关于破乳的英文论文 Characterization and Rheology of Water-in-Oil Emulsion from
Figures…………………………………………………………………………...viList of Tables………………………………………………………………………….....x
CHAPTER 1: INTRODUCTION................................................................................ 1
1.1 Importance of Deepwater Fields.............................................................. 1
1.2 Problem Statement.................................................................................. 4
1.3 Objectives................................................................................................ 6
CHAPTER 2: THEORETICAL BACKGROUND.................................................... 8
2.1 Basic Principles of Emulsions.................................................................. 8
2.2 Emulsions Properties............................................................................. 10
2.2.1 Morphology of Emulsion ................................................................. 10
2.2.2 Phase Inversion .............................................................................. 11
2.2.3 Drop size distribution ...................................................................... 14
2.3 Emulsions Rheology and Shear Viscosity ............................................. 18
2.3.1 Models at constant temperature ..................................................... 19
2.3.2 Models with variation of temperature .............................................. 20
2.4 Emulsion Stability .................................................................................. 22
2.4.1 Sedimentation and Creaming ......................................................... 23
2.4.2 Aggregation .................................................................................... 24
2.4.3 Coalescence ................................................................................... 28
2.5 Demulsification ...................................................................................... 29
2.5.1 Effect of surface-active materials.................................................... 31
2.5.2 Chemical Demulsifier Efficiency...................................................... 32
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CHAPTER 3: CHARACTERIZATION OF EMULSIONS BY NMR...................... 38
3.1 Introduction ........................................................................................ 39
3.2 Fundamentals .................................................................................... 39
3. CPMG Pulsed Sequence ................................................................... 40
3.4 PGSE and PGSTE Pulsed Sequences .............................................. 44
3.5 T1 weighted 1-D Profile Measurement................................................ 50
CHAPTER 4: EXPERIMENTAL PROCEDURES............................................... 53
4.1 Materials................................................................................................ 53
4.2 NMR Measurements.............................................................................. 54
4.3 Demulsifier Selection............................................................................. 55
4.4 Viscosity Measurements........................................................................ 57
4.5 Accuracy and Reproducibility ................................................................ 60
CHAPTER 5: RESULTS AND DISCUSSION..................................................... 62
5.1 Interfacial Tension Measurements ........................................................ 62
5.2 Emulsion Characterization by NMR....................................................... 62
5.2.1 T2 Distribution from CPMG Measurements..................................... 64
5.2.2 Drop size distribution from restricted diffusion measurement ......... 69
5.2.3 1-D T1 weighted profile measurement ............................................ 78
5.3 Emulsion Rheology ............................................................................... 86
5.3.1 Effect of temperature and shear rate .............................................. 87
5.3.2 Effect of water cut ........................................................................... 90
5.4 Demulsifier Performance and Selection ................................................ 91
5.4.1 Bottle testing ................................................................................... 92
5.4.2 Viscosity reduction and optimum dosage........................................ 94
5.4.3 Effect of mixing order ...................................................................... 99
CHAPTER 6: CONCLUSIONS AND FUTURE WORK..................................... 101
6.1 Conclusions......................................................................................... 101
6.2 Suggested Future Work....................................................................... 102
REFERENCES. ................................................................................................ 108
Reducing such a high viscosity requires better understanding of emulsion
properties. Separation topsides can also be an issue; emulsions can be very
stable depending on the properties of the oil and may not easily break under
gravity. Therefore, the use of chemicals that work as demulsifiers is commonly
employed. Injecting the chemical subsea, either at the manifold or at the tree,
can obtain great benefits as it will reduce pressure drop in pipelines and/or
enhance the emulsion separation and handling.
Hence, it is important for the industry to find an efficient way of testing and
evaluating these chemicals in the lab before applying them in the field. An
efficient testing method will lead to an optimization and potential reduction of the
quantity of the chemical needed for this purpose, resulting in monetary and most
important, environmental benefits. So far, mainly bottle testing has been
employed to conduct such measurements. The use of nuclear magnetic
resonance (NMR) method will help in characterizing an emulsion and evaluating
chemicals’ effectiveness to break/invert it. This study focuses on characterizing
of water-in-oil emulsions, that formed in deepwater production, by nuclear
magnetic resonance (NMR) and studying their rheological behavior at different
operation temperatures with and without demulsifiers present.
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1.3 Objectives
The main objective of the project is to study and characterize emulsion
stability for deepwater oil fields and evaluate chemicals’ effectiveness to
break/invert such emulsions in order to reduce their viscosity. This study will,
specifically, focus on the viscosity of the emulsions created at different
temperatures and their tendency to separate with and without the injection of
commercial de-emulsifiers. In addition to the bottle testing, the identification of
the separation is conducted with the use of NMR technique that can obtain quick
information on phase distribution of the emulsion under study. Furthermore, the
use of viscosity measurement is also applied to determine the rheological
behavior at different operating conditions. Transporting emulsion as water-in oil
type, oil continuous, increase the viscosity and, therefore, could have cost impact
associated with high pumping requirements. Inverting this type of emulsion into
oil-in-water will decrease the viscosity as the continuous phase will change to
water and consequently help reducing the cost of pumping. This study could help
in identifying whether it is more cost effective for crude oils of moderate viscosity
to add a demulsifier to produce coalescence and hence separate/invert emulsion
without depending on only conventional bottle testing or sampling.
In this thesis, Chapter 2 presents an overview of the theoretical
background and summarizes the basic knowledge on emulsions. These include
the emulsion properties, stability, rheology and the demulsification mechanisms
used to destabilize emulsion.
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Chapter 3 illustrates the use of low-field nuclear magnetic resonance,
NMR, and MRI techniques and how they can be effectively utilized to estimate
and characterize the emulsion properties.
After that, Chapter 4 is devoted to explain the experimental procedures and
the materials used in this work. The procedures of executing the NMR
experiment and emulsion preparation method are also described.
The results obtained from this work along with detailed discussion are then
described in Chapter 5. Finally, Chapter 6 highlights the conclusions obtained
from this work and proposes some possible future ideas that can be applied in
the extension of this work.
.
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CHAPTER 2
THEORETICAL BACKGROUND
2.1. Basic Principles of Emulsions
Emulsions can be found in almost every part of the petroleum production
and recovery process and can be encountered at many stages during drilling,
producing, transporting and processing of crude oil. Emulsion can be defined as
a dispersion of a liquid within another liquid. The stability is conferred by the
presence of agents at the interfaces that may delay the spontaneous tendency of
the liquids to separate. Such agents are most commonly molecules with polar
and non-polar chemical groups in their structure usually referred to as
surfactants- or finely divided solids. The dispersed phase is commonly present in
an emulsion in the form of spherical drops .
Phase separation in emulsions is imposed by thermodynamics because as
the oil and water form two continuous phases while they separate, the interfacial
area and therefore the free energy of the dispersion are reduced. As a
consequence, the characteristics of the emulsion (drop size distribution, mean
drop size and other properties) cannot remain unchanged in time. Therefore, the
stability of an emulsion refers to the ability of the dispersion to preserve its
properties within a given timeframe . Most of the petroleum emulsions that will
be encountered in practice contain oil, water and emulsifying agents and exist in
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a metastable state that has high potential barrier to prevent coalescence of the
particles.
An emulsion can be classified according to different criteria. In the classic
type of emulsion, the two immiscible liquids involved are water and oil. As should
be clear from the foregoing discussion, either of these two liquids can be defined
as the disperse phase. The disperse phase is sometimes referred to as internal
phase, and the continuous phase as the external phase. Depending on which
one is the disperse phase, emulsions of quite different physical characteristics
are usually obtained . The following types of emulsions are now readily
distinguished in principle:
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