MICROSCOPIC STUDY OF EMULSION FLOW IN POROUS …eprints.utm.my/id/eprint/18650/1/MuhammadAMananPFKKKSA2006.pdfMICROSCOPIC STUDY OF EMULSION FLOW IN POROUS MEDIA MUHAMMAD BIN A.MANAN

MICROSCOPIC STUDY OF EMULSION FLOW

IN POROUS MEDIA

MUHAMMAD BIN A.MANAN

UNIVERSITI TEKNOLOGI MALAYSIA

MICROSCOPIC STUDY OF EMULSION FLOW IN POROUS MEDIA

MUHAMMAD BIN A.MANAN

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Doctor of Philosophy

Faculty of Chemical and Natural Resources Engineering

Universiti Teknologi Malaysia

DECEMBER 2006

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DEDICATION

I dedicated this Ph D Thesis to my lovely parents; Hj. A.Manan Hitam and Hjh.

Hasnah Janom, to my parent-in-laws; Hjh. Habibah Sepit and late Hj. Maarof Rumit,

to my wife; Nathrah, to my children; Pali, Munah and Ain, and to my other family

members. Your deep understanding, patience and continuous support have

encouraged me to complete this thesis.

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ACKNOWLEDGEMENTS

I first wish to thank my supervisor, Prof. Dr. Ahmad Kamal Idris, for his support and

guidance throughout my doctoral program. My colleagues have also been a great

help, in particular, Ramli Mat and Onn Hassan for his invaluable encouragement for

me to complete this thesis.

Many others have contributed to this thesis. I would like to thank Roslan Jas and

Othman Adon for their help in the reservoir lab, Dr. Sugiatmo for his assistance with

micromodel setup, Ahmad Norani Sadiron for his expertise in the chemical selection,

and all my other friends for their moral supports at the time of depress, directly or

indirectly. Finally, I am also grateful to UTM and the Government of Malaysia for

their financial support - scholarship and full-paid leave.

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ABSTRACT

Emulsion applicability as an oil recovery agent has long been recognized in petroleum industry. However, investigations of emulsion flow in porous media for petroleum recovery applications are scarce; particularly the flow effects have not been explained in detail in term of events occurring at the pore level. Thus, this research was carried out to investigate the physics of emulsion flow in porous media. The objectives of the experiments are to study the behavior and mechanism of emulsion flow in porous media, to evaluate the effectiveness of emulsion as an oil recovery agent, and to determine the emulsion blocking processes. In this research, well characterized emulsions of water-in-oil emulsion (model oil of 86.5% dibutylphthalate + 13.5% n-heptane, and distilled water system) and oil-in-water emulsion (paraffin oil, distilled water, and Triton-X100 surfactant system) were injected into two-dimensional etched glass micromodels. Visualization experiments by using microscope on the micromodels were conducted to observe and record the emulsion droplet motion, captured mechanisms, and blockage processes. The results demonstrate the three possible flow regimes that may occur when emulsion flow in porous media are mainly due to the difference of emulsion droplet size to pore throat ratios. Flow phenomena of emulsion droplet formation, deformation and destruction, blob and rivulet were observed to be associated with less stable emulsion system. Other emulsion flow phenomena were the microstructures of droplets adhesion and entrainment from the solid surface, and droplets undergone snap-off and division from pore-to-pore. The results show that the emulsion droplets were found to be captured at the throat and the pore body according to straining and interception capture mechanisms. Also, the results indicate that wettability has a direct influence on the droplet capture mechanism. Emulsion water droplet colliding with the water-wet surface could easily adhere to the surface and formed thick water films. On the other hand, emulsion water droplet contacting oil-wet surface could be displaced from the surface by the continuous oil phase. Moreover, the results reveal that continuous emulsion injections could provide additional oil recovery, but by injecting smaller size emulsion slugs prior to water injection would result in insignificant additional oil recovery. Microscopic mobility control was found to contribute to the oil recovery processes in homogeneous porous media, while macroscopic mobility control due to the emulsion blocking effect would contribute to the oil recovery processes in heterogeneous porous media. The emulsion blockage process was observed to be accelerated with large ratio of emulsion droplet-to-pore throat, coalescence of captured droplet, low emulsion flow rate, more viscous emulsion droplets, and emulsion droplet wetting the solid surface. In conclusion, this research characterizes the physics of emulsion flow in porous media and demonstrates its application as an effective oil recovery agent through emulsion blocking mechanisms. The novelty is the revelation of the process for emulsion droplet blockage effects in porous media.

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ABSTRAK

Kegunaan emulsi sebagai agen perolehan minyak sudah lama diiktiraf dalam industri petroleum. Walau bagaimanapun, penyiasatan tentang aliran emulsi di dalam media poros dalam aplikasi perolehan minyak masih berada pada tahap yang kurang sempurna; terutama kesan aliran emulsi yang masih tidak dijelaskan secara terperinci dari aspek perlakuan kejadian pada tahap liang. Oleh itu, penyelidikan ini dijalankan untuk menyiasat perlakuan fizik aliran emulsi di dalam media poros. Objektif kajian adalah untuk mengkaji tingkahlaku dan mekanisme aliran emulsi di dalam media poros, menilai emulsi sebagai agen perolehan minyak yang berkesan, dan menentukan proses penyekatan emulsi. Dalam penyelidikan ini, emulsi air-dalam-minyak (sistem model minyak 86.5% dibutilfatalat + 13.5% n-heptana, dan air suling) dan emulsi minyak-dalam-air (sistem minyak parafin, air suling, dan surfaktan Triton-X100) yang mempunyai ciri tertentu disuntik ke dalam mikromodel gelas tersurih dua dimensi. Ujian gambaran dengan menggunakan mikroskop ke atas mikromodel dilakukan untuk memerhati dan merakam pergerakan titisan emulsi, mekanisme pemerangkapan, dan proses penyekatan. Keputusan ujian menunjukkan bahawa tiga jenis regim aliran boleh berlaku terutama bila emulsi mengalir di dalam media poros adalah berpunca daripada perbezaan nisbah saiz titisan emulsi terhadap leher liang. Fenomena aliran misalnya pembentukan titisan emulsi, ubah bentuk dan pemusnahan, titisan besar, dan sungai titisan emulsi hanya berlaku pada sistem emulsi yang kurang stabil. Tingkahlaku aliran emulsi yang lain ialah terdapat mikrostruktur rekatan dan pembebasan titisan emulsi dari permukaan pepejal, dan titisan emulsi mengalami pemutusan dan pembahagian dari satu liang ke liang yang lain. Keputusan menunjukkan bahawa titisan emulsi terperangkap di leher liang dan jasad liang berdasarkan mekanisme penyekatan dan pemintasan. Keputusan juga mempamerkan bahawa keterbasahan mempunyai kesan langsung terhadap mekanisme pemerangkapan titisan. Titisan air emulsi berlaga dengan permukaan basah air mudah terekat pada permukaan dan membentuk lapisan air yang tebal. Sebaliknya, titisan air emulsi yang berlaga dengan permukaan basah minyak dianjakkan dari permukaan oleh fasa minyak yang berterusan. Selanjutnya, keputusan mendedahkan bahawa suntikan emulsi secara berterusan mampu menghasilkan perolehan minyak tambahan, tetapi suntikan slug emulsi yang kecil sebelum suntikan air tidak memberi kesan terhadap perolehan minyak. Kawalan pergerakan secara mikroskopik didapati menjurus kepada proses perolehan minyak dalam media poros homogen, sementara kawalan pergerakan secara makroskopik yang disebabkan oleh kesan penyekatan emulsi menjurus kepada perolehan minyak dalam media poros tak homogen. Proses penyekatan emulsi mampu dipercepatkan oleh nisbah titisan emulsi terhadap leher liang yang besar, penautan titisan yang terperangkap, kadar aliran yang rendah, titisan emulsi yang lebih likat, dan titisan emulsi yang membasah permukaan pepejal. Kesimpulannya, penyelidikan ini berjaya mencirikan fizik aliran emulsi di dalam media poros dan menunjukkan kegunaannya sebagai agen perolehan minyak yang berkesan melalui mekanisme penyekatan emulsi. Keaslian kajian ialah pendedahan kesan penyekatan emulsi di dalam media poros.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xiii

LIST OF FIGURES xvii

NOMENCLATURE xxvii

LIST OF APPENDICES xxiv

1 INTRODUCTION

1.1 Background 1

1.2 Emulsion Applications in Oil Recovery 3

1.3 Problem Statement 8

1.4 Objective of Research 9

1.5 Scope of Research 10

1.6 Overview of Thesis Contents 12

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2 FUNDAMENTAL PRINCIPLES OF EMULSIONS AND EMULSIONS FLOW IN POROUS MEDIA

2.1 Introduction 13

2.2 Definition and Classification of Emulsions 14

2.3 Crude Oil Emulsions 17

2.3.1 Crude Oil Emulsion Formation 17

2.3.2 Physicochemical and Chemical Properties 18

2.4 Interfacial Properties 21

2.4.1 Surfactants 21

2.4.2 Interfacial Tension 23

2.4.3 Interfacial Rheology 24

2.5 Surface Activity 24

2.5.1 Surface Phenomena 24

2.5.2 Critical Surface Tension 25

2.5.3 Wettability 27

2.5.4 Contact Angles and Surface Energy 29

2.5.5 Surface Chemistry 30

2.6 Forces Acting on Emulsion Droplets 31

2.6.1 Dispersion Forces 31

2.6.2 Electrostatic Forces 31

2.6.3 Steric Forces 32

2.6.4 Brownian Force 32

2.6.5 Viscous, Inertial and Gravitational Forces 33

2.7 Stabilization and Destabilization of Emulsions 33

2.7.1 Creaming or Sedimentation 39

2.7.2 Flocculation 39

2.7.3 Coalescence 40

2.7.4 Ostwald Ripening 41

2.7.5 Stability of Water-in-Oil and Oil-in-Water Emulsions 41

2.7.6 Destabilization Actions of Emulsions 42

2.7.6.1 Adsorption of Surfactant at Liquid-Liquid 44

Interface

2.7.6.2 Emulsion Breakdown 45

2.8 Porous Media Characteristics 46

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2.8.1 Porous Medium 46

2.8.1.1 Heterogeneity 47

2.8.1.1 Aspect Ratio 47

2.8.1.1 Coordination Number 47

2.8.2 Porosity 48

2.8.3 Permeability 48

2.8.4 Pore Size Distribution 49

2.8.5 Specific Surface Area 49

2.9 Emulsion Flow in Porous Media 49

2.9.1 Flow of Emulsions in Fibrous Low Droplet-to-Pore 52

Ratio Porous Media

2.9.2 Flow of Emulsions in Petroleum Reservoirs 54

2.10 Oil Mobilization and Entrapment in Porous Media 54

2.10.1 Viscosity and Mobility Ratios 55

2.10.2 Interfacial Tension of Water and Crude Oil 56

2.10.3 Capillarity 56

2.10.3.1 Capillary Pressure 57

2.10.3.2 Capillary Number 58

2.9.4 Wettability of Reservoir Rock 59

2.9.5 Relative Permeability 62

2.9.6 Oil Entrapment in Porous Media 63

2.11 Concluding Remarks 64

3 LITERATURE REVIEW

3.1 Introduction 66

3.2 Emulsion Flow in Porous Media 66

3.2.1 Emulsion Flow Mechanism in Porous Media 67

3.2.2 Emulsion as Mobility Control and Blocking Agents 69

3.2.3 In-situ Emulsion Generation 71

3.2.4 Simultaneous Flow of Emulsions and Bulk Oil and Water 72

3.3 Effects of Some Variables on Emulsion Flow in Porous Media 74

3.3.1 Porous Media Characteristics 74

3.3.2 Emulsion Characteristics 76

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3.3.2.1 Emulsion Stability 76

3.3.2.2 Emulsion Quality 77

3.3.2.3 Droplet Size and Droplet Size Distribution 79

3.3.2.4 Dispersed Phase Viscosity 82

3.3.3 Flow Velocity 83

3.4 Macro and Micro Scales Flow Study 83

3.4.1 Macroscopic Study of Emulsion Flow in Porous Media 84

3.4.2 Microscopic Study of Emulsion Flow in Porous Media 87

3.4.2.1 Background of Micromodels 87

3.4.2.2 Micromodel for Emulsion Flow in Porous Beds 92

3.5 Mathematical Models of Emulsion Flow in Porous Media 94

3.5.1 Homogeneous Phase Models 94

3.5.2 Droplet Retardation Models 98

3.5.3 Filtration Models 99

3.5.4 Droplet Regeneration Models 100

3.6 Discussion on the Literature Reviews 102

3.7 Concluding Remarks 104

4 RESEARCH METHODOLOGY

4.1 Introduction 105

4.2 Fluids, Chemicals and Measurement Apparatus 106

4.2.1 Fluids and Chemicals 106

4.2.2 Measurement Apparatus 107

4.3 Micromodel Construction and Its Properties 107

4.3.1 Regular Hexagonal Patterns 108

4.3.2 Irregular Homogeneous and Heterogeneous patterns 111

4.3.3 Physical Properties of Micromodels 111

4.3.4 Wettability of Micromodels 113

4.3.4.1 Water-wet micromodels 113

4.3.4.2 Oil-wet micromodels 114

4.3.4.3 Mixed-wet micromodels 116

4.4 Model Oil - Distilled Water Emulsion System 117

4.4.1 Determination of Model Oil System 117

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4.4.2 Characterization of Model Oil – Distilled 117

Water Emulsion System

4.5 Emulsion Flow Experiments in Micromodels 117

4.5.1 Experimental Setup 118

4.5.2 Scale Level of Observations 119

4.5.3 Emulsion System and Emulsion Preparation 120

4.6 Concluding Remarks 125

5 EMULSION CHARACTERIZATION

5.1 Introduction 126

5.2 Characterization Tests 126

5.2.1 Emulsion Preparation 127

5.2.2 Emulsion Stability Tests 127

5.2.3 Rheology Tests 128

5.2.4 Droplet Size Measurements 128

5.3 Results and Discussions of Model Oil – Distilled 129

Water Emulsion System

5.3.1 Emulsion Quality 129

5.3.2 Emulsion Rheological Properties 134

5.3.3 Droplet Size, Concentration and Distribution 137

5.4 Summary of Model Oil – Distilled Water Emulsion System 143

6 MICROMODEL FLOW EXPERIMENTS

6.1 Introduction 145

6.2 Material, Apparatus and Procedures 145

6.2.1 Materials 145

6.2.2 Apparatus 146

6.2.3 Procedures 146

6.2.4 List of Micromodel Experiments 147

6.3 Results of Emulsion Displacement Tests 150

on Micromodels

6.3.1 Emulsion Flow Mechanism in Porous Media 150

6.3.2 Flow Behavior on Emulsion 153

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6.3.2.1 Effect of Emulsion Flow Rate 156

6.3.2.2 Effect of Emulsion Quality 159

6.3.2.3 Effect of Micromodel Grain Characteristics 160

6.3.3 Effect of Wettability 165

6.3.3.1 Water-Wet Micomodel 166

6.3.3.2 Oil-Wet Micromodel 167

6.3.3.3 Mixed-Wet Micromodel 169

6.3.4 Emulsion Flood Experiments 172

6.3.4.1 Oil Saturated at Residual Water Saturation 175

Micromodel

6.3.4.2 Oil Residual Saturated Micromodel 180

6.3.5 Effect of Reverse Water Injection 183

6.3.6 Flow Test with Surfactant Added Emulsion Systems 184

6.4 Discussion of Results 189

6.4.1 Emulsion Flow Behaviors in Porous Media 190

6.4.2 Emulsion Regeneration in Micromodel 192

6.4.3 Emulsion as an Recovery Agent 194

6.4.4 Emulsion Blocking Phenomena 196

6.5 Summary and Implications of Micromodel Results 198

7 SUMMARY OF PRESENT WORKS, CONCLUSIONS,

RECOMMENDATIONS, AND FUTURE WORKS

7.1 Summary 201

7.1.1 Emulsion System 201

7.1.2 Emulsion Flow Behaviors and Mechanism in 202

Porous Media

7.1.3 Emulsion Blocking Process 203

7.1.4 Emulsion for Oil Recovery Agent 203

7.2 Conclusions 204

7.3 Recommendations 205

REFERENCES 207

APPENDICES 222

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LIST OF TABLES

Table Page

1.1 Area of Study in the Understanding of Both Qualitative and Quantitative 3 Aspects for Emulsion Flow in Porous Media (Kokal et al., 1992). 1.2 Differences and Similarities between the Flow of Emulsion and the 5 Simultaneous Flow of Oil and Water in a Porous Medium (Schramm, 1992; Kokal et al., 1992). 2.1 Types of Emulsion in the Petroleum Industry (Schramm, 1992). 14 2.2 Physicochemical Properties of Norwegian Continental Shelf Crude 19 Oils at 20oC (Sjoblom et al., 1990b). 2.3 Some Chemical Properties of Norwegian Continental Shelf Crude 20 Oils (Sjoblom et al., 1990b). 2.4 Physicochemical Properties of the East Coast of Malaysia Crude Oils 20 at 25.5oC, unless stated otherwise (Bambang et al., 2002). 2.5 Some Chemical Properties of the East Coast of Malaysia Crude Oils 21 (Bambang et al., 2002). 2.6 Critical Surface Tension of Solid Surface Against Water and Oil 25 Surface Tension (Berg, 1993). 2.7 Some Materials with Low-Energy and High-Energy Surfaces with Their 26 Critical Surface Tensions (Berg, 1993). 2.8 Comparing Wettability of Different: (a) Low-Energy surface, and 26 (b) High-Energy Surface by Test Liquids (Sharifi, 1995). 3.1 Comparison of Placement Properties in a Two-Layer Linear System 70 with 10% Permeability Contrast (Seright and Liang, 1995). 3.2 Visual Study on Snap-off for Emulsion Generation in Porous Media. 72 3.3 The Effects of Droplet Size and Droplet Size Distribution on Emulsion 79 Properties and on Flow Behavior in Porous Media.

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3.4 Viscosity (at 75oC) of o/w Emulsions Prepared from Different Crude 82 Oils (McAuliffe, 1973a). 3.5 Some Examples of Multiphase Flow Studies using Micromodels. 88 3.6 Some Examples of Enhanced Oil Recovery (EOR) Studies using 89 Micromodels. 3.7 Some Characteristics of Micromodels. 91 3.8 Some Observational Terms used to Describe Emulsion Flow Behaviors 92 in Porous Media. 3.9 Conclusions on Dilute and Stable Emulsion Flow in Porous Media 93 (Porous Beds) for Increasing Coalescence Performance.

3.10 Viscosity correlations for Newtonian emulsions (Abou-Kassem and 96

Ali, 1995).

4.1 General Properties and Dimensions of Regular Pattern Micromodels. 112 4.2 Specific Physical Properties of the Micromodels. 113 4.3 Contact Angles Measured (Advancing) of Water in Model Oil on 114 Clean and Treated Glass Surfaces, and the Critical Surface Tensions at 27.5oC. 4.4 Summary of Organosilanes. 116 4.5 Physical properties of Fluid used in the Emulsion Flow Experiments. 121 5.1 Rheological Data for o/w Emulsions at 27.5oC 135 (Model Oil/Distilled Water). 5.2 Rheological Data for w/o Emulsions at 27.5oC 136 (Model Oil/Distilled Water). 5.3 Droplet Size Distribution Data of 0.1% o/w Emulsion. 139 6.1 Summary of Micromodel Floods (Emulsion Floods) in Regulars 149 (Hexagonal Pattern), and Irregulars (Homogeneous and Heterogeneous Patterns) Micromodels. 6.2 Summary of Continuous Emulsion Floods (Injection) in Water-Wet and 155 Dried Regular Hexagonal Pattern Micromodels. 6.3 Summary of the Experiments at Different Flow Rates. 159 6.4 Summary of the Experiments at Different Grain Sizes. 164

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6.5 Summary of the Observations of Emulsion Flow at Different 171 Wettability. 6.6 Characteristics of Triton X-100 Surfactant. 185 6.7 Properties of 10% Emulsion of Paraffin Oil-in-Distilled Water at 185 0.05 % v/v and 0.15% v/v Triton X-100 Concentrations. A.1 Macroscopic Flow of Emulsion through Porous Bed Coalescers: 222 System Parameters. A.2 Macroscopic Flow Study of Emulsions Through Porous Bed 224 Coalescers. A.3 Experimental and Field Studies on Emulsion Properties and Flow 226 Mechanisms. A.4 Microscopic Flow of Emulsion through Porous Bed Coalescers: 231 System Parameters. A.5 Microscopic Flow Study of Emulsions Through Porous Bed 232 Coalescers. A.6 Mathematical Modeling of Emulsion Flow in Porous Media. 233 D.1 Physical Properties of Model Oil A and Distilled Waters. 249 D.2 Physical Properties of Model Oil A – Distilled Water Systems. 249 D.3 Rheological Data for o/w Emulsion (100% TBP/Distilled Water). 250 D.4 Rheological Data for o/w Emulsion (75% TBP+ 250 25%DBP / Distilled Water). D.5 Rheological Data for o/w Emulsion (50% TBP+ 251 50%DBP / Distilled Water). D.6 Rheological Data for w/o Emulsion (50% TBP+ 251 50%DBP / Distilled Water). D.7 Physical Properties of Various Concentrations of Model Oil B. 254 D.8 Physical Properties of Model Oil B – Distilled Water Systems. 255 D.9 Physical Properties of Model Oil C – Distilled Water Systems. 256 D.10 Kinematic Viscosity Data for o/w Emulsion Model Oil C / Distilled 257 Water at Various Temperatures.

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D.11 Physical Properties of Some Alkane – Distilled Water Systems 258 (oily phase is the dispersed phase and water is the continuous phase). D.12 Summary of Model Oil Systems 259 E.1 Raw data of diameters and top-view areas of emulsion droplets, 264 where 193, 226 and 266 droplets are captured under microscope for photos #1, #2 and #3, respectively..

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LIST OF FIGURES

Figure Page

2.1 Schematic representation of fluid systems: (a) non-dispersed system, 15 (b) oil-in-water emulsion, and (c) water-in-oil emulsion (Bansbach, 1989). 2.2 Schematic illustration of w/o/w and o/w/o multiple emulsions. 15 (Bansbach, 1989). 2.3 Surfactants can have various molecular structures (Kouloheris, 1989). 22 2.4 Some surfactant structures (Yarranton, 1997). 23 2.5 Contact angle as a measurement of preferential wettability. A small 27 contact angle, θ, means that phase A preferentially wets the solid in the presence of phase B. 2.6 Correlation of θow and θwo with critical surface tension for aviation 30 kerosene-in-water emulsion system (Clayfield et al., 1985a). 2.7 Electrostatic and steric stabilization of emulsions (Yarranton, 1997). 32 2.8 Schematic representation of (a) Gibbs effect, and (b) Marangoni effect 34 (Jimeno, 1987).

2.9 Origin of interfacial tension gradients due to presence of natural 34 surfactant, leading to stabilization of film (Jimeno, 1987; Panoussopoulos, 1998). 2.10 Colloidal particles stabilizing emulsion droplets (Tambe and 38 Sharma, 1994). 2.11 (a) Schematic representation of various possible mechanisms of 38 emulsion breakdown processes (Tadros, 1984), and (b) flocculation leaves aggregates of droplets, and coalescence leaves an emulsion with a wide distribution of droplet size (Friberg, 1992). 2.12 Potential energy curves between two droplets for (a) electrostatic and 40 dispersion forces, and (b) steric dispersion forces (Ross and Morrison, 1988).

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2.13 Characteristics of pore system: (a) pore shape, (b) connectivity or 46 number of throats which connect with each pore (3 and 6 illustrated). (c) uncorrelated pore-throat structure, (d) correlated pore-throat structure, (e) spatially disordered pores (not clustered), and (f) spatially ordered pores (clustered) (Yun and Wardlaw, 1991).

2.14 Example of possible mechanisms for contact and coalescence droplets 50 in a porous beds: (a) drop contact due to flowing drop colliding with stationary drop, (b) drop contact due to adjacent, stationary drops contacting, (c) drop contact and/or coalescence due to shear forces in the pores driving drops together and distorting drops, (d) coalescence due to drop contact with a coalesced, wetting region, and (e) coalescence due to two wetting fluids contacting on a solid surface during spreading or flow (Anklam, 1997). 2.15 Typical Relationship between Mobility Ratio and Oil Recovery 56 (Haberman, 1960). 2.16 Possible mechanisms leading to a capillarity factor: (a) contact 58 sngle hysteresis, (b) dontact line variation, and (c) surface area increase (Devereux, 1974a). 2.17 Capillary desaturation curve for water-wet Brea Sandstones 59 (Mendez, 1999). 2.18 Different types of wetting conditions of a single pore: (a) water-wet, 60 (b) oil-wet, (c) intermediate-wet, (d) fractional-wet, and (e) mixed wet (Mat Hussin, 1996).

2.19 Contact angle as a measurement of preferential wettability. A small 61 contact angle, θ, means that water preferentially wets the solid in the presence of oil. 2.20 Relative permeabilities for (a) an oil-wet system, and (b) a water-wet 63 system. kro is the relative oil permeability, and krw is the relative water permeability (Schramm, 1992). 2.21 Oil entrapment mechanisms: (a) pore doublet model, and (b) pore 64 snap-off model (Lake, 1989). 3.1 Emulsion blockage mechanism (r1 and r2 are the radii of curvature 68 at the leading and trailing edges of the drop, respectively) (McAuliffe, 1973). 3.2 Emulsion retention mechanisms. (MPHR: multi-particle hydrodynamic 69 retardation). (Soo and Radke, 1986; Mendez, 1999).

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3.3 Schematic pictures showing (a) simultaneous oil and water flow in 73 porous media, and (b) emulsion flow in porous media (Vittotos,1990). 3.4 Schematic pictures showing simultaneous flow of emulsified and 74 bulk dispersed phase in porous media: (a) o/w emulsion in oil-wet porous media, part of the oil flow as a free phase, (b) o/w emulsion in water-wet porous media, bulk oil phase flows through a network of larger pores (Vittotos, 1990). 3.5 (a) Pore size distribution of the sand-packed core at two different 75 permeabilities (Soo and Radke, 1984). (b) Experimental permeability reduction (filled symbols) and breakthrough concentration histories (open symbols) for two initial permeabilities with a 3.3-µm droplet size emulsions (Soo and Radke, 1984). (c) Reduction in water permeability by emulsion injection and residual effect of emulsion. Percentages at arrows compare fluid permeability at that point with original water permeabilities (McAuliffe, 1973a). 3.6 (a) Newtonian and non-Newtonian behavior of flow of o/w 78 macroemulsions through porous media, fe is percentage of oil in emulsion. (b) A log-log plot of Newtonian and non-Newtonian behavior of flow of o/w macroemulsions through porous media, fe is percentage of oil in emulsion (Alvarado and Marsden, 1979). 3.7 Apparent viscosity: (a) vs. shear rate at various emulsion qualities (Γ), 78 (b) vs. shear rate at various emulsion qualities in the low-shear apparatus, and (c) vs. emulsion qualities (Uzoigwe and Marsden, 1970). 3.8 Size distribution of emulsions: (a) prepared from Midway-Sunset 26C 80 crude-oil and NaOH solution. Oil content of emulsions was 70% (McAuliffe, 1973a), (b) prepared from Richfiled-Kraemer crude-oil, injection water, and Chevron dispersant NI-W. Oil content of emulsions was 60% (McAuliffe, 1973a), and (c) O/W emulsion with a viscosity of 1.5 mPa.s (Soo and Radke, 1984). 3.9 (a) Experimental permeability reduction (filled symbols) and 81 break-through concentration histories (open symbols) for varying droplet size in the 1170-mD core. Oil Viscosity was 1.5 cP; ci is reduced effluent volume concentration, and Dd is droplet diameter (Soo and Radke, 1984). (b) Change in apparent fluid permeability when Boise sandstone was flooded with an emulsion of two different droplet sizes (McAuliffe, 1973a). (c) Comparison between inlet and effluent droplet size distribution after injection of 7 and 15 pore volumes. (d) Permeability reduction (filled symbols) and breakthrough concentration histories (open symbols) of a 20-pore-volume pulse followed by a pH 10 solution. (Soo and Radke, 1984).

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3.10 Experimental permeability reduction (filled symbols) and 83 break-through concentration histories (open symbols) for two viscosities of oil phase with a 3-µm droplet size (Soo and Radke, 1984). 3.11 Various micromodel patterns previously studied at 90 Universiti Teknologi Malaysia: Models (a) – (f) constructed by Mat Hussin (1996), and model (g) introduced by Sugiatmo (2004). 3.12 Experimental permeability reduction (filled symbols) and break-through 99 concentration histories (open symbols) of a 20-pore-volume pulse followed by a pH 10 solution (Soo and Radke, 1984). 3.13 The two types of capture mechanisms of emulsion flow in porous 100 media straining capture and interception capture (Soo and Radke, 1986). 4.1 Schematic diagram of the top and cutaway views of the regular pattern 109 micromodels (figures are not in actual scale). (Moses and Ng, 1985). 4.2 Top view of micromodel templates with regular patterns, repeated 109 throughout the model: (a) graded-micromodel, (b) micromodel with 1000 µm grain, and (c) mixed grain size-micromodel. 4.3 Closed-up view of micromodel templates (flooded with red dyed oil): 110 (a) micromodel with 700 µm grain, (b) 1000 µm grain, (c) 2000 mm, and (d) mixed models. 4.4 Closed-up view of micromodel grains with tapped edges (empty): 100 (a) 700 µm grain model, and (b) 1000 µm grain model. 4.5 Irregular Pattern Template Micromodels: (a) homogeneous, and 111 (b) heterogeneous models. 4.6 Example of different micomodel wettabilities: (a) water-wet 115 condition in the clean glass micromodels, (b) oil-wet condition in the micromodel after treatment with Dimethyldichlorosilane, and (c) mixed-wet condition in the micromodel after aging with crude oil. 4.7 Schematic diagram of the micromodel experimental apparatus. 119 4.8 Actual photographs of micromodel experimental setup: 119 (a) connection to computer system, and (b) micromodel visualization section. 4.9 Schematic of the micromodel. A, B and C are examples of pore or 120 point locations. The target area is a rectangle of point D and the bulk model is the entire micromodel.

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4.10 Preparation of laboratory emulsions: (a) schematic of dispersing 123 element, and (b) preparation procedures. 4.11 Microscope view of w/o emulsion droplets at (a) 0.01% water, 124 (b) 0.1%, (c) 0.5%, (d) 1%. (The background is a microscale). 4.12 Microscope view of other w/o emulsion droplets of high quality 124 emulsions: (a) 5% quality, (b) 10%, (c) 15%, and (d) 20%. 5.1 Number of droplets necessary for a reliable droplet counts 129 (Panoussopoulos, 1998; Saether et al., 1998). 5.2 Photomicrographs showing emulsion droplets of oil-in-water 131 emulsions: (a) 0.1% quality emulsion, (b) 1 %, and (c) 2 %. 5.3 Photomicrographs showing emulsion droplets of water-in-oil 132 emulsions: (a) 0.1% quality emulsion, (b) 1 %, and (c) 2 %. 5.4 Effect of emulsion qualities in w/o emulsion at 6500 RPM for 133 10 minutes homogenization: (a) 25% (32,800 droplets/ml, 74 µm mean size), (b) 50% (20,000 droplets/ml, 138 µm), (c) 60% (6000

droplets/ml, 270 µm). 5.5 Effect of RPM in w/o emulsion at 25% quality for 10 minutes mixing: 133 (a) 1400 RPM (10,800 droplets/ml, 73 µm), (b) 950 RPM (18,400

droplets/ml, 48 µm). 5.6 Droplet behavior with increasing emulsion quality at 950 rpm 134 homogenization. 5.7 Rheological data of oil-in-water emulsions of model oil/distilled water. 136

5.8 Rheological data of water-in-oil emulsions of model oil/distilled water. 137 5.9 Concentration (number) of droplets at different emulsion quality for 138 o/w and w/o emulsions of model oil/distilled water at time zero.

5.10 Percentage of concentration reduction of droplets at different emulsion 139 quality: (a) o/w, and (b) w/o emulsions of model oil/distilled water.

5.11 Droplet size distribution at different emulsion quality for (a) o/w, and 140 (b) w/o emulsions of model oil/distilled water at time zero. 5.12 Droplet size distribution at different o/w emulsions at various times: 141 (a) 0.1% quality, (b) 1%, and (c) 2%. 5.13 Droplet size distribution at different w/o emulsions at various times: 142 (a) 0.1% quality, (b) 1%, and (c) 2%. 6.1 Summary chart of the micromodel experiments. 148

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6.2 Time steps of emulsion flow behaviors in micromodels: (a) adhesion, 152 (b) blob formation, (c) entrainment and re-deposition of an adhered droplet, and (d) blob breakup. (Time format: hour:minute:sec.frame. There are 30 frames in a second). 6.3 Various microstructures: (a) water filament and tongue, (b) oil rivulets, 153 (c) water pocket, and (d) water multiple connecting. 6.4 Typical photomicrographs showing w/o emulsion flowing in porous 155 media. The micromodel is 400 µm grain, emulsion is 1%, and flow rate is 0.05 ml/min: (a) Piston like movement of emulsion, (b) - (c) Emulsion coalesce at the inlets, (d) - (g) Microstruture phenomena in

micromodel, (h) Emulsion blob leaving the micromodel, and (i) Inlet region satururated with coalesced droplets.

6.5 Pressure drop profile at different flow rate: (a) 1% quality emulsion, 157 and (b) 2% quality emulsion. (#5 = 0.01 ml/min, #16 = 0.05 ml/min, #3 = 0.1 ml/min, #10 = 10 ml/min, #4 = 1 ml/min, and #12 = 2 ml/min; with 700 µm micromodel). 6.6 Photomicrographs showing microstructures of emulsion droplets 158 captured or trapped in the 700 µm micromodels of different flow rates at three different times of emulsion injected. 6.7 Pressure drop increases as injection continues. Effect of emulsion 160 quality. (#2 = 0.5% quality, #16 = 1%, #1 = 2%, and #9 = 5% at 0.05 ml/min, 700µm grain size and water-wet micromodel). 6.8 Photomicrographs showing microstructures of emulsion droplets 161 captured or trapped in the micromodels of different emulsion qualities at three different times of emulsion injected. (Injection rate = 0.05 ml/min, and 700µm grain size). 6.9 Pressure increases as injection continues. Effect of grain size. 162 (#13 = 400 µm grain size, #16 = 700 µm, #8 = 1000 µm, #6 = Graded, flow from smaller to bigger grain size, and #14 = Graded, flow from bigger to smaller grain size at flow rate = 0.05 ml/min, 1% quality emulsion and water wet micromodel). 6.10 Photomicrographs showing microstructures of emulsion droplets 163 captured on the grain surfaces in the micromodels of different grain sizes at three different times of emulsion injected. (Scales are as per grain sizes). 6.11 Photomicrographs showing microstructures of emulsion droplets 166 captured or stranded in the micromodels of graded and mixed grain size micromodels at three different times of emulsion injected.

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6.12 Photomicrographs showing: (a) bulk area of fluid distribution after 168 completion of emulsion injection in water-wet micromodel, and (b) flow behavior and fluid distribution captured at the center of the micromodel. 6.13 Photomicrographs showing: (a) bulk area of fluid distribution after 169 completion of emulsion injection in oil-wet micromodel, and (b) Emulsion droplet captured at the center of the micromodel. 6.14 Photomicrographs showing: (a) bulk area of fluid distribution after 170 completion of emulsion injection in mixed-wet micromodel, and (b) flow behavior and fluid distribution captured at the center of the micromodel. 6.15 (a) Oil saturated homogeneous micromodel at residual water 172 saturation (oil injected at 0.017 ml/min), and (b) Residual oil saturated homogeneous micromodel after water flooding (water injected at 0.017 ml/min). 6.16 (a) Oil saturated heterogeneous micromodel at residual water 173 saturation (oil injected at 0.017 ml/min), and (b) Residual oil saturated heterogeneous micromodel after water flooding (water injected at 0.017 ml/min). 6.17 Residual oil saturated homogeneous micromodels after water 174 floodings: (a) water injected at 0.017 ml/min, (b) water injected at 0.1 ml/min, and (c) water injected at 1 ml/min. 6.18 Residual oil saturated heterogeneous micromodels after water 175 floodings: (a) water injected at 0.017 ml/min, (b) water injected at 0.1 ml/min, and (c) water injected at 1 ml/min. 6.19 Injection pressure profiles for oil saturated at residual water 177 saturation at continuous emulsion injection of water-wetted micromodels. 6.20 Captured droplets as a function of time for homogeneous and 177 heterogeneous micromodels. 6.21 Captured droplet sites at the end of the continuous emulsion 178 injection for homogeneous micromodel. 6.22 Injection pressure profiles for oil saturated at residual water 179 saturation at EAW injection (emulsion injection followed by water injection) of water-wetted heterogeneous micromodels. 6.23 Emulsion Alternate Water (EAW) injection for heterogeneous 179 micromodel.

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6.24 Injection pressure profiles for oil residual saturated micromodel at 181 continuous emulsion injection (Run #25) of water-wetted heterogenous micromodels. 6.25 Captured droplet sites for the residual saturated micromodel at 181 continuous emulsion injection (Run #25). 6.26 Injection pressure profiles for oil residual saturated micromodel at 182 EAW injections (Runs #26 and 27) (water flooding followed by Emulsion and water flooding) of water-wetted heterogeneous micromodels. 6.27 Emulsion Alternate Water (EAW) injection for heterogeneous 183 micromodel of oil residual saturated condition. 6.28 Injection pressure profiles for reverse water injection 184 (extension of Run #17). 6.29 Captured droplet sites of the reverse water injection for 184 homogeneous micromodel (extension of Run #17). 6.30 Rheological properties of TX1 and TX2 emulsions. 185 6.31 Stable paraffin oil o/w TX2 emulsion flow in micromodel at 187 0.017 ml/min: (a) at the inlet section, (b) at the middle section, and (c) at the outlet section. 6.32 Sequence of emulsion movement and accumulation for TX2 188 emulsion in a pore at injection rate of 0.017 ml/min. 6.33 Emulsion coalescing sequences of TX1 emulsion at 0.017 ml/min. 189 6.34 Schematic pictures showing the different flow regimes of emulsion 191 flow through pore throats: (a) smaller emulsion droplets passed through larger pore throat undisturbed, (b) large emulsion droplet deformed and passed through pore throat, and (c) smaller emulsion droplets passed through pore throat, but larger droplets deposited, accumulated and coagulated at pore throat. 6.35 Schematic showing the sequences of emulsion flow mechanisms in 192 porous media: (a) initially, (b) small emulsion droplets break through first, (c) large droplets begin to elute and move deeper into the model, and (d) captured droplets block or restrict pores. 6.36 Entrainment of oil in porous media: (a) three residual oil or 193 captured oil rivulets, (b) oil re-emulsified into smaller oil droplets by snap-off, and (c) oil droplet re-captured and coalesced to form bigger droplets or emulsion blobs.

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6.37 Schematic diagrams: (a) microscopic mobility control of emulsion 195 in homogeneous porous media, and (b) macroscopic mobility control of emulsion flow in heterogeneous porous media. 6.38 Schematic diagram showing the effects of the presence of oil 195 saturation in porous media during emulsion flow: (a) homogeneous porous media, (b) heterogeneous porous media. 6.39 Schematic representation of penetration sequences of emulsion 197 droplets at the pore throats and the pore bodies. B.1 Image Analysis Carl Zeiss KS300 system at the Geology 237 Laboratory, Univeristi Teknologi Malaysia. B.2 Image analysis flow chart for droplet size and distribution 238 determinations, as well as for saturation area calculations. B.3 Kruss Digital Tensiometer K10ST for surface and IFT measurement 240 at the Petroleum Testing Laboratory, Univeristi Teknologi Malaysia. B.4 Kruss Contact Angle Meter G1 at the Reservoir Engineering 241 Laboratory, Universiti Teknologi Malaysia. B.5 Anton Paar Digital Density Meter DMA 55 at the Petroleum Testing 242 Laboratory, Universiti Teknologi Malaysia. B.6 Viscosity measurement: (a) Brookfield Rotational Digital Viscometer 243 at the Reservoir Laboratory, Universiti Teknologi Malaysia, and (b) Schematic of rotational viscometer. B.7 Viscometer apparatus at the Petroleum Testing Laboratory, Universiti 244 Teknologi Malaysia: (a) Heating/cooling bath and cleaning apparatus, (b) Canon-Pensky Viscometer Tubes. C.1 Fabrication procedures of etched glass micromodels (Buckley, 1992; 245 Dawe and Grattoni, 1998). For this study, the actual fabrication of the

micromodels was done at Rep Graphic Sdn. Bhd. in Petaling Jaya, Selangor. D.1 Viscosity of o/w and w/o emulsions by varying concentration of 252 TBP and DBP in Model Oil A. D.2 Typical separation profile of o/w emulsion systems of 253 Model Oil A – Distilled Water: (a) Oil phase of 100% TBP, (b) Oil of 100% DBP, and (c) Oil of 75%TBP and 25%DBP mixture. D.3 Separation profile of o/w and o/w emulsion of System B Oil 255 (86.5 % DBP + 13.5% n-C7H16) / Distilled Water at 27.5oC.

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D.4 Separation profile of o/w emulsion of System C Oil / Distilled 257 Water. D.5 Separation profile of o/w emulsion of n-Heptane / Distilled 258 Water systems. E.1 (a) Photo #1 shows droplets captured under microscope, and (b) 261 plot showing droplets size and area distributions and some statistical analysis of Photo #1. E.2 (a) Photo #2 shows droplets captured under microscope, and (b) plot 262 showing droplets size and area distributions and some statistical analysis of Photo #2. E.3 (a) Photo #3 shows droplets captured under microscope, and (b) plot 263 showing droplets size and area distributions and some statistical analysis of Photo #3. E.4 Statistical analysis of droplets in Photos #1, #2 and #3. 264

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NOMENCLATURE

Roman Letters

w/o water-in-oil emulsion

o/w oil-in-water emulsion

o/w/o oil-in-water-in-oil multiple emulsion

w/o/w water-in-oil-in-water multiple emulsion

ppm part per million

k permeability

L length or distance

p or P pressure

q or Q flow rate

v velocity

r or R radius

h height

m matrix

mN/m millinewton per meter

g gravity constant

a acceleration

Greek Letters

σ surface tension or interfacial tension

θ contact angle

υ settling velocity

η , µ viscosity

ρ density

xxviii

∆ differential

φ porosity

Subscripts

o oil phase

i initial or internal

t total

f fiber

1 and 2 leading and trailing curvatures

c capillary or continuous

e external

wo water-in-oil

ow oil-in-water

w water

ri initial relative permeability

sb surface solid and phase b

sa surface solid and phase a

ab surfaces a and b

oi relative to oil

Superscripts

o degree

xxix

LIST OF APPENDICES

Appendix Page

A Summary of Some Literature Review 222

B Measurement Apparatus 236

C Micromodel Fabrication Procedures 245

D Selection of Model Oil System 247

E Sampels of Image Analysis 260

F Raw Data of Some Measurements 269

G Experimental Procedures for Emulsion Flow in Micromodel 286

as Discussed in Chapter 6

H List of Papers 291

CHAPTER 1

INTRODUCTION

1.1 Background

Emulsion flows in porous media can take place in many instances for

practical applications, both in petroleum or non-petroleum related processes.

Emulsion flows through oil reservoirs are important in secondary oil recovery

methods, such as the use of high viscosity emulsions to displace oil, the use of

emulsion slugs as boundaries between the driven fluid (oil) and the driving fluid

(water) in conventional water-flooding operation, the combination of a soluble-oil

slug and a slug of emulsions, and the use of microemulsions (Uzoigwe and Marsden,

1970). Similar situations occur in enhanced oil recovery techniques, such as

emulsion flow during micellar-polymer flooding and alkali-surfactant-polymer

flooding (Gogarty, 1974; Gogarty, 1978; Jennings et al., 1974; Grude and Johnson,

1974). Other emulsion applications are in heavy-oil reservoirs as a blocking agent or

mobility control agent to improve sweep efficiency (Fiori and Farouq Ali, 1989;

McAuliffe, 1973a; Schmidt et al., 1984; Romero et al., 1996), in steam-flooding

processes (Decker and Flock, 1988; French, 1986; Garthoffner, 1979), and in

retarding mineral dissolution rate of matrix acidization processes (Hoefner and

Fogler, 1985).

Emulsion flows in porous media may also be encountered during produced

water reinjection into subsurface formations (Mendez, 1999), and during chemical

process in fixed-bed catalytic reactors involving two immiscible liquids (Trambouze,

1990). Flow of emulsions can also occur in the separation of emulsions by porous

2

media coalescers (fibrous or granular coalescers). Reported applications of porous

coalescers include the separation of water from aviation fuel (Bitten, 1970; Bitten

and Fochtman, 1971), desalination of crude oil and bilge water treatment (Douglas

and Elliot, 1962), separation of emulsified oil from water (Sareen et al., 1966),

break-up of freon from water (Johnson, 1980), and oil recovery from oil spill

emulsions on the sea surface and from refinery sludges (Anklam, 1997). Most of the

porous coalescer applications are for unstable and dilute emulsion systems, which the

dispersed phase contents are usually less than 0.1 % v/v (1000 ppm). Anklam (1997)

was among the few people who used concentrated emulsion systems of 65 to 96% in

his study.

Having mentioned the importance of emulsion flow in porous media, this

author is interested to study further the flow behavior of emulsion in porous media in

petroleum reservoir applications. The particular areas of interests are emulsion as a

mobility control, a blocking agent and/or a plugging agent in secondary and tertiary

waterflooding to improve swept efficiency and to increase oil recovery (Romero et

al., 1996; Thomas and Farouq Ali, 1989). Emulsion flows in porous media are also

always being associated with the overall permeability impairment of the porous

media. Thus, this study investigates and explains the physics at pore scale level and

pore network level behind the magnitude, extent and rate of permeability reductions

as emulsions flow through the porous media.

The physics of emulsion flows in porous media is very complicated because

they involve a complex emulsion system and extremely complex porous media

geometry. Therefore, the knowledge of the nature and properties of emulsions, the

characteristics of porous media, and the basic mechanisms involved in the flow of

simpler fluids in porous media are important in order to understand the behavior of

emulsion flow in porous media (Kokal et al., 1992). Table 1.1 indicates area of

study in the understanding of emulsion flow in porous media, both qualitative and

quantitative aspects.

3

Table 1.1 : Area of Study in the Understanding of Both Qualitative and Quantitative

Aspects for Emulsion Flow in Porous Media (Kokal et al., 1992).

Area of Interest

Important Parameters to Consider

• Emulsion Characteristics

• Stability • Quality • Droplet size distribution • Rheology

• Porous Medium Characteristics

• Average pore size • Pore size distribution • Wettability • Porosity • Permeability • Specific surface area • Chemical composition

• Fluid-rock interaction

• Emulsion-rock interaction • Simultaneous flow of emulsion • Bulk dispersed phase

• Hydrodynamic

• Flow velocity

• Theoretical analysis

• Taking into account all of the aforementioned

1.2 Emulsion Applications in Oil Recovery

Emulsion flow in porous media occurs in petroleum reservoirs during the

production of oil from underground reservoirs containing oil, water, and gas.

Emulsions may form naturally during simultaneous flow of oil and water in porous

rock formations, or they may be promoted by injection of external chemicals. In

emulsion flooding for heavy-oil recovery, externally generated emulsions are

injected into the reservoir. A good review of the fundamentals and applications of

emulsions in petroleum industry can be found in the advanced chemical series edited

by Schramm (1992).

4

Emulsions could be formed in the reservoir rock itself, particularly, within the

porous rock near the well bore where the velocity gradients were very high.

Emulsions within the porous medium are formed as a result of the presence of

surface active-agents, either native or externally added, and shear by the movement

of fluid through pore to the throats. Natural emulsifiers exist in oil reservoirs from

the following materials: asphaltic and resinous materials found in crude; asphaltenes

found in heavy crude; oil-soluble organic acids such as napthenic acids; fatty acids or

aromatic acids; cyclic compounds (cyclic aromatic) such as toluene, benzene,

decalin, methylcyclohexane and cyclooctane in crude oils (Khambharatana, 1993);

and some finely divided insoluble materials (Uzoigwe and Marsden, 1970). These

emulsifiers absorb at the oil-water interface and form a film that prevents the

coalescence of the droplets in natural oil field emulsions. The emulsifiers also

decrease the interfacial tension of the oil and water, which plays a dominant role in

the emulsification of these liquids in porous media (Raghavan and Marsden, 1971).

Vittotos (1990) and Chen et al. (1991) have shown that in-situ emulsification

can be formed in porous media. Their studies have shown that during a cyclic steam

flooding, part of the produced water flows as a single phase, and part of the water

will flow as an emulsion with the oil. This finding is different from the normal

phenomena of the flow of water and oil in which the two phases are considered to be

flowing separately. The implication of emulsion flow in porous media is that the

immiscible displacement should be modified to allow for the mixing of the two

phases to flow as an emulsion. Table 1.2 lists the differences and similarities

between the flow of emulsion and the simultaneous flow of oil and water in a porous

medium. Vittotos (1990) also suggested that flow of water-in-oil emulsions in

porous media should get more attention with the recognition that it may be an

important factor in controlling the oil-water ratio in the production from steam

stimulated wells.

5

Table 1.2 : Differences and Similarities between the Flow of Emulsion and the

Simultaneous Flow of Oil and Water in a Porous Medium (Schramm ,1992; Kokal et

al., 1992).

Simultaneous flow of oil and water

Flow of emulsions

• Both oil and water occupy a

continuous but separate flow channel

• The non-wetting phase is discontinuous at its residual saturation and it ceases to flow

• Total relative permeabilities of oil and water in the porous medium is equal to one

• Oil droplets or ganglia become trapped in the porous medium by the process of snap-off of oil filament at the pore throats

• Both oil and water (emulsion)

occupy the same flow channels

• The dispersed phase consists of very small droplets and about the same size of the pore sizes, these droplet are surrounded by the continuous phase

• At the same wetting phase saturation, the relative permeabilities to water and oil are quite different

• Dispersed phase become trapped by the mechanism of straining capture at the pore throat smaller than the dispersed phase drop

Other in-situ emulsifications in enhanced oil recovery methods are carbon

dioxide flooding, chemical flooding and thermal flooding. Spontaneous

emulsification occurs during chemical flooding when there is a mass transfer of

surfactant between the oil and water phases under sufficient shearing action at the

oil/water interface (Cash et al., 1975). In micellar-polymer flooding and alkali-

surfactant-polymer flooding, in-situ emulsification and entrapment of emulsion

droplets occur to result in reduced water mobility, which in turn improves both

vertical and areal sweep efficiencies (Jenning et al., 1974; Taylor and Hawkins,

1992). Similarly, in immiscible carbon dioxide flooding, an emulsion bank formed

seems to improve oil displacement efficiency without pressure drop increases.

6

Soo and Radke (1984), Alvarado and Marsden (1979), McAuliffe (1973a)

and Deveraux (1974b) have conducted the most relevant experimental investigations

related to the flow of emulsion in porous media. They evaluated some pore plugging

mechanisms associated with the injection of emulsified oil droplets into fully brine-

saturated cores. They have also found out that the stability of emulsions in porous

media is affected by a number of factors such as drop size to pore size ratio,

concentration of the droplets, flow rate, wettability and the surface chemistry of the

porous medium. For dilute, surfactant-free o/w emulsions, solid surface behaves

more like a filter and is not affected by wettability. Emulsion instability due to

droplet coalescence then arises from the captured droplets coming into contact with

each other, and from the effects of surface chemistry alterations may be due more to

electrostatics than wettability (Basu, 1993; Jachowicz and Berthiaume, 1989). For

w/o emulsions with low dielectric oils, the electrostatic interactions will be negligible

compared to other colloidal interactions and wettability to have a large effect on

coalescence.

Mendez (1999) has experimented similar core flow experiments but he

investigated the effect of the flow of emulsions in porous media containing residual

oil saturation. He has compared the flow of emulsion in porous media in deep-bed

filtration processes to emulsion flows occurring in oil recovery. Oil reservoirs, as

compared to filters, usually have fairly low permeabilities. So the ratio of emulsion

droplet to pore size is larger than that in standard filtration processes.

Some researchers have concluded that the formation of stable

macroemulsions in the oil fields is considered undesirable and can cause severe

problems. Strange and Talash (1977), Whiteley and Ware (1977), and Widmyer et

al. (1977) have reported poor oil recovery due to problems associated with stable

emulsions. They were right with respect to a very high energy is required to flow a

high viscosity emulsions formed in the reservoir of homogeneous permeability.

However, McAuliffe (1973a) and Khambharatana et al. (1997) have shown

beneficial effects of macroemulsions in oil recovery as their injection into sandstone

cores increased sweep efficiency. Emulsions (o/w or w/o emulsions) offer

considerable promise as effective oil recovery agents. Emulsions can provide

mobility control in certain situations, and may even serve as blocking agents. The

7

results show that the emulsion drop retained – hence mobility control – is rate-

dependent and related to pore size distribution. According to the process, the

emulsion droplets must be larger than the pore-throat constrictions in the porous

media in order for the emulsion to be most effective. The injected emulsion enters

the highly permeable zones, which in turn reduces the channeling of water.

Therefore, water starts to flow into low permeable zones, resulting in greater sweep

efficiency. A field test for emulsion flooding process conducted in the Midway

Sunset field, California, has showed an improvement in oil recovery, an increase in

sweep efficiency, and a lower in water-oil-ratio (McAuliffe,1973b).

Most of the research works conducted so far have been carried out on core

flooding or analytical and numerical simulations, and sometimes alongside field

trials. The behaviors of emulsion flow in porous media, permeability reduction and

oil recovery have been empirically investigated using core displacement

experiments, and generally with water-wet cores. Although micromodel techniques

have become more accepted and have grown rapidly for fluid displacement study, a

very limited micromodel visualization study of emulsion flow in porous media has

been carried out to directly observe the physical processes taking place in the porous

media. Most micromodel studies of emulsion flow in porous media were in the

emulsion separation in porous coalescers (fibrous or granular) for unstable and dilute

emulsion systems, and at very low emulsion droplet-to-pore size ratio. Soo and

Radke (1984) have used a micromodel of Ottawa sand sandwiched between two

glass plates to study o/w emulsion flow. They only described the flow profiles of the

injected emulsion in micromodel, but they did not produce any photograph of the

pore level events in their report.

For possible implementation of an emulsion flooding/injection, the prior

performance and recovery predictions for economic evaluation are needed by using a

reliable simulation incorporating proper reservoir fluid and rock description which

reflect the actual physics of the emulsion flow realistically. 2-D glass micromodel

experiments were performed to test a series of emulsion flow in porous media to

observe and record the flow processes and measure the model fluid saturations and

recoveries. The results of this study can be used in the future by others to verify the

accuracy of the predictions made by the network model simulator (the network

8

model simulation is not part of this study).

1.3 Problem Statement

It is understood that emulsion flow in porous media has significant

engineering applications in oil recovery processes. A great deal of work has been

conducted on the flow (transport) of emulsions in porous media. The primary

problem of interest in this study is the emulsion flooding for oil recovery technique.

A review of the literature indicates that there has been limited micromodel

experimental work done on determining the pore level behaviors of porous media

when emulsions are flooded into the formation. Emulsions have been shown to be

effective blocking agents (Bragg, 1999; Varadaraj et al., 2004; Zeidani el al., 2006),

but limited work has been reported on their use at waterflooding. In this study,

microscale studies are conducted to investigate the emulsion flow behavior through

porous media. The microscale flow study will demonstrate the pore level mechanism

and micro structure of the emulsion droplets.

A number of questions are addressed with respect to the micromodel flow

experiments in this study.

(a) What are the mechanisms responsible for the permeability reduction of

emulsion flow in porous media at different emulsion quality, emulsion flow

rate, emulsion droplet size, emulsion stability, and droplet-to-pore size ratio?

(b) What is the nature of emulsion at pore level and at pore network level? Does

it consist of single or multiple droplet straining and interception captured

mechanisms at the pore throat and at the pore body? Are there any preferred

conditions that emulsion droplet will under goes re-entrainment and

displacement?

(c) How wetting interaction of the emulsion droplets with the porous media

surfaces lead to different flow phenomena, and how does wettability

9

influences the emulsion stability? Will droplet spreading on the surface and

droplet wetting film on the solid substrate be more likely to coalesce with the

droplets than the droplets to coalesce with other free droplets?

(d) How flow rate and emulsion quality are important, how do these parameters

effect emulsion distribution in the porous media?

(e) How the two systems of stable dilute and stable concentrated emulsions

provide different flow mechanism in porous media?

(f) How emulsions can assist in oil recovery from the porous media? It is

through mobility improvement or profile improvement?

1.4 Objective of Research

This research is aimed at visualizing the fundamental mechanism of the

permeability impairment caused by the flow of emulsions in porous media of two-

dimensional glass-etched micromodels with novel design, and quantifying some of

the observation results. This research was carried out with the objective of

investigating the problems of the flow nature of emulsions through porous media as

specifically stated below.

a) To observe, elucidate and identify the main microscopic mechanisms

involved in the permeability reduction phenomena of the flow of

emulsions in porous media, and to evaluate the factors such as,

dispersed phase contents, emulsion flow rates, and wettability

conditions that may affect such a process. The initial conditions of the

flow models are dry (100% air filled), fully water-saturated, and filled

by residual oil saturations.

b) To observe the emulsion blocking phenomena in micromodel by

identifying the blockage processes.

10

c) To quantify some of the observations by employing digital image

analysis techniques to measure the relative saturation of the phases in

the micromodels.

These results are examined and produced at three scale levels: (i) at the pore

scale observation, using individual pores; (ii) at the target area, comprising a number

of representative elementary volumes (REV); and (iii) at the bulk model, i.e., the

entire model domain.

The overall objective of this research is to contribute to the understanding of

the fundamental scientific principles of emulsion flow phenomena and mechanisms,

the factors that control them, and the emulsion stability in the porous media. This

understanding is important in providing the information of the behaviors of

emulsions within a porous medium.

1.5 Scope of Research

In order to materialize the objectives, this research is interested both in the

mechanical behavior of the complex system of emulsions during flow, and the

stability of the emulsion during flow. The experimental works involved the

investigation of emulsion flow behaviors in the micromodel. All experiments are

conducted at room conditions of about 27oC and 14.65 psia. Visualization study of

microscopic model would use 2-D- etched glass flow models as its porous media.

The detail descriptions of these micromodels are presented in Chapter 4.

The oil system of Model Oil of a mixture of 86.5% Dibutyphtalate and 13.5%

n-Heptane, and paraffin oil are used for this study. The aqueous phases are distilled

water. Surfactant Triton-X100 was added in the paraffin oil emulsion. The emulsion

systems are prepared with the dispersed phase contents ranging from 0.5% to 10%

v/v. The emulsion flow rates are from 0.01 ml/min (about 1 ml/hr) to 2 ml/min.

Flow rate of 2 ml/min would give very high terminal fluid velocity in the

micromodel, however the flow test at this high flow rate is needed to see whether

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pressure drop affected not only by emulsion droplet but also by the hydrodynamic

forces.

The wetting conditions generated are water-wet, oil-wet and mixed-wet with

reference to the dispersed droplets. Qualitatively, the degree of wettability of the

porous media surfaces against the dispersed phase droplet and surrounded by

external phase are determined by contact angle measurements.

The results of emulsion flowing through etched glass micromodels can

provide visual observation of the mechanisms, the fluid distributions and the fluid

flow behaviors in situ of porous media. The emulsions are allowed to flow

continuously through the porous media up to several pore volumes. Pressure drop

(permeability reductions) across the model and the droplet distributions at outlet of

the model are measured as a function of the number of pore volumes of emulsion

passed through the micromodel.

However, some limitations of this study are identified as follow.

(a) The results of the micromodel tests were not represent the actual reservoir

conditions of high pressure and high temperature. The measured average

properties in micromodels, such as permeability and fluid saturations can be

valuable in a relative rather in absolute sense.

(b) The studies are more interested in the local pore-level physics of 2-D rather

than the topological of fluid flow behavior in 3-D.

(c) The emulsion was injected under a constant flow rate. Therefore, any

obstruction of the emulsion flow in the micromodel would cause an increase

of pressure drop.

(d) The current design characteristics and techniques of the 2-D glass

micromodel fabrication produce large pore and throat sizes as compared to

emulsion droplet sizes. So, droplet straining capture mechanisms were

hardly observed under the microscope in the experiments.

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1.6 Overview of Thesis Contents

This thesis consists of seven chapters, where in Chapter 1, the background,

the research problem statements, the objective and scope of research and the

importance of research were discussed. Chapter 2 would summarize all aspects of

fundamental theory of emulsions, and their flows in porous media and the factors

that affect their flow behaviors. The literature review for the emulsion study,

particularly for emulsion flow in porous media, is presented in Chapter 3. Research

methodology and experimental setups and requirements are given in Chapter 4.

Chapter 5 would provide the results and discussion of emulsion characterizations,

while in Chapter 6 discussed the results of the experimental works of emulsion

displacement flow in micromodels. Finally, Chapter 7 would give the overall

summary of the works, the conclusions of the research and the recommendation for

future works.