STUDIES OF HYDRATE COHESION, ADHESION AND INTERFACIAL PROPERTIES USING ...

193 Pages·2016·3.02 MB·English

by  Erika P. Brown

STUDIES OF HYDRATE COHESION, ADHESION AND INTERFACIAL
PROPERTIES USING MICROMECHANICAL FORCE
MEASUREMENTS
by
Erika P. Brown
(cid:13)c Copyright by Erika P. Brown, 2016
All Rights Reserved
A thesis submitted to the Faculty and the Board of Trustees of the Colorado School
of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy
(Chemical Engineering).
Golden, Colorado
Date
Signed:
Erika P. Brown
Signed:
Dr. Carolyn A. Koh
Thesis Advisor
Golden, Colorado
Date
Signed:
Dr. David Marr
Professor and Head
Department of Chemical and Biochemical Engineering
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ABSTRACT
The oil and gas production industry continues to innovate in new exploration and pro-
duction techniques that allow the extraction of energy resources from increasingly extreme
conditions. One consequence of this advancement is the increasing threat of hydrate plugs
forming in the oil and gas production lines due to favorable thermodynamic conditions for
hydrate formation. Complete inhibition of hydrates, which is traditionally the preferred
method in hydrate treatment, can become prohibitively expensive or challenging due to en-
vironmental regulations. As such, the industry has observed a shift in focus from hydrate
avoidance to hydrate management. In this strategy, hydrates are allowed to form and flow
as a slurry. The goal in hydrate management is to prevent the aggregation and deposition
of hydrates so that the flowline can produce without impediment. In order to accomplish
this, a sound understanding of the cohesive (particle-particle) and adhesive (particle-surface)
forces of hydrates particles is needed. This thesis seeks to advance the knowledge available
on hydrate cohesion and adhesion, especially in the presence of surfactant additives.
Several models involve the cohesive/adhesive force in their calculations; the Capillary
BridgeTheory usesinterfacial variablesto predictthe inter-particleforce, while theCamargo
and Palermo Model balances the cohesion force with shear forces to predict the extent
of aggregation in a hydrate-bearing system. Each of these systems was analyzed for the
sensitivity of each variable and how the inter-particle force affects each system.
A method for measuring the contact angle of water on the hydrate surface was developed
tostudychangesinhydratewettabilityinsystemsbothwithoutandwithsurfactantspresent.
This method was verified using two apparatuses and three operators, and it was shown that
the contact angle measurement was repeatable. Using this method, the contact angle of a
water droplet on a cyclopentane surface was found to be 94◦±5◦. This contact angle is less
hydrophilic than previous estimates, and it represents an important update to prediction
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efforts using Capillary Bridge Theory. Based on the updated estimate of the contact angle,
◦
the embracing angle for a pure system was estimated as α = 4.9 .
Studies were also conducted to determine whether the Micromechanical Force (MMF)
apparatus could be used to rank anti-agglomerants (AAs) by their performance. Four AAs
were used in a blind test and were ranked based on the reduction in cohesion force measured.
The final ranking determined agreed closely with the results provided by an industrial lab us-
ing a typical macro-scale method. The MMF, which focuses on interfacial-scale interactions,
is attractive for ranking measurements due to the speed, precision, visualization capabilities
and small sample size needed. The visual nature of the MMF measurements also provided
insight into the mechanisms of the AAs and morphological changes that resulted from AA
addition. Changes in the wettability of the particles were proposed as a mechanism due to
a strong correlation between contact angle and force measured in the presence of the AAs.
In addition to particle-particle interactions, particle surface interactions were studied in
the presence of AAs. It was found that AAs decreased the adhesion force between a stainless
steelsurfaceandahydrateparticle, butthattheforcesmayincreaseifthesurfacewascoated
with a petroleum wax. Forces also increased with the addition of dissolved wax for a system
with no AA as well as an oil-soluble AA. A water-soluble AA exhibited no changes with the
addition of wax to the system.
Changes in the hydrate shell micro-structure were studied by measuring the force neces-
sary to puncture a hydrate particle using a glass cantilever. It was found that the addition
of model surfactants caused the force needed to puncture the shell to decrease. The reduced
shell strength was compared to other phenomena in the system such as interfacial tension,
growth rate and cohesion force. Model surfactant studies were continued by comparing the
force reduction for several chemicals that were added simultaneously to the system. Three
classes of interactions were identified based on these measurements: synergistic, antagonistic
and those showing no interaction.
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The effect of subcooling on cohesion was investigated based on improved measurement
and error calculation techniques. It was found that the cohesion force increases significantly
near the equilibrium temperature, but tapers to a near-constant value at high subcoolings.
This trend agrees with measurements made on ice systems, as well as trends observed in the
water layer on ice particles. The temperature dependence was found to persist for annealing
times up to two hours.
Finally, design of a high pressure Micromechanical Force apparatus was performed, in-
cluding the identification of nano-manipulators which make the cell design possible. This
system was tested using 3D printing for low pressure experiments before the final design was
produced. Initial tests indicated reproducible experiments using gas hydrates and showed
that CO was not an appropriate hydrate former for this system.
2
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TABLE OF CONTENTS
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
LIST OF SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxii
LIST OF ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiv
ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv
CHAPTER 1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Clathrate Hydrate Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Agglomeration Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 History of the Micromechanical Force Apparatus . . . . . . . . . . . . . . . . . 13
1.4 Hydrate Interfacial and Growth Studies . . . . . . . . . . . . . . . . . . . . . . 16
1.5 Thesis summary and organization . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.5.1 Publications arising from this work . . . . . . . . . . . . . . . . . . . . 20
CHAPTER 2 APPARATUS AND PROCEDURE . . . . . . . . . . . . . . . . . . . . 21
2.1 Micromechanical Force Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.1.1 Cohesion/Adhesion Force . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.1.2 Shell Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.1.3 Shell Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.1.4 Growth Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.1.5 Contact Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
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2.2 High Pressure Micromechanical Force Apparatus . . . . . . . . . . . . . . . . . 30
2.3 Interfacial Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.4 Note on Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
CHAPTER 3 SENSITIVITY OF PARTICLE COHESION . . . . . . . . . . . . . . . . 38
3.1 Capillary Bridge Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2 Camargo and Palermo Model . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
CHAPTER 4 CONTACT ANGLE MEASUREMENTS ON HYDRATE SURFACES . 56
4.1 Pure Hydrate Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.2 Predictions Using Capillary Bridge Theory . . . . . . . . . . . . . . . . . . . . 59
4.3 Contact Angle Changes with Surfactants . . . . . . . . . . . . . . . . . . . . . 61
4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
CHAPTER 5 INDUSTRY AA RANKING STUDY . . . . . . . . . . . . . . . . . . . . 68
5.1 Cohesion Tests and IFT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.2 Morphological Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.3 Contact Angle Measurements of Industrial AAs . . . . . . . . . . . . . . . . . 82
5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
CHAPTER 6 ADHESION MEASUREMENTS WITH WAXES AND
ANTI-AGGLOMERANTS . . . . . . . . . . . . . . . . . . . . . . . . . 90
6.1 AA Baselines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.2 Wax Baselines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6.3 Wax/AA Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.4 Crude Oil Addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
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6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
CHAPTER 7 SHELL STRENGTH . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
7.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
7.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
7.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
CHAPTER 8 COMPETITIVE EFFECTS OF CHEMICALS . . . . . . . . . . . . . 120
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
8.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
8.3 Single Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
8.4 Chemical Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
8.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
CHAPTER 9 FUNDAMENTAL COHESION STUDIES . . . . . . . . . . . . . . . . 130
9.1 Temperature Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
9.2 Annealing time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
9.3 Glass Beads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
9.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
CHAPTER 10 HIGH PRESSURE MICROMECHANICAL FORCE APPARATUS . 139
10.1 Apparatus Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
10.2 Initial Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
10.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
CHAPTER 11SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . 147
CHAPTER 12SUGGESTIONS FOR FUTURE WORK . . . . . . . . . . . . . . . . 152
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12.1 Expansion of surfactant studies . . . . . . . . . . . . . . . . . . . . . . . . . 152
12.2 High pressure apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
REFERENCES CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
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