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Crude Oil Chemistry Effects on Corrosion Inhibition and Phase Wetting in Oil-Water Flow

Dissertation
Author: Francois Ayello
Abstract:
The presence of water, even in small amounts, is often the cause of internal corrosion problems in crude oil transportation. Understanding the factors influencing steel pipeline corrosion rates is a safety as well as an economic matter. The objective of this dissertation is to quantify the effects that are known to have an influence on corrosion in crude oil-brine flow. - The first effect is the corrosiveness of the brine. Crude oil's compounds can partition between the oil phase and the water phase to create brines with inhibitive or corrosive properties. - The second effect is related to which phase wets the pipe wall. This depends on steel wettability and also on the flow pattern. Crude oil's polar compounds can change the steel hydrophilic surface nature. They also change the flow properties. The problem has been investigated at the Institute for Corrosion and Multiphase Technology at Ohio University on a small scale with specifically designed experiments as well as on a large scale, in a 60 meter-long flow loop loaded with 1600 gallons of oil and water. Results show that only a small percentage of the crude oil's complex chemistry controls its corrosion inhibitive and wettability properties. The knowledge generated from these experiments can be used as a useful reference for corrosion engineers and pipeline operators to maintain oil-water flow systems under corrosion-free conditions.

6 TABLE OF CONTENTS Page

ABSTRACT........................................................................................................................3 ACKNOWLEDGEMENTS................................................................................................4 PREFACE...........................................................................................................................5 LIST OF TABLES............................................................................................................10 LIST OF FIGURES..........................................................................................................11 LIST OF SYMBOLS........................................................................................................21 CHAPTER 1 INTRODUCTION......................................................................................23 Motivation.....................................................................................................................23 Research objectives.......................................................................................................24 Thesis outline................................................................................................................26 CHAPTER 2 LITERATURE REVIEW...........................................................................27 Introduction...................................................................................................................27 Carbon dioxide corrosion mechanism..........................................................................27 Phase wetting in oil-water flow: adaptation of Hinze’s model.....................................29 Introduction...............................................................................................................29 Overview of the phase wetting model......................................................................29 Droplet size calculations...........................................................................................31 Model predictions.....................................................................................................41 Crude oil chemistry effects on carbon dioxide corrosion.............................................49 Effect of crude oil chemistry on corrosion inhibition...............................................49 Effects of crude oil chemistry on steel wettability....................................................50

7 Effect of crude oil chemistry on steel wettability; at the metal surface................50 Effect of crude oil chemistry on steel wettability; In the bulk flow.....................51 Crude oil chemistry, choice of few representative chemicals...................................52 General crude oil chemistry..................................................................................52 Aromatic compounds............................................................................................52 Oxygen compounds..............................................................................................53 Sulfur compounds.................................................................................................54 Nitrogen compounds.............................................................................................55 CHAPTER 3 CRUDE OIL CHEMISTRY EFFECT ON CORROSION INHIBITION..57 Introduction...................................................................................................................57 Experimental technique: glass cell...............................................................................57 Experimental results.....................................................................................................61 The baseline..............................................................................................................61 Aromatics..................................................................................................................64 Oxygen containing compounds.................................................................................65 Small chain organic acids.....................................................................................65 Long chain organic acids......................................................................................68 Sulfur containing compounds...................................................................................72 Nitrogen containing compounds...............................................................................78 Modeling the crude oil inhibition of corrosion.............................................................84 Corrosion inhibition model.......................................................................................84 Calculation of the parameters i

and i

..................................................................86 Model validation.......................................................................................................91 Validation of assumption 1: Adsorption measurements.......................................91 Validation of assumption 2: Corrosion measurements.........................................94 Model validation with crude oil............................................................................95 Discussion.....................................................................................................................96 Conclusion....................................................................................................................99

8 CHAPTER 4 CRUDE OIL CHEMISTRY EFFECTS ON PHASE WETTING............100 Introduction.................................................................................................................100 Part 1 - Study of flow pattern......................................................................................100 Introduction.............................................................................................................100 Experimental technique: Tensiometer....................................................................102 Experimental results................................................................................................103 Discussion...............................................................................................................106 Conclusion..............................................................................................................107 Part 2 - Study of steel wettability................................................................................107 Introduction.............................................................................................................107 Experimental technique: Static contact angle measurement...................................108 Experimental results................................................................................................110 Aromatic compounds..........................................................................................115 Oxygen containing compounds...........................................................................115 Sulfur containing compounds.............................................................................116 Nitrogen containing compounds.........................................................................116 Discussion...............................................................................................................116 Conclusion..............................................................................................................117 Part 3 – Study of the synergy between steel wettability and flow pattern..................118 Introduction.............................................................................................................118 Experimental technique..........................................................................................118 Small scale: Doughnut cell.................................................................................118 Large scale: Flow loop........................................................................................121 Experimental results................................................................................................126 Small scale results...............................................................................................126 Large scale results...............................................................................................133 Phase wetting prediction.............................................................................................157 Introduction.............................................................................................................157 Model prediction for hydrophilic steel...................................................................157

9 Model prediction for hydrophobic steel..................................................................159 Model calibration....................................................................................................163 Summary of the prediction......................................................................................170 CHAPTER 5 CONCLUSION.........................................................................................171 Achievements...............................................................................................................171 Recommendations for future work..............................................................................172 BIBLIOGRAPHY...........................................................................................................174

10 LIST OF TABLES Page

Table 1. Steel composition in wt.% (Fe is in balance).......................................................57 Table 2. LPR, EIS, and polarization sweep main parameters to study the adsorption of surface active compound from the water phase.................................................59 Table 3. LPR, EIS, and polarization sweep main parameters to study the adsorption of surface active compounds from the water phase...............................................60 Table 4. Model oil (LVT-200) properties..........................................................................60 Table 5. “Acridine like” compounds tested.......................................................................82 Table 6. Summary of the inhibitive effect of the compounds tested in this study...............87 Table 7. Inhibition model’s constants calculated from experiments.................................89 Table 8. Inhibition model’s constants calculated from experiments for asphaltene.........89 Table 9. Inhibition model’s constants calculated from experiments for corrosion inhibitors................................................................................................................90 Table 10. Evolution of the corrosion rate for different ratios of acridine / myristic acid.........................................................................................................................95 Table 11. Crude oil tested. Chemical composition and corrosion inhibition....................96 Table 12. Oil-water interfacial tension testing................................................................103 Table 13. Evolution of the oil-water interfacial tension function of the polar compound added to the oil phase (exception: acetic acid)..................................104 Table 14. Static contact angle measurements test matrix................................................110 Table 15. Contact angle measurements...........................................................................113 Table 16. Doughnut cell test matrix.................................................................................120 Table 17. Composition of the crude oil from the North Sea tested in the doughnut cell.131 Table 18. Test matrix: model oil test in large flow loop..................................................133 Table 19. Test matrix: myristic acid tests in large flow loop...........................................144 Table 20. Contact angle measurement: water droplet in model oil (the steel is previously wetted by crude oil) with the empirical value of IW..........................169 Table 21. pH effect on carboxylic acid and pyridine.......................................................173

11 LIST OF FIGURES Page

Figure 1. Schematic representation of a horizontal pipe...................................................33 Figure 2. Evolution of the maximum droplet size in dispersed systems as a function of water cut and flow velocity, calculated with = 800 kg·m, =1000 kg·m, = 0.04 N·m, D = 0.1 m, friction factor calculated for smooth pipe using Colebrook formula. c -3 w -3 -1 ......................................................................................34 Figure 3. Evolution of the maximum droplet size in dense systems as a function of water cut and flow velocity, calculated with = 800 kg·m, =1000 kg·m , = 0.04 N·m, D = 0.1 m, friction factor calculated for smooth pipe using Colebrook formula. c -3 w - 3 -1 ................................................................................................36 Figure 4. Schematic representation of an inclined pipe, with forces applied to a water droplet....................................................................................................................37 Figure 5. Evolution of the maximum droplet size in dense systems as a function of water cut and flow velocity, calculated with = 800 kg·m, =1000 kg·m , = 0.04 N·m, D = 0.1 m, horizontal pipe, friction factor calculated for smooth pipe using Colebrook formula. c -3 w - 3 -1 ..................................................................39 Figure 6. Evolution of dilute d max (light blue) and dense d max (dark blue) as a function of water cut and flow velocity, calculated with = 800 kg·m, =1000 kg·m, = 0.04 N·m, D = 0.1 m, friction factor calculated for smooth pipe using Colebrook formula. c -3 w -3 -1 ................................................................................................42 Figure 7 . Evolution of the

gmincrea crit gravity crit dd,min as a function of water cut and flow velocity, calculated with

= 800 kg·m,

=1000 kg·m,

= 0.04 N·m, D = 0.1 m, horizontal pipe, friction factor calculated for smooth pipe using Colebrook formula. c -3 w -3 -1 ................................................................................................43 Figure 8. Evolution of

greaminc crit gravity crit dd,min (green), (light blue) and (dark blue) as a function of water cut and flow velocity, calculated with

= dilute d max dense d max c

12 800 kg·m,

=1000 kg·m,

= 0.04 N·m, D = 0.1m, friction factor calculated for smooth pipe using Colebrook formula. -3 w -3 -1 ...........................................44 Figure 9. T ransition of the phase wetting map from 3-dimensions to 2-dimensions, calculated with

= 800 kg·m,

=1000 kg·m,

= 0.04 N·m, D = 0.1 m, friction factor calculated for smooth pipe using Colebrook formula. c -3 w -3 -1 ....................45 Figure 10. Evolution of

greaminc crit gravity crit dd,min (green) and dense d max (dark blue) as a function of water cut and flow velocity, calculated with

= 800 kg·m,

=1000 kg·m,

= 0.04 N·m, D = 0.1 m, friction factor calculated for smooth pipe using Colebrook formula. c -3 w -3 -1 ..............................................................................47 Figure 11. P hase wetting map in 2-dimensions without the dilute d max equation, calculated with

= 800 kg·m,

=1000 kg·m,

= 0.04 N·m, D = 0.1 m, friction factor calculated for smooth pipe using Colebrook formula. c -3 w -3 -1 ................................48 Figure 12. Interfacial tension forces applied to a water droplet in model oil resting on a steel surface. The shape of the droplet is determined by the interaction of the interfacial forces of oil-water ( wo /

os /

ws /

Figure 13. Crude oil’s arom atic compound examples, from left to right: benzene, naphthalene, phenanthrene and benz(a)anthracene................................................53 Figure 14. Structure of 1,2,3,4-tetrahydronaphthalene used as model compound for the aromatic class...................................................................................................53 Figure 15. Crude oil’s carboxylic acid examples, from left to right, cyclohexyl carboxylic acid and 2-phenanthrene carboxylic acid.............................................54 Figure 16. Structure of acetic acid an d myristic acid used as model compound for the oxygen compounds class........................................................................................54 Figure 17. Crude oil’s sulfur com pound examples, from left to right 1-butanethiol, thiophenol and 4,6 dimethyldibenzothiophene......................................................55 Figure 18. Structure of sulfur compound used as m odel compound, dioctyl sulfide, dibenzothiophene and 1-tetradecanethiol..............................................................55 Figure 19. Crude oil’s sulfur com pound examples, from left to right, quinoline, 9- propyl-9H-carbazole and 2(1H)-quinolinone........................................................56

13 Figure 20. Structure of the nitrogen com pounds used as model compounds, carbazole, and acridine............................................................................................................56 Figure 21. Representation of glass cell apparatus.............................................................58 Figure 22. Corrosion rate for the base line experim ent recoded by LPR. Conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 .............................................................................61 Figure 23. E IS measurement of the impedance, Nyquist plot. Base line (1 wt.% NaCl, 1 bar CO, pH 5.0). 2 ................................................................................................62 Figure 24. Polarization s weep: base line (1 wt.% NaCl, 1 bar CO, pH 5.0). 2 ..................62 Figure 25. Evolution of the corrosion rate in water (1 wt.% NaCl, 1 bar CO, pH 5.0) after the steel coupon has been immersed in model oil 20 min. 2 ............................63 Figure 26. EIS m easurement of the impedance, Nyquist plot. EIS experiments in water (1 wt.% NaCl, 1 bar CO, pH 5.0) after the steel coupon has been im mersed in model oil for 20 min. 2 .........................................................................64 Figure 27. Corrosion m easurements by LPR for aromatics added to the model oil (Base Line: model oil, no tetrahydronaphthalene), water phase: 1%NaCl, 1 bar CO, pH 5.0. 2 ..........................................................................................................65 Figure 28. Evolution of the corrosion rate as a function of t he amount of acetic acid added to the water phase (0 ppm baseline, then 10 ppm, 100 ppm and 1000 ppm) conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ..............................................66 Figure 29. EIS m easurement of the impedance, Nyquist plot. EIS experiments in water (1 wt.% NaCl, 1 bar CO, pH 5.0) base line has no acetic acid, and 10 ppm , 100 pm and 1000 ppm acetic acid. 2 ...............................................................67 Figure 30. Polarization sweep function of the amount of acetic acid added to the water phase (0 ppm baseline, then 10 ppm, 100 ppm and 1000 ppm) conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ........................................................68 Figure 31. Evolution of the corrosion rate function of acid added to the water phase (10 ppm). Conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ......................................69 Figure 32. EIS m easurement of the impedance, Nyquist plot. EIS experiments in water (1 wt.% NaCl, 1 bar CO, pH 5.0) for different high m olecular weight 2

14 organic acids. Base line has no organic acid, 10 ppm myristic acid and 10 ppm naphthenic acid (TCI)............................................................................................70 Figure 33. Polarization sweep function of the long chain organic acid added to the

water phase (10 ppm). Conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ..................70 Figure 34. Corrosion m easurements by LPR for long chain organic acids added to the model oil phase, water phase 1 wt.% NaCl, 1 Bar CO, pH 5.0. 2 ..........................71 Figure 35. EIS m easurement of the impedance, Nyquist plot. EIS experiments for long chain organic acids added to the model oil phase, water phase 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 .......................................................................................72 Figure 36. Evolution of the corrosion rate function of sulfur containing com pounds added to the water phase (10 ppm). Conditions: 1 wt. % NaCl, 1 bar CO, pH 5.0. 2 ..........................................................................................................................73 Figure 37. EIS m easurement of the impedance, Nyquist plot. EIS experiments in water (1 wt.% NaCl, 1 bar CO, pH 5.0) for different sulfur containing com pounds. Base line has no sulfur containing compounds, 10 ppm dibenzothiophene,10 ppm dioctyl-sulfide and 10 ppm 1-tetradecanethiol. 2 ...........74 Figure 38. Full scale for Figure 37....................................................................................74 Figure 39. Polarization sweep func tion of the sulfur containing compound added to the water phase (10 ppm) conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ..............75 Figure 40. Corrosion measurem ents by LPR for sulfur containing compounds added to the model oil phase, water phase 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 .................76 Figure 41. EIS m easurement of the impedance, Nyquist plot. EIS experiments for sulfur containing compounds added to the model oil phase, water phase 1% NaCl, 1 bar CO, pH 5.0. 2 .......................................................................................76 Figure 42. Chemical structure comparison of myristic acid (left) with 1- tetradecanethiol (right)...........................................................................................77 Figure 43. Evolution of the corrosion rate function of the nitrogen added to the water phase (10 pp m). Conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ............................78 Figure 44. EIS m easurement of the impedance, Nyquist plot. EIS experiments in water (1 wt.% NaCl, 1 bar CO, pH 5.0) for different nitrogen containing 2

15 compounds. Base line has no nitrogen containing compounds, 10 ppm carbazole and 10 ppm acridine..............................................................................79 Figure 45. Full scale for Figure 44....................................................................................79 Figure 46. Polarization sweep function of the nitrogen containing com pound added to the water phase (10 ppm). Conditions: 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ............80 Figure 47. Corrosion m easurements by LPR for nitrogen containing compounds added to the model oil phase, water phase 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 .......81 Figure 48. EIS m easurement of the impedance, Nyquist plot. EIS experiments for different nitrogen containing compounds added to the model oil phase, water phase 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ................................................................81 Figure 49. Corrosion m easurements by LPR for pyridinic compounds added to the model oil phase, water phase 1 wt.% NaCl, 1 bar CO, pH 5.0. 2 ...........................83 Figure 50. EIS m easurement of the impedance, Nyquist plot. EIS experiments in water (1 wt.% NaCl, 1 bar CO, pH 5.0) after the steel coupon has been imm ersed in model oil mixed with 3 different pyridinic compounds. 2 ...................83 Figure 51. Inhibition of corrosion calculated from Table 6 for the natur ally occurring chemicals in crude oil that have induced significant corrosion inhibition.............88 Figure 52. Iron coated q uartz crystal used in the Quartz Crystal Microbalance...............92 Figure 53. Evolution of the mass adsorbed for different surface active compounds as a function of time...................................................................................................93 Figure 54. R elationship between mass adsorbed and inhibition of corrosion...................94 Figure 55. Com parison between inhibitions of corrosion calculated and measured for oxygen, sulfur, nitrogen containing compounds, asphaltenes and corrosion inhibitors................................................................................................................99 Figure 56. Representation of a polar m olecule with a hydrophilic head group and hydrophobic tail, C14 chain organic acid: myristic acid.....................................101 Figure 57. Platinum ring tensiometer used in these experiments....................................103 Figure 58. Evolution o f the transition line calculated using the water wetting model for three concentrations of TCI added to model oil (0 wt.%, 0.1 wt.% and 1 wt.%)....................................................................................................................105

16 Figure 59. Drawing of the contact angle m easurement setup, the cell is made of acrylic to allow the camera on the right to video. 80 ................................................109 Figure 60. 3D picture of the m etal surface after polishing with 600 grit sandpaper, roughness: 1.1 μm................................................................................................110 Figure 61. Evolution of a water droplet in m odel oil during the first 10 minutes as the contact angle evolves from 180° to 58°...............................................................111 Figure 62. W ater-Steel contact angle after 5 minutes. Organic acids have the strongest effect on steel wettability......................................................................114 Figure 63. W ater-Steel contact angle after 120 minutes. Organic acid effect on steel wettability is not time dependent.........................................................................114 Figure 64. Phase wetting experim ent apparatus called the ‘doughnut cell’....................119 Figure 65. T he bottom of the doughnut cell shows conductivity probes........................119 Figure 66. One conductivity probe, 160 conductivity probes are used in the doughnut cell........................................................................................................................120 Figure 67. Schem atic of the flow loop............................................................................121 Figure 68. Pictu re of the flow loop in horizontal position..............................................122 Figure 69. Picture of the flow loop in 15° position.........................................................122 Figure 70. Representation of the test section...................................................................124 Figure 71. Exam ple of flow visualization picture, water appears green under UV light, oil is black...................................................................................................125 Figure 72. R epresentation of the instrumentation of the test section..............................126 Figure 73. Phase wetting m ap obtained in a doughnut cell with pure model oil. No chemicals are added to the oil phase. Points are measurements, line is just an indicator separating oil and water wetting regions..............................................127 Figure 74. Phase wetting m ap obtained in a doughnut cell with 0.01 wt.% myristic acid added to the oil phase. Points are measurements, line is just an indicator separating oil and water wetting regions.............................................................127 Figure 75. Phase wetting m ap obtained in a doughnut cell with 0.05 wt.% myristic acid added to the oil phase. Points are measurements, line is just an indicator separating oil and water wetting regions.............................................................128

17 Figure 76. Phase wetting map obtained in a doughnut cell with 0.1 wt.% myristic acid added to the oil phase...........................................................................................128 Figure 77. Phase wetting m ap of Middle Eastern crude oils API 50 to 34. Experiment done by Li. 66 .........................................................................................................129 Figure 78. Phase wetting m ap comparison between model oil and crude oil API37, doughnut cell experimental results. Experiment done by Li. 66 ............................131 Figure 79. Phase wetting m ap comparison between model oil mixed with myristic acid and crude oil API37, similar organic acid concentration.............................132 Figure 80. Model oil phase wetting m ap measured in large flow loop in horizontal position. Points are measurements, line is just an indicator separating oil and water wetting regions...........................................................................................134 Figure 81. Picture of t he flow in 4 inch pipe, oil-water mixture velocity 0.5 m·s, water cut 5%. -1 .......................................................................................................135 Figure 82. Picture of t he flow in 4 inch pipe, oil-water mixture velocity 0.5 m·s, water cut 10%. -1 .....................................................................................................135 Figure 83. Picture of t he flow in 4 inch pipe, oil-water mixture velocity 0.5 m·s, water cut 15%. -1 .....................................................................................................136 Figure 84. Picture of t he flow in 4 inch pipe, oil-water mixture velocity 0.5 m·s, water cut 20%. -1 .....................................................................................................136 Figure 85. P icture of the flow in 4 inch pipe, oil-water mixture velocity 1 m·s, water cut 5%. -1 .................................................................................................................137 Figure 86. P icture of the flow in 4 inch pipe, oil-water mixture velocity 1 m·s, water cut 10%. -1 ...............................................................................................................138 Figure 87. P icture of the flow in 4 inch pipe, oil-water mixture velocity 1 m·s, water cut 15%. -1 ...............................................................................................................138 Figure 88. P icture of the flow in 4 inch pipe, oil-water mixture velocity 1 m·s, water cut 20%. -1 ...............................................................................................................139 Figure 89. Picture of t he flow in 4 inch pipe, oil-water mixture velocity 1.5 m·s, water cut 5%. -1 .......................................................................................................140

18 Figure 90. Picture of t he flow in 4 inch pipe, oil-water mixture velocity 1.5 m·s, water cut 10%. -1 .....................................................................................................140 Figure 91. Picture of t he flow in 4 inch pipe, oil-water mixture velocity 1.5 m·s, water cut 15%. -1 .....................................................................................................141 Figure 92. Flow pattern m ap with model oil, horizontal flow through a 4” pipe............142 Figure 93. P hase wetting map measured in a large flow loop (4” ID, horizontal flow), with 0.01 wt.% myristic acid added to the model oil. Points are measurements, line is just an indicator separating oil and water wetting regions........................145 Figure 94. P hase wetting map measured in a large flow loop (4” ID, horizontal flow), with 0.05 wt.% myristic acid added to the model oil. Points are measurements, line is just an indicator separating oil and water wetting regions........................145 Figure 95. P hase wetting map measured in a large flow loop (4” ID, horizontal flow), with 0.08 wt.% myristic acid added to the model oil. Points are measurements, line is just an indicator separating oil and water wetting regions........................146 Figure 96. Evolution o f the transition line oil wetting to intermittent wetting as a function of the quantity of myristic acid added to the oil phase..........................147 Figure 97. Flow loop experim ent, phase wetting map of Middle Eastern oil API 50. Points are measurements, line is just an indicator separating oil and water wetting regions.....................................................................................................148 Figure 98. Flow loop experim ent, phase wetting map of Middle Eastern oil API 40. Points are measurements, line is just an indicator separating oil and water wetting regions.....................................................................................................149 Figure 99. Flow loop experim ent, phase wetting map of Middle Eastern oil API 34. Points are measurements, line is just an indicator separating oil and water wetting regions.....................................................................................................151 Figure 100. Flow loop experim ent, phase wetting map of Middle Eastern oil API 30. Points are measurements, line is just an indicator separating oil and water wetting regions.....................................................................................................152 Figure 101. Com posite of 16 pictures taken with a microscope of the water in oil emulsion...............................................................................................................154

19 Figure 102. Flow loop experim ent, phase wetting map of Middle Eastern oil API 27. Points are measurements, line is just an indicator separating oil and water wetting regions.....................................................................................................155 Figure 103. Phase wetting m aps of Middle Eastern crude oils API 27 to 50..................156 Figure 104. Comparison: transition line oil wetting to intermittent wetting function for the model oil (dashed line) with water wetting model’s prediction (solid line)......................................................................................................................158 Figure 105. Com parison: size of water droplet measured experimentally and prediction of the water wetting model oil (Equation 21).....................................159 Figure 106. C omparison of transition lines for oil wetting to intermittent wetting as a function of the concentration of myristic acid including the water wetting model prediction..................................................................................................160 Figure 107. Evolution of the transition line oil wetting to intermittent wetting as a function of the inhibition of wettability (IW).......................................................162 Figure 108. Picture of a water droplet (1 wt.% N aCl, pH 5.0) immersed in model oil mixed with 1 wt.% myristic acid on a steel surface. The water droplet is gently moving on a slightly inclined steel surface, the water droplet does not wet the steel surface..........................................................................................................163 Figure 109. C omparison between large scale tests (with myristic acid) and modified water wetting model (values of IW are empirical)...............................................164 Figure 110. C omparison of the wettability alteration (IW), experimental results vs. the prediction made by Equation 49..........................................................................165 Figure 111. Large scale experiment results with Middle Eastern oil API 50 from Figure 97 and the prediction from the water wetting model (IW = 0) and the prediction from the corrected water wetting model with IW = 0.3......................166 Figure 112. Large scale experiment results with Middle Eastern oil API 40 from Figure 98 and the prediction from the water wetting model (IW = 0) and the prediction from the corrected water wetting model with IW = 0.3......................166

20 Figure 113. Large scale experim ent results with Middle Eastern oil API 34 from Figure 99 and the prediction from the water wetting model (IW = 0) and the prediction from the corrected water wetting model with IW = 0.3......................167 Figure 114. Large scale experiment results with Middle Eastern oil API 30 from Figure 100 and the prediction from the water wetting model (IW = 0) and the prediction from the corrected water wetting model with IW = 0.3......................167 Figure 115. Large scale experiment results with Middle Eastern oil API 27 from Figure 102 and the prediction from the water wetting model (IW = 0) and the prediction from the corrected water wetting model with IW = 0.3......................168

21 LIST OF SYMBOLS Latin Symbol

Dimensions

d

Droplet diameter L D

Pipe internal diameter L e

Turbulent energy dissipation M/t 3

f

Friction factor - F Force ML/t 2

g

Gravitational acceleration L/t 2

K

Arbitrary constant - l

Length L L

Pipe length L m

Mass M N

Number - P

Pressure M/Lt 2

Q

Volumetric flow rate L 3 /t T

Temperature T u

Velocity L/t Greek Symbol

Viscous shear stress M/Lt 2

Interfacial tension M/t 2

22

Difference - Superscript

Turbulent Subscript

crit

Critical droplets

Droplets k

Kolmogoroff m

Mixture max

Maximum o

Oil w

Water wc

Water Cut *

Friction

Infinity

23 CHAPTER 1 INTRODUCTION

Motivation

Oil and gas pipelines are generally m ade out of carbon steel. Such pipelines are vulnerable in the presence of small amounts of water due to corrosion. The oil industry pays a heavy price every year. On March 2 nd 2006 267,000 US gallons of crude oil were spilled over a little less than 2 acres in Prudhoe Bay, Alaska. The spill originated from a quarter inch hole in BP’s production line. “Early indications are that water accumulated in the pipeline, causing the corrosion” 7 . The spill had a major impact on BP’s image and induced a major financial loss. On May 21 st 2008 in Anchorage, Alaska a relatively small oil leak, 170 gallons, was discovered on a ConocoPhillips' pipeline. The leak was a surprise because the installation was only eight years old. Ed Meggert, the Department of Environmental Conservation coordinator, said that corrosion was “caused by water settling in low parts of the line” 8 . Often, the water phase contains dissolved corrosive species such as carbon dioxide, hydrogen sulfide and organic acids. Therefore, the water is corrosive. In the past, low volume fractions of water were associated with non- corrosive situations because the flowing oil phase can sweep out the water from the bottom of the pipe and therefore oil prevents the water from corroding the bottom of the pipe. However, recent incidents, such as in Prudhoe Bay and Anchorage show that even low volume fractions of water can lead to corrosion problems and large financial losses. All the more so when the volume fraction of water increases, water drops out of the oil phase and forms a continuous water layer corroding the bottom of the pipe. The complete understanding of the transition from oil wetting to water wetting in mild steel pipelines is necessary for engineers to improve their ability to combat corrosion.

The first significant research on the transition from water wetting conditions to oil wetting conditions in oil-water flows was published in 1975 by Wicks and Fraser 9 . Wicks proposed a model predicting the minimum velocity required to sweep out settled water on the bottom of the pipe. This assumption makes the model suitable only for low water

24 volume fraction as the model significantly underestimates the minimum velocity at high water volume fractions. In 1987, Smith et al . 10 stated that crude oil has the capability to carry up to 20% water at a velocity larger than 1 m·s -1 . Water wetting as a function of fluid velocity and water cut have been studied in the 1990s. C. de Waard and Lotz 11

Full document contains 181 pages
Abstract: The presence of water, even in small amounts, is often the cause of internal corrosion problems in crude oil transportation. Understanding the factors influencing steel pipeline corrosion rates is a safety as well as an economic matter. The objective of this dissertation is to quantify the effects that are known to have an influence on corrosion in crude oil-brine flow. - The first effect is the corrosiveness of the brine. Crude oil's compounds can partition between the oil phase and the water phase to create brines with inhibitive or corrosive properties. - The second effect is related to which phase wets the pipe wall. This depends on steel wettability and also on the flow pattern. Crude oil's polar compounds can change the steel hydrophilic surface nature. They also change the flow properties. The problem has been investigated at the Institute for Corrosion and Multiphase Technology at Ohio University on a small scale with specifically designed experiments as well as on a large scale, in a 60 meter-long flow loop loaded with 1600 gallons of oil and water. Results show that only a small percentage of the crude oil's complex chemistry controls its corrosion inhibitive and wettability properties. The knowledge generated from these experiments can be used as a useful reference for corrosion engineers and pipeline operators to maintain oil-water flow systems under corrosion-free conditions.