher the foam quality, the greater

the apparent foam viscosity.



2.3.6 Rate of Drainage

The rate of drainage is the rate at which liquid

drains from the films of the foam bubbles. The method of

determination is static. The mechanism of drainage of

aqueous solutions is affected by gravity, the capillary








force [59,14], gas diffusion between adjacent bubbles of

different size, and the statistical rupture of films [60].

Drainage under the influence of gravity is obvious.

Drainage due to capillary forces is illustrated in Figure

2.4. It is easy to prove P > Px by applying the Laplace

equation [54]. The mechanism of transfer of air from the

smaller bubbles to the larger ones is by dissolving in,

followed by diffusion through the liquid film. The rate of

gas diffusion is influenced by the molecular packing of

surfactant at the air/liquid interface which in turn

affects the thinning of the film.

For rapid drainage, the rate of drainage may be

described by the following equation [59]:

V = V {I EXP[-(K1 t+K )]}

or -ln[l (V/Vo)] = K t + K2

where V the total volume of the liquid drained from the

foam, ml

V0 = the total liquid volume in the container, ml

t = time, seconds

K K2 = the constants of the drainage process.

Ki and K are determined by curve fitting using linaer

regression.



2.3.7 Bubble Size Distribution

The factors that influence the bubble size of foam are

surface tension, interbubble gas diffusion, drainage due to

gravity, pressure, and temperature. The rate of foam decay























Gas


0
120
Gas


Gas


Foam


Figure 2.4. Plateau Border in a Foam.








resulting from interbubble gas diffusion and gravity

drainage has been shown [60] theoretically and

experimentally to be a sensitive function of the initial

distribution of bubble sizes. This may explain why some

foam stability tests are difficult to reproduce. The rate

of gas diffusion between bubbles and the mechanism of

gravity drainage can be dramatically changed by the

molecular packing of surfactant at the liquid/air interface,

which in turn affects the collapse of foams. The bubble

size increases with elapsed time due to coalescence of

bubbles and collapse of foams.

Although the experiments for bubble size distribution

measurement are difficult to reproduce, the comparison of

measurements of bubble size distribution are still very

useful in predicting foam stability. With the aid of image

analysis, the bubble size distribution and mean bubble size

are especially meaningful from statistical point of view.



2.3.8 Microscopic View of Foam Flow in Micromodel

Many researchers [31,53,61-64] have studied the

theology of foam in porous media. The flow behavior of foam

in a porous medium is a complex one, which cannot be

correctly described in terms of the high apparent viscosity

or bubble stability of the foam. There is a general

agreement that foam behaves like a pseudoplastic fluid with

high apparent viscosity. However, there are diverse opinions








on how foam and its components are transported through a

network of pores.

Fried [65], Marsden and Khan [1], and David and

Marsden [66] proposed that foam behaves as a single,

homogeneous fluid: the gas and the liquid flow at the same

rate. However, Raza [31] and Minssieux [27] suggested that

foam cannot be described as a single fluid because the

viscosity and quality of a bulk foam are quite different

from those of a foam flowing through a porous medium. Foam

with large and less stable bubbles is propagated inside a

porous medium by the breaking and reforming of foam bubbles

[26,63,65].

Micromodels permit a pore-size level study of foam

flow processes. Several approaches such as capillary tubes

[1,66], single layer glass bead model [67,68], and a

network of etched micromodels [26,69,70] have been used for

the microscopic study of foam flow. The capillary tube is

the simplest micromodel which has been employed to study

the theology of foam. The single layer glass bead model and

the etched network micromodel are essentially two

dimensional systems. The latter is much easier to

manipulate, reproduce, and observe under a microscope. Both

models can be used to study the foam drive process, fluid

distributions, and mechanism of fluid displacement by foam.

In this work, the micromodel was only used as a tool

for the study of microscopic foam flow in a porous medium.

The observations were related to other surface properties








of the foaming agent. Details of the fabrication techniques

of the micromodels can be found in literatures [67-70].



2.4 Results and Discussion



2.4.1 Surface Tension

Surface tension was measured as a function of the

concentration of surfactant solutions and the results are

shown in Figure 2.5 and 2.6. The surface tension of the

surfactant solution decreased with the increase of

surfactant concentration, and it remained constant or

decreased slightly beyond the CMC. Among the surfactant

solutions tested, Suntech IVA, B, and C, Suntech IVA had

the lowest CMC (Figure 2.5). It seems that Suntech IVA,

among the samples of Suntech IV, appears to be the most

surface active agent. The surface tensions of another

series of commercial surfactants, Stepanflo 20, 40, 50, 60,

70, and 80, were also measured at various concentrations

(Figure 2.6). The CMCs of Stepanflo surfactants were very

close. It is hard to tell which surfactant is the most

surface active agent.

For the pure surfactant SDS, it was observed [32] that

the surface tension was the lowest for the system

consisting of SDS and dodecyl alcohol as compared to that

of SDS with other long chain alcohols. Figure 2.7 shows

that indeed the lowest surface tension was found when both

components of the mixed surfactants had the same chain






























C




r-














I C
E

E




n

C
2
0














I
E









2
0









z z 3
I

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tn r.-
(N


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__ SDS(2 mM) + CnOH (0.2 nM)


50
50 SDS(5 m1) + CnOH(0.5 mM)




E 45
U



S40

0 0
z


w 35
E-

u

I 30




25




20 I I I
C8OH C1OH C12OH C14OH C16OH


Figure 2.7. Surface Tension for Solutions of SDS
and Alkyl Alcohols.








length (i.e., SDS + C12OH). Note that at the higher

concentration the surface tension was also very low for the

system consisting of SDS + C1oOH and SDS + C14OH,

respectively. The situation became complex for the mixed

surfactant systems, SDS + C OH (n = 8, 10, 12, 14, and 16),

in the presence of brine since the precipitation of mixed

surfactants occurred. Sharma and Shah [33] have shown that

the addition of NaC1 to the mixed surfactant systems of SDS

+ C12OH results in an increase in surface tension. This

increase in surface tension is presumably related to the

decrease in solubility of dodecyl alcohol in the solution

and the precipitation of the complex of SDS + C12 OH. The

concentrations of the mixed surfactant system for the above

observations were above the CMC. But for concentrations

below the CMC, the surface tensions of mixed surfactant

systems, SDS + C OH, were decreased by adding a small

amount of NaCl (Figure 2.8). The main reasons were due to

the salting out effect and the tight packing of surfactant

molecules at the interface. Figure 2.9 shows the surface

tension of mixed surfactant systems with same concentration

of sodium chloride and long chain alcohols at various

concentrations of SDS. Again, the lowest surface tension

was found for the system consisting of SDS and dodecyl

alcohol.

A commercial surfactant, Stepanflo 40, was also

influenced by the addition of long chain alcohols, while,

there was little effect on the surface tension of Suntech


















60
0- SDS(2 nm1) + C OH(0.2 mM)

55 _- SDS(2 mM) + CnOH(0.2 mM) + NaC1
(0.5%)



E 50


a)
CO



o -
, 45


40
z


U35



30



25



20
C 10 OH C12OH C14OH C6OH


Figure 2.8. Surface Tension for Solutions of
SDS + Alkyl Alcohols with and
without Salt.







































000o0
0 0 0 0
o o (N tzr U
-I -4 -4 -4 -4



(1 (1 u 0 (
00000
(12 12 (2 (1 (1


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om
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IVA by adding long chain alcohols (Figure 2.10). The major

components of Stepanflo 40 and Suntech IVA are C12 +

benzene sulfonate and C1_5-1 + Toluene, respectively

[71,72]. Since the number of carbon atoms in Suntech IVA

molecules is from 22 to 24 and the structure of the

molecules is not straight hydrocarbon chains, the addition

of long chain alcohols exhibits little effect on the

surface tension of mixed surfactant systems. Although the

molecular structure of Stepanflo 40 is not available, the

lowest surface tension was observed for the system

consisting of Stepanflo 40 and dodecyl alcohol. This

implies that there exists an interaction between Stepanflo

40 and alkyl alcohols. If the effect of electrolytes is

considered, the situation becomes much more complicated.

Generally speaking, the surface tensions of mixed

surfactant systems, Stepanflo 40 + CnOH, were significantly

decreased by adding NaC1, whereas little effect on the

surface tensions of Suntech IV + C OH was observed.
n


2.4.2 Surface Viscosity

A slight increase in surface viscosity was observed

with increasing surfactant (i.e., Suntech IVA, B, and C)

concentration, whereas beyond the CMC, the surface

viscosity remained constant (Figure 2.11). It has been

observed [32] that the surface viscosity is the highest

when both components have the same chain length (i.e., SDS

+ C12 OH). Shah and co-workers [73,74] have shown that the





39











60 -0- Stepanflo 40(5xl0 9m /Ml) + C nOH(0.1 mM)
-E0- Suntech IVA(1xlO gm /ml) + C nOH(0.2 mM)
-Ai- Suntech IVA(1xl0- gm /ml) + C n O (0.2 mMl)
55 + NaCl (0.5%)n
-D -Stepanflo 40(5xl0- gm /ml) + C nOH(0.1 mM)
+ NaC1(0.5%)n

50
E
U

45


40



40


25 -



30




C 8OH C 10 OH C 120OH C 14 H C160H


Figure 2.10. Effect of Surfactants with Different
Alkyl Alcohols on Surface Tension.





























O -
E



E-
z
0

I E-
O
Z

0
O

0 -
I Z

U

O




-I
,-4


I ISO1 I 1S
00 CO N 0

'AL.ISO0SIA aovalns


4)


0
4-1
C
0
-,- 1







4-1









. 0
U








-LJ



Or
(0
U
>J0





I4-
C

4J
:r




>O




ro
Cr

-4
( O





S- -I
r-l-


(N C
-I .-- H r-4

ds OT


I


9~9








increase in foam stability of decanoic acid solutions in

the presence of decanol is due to the increase in surface

viscosity caused by the alcohol. These results suggest that

the surfactant molecules that have similar chain length are

more tightly packed at the interface as compared to

molecules with dissimilar chain lengths.



2.4.3 Foaminess

Figure 2.12 shows foaminess as a function of the

concentration of Suntech IVA, B, and C. As the

concentration of surfactants increased, foaminess

increased. Beyond a certain concentration, foaminess

remained constant for all of these surfactants. However,

solutions of Suntech IVA and B can produce more foam as

compared to that of Suntech IVC. Usually, the lower the

CMC, the more efficient the foaminess of surfactants. But

this relationship is not always true. For instance, Suntech

IVA had a lower CMC than that of Suntech IVB, but both

surfactants possessed almost same ability to produce foam

under a given condition as shown in Figure 2.12. For a

series of surfactants, Stepanflo 20, 30, 40, 50, 60, 70,

and 80, the highest volume of foam was found for Stepanflo

40 (Figure 2.13). Therefore, Stepanflo 40 was chosen for

further study of the effect of chain length compatibility.

Figure 2.14 indicates that the highest volume of foam

was found for the mixed surfactant systems of SDS + C2 OH

and Stepanflo 40 + C2 OH, respectively. There was little




















112
--- Suntech IVC


96 -



80 -
-4T
E
64 -


0
> 48 -
/ INLET PRESSURE: 5 psi
TIME INTERVAL: 1 minute
32 -



16 -



0 5II I 3 l ll i
10-5 10-4 10-3 10-2
SURFACTANT CONCENTRATION, gm/ml


Figure 2.12. Effect of the Concentration of Suntech IV
Surfactants on Foaminess.












200 J
SSURFACTANT CONC.= 10-3 gm/ml

INLET PRESSURE = 4 psi
180
-0- TIME INTERVAL=2 min.
-Q-- TIME INTERVAL=1 min.

160




140 -




120




100




80 /




60



STP = Stepanflo
40



20 I I I I l
STP STP STP STP STP STP STP
30 20 40 70 80 50 60

Figure 2.13. Variation in Foaminess for Stepanflo
Surfactants.












500



450


400



350


ALCOHOL C OH
ALCOHOL 8 10


C OH C 4OH
12 14


C OH
16


Figure 2.14. Effect of Surfactants with Different Alkyl
Alcohols on Foaminess.


DIMENSION OF FOAM GENERATOR: 45mm OD x 42cm LENGTH
POROSITY OF FRIT: 25 50 microns
PPESSUPE APPLIED: 1.1 psi
TIME IN;TEPVAL: 5 minutes ,



-









- SDS (2mM) + C H OH (0.2mM)
X n 2n+1
STEPANlFLO 40 (0.05 wt..) + CnH O2n H (O.lmM)

S SUNTECH IVA(0.05wt.'.-) + C nH nOH (0.2mi1)













I 1 I 1 I I


300



250



200


150



100



50



0








influence on the foaminess by the addition of long chain

alcohols to Suntech IVA. It is noted that foaminess of SDS

+ C oOH was quite similar to SDS + C12OH. It is hard to say

whether SDS + C2 OH or SDS + C1 OH produced the maximum

foam volume, since the experimental results were very

sensitive to the pressure applied and the experimental

error was about 10%. Similarly, foam volumes were almost

the same for Stepanflo 40 + C2 OH and Stepanflo 40 + C,0OH.

Foaminess of both pure and commercial surfactants

increased with the increase of temperature [33]. At room

temperature, a decrease in foaminess was observed for the

mixed surfactant systems with the addition of NaC1,

presumably due to the precipitation of mixed surfactants or

the decrease of solubilization of alkyl alcohols in the

solution. On the other hand, the effectiveness of brine in

reducing foaminess decreased at higher temperature [75].

Since so many factors affect foaminess, there is still no

clear relationship found between foaminess and surface

properties of foaming agents.



2.4.4 Foam Quality

The foam quality of a series of Stepanflo surfactants

at different time intervals (5 min., 10 min., and 20 min.)

is shown in Figure 2.15. Foam quality varied with time

because the static foam collapsed gradually and the liquid

drained from the thin liquid films. It is clear that

Stepanflo 40 had the lowest foam quality of all Stepanflo




46







95
INLET PRESSURE: 2 psi
-3
SURFACTANT CONC.: 10 g /ml
m'
90 -
-9- TIME INTERVAL = 5 min.
-0- TIME INTERVAL = 10 min.

85 --T- TIME INTERVAL = 20 min.




80




S75 O




70




65




60

STP = Stepanflo

55




50 I I I
STP STP STP STP STP STP STP
30 20 40 70 80 50 60


Figure 2.15. Variation in Foam Quality for Stepanflo
Surfactants.








surfactants. Most of these surfactants at concentration of

0.1% g,/ml produced "wet" foams. Figure 2.16 shows the foam

quality as a function of the concentration of Stepanflo 40.

The foam quality decreases with increase in concentration

in the pre-CMC range. Beyond CMC, the foam quality remained

constant or slightly decreased. Hence, the measurement of

foam quality is one of many methods to determine the CMC of

a foaming agent.

The foam quality of mixed surfactants as a function of

alkyl chain length at different time intervals (5 min., 10

min., and 20 min.) is shown in Figure 2.17 and 2.18 [76].

Foams produced by these mixed surfactants were considerably

"dry." For the system of SDS + C OH, foam quality decreased

with the increase of chain length of alcohols from Cs to

CI0, then it increased as chain length increased further.

For the mixture of Stepanflo 40 with different long chain

alcohols, foam quality also decreased as hydrocarbon chain

length of alcohols increased from C, to CI0. There was

almost the same effect on foam quality by adding decyl or

dodecyl alcohol in Stepanflo 40 solution. Interestingly,

the foam generated by adding hexadecyl alcohol was even

"dryer" than that without adding any alcohol. This Iay be

due to the effect of hydrophobicity of hexadecyl alcohol.



2.4.5 Apparent Foam viscosity

Figure 2.19 shows the apparent foam viscosity of

various Stepanflo surfactants at intervals of five and ten





















INLET PRESSURE: 2 psi


{-- TIME INTERVAL = 1 min.

-A-- TIME INTERVAL = 5 min.

0- TIME INTERVAL = 10 min.


40 1 L
5xl0-5


Figure 2.16.


I I I I


I I I I I I I


10-4 10-3
STEPANFLO 40 CONCENTRATION, gm/ml

Variation in Foam Quality as a Function
of the Concentration of Stepanflo 40.


100





90





80





49










-- TIIIE = 5 Imin

100 --- TIME = 10 min

-0-- TIME = 20 iini
MIYED SUPFACTANTS : C2SOra = 2 mM
95 C H 2 OH = 0.2 fmM
n 2n+1



90

1-
_J

o 85

C,
Uj-

80



75




70
SDS SDS SDS SDS SDS
+ 4 + + +
C8011 C10OH C120H C140H C16OH



Figure 2.17. Variation in Foam Quality as a Function of
SDS with Different Alkyl Alcohols.





































LL-
-_J



C




85












80
N C OH C10OH C12 OH C14 OH C16OH
ALCOHOL 8 10 12 14


Figure 2.18. Variation in Foam Quality as a Function of
Stepanflo 40 with Different Alkyl Alcohols.






















-3-gm
4 SURFACTANT CONC.: 10 g /ml
O



o

2 -
>4 3




S\ / i
E-41



> 3

0





2 -









STP STP STP STP STP STP STP
30 20 40 70 80 50 60

Figure 2.19. Variation in Apparent Foam Viscosity for
Stepanflo Surfactants.








minutes. The lowest apparent viscosity was found for the

surfactant Stepanflo 40. The combination of high foaminess,

low apparent viscosity and foam quality in Stepanflo 40

produces the most uniform, stable foam of all Stepanflo

surfactants. The effects of adding different chain alcohols

to SDS and Stepanflo 40 solutions are illustrated in

Figures 2.20 and 2.21, respectively. Among the SDS systems,

the lowest apparent viscosity was observed for SDS + CI OH,

although a smiliar value was found for the SDS + C2 OH

system. A similar minimum was observed with Stepanflo 40 +

C,0OH and Stepanflo 40 + C2 OH.

The apparent foam viscosity depends on: (1) slugs of

liquid between bubbles, (2) the resistance to deformation

(i.e., elasticity) of the interfaces of foam bubbles

passing through a capillary, and (3) the surface tension

gradient that occurs when surfactant molecules are swept

from the front of a bubble to the back of it. Hirasaki and

Lawson [77] have shown that the transition from bulk foam

to individual lamellae is a function of r /Rp, where rB and

Rp are the equivalent radius of the bubbles and the

capillary radius, respectively. Foam exists as bulk foam

when r /R, < 1.0. They suggested that the apparent

viscosity of the bulk foam, where the surface tension

gradient effect is insignificant, does not change as long

as the r /R, ratio is kept constant. Since the radius of

the capillary used in experiments is 0.378 cm and the

bubbles are of the order of several microns in diameters,



















3.0



-0



00
--





O


S2.0(5
>4



4--I






E-
<
-)









<
-I
>2.0










1.5










1.0
NO
ALCOHOL 8C


C10OH C12OH C140H


Figure 2.20. Apparent Foam Viscosity for Mixed Foaming
Agents of Stepanflo 40 and Alkyl Alcohols.


C OH
16













INLET PRESSURE = 2 psi
TIME INTERVAL = 5 minutes
16
MIXED SURFACTANTS: SDS(2nmM) +
CH 2 OH(0.2mr
n 2n+1

14




-4 12
0


E-4
a 10 -




2 8 -
0

E-
z
: 6




4




2 -




0 I I
NO OH C OH OH C OH C OH
ALCOHOL 8 10 12 14 16


Figure 2.21. Apparent Foam Viscosity for Mixed Foaming
Agents of SDS and Alkyl Alcohols.








r /R << 1.0 and the surface tension gradient effect is

negligible. Therefore, the low apparent foam viscosity is

expected resulting from the high liquid containing bubbles

and from the low elasticity of the films. These two factors

account for the low apparent foam viscosity. SDS and C12OH

molecules are tightly packed at the interface due to chain

length compatibility, which produces a more elastic film

than that of SDS with C1oOH. Moreover, dodecyl alcohol is

more hydrophobic than decyl alcohol. The latter can bring

more water into bubble films and these water molecules can

be retained by the moderate elasticity films. That is the

reason why the lowest foam quality and apparent viscosity

was found for the system of SDS + C1 OH.

If foam quality and apparent foam viscosity were

measured in separate experiments at a series of times under

the same conditions, then a plot of apparent foam viscosity

vs. foam quality can be obtained as shown in Figure 2.22.

It is clear that the higher the foam quality, the higher

the apparent viscosity. The primary effect of the quality

is to change the radius of curvature of the bubbles. When

the ratio of r /Rp is greater than one, the foam exists

more like a bubble chain where each pair of bubbles is

separated by an individual lamella. This effect is much

more important at high foam qualities. The surface tension

gradient effect can not be ignored and tends to increase

the apparent viscosity. The effects of foam quality on the

apparent viscosity are mainly due to the number of bubbles
















MIXED SURFACTANTS: SDS(2 mM) + C12OH
(0.2 1mM)
I[LET PRESSURE: 2 psi


8 F-


84 85 86 87 88


FOAM QUALITY, %

Figure 2.22. Apparent Foam Viscosity as a Function
of Foam Quality.








per unit length, the radius of curvature of the gas/liquid

interface, and the thickness of liquid films [77].

These results have practical significance for foam

flowing through porous media. The apparent viscosity of the

foam will not change with pore size if r,/Rp < 1.0, but

will increase with decreasing pore size if r /Rp > 1.0.



2.4.6 Rate of drainage

Figure 2.23 and 2.24 show the volume ratio of liquid

drained from the foam column as a function of time. For the

mixed foaming systems, SDS + C OH (n = 8, 10, 12, 14, and

16), the overall slowest drainage was observed for the

system consisting of SDS + C14OH while the fastest drainage

was found for the system of SDS + C OH. The correspondence

of chain length compatibility with rate of drainage was not

observed in this study. Shiao [46] also reported that chain

length compatibility was not observed for the rate of

drainage of mixed foaming systems of SDS with different

long chain alcohols. One interesting phenomenon observed

during the experiment was that a large amount of foam was

easy to produce by shaking for the systems of SDS + C OH,

SDS + C1oOH, and SDS + C12OH, but not for the systems of

SDS + C14OH and SDS + C16OH.

If the same amount of liquid is distributed in the

foam, then the foam with lesser volume possesses thicker

liquid films. The SDS + C12OH solution had the highest

surface viscosity, followed by SDS + C14 OH, SDS + C16OH,























r1


0


U)
(-~
tO


00 <
iI c









0 0 00 a


,- E
(N (N (N (N (M F X






S0H

LE fl











.C
.CO







\ I- a 0 0 a


I 0 O fL m m 0









% c co If 0 o o ( w


















O


r11 r-1
0






4 -I "1 -J

0 0 0 0

S0 0 0
o 0 0
cO -l r r r- 4J

+ + + + + t0

\-I r-I r- -I .- -
E E E E E c

SEE E E O m E
\ cr c cc) (U ro
\ o'P Of u3 ooo oo p [ [-o
\o oo On o o 4 0

\ \* * * -'
0 0 0 00E
0 0o"o 0 "
o c o on a -4

II

S\ En En E -4












00
C:M E












% 'In O G OIIH








SDS + C.00H, and SDS + C OH [21]. As mentioned in the

previous section, a high surface viscosity leads to a

retardation of bulk liquid flow near the surfaces which in

turn reduces the rate of drainage of the liquid films.

Therefore, the slowest drainage for the first five minutes

was found for the system of SDS + C12OH rather than SDS +

C14OH (Figure 2.23). However, after a certain time has

passed (e.g., 10 minutes or longer) and a critical thin

film thickness is reached, another factor that has to be

considered is the effect of Marangoni flow [42]. It has

been shown [78] that the molecular interactions between

dodecyl alcohol and SDS are stronger than those of

tetradecyl alcohol and SDS. The thermal motion of the

terminal segment of tetradecyl alcohol at the interface

causes the thin film of SDS + C14OH to possess a higher

fluidity compared to SDS + C12OH. According to the

Marangoni effect, thin film with high fluidity can easily

restore the instability of the film due to a small

disturbance. Thin film of SDS + C 1OH is too rigid to

resist a small disturbance and, in consequence, foam is

easy to break. Hence, the slowest drainage was observed for

the system of SDS + C OH at the later period of drainage

(Figure 2.23).

In Figure 2.24 the slowest drainage was observed for

the mixed surfactants consisting of Stepanflo 40 and C6 OH.

The rate of drainage and the total foam volume generated by

shaking decreased with the increase of hydrocarbon chain








length of alcohols. Again this result is not compatible

with the trend of the other foam surface properties

described before. The argument mentioned above may be

employed to explain this result, but the actual reasons are

still unknown. More information about Stepanflo 40 such as

major components, molecular structures, and physical

properties are needed.

The rate constants, K1 and K2, of the drainage process

were calculated by linear regression and are shown in

Figure 2.25 and 2.26. The smallest value in K1 corresponds

to the slowest drainage.



2.4.7 Bubble Size Distribution

Photographs of the foams taken at different time

intervals are presented in Figures 2.27-2.30. An increase

in bubble size with elapsed time was observed. The bubble

size increased with elapsed time due to coalescence. The

bubble size increased more rapidly with elapsed time for

Suntech IVC than for Suntech IVA. These results imply that

the surfactant solution with low CMC and high surface

viscosity produces relatively stable foam. Figure 2.31-2.33

show the histograms of bubble size distributions of Suntech

IVA, B, and C after 60 minutes. These distributions were

determined from Figure 2.27 using a digital image analyzer.

It is clear that the number of bubbles with small radius

(e.g., less than 0.1 cm) is larger for Suntech IVA than for

Suntech IVB and C. The mean radii of the foam bubbles for





62








8

MIXED SURFACTANTS: SDS(2 mNM) +
6 C OH(0.2 mNl)





5



1 \ ~ 6

Io 4 5 I

4 \ 51


z 4 I E,
< z
E-) 3 0






/ 2
U 0
33









o- 1
2 2












0 I I I I 0
NO
COH C OH C OH C OH C OH
ALCOHOL 8 10 C12H C140H C16


Figure 2.25. Rate Constants of Drainage Process for
Mixed Faoming Agents of SDS and Alkyl
Alcohols.





63








12 12


11 11


10 10


9 9


8 8
nI I
o o
7 -7 7


E6 6


z 5 5
O o
U U

4 4


3 MIXED SURFACTANTS: STEPANFLO 40 3
(0.05%g /ml) + CnOH(0.1 mM)

2 -2


1 -1


0 i I I I I 0
NO
SC OH C OH C OH C OH C OH
ALCOHOL 8 10 12 14 16


Figure 2.26. Rate Constants of Drainage Process for
Mixed Foaming Agents of Stepanflo 40
and Alkyl Alcohols.















I. SUNTECH IV A


(I) After 15 minutes


2. SUNTECH IV B










(I) After 15 minutes



3. SUNTECH IV C


(I) After 15 minutes


( II) After 60 minutes


( II) After 60 minutes


( II) After 60 minutes


Figure 2.27. Photographs of Suntech IV Foams at Various Time
Intervals after the Foams Were Produced.





65










8U88LES CAO LMfLY CUOLLAPSEC
















SOS C8011 SOS C N





































Figure 2.28. Photographs Of Foams for Mixture of SDS
with Alkyl Alcohols at Various Time intervals
after the Foams Were Produced.














AFTEP 72 HOU


SDS + C120H


FOAMINrG AGENTS: SDS(5mM) + C OH(0.5mM)
PS AFTER 120 HnURS






BUBBLES COMPLETELY COLLAPSE'







SDS + C120H


SOS + C14C SOS + C140H


SOS + C160H SDS C16OH


I

Figure 2.29. Photographs of Foams for .'ixture of SDS with
Alkyl Alcohols at Various Time Intervals after
the Foams Were Produced.













FOAMING AGENTS: STEPANFLO 40(5x101 gm/ml) *CnOH(O.3mM)


STEPANFLO 40 + CaOH


STEPANFLO 40 + C100H


STEPANFLO 40 + C120H


STEPANFLO 40 + C40H


Figure 2.30. Photographs of Foams for 1
with Alkyl Alcohols at 24'
Were Produced.
: iiib,. ......,iii1


AFTER 24 HOURS











































1~* -


r~. .-.;-_-- -.-r.


I . . --


E



: U)

0H
Q








C. -


*C.


U
u
QJ





O O



O
0 0










ci n


.0










OE


mr
4J



















O
.I E
H a
)4J
Qtj




- 1




C) C

0 z

UL 0




0


X l


----I ---- ------- 7___- 0


S.~rIgns JO tH1f,'iN


C-;- ~
I`


r-
L~..`~_c~-~IL~~

















































1--I
o E
U


C4


Q)

4


4I
cnl


s3i88n8 o0 H2NnlN


m

I--I

,C


c.)


oul







-,-
H *





4 -)
0

W3e

3









O4-
.Q 0
4-I












0 E



ra
4)J
E(n
Ilv]








4-1 .
0

E U
n3l
n *P


I________l^ > ^ ^ S_
IV N, \ \ N % \ \ % \
i\ ^ T. %


1\ \ \ \ v\ \ "\




I \ \. \ \
I\ ~r \ \ % '% %. f- %,v "%
l\" \ ." \ s \, "\ "\ ". %. % "\ \ \ \ "** \ \ -

________ I \. \ \ -% \ \ \ Y._%%.% % ,



['. ~ I% %. X '. % "\ \ "\ ". \ '. \ ',\\ \ \

fI~ % % % v



\, %. \, \ \a %- "- % \ \ '\ %. '% \ \ \ % \ "% \ % \ -











































L- \ S ~ Sr - -. 'S

Ezz.`. .. \ z,.

'N~~ .










~2-. -


I
Yi '4


S3qu8nf J0 H3SwfN


U
1-4

.c


:-
U

(I


C ) U



0 0



.H


4-1
.,-I (0
0





LJ

'U)












-O
E-E
r

Q U)




r-O

nC
E ^



0
4J E

mn J-


6
B>


E
a U



C1-




2
4 <


C, C

(U

-4








Suntech IVA, B, and C are 8.97x10-2 cm, 10.3x10 2 cm, and

10.64x10-2 cm, respectively.

The average bubble size was a minimum for the mixed

foaming systems SDS + C16OH (Figures 2.28 and 2.29). The

experiment was repeated at least five times and the trends

were very reproducible. As mentioned previously, a large

amount of bubbles were easy to produce for the system of

SDS + C OH, SDS + C1 OH, and SDS + C12OH, but not for the

system of SDS + C14OH and SDS + C16OH. It seems that the

energy required to generate bubbles increases with the

increase of hydrocarbon chain length of alcohols. The

higher the required energy, the smaller the bubble size and

the less foam produced for a given concentration of foaming

agent. Once the bubbles (i.e., SDS + C14OH or SDS + C16OH)

were formed, they could last a long time without breaking.

This can be interpreted in terms of the hydrophobicity of

hydrocarbon chain and the rate of adsorption/desorption of

solute at the interface. The hydrophobic force keeps the

surfactant molecules at the interface. It does not mean

that SDS + C14OH or SDS + C6 OH can always produce stable

foams because the work applied to the foam has to be

considered. For instance, they may not produce any foam at

a low pressure. Although the rate of drainage of SDS +

C 1OH foam is faster than that of SDS + C4 OH foam (Figure

2.23), the former can stay at a very high foam quality

without breaking. Therefore, the slowest rate of

coalescence of the bubbles was observed for the system of








SDS + C16OH and, consequently the smallest average bubble

size was found after a long period of time (Figure 2.29).

Similar results (Figure 2.30) were observed for the mixed

foaming systems Stepanflo 40 + CnOH and were consistent

with the trend of the rate of drainage. Based on relative

comparison, the measurements of bubble size distribution

for the mixed foaming systems are still very useful in

comparing the foam stability.



2.4.8 Microscopic View of Foam Flow in Micromodel

Figure 2.34 shows the photomicrographs of foams

generated inside the micromodel. It is evident that the

mixed surfactants of same chain length (SDS + C12OH)

produced smaller foam bubbles and more lamellae than the

surfactant system with dissimilar chain length. These

photomicrographs indicate that the injection of a gas in

the micromodel filled with surfactant solution can generate

foam in-situ.

From these photomicrographs and the results of the

previous section it is clear that the bubble size

distribution is different for mixed foaming systems, SDS +

C OH (n = 8, 10, 12, 14, and 16), inside and out of the
n
micromodel. It is evident that for a given concentration,

the bubble size of a foaming agent depends on the

foaminess, foam stability, pore size, pressure, etc.

The mechanism of foam flow through porous media

described by Holm [63] is of a moving continuous liquid



















Ci9.SiNoi+ C 100H


C cr H CeS No + COH

Figure 2.34. Photomicrograph of Foams in Micromodel.








phase and a discontinuous, internal gas phase moving

discretely or by rupture of the gas cells. Sharma et al.

[79] proposed two mechanisms of gas flow in porous media in

the presence of surfactant solution (Figure 2.35). Foams

with high stability follow the bubble-train mechanism,

whereas foams with low stability follow the pop and burst

mechanism in a given porous medium. Of course, this

mechanism also depends on the amount of foam generated

in-situ and the bubble size relative to the pore size.



2.5 Conclusions



In this chapter the surface properties of the foaming

agents and the foam stability were discussed. The effects

of adding long chain alcohols on the foaming agents were

also investigated. The following conclusions were drawn

from the studies in this chapter.

1. The presence of long chain alcohols in the foaming

agents, SDS and Stepanflo 40, had considerable

influence on their surface properties as well as on

the foam stability. There was no such influence on

Suntech IV.

2. For mixed foaming systems, SDS + C OH (n=8, 10, 12,

14, and 16), minimum surface tension, maximum surface

viscosity [33], maximum foaminess, and the slowest

rate of drainage at the early stage were observed when

both components of the system had the same chain























GAS --

















GAS _I
-0I


BUBBLE-TRAIN MECHANISM (HIGH BUBBLE STABILITY)


POP AND BURST MECHANISM (LOW BUBBLE STABILITY)


Figure 2.35. Two Mechanism of Gas Flow in Porous Media
Filled with Surfactant Solution.








length (SDS + C2 OH). However, the minimum foam

quality and minimum apparent foam viscosity were

observed for the system consisting of SDS + CoOH; the

slowest rate of drainage at the later period was found

for the system of SDS + C 4OH.

3. For mixed foaming systems, Stepanflo 40 + C OH (n=8,

10, 12, 14, and 16), minimum surface tension was

observed for Stepanflo 40 with the addition of dodecyl

alcohol; whereas, maximum foaminess, minimum foam

quality, and minimum apparent foam viscosity were

observed for the system consisting of either Stepanflo

40 + C,,OH or Stepanflo 40 + C12OH; the slowest rate

of drainage was found for the system of Stepanflo 40 +

C,6 OH.

4. The foaming agent, SDS + C12OH, produced the smallest

bubbles in the micromodel. The number of lamellae

decreased as the difference in SDS + C OH chain length

increased.

5. From the bubble size distribution measurements, the

average bubble size decreased as the hydrocarbon chain

length of alcohol increased. It seems that the energy

required to generate foam bubbles increases with the

increase of chain length of alcohols. The higher the

required energy, the smaller the bubble size and the

less foam produced for a given concentration of mixed

foaming system.

6. The overall studies on the surface properties of the








mixed foaming systems show that the effect of chain

length compatibility is not observed for the rate of

drainage and bubble size distribution. These

exceptional cases can be explained by the surfactant

molecules' packing pattern at the liquid/air

interface, rate of adsorption/desorption of solute at

the interface, and the theology of the thin liquid

films. It should be noted that it does not mean that

the theory of chain length compatibility is not true.

It illustrates that not all surface properties of the

mixed foaming agents can be predicted from the chain

length compatibility effects. In addition to the

factors mentioned above, other factors such as the

work done on the system and the method used to generate

the foam have to be considered.














CHAPTER III


FLUID DISPLACEMENT IN POROUS MEDIA BY IN-SITU FOAM



3.1 Introduction



It has been shown [64] that the foam generated in-situ

can be used to block the flow of gas in both consolidated

and unconsolidated porous media. The pressure at which gas

flow is blocked increases with the saturation of surfactant

solution in porous media as well as the concentration of

surfactant in the solution. From gas tracer studies, Nahid

[80] also showed that the existence of an immobile gas

saturation increased with the concentration of the

surfactant. The immobile gas saturation ranged from 4% in

the absence of a surfactant up to 30% at a surfactant

concentration of 1%. The effect of foam on gas permeability

is one of the most important aspects for tertiary oil

recovery processes. In the presence of foams, the effective

permeability of a porous medium to each phase is

considerably reduced as compared to the permeability

measured in the absence of foams [63,65]. The presence of

oil in a porous medium decreased the effectiveness of foams

in reducing permeabilities of gas and water [6,81].








However, it was found that certain surfactants were very

effective in reducing gas permeability even in the presence

of oil. The continuous injection of several other

surfactants also increased their effectiveness in the

presence of oil.

The main objective of this study was to correlate the

effect of surface properties of foaming agents and foam

stability on the foam behavior in porous media. The

parameters measured and correlated for foam flooding

processes included fluid displacement efficiency,

breakthrough time, effective air mobility, and pressure

distribution in porous media. The fluid displacement

efficiency is defined as the ratio of the fluid recovered

to the total fluid in a porous medium until the

breakthrough of gas phase. The breakthrough time is the

time taken by the gas to breakthrough at the producing site

of the porous media. The fluid displacement efficiency of

foam in heterogeneous porous media was also studied. The

results of these investigations would be relevant in

evaluating foam as a blocking agent for controlling

underground gas flow as well as an oil recovery agent under

specific reservoir conditions.



3.2 Materials and Methods



3.2.1 Materials

All chemicals used in the experiments were the saie as








described in Chapter II. The sand used as a porous medium

was purchased from AGSCO Corp., Paterson, New Jersey. The

sand had absolute permeability of 2-3 darcys and porosity

of 38%. The pressure transducers (DP-15) used for the

measurements of pressure across a porous medium were

obtained from Validyne Engineering Corp., Northridge,

California. The chart recorders (Health/Schlumberger Model

225) were purchased from Health Company, Benton, Michigan.

The liquid was pumped using Cheminert metering pump (Model

EMP-2), Laboratory Data Control, Riviera Beach, Florida.

The sand was packed using wrist action shaker (Model 75),

Burrell Corp., Pennsylvania. Compressed air and CO, were

purchased from AIRCO Company, Gainesville, Florida.



3.2.2 Methods

At room temperature, the experiments were conducted

under different concentrations of foaming agents and types

of the porous medium to analyze foam behavior in porous

media. A polyvinyl pipe (2"IDx18"L) was packed with sand

using a wrist action shaker at a flow rate of sand about

5 cm'/min. The sandpack (Figure 3.1) was flushed vertically

with CO2 about an hour to replace interstitial air.

Deionized water was pumped through using a Cheninert

metering pump, and the pore volume (Vp) of the porous

medium was determined. About three pore volume; of water

(or brine) were pumped through at various flrw rates to

wash out CO as well as to determine absolute permeability



















O 0
Liquid
fu


or CO








Water or





Solution
L4-
E- )

:3 :



Liquid -
Collector o



Model u




Air or CO Pru M Std
Supply

Water or
Surfactant
Solution












Figure 3.1. Schematic Diagram.of the Experimental Set Up
for Flow through Porous Media Studies.








of the porous medium using Darcy's law [82]. After the

porous medium was saturated with water (or brine), about

three pore volumes of foaming solution with known

concentration were pumped at constant flow rate (4 ml/min),

followed by air injection. The pressure differences across

the porous medium were measured using pressure transducers

and chart recorders. The liquid at outlet was collected at

different time intervals. The breakthrough time and total

fluid recovery were recorded.

In order to determine the fluid displacement

efficiency in heterogeneous porous media, a series of

experiments were conducted. The sand packs containing a

non-porous (e.g., stainless steel) core or a porous (e.g.,

Berea core) core were prepared as shown in Figure 3.2. The

Berea core had permeability of about 275 millidarcys and

porosity of 20%. The dimensions of the pipe used for sand

packs were 12" diameter and 18" length. The stainless steel

core and Berea core packed inside the sand had the same

shape and the size (l"xl"x12"). From these two types of

porous media, one can easily determine the fluid displaced

from low permeability porous media (i.e., Berea core) in

the absence and presence of foam.



3.3 Effective Mobility of Air in the Presence of Foam



In order to interpret the flow behavior of foam in a

porous medium, the effective air mobility was calculated




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