ABSTRACT
The research studied the modeling of a multiphase downward flow in a vertical pipe using CO2-kerosene-water flow system. The objective was to characterize the transport CO2 for further application to carbon capture and sequestration in a three-phase downward flow in a vertical pipe. The study developed an experimental test bed integrated with a high speed video camera to record the observed flow patterns, and the pressure drops across the length of the vertical pipe. The three-phase flow characteristics were studied at 25°C for the measured range of water and oil velocities from 0.008889 to 13.0734m/s at different water cuts (WCs) of 20, 50, 70 and 90%. Equally, the CO2 phase velocity was varied for the measured values from 0.452 to 32.868m/s to cover a wide range of the developed flow patterns. The results developed a flow pattern map of the flow system, and obtained the homogenous flow model calculated pressure drop of 336.75N/m3 at a lowest gas superficial velocity for 20% WC; while the largest value was obtained at 4570.431N/m3 for 90% WC at the highest value of the superficial gas velocity. Additionally, a drift-flux flow model was developed to study the effect of gas velocity for the experimental multiphase system. The analysis of the simulated model result showed that the values of the pressure drops increased as the gas velocity and the WCs were increased. Also, the gas flow film thickness was found to increase from 0.011m, due to high interfacial force observed in the developed bubble/slug flow, to 0.02362m for all studied WCs; where the lowest and highest values were experienced at 90 and 20%WC. Consequently, the transition criterium from one flow pattern to another was established as a function of the gas film thickness (radius) and superficial velocity; where the developed flow patterns revealed a strong dependence on the interfacial forces among the phases when compared to the pipe wall shear force for all studied WCs of the flow system. Hence, the effect of the CO2 gas phase on the total pressure drop of the studied multiphase flow pressure was averaged at 20% for all WCs, with an exception at 90% WC due to the full liquid phase inversion occurrence in the flow system. However, the comparative analysis of the pressure drops calculated from the two mathematical approaches revealed on the average an over-prediction of 8.685% for the drift-flux flow model and 12.981% under-prediction for the homogenous flow model for all WCs; where the initial demonstrated similarities with other models in open literature. These preceding inferences generally provided an adequate understanding for further application of the studied flow system modeling technique to carbon capture and sequestration.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables ix
List of Figures x
List of Plates xiv
Nomenclature xv
Abstract xviii
CHAPTER 1: INTRODUCTION 1
1.1 Background of Study 1
1.2 Statement of Problem 4
1.3 Aim and Objectives of the Study 6
1.4 Scope of study 6
1.5 Justification for the Study 7
CHAPTER 2: LITERATURE REVIEW 8
2.1 Overview of Multiphase Flow in Pipe 8
2.2 Types of Multiphase Flow in Pipes 9
2.3 Three-Phase Flow Patterns in Pipes 14
2.4 Multiphase Flow Pattern Maps 16
2.5 Types of Multiphase Flow Modeling Techniques 21
2.6 Mathematical Approaches for Simulating Multiphase Flow in Pipes 24
2.6.1 Homogenous Flow Model 24
2.6.2 Separate Flow model 25
2.6.3 Drift-flux flow model 25
2.6.4 Volume of fluid flow model 26
2.6.5 Equation of state flow model 27
2.6.6 Energy flow model 28
2.7 Multiphase Simulating Flow Parameters 29
2.7.1 Superficial velocity 30
2.7.2 Pressure drop 31
2.7.3 Closure relationship forces in pipes 32
2.8 Recent Studies on Models of Three-Phase in Pipes 37
2.9 Applications of Three-Phase Flow in Pipes 52
CHAPTER 3: MATERIALS AND METHODS 55
3.1 Materials 55
3.2 Methods 55
3.2.1 Model design, concept and considerations 55
3.2.2 Experimental setup 57
3.2.3 Experimental procedure 59
3.2.4 Homogenous flow model analysis procedure 65
3.2.5 Development of the drift-flux model 67
3.2.6 Model solution and simulation procedure 70
3.2.8 Model validation procedure 72
CHAPTER 4: RESULTS AND DISCUSSION 74
4.1 Results of the Experimental Procedure 74
4.2 Homogenous Flow Model Analysis of the Multiphase flow System 84
4.3 Drift-Flux Flow Model Analysis of the Effect of the CO2 Gas Phase on the
Multiphase flow System 90
4.4 Results of the Developed Flow Pattern Transition Criteria 95
4.5 Parametric Analysis of the Effect of the Gas Superficial Velocity on the Three-phase flow Pressure Drop in the Pipe 100
4.6 Sensitivity Analysis of the Gas Film Thickness 105
4.7 Comparative Evaluation of the Calculated Pressure Drop for the Homogenous and the Drift-flux Flow Models 113
4.8 Comparative Evaluation of Results from the Drift-Flux Flow Model with Other Similar Models of in Open Literature 116
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 121
5.1.1 Contributions to Knowledge 123
5.2 Recommendations 124
REFERENCES 125
LIST OF TABLES
3.1 Fluid Properties at 25oc 55
3.2 Characteristics of the Experimental Instruments 55
4.1 Calculated Superficial Velocity of the Phases for the Developed Flow Pattern at the various for the studied water cuts 76
4.2 Results of the Homogenous Flow Parameters at 20% Water Cut 85
4.3 Results of the Homogenous Flow Parameters at 50% Water Cut 86
4.4 Results of the Homogenous Flow Parameters at 70% Water Cut 87
4.5 Results of the Homogenous Flow Parameters at 90% Water Cut 88
4.6 Results of the Drift-flux Flow Simulation Model at 20% Water Cut 93
4.7 Results of the Drift-flux Flow Simulation Model at 50% Water Cut 94
4.8 Results of the Drift-flux Flow Simulation Model at 70% Water Cut 94
4.9 Results of the Drift-flux Flow Simulation Model at 90% Water Cut 95
4.10 Results of the Wall Friction Pressure Drop and the Total Pressure Drop at 50% WC 113
4.11 Calculated Total Pressure Drop of Flow Models 117
4.12 Result of the Statistics Analysis of the Sample Pressure Drop 117
LIST OF FIGURES
2.1 Multiphase flow Pattern 8
2.2 Flow Pattern in horizontal gas – liquid flow 10
2.3 Gas-Oil-Water stratified flow 11
2.4 Flow pattern in a horizontal three phase flow 13
2.5 Typical flow pattern in vertical upward gas/liquid flow 14
2.6 (a) Flow pattern maps for square cross-section pipe 17
2.6 (b) Flow pattern maps for circular cross-section pipe 17
2.7 Flow pattern map for the flow of oil and water in horizontal 39.4 mm
ID pipe 17
2.8 Flow pattern map for water/air in 82.6 mm in vertical tube 18
2.9. Shear forces on cylindrical fluid element. 33
2.10 (a) Vertical pipe flow patterns 36
2.10 (b). Horizontal pipe flow patterns 36
2.11 The effect of external force on multiphase flow in pipe 37
2.12: Observed flow patterns 38
2.13: Droplet entrainment experienced in the experimental three phase
flow study 39
2.14 Images of the observed flow patterns 40
2.15 Average velocity profile in 200mm and 600mm pipes 40
2.16: Reynolds number Flow pattern maps 41
2.17: Observed flow patterns for two immiscible fluid phase flow 42
2.18 Multiphase flow in different pipe orientations 43
2.19 Flow pattern map for multiphase flow at 90o vertical pipe orientation 44
2.20: Schematic diagram of the experimental setup 45
2.21 Flow pattern experimental observation technique using high speed camera 47
2.22 Pressure drop Analysis for different pipe dimensions 47
2.23: Modified stratified model 48
2.24: Observation of discrete bubble flow in horizontal pipe 49
2.25: Cross-plot comparative analysis 50
3.1 Experimental set up 58
3.2 (a) Experimental design schematics 58
3.2 (b) Test Section pipe schematics 58
3.3 Experimental procedure flow chart 60
3.4. The cross volume of the multiphase flow test section pipe 64
3.5 Flowchart of procedures for the development of the drift-flux model 73
4.1 Representation of flow patterns at 20% WC 81
4.2 Representation of the flow Patterns at 50% WC 82
4.3 Representation of the flow Patterns at 70% WC 83
4.4 Representation of the flow Patterns at 90% WC 84
4.5 Effect of gas velocity on the overall pressure drop for the homogenous model 89
4.6 Effect to the gas velocity on the wall friction for the homogenous model 90
4.7 Interface for the design vertical pipe model 91
4.8 Program of the MATLAB2015a interface for the developed drift-flux flow model 92
4.9a Display interface of the MATLAB2015a results for the developed drift-flux flow model 92
4.9b Display interface of the MATLAB2015a results for the developed drift-flux flow model 93
4.10 Flow pattern map for CO2-Kerosene-Water flowing downwards in vertical pipe of L/D 0.0231 100
4.11 Effect of the gas superficial velocity on pressure drop 102
4.12 Effect of gas velocity on the pressure drop due to interfacial friction force 103
4.13 Effect of gas phase velocity on the pressure drop due to pipe wall friction 104
4.14 Effect of the gas superficial velocity on the gas film thickness 106
4.15 Relationship between the gas film thickness and the interfacial pressured drop 107
4.16 The effect gas film thickness, Rg on the pressure drop due to interfacial force at 20% WC 108
4.17 The effect of the gas film thickness, Rg on the pressure drop due to interfacial Force at 50% WC 109
4.18 The Effect gas film thickness, Rg on the pressure drop due to interfacial force at 70% WC 109
4.19 The Effect gas film thickness, Rg on the Pressure drop due to interfacial force at 90% WC 110
4.20 The Effect of the gas film thickness, Rg on the pressure drop due to wall fiction force at 20% WC 111
4.21 The effect of the gas radius, Rg on the pressure drop due to wall friction force at 50% water cut 111
4.22 The effect of the gas radius, Rg on the pressure drop due to wall friction force at 70% water cut 112
4.23 The effect of the gas radius, Rg on the pressure drop due to wall friction force at 90% water cut 112
4.24 Cross plot comparative evaluation of the overall pressure drop for the measure homogenous model and the calculated separate flow model 114
4.25 Cross plot comparative evaluation of the pressure drop due to wall friction for the measure homogenous model and the separate flow model 115
4.26 The effect of the gas phase pressure drop on the overall pressure drop 116
4.27 Cross plot of pressure drop for the calculated drift flux pressure drop and the selected correlated Pressure drop. 118
4.28 Air/water/oil upward flow pattern map (Balasubramaniam, 2006) 120
4.29 Flow pattern map of water-air downward flow (Bratland 2013) 120
LIST OF PLATES
3.1 Test Section and Instrumentation 61
4.1 Observed Flow Patterns 75
NOMENCLATURE
Pressure drop of the homogenous model
Wall friction pressure drop of the homogenous model
Wall friction pressure drop of the drift-flux model
Interfacial pressure drop of the drift-flux model
Gravitational pressure drop of the drift-flux model
Total pressure drop of the drift-flux model
a Volume fraction
rg Density of the gas phase
Cai Absolute value of the measure
rI Density for the homogenous liquid
mi Viscosity for the homogenous liquid
Aig Cross sectional area of the input pipe for gas
Aio Cross sectional area of the input pipe for oil
Aiw Cross sectional area of the input pipe for water
Am area of pipe
Cam mean value
N Number of the measure of flow
Finlet Flow from the pipe inlet
fm1 Laminar flow
fm2 Turbulent flow
Foutlet Flow from the pipe outlet
h Ration of the gas phase radius to the radius test-section pipe
l pipe length
M Effective mass flow rate
n number of total uncertainty variable
P Pressure
qg Gas phase superficial measure flow rate
qm Total Volumetric flow rate
qo Oil phase superficial measure flow rate
qw Water phase superficial measure flow rate
Ra Radius for the ‘a’ phase
Rea Reynolds number for the ‘a’ phase
Rem Reynolds number of the multiphase homogenous phase
Rg Radius of the gas phase
Ri Radius of the liquid
Rm Radius of the test-section pipe
U Superficial velocity
Ua Total uncertainty
Uai Uncertainty variable
Vg Gas phase superficial velocity
vg Gas phase superficial velocity
vl Liquid phase superficial velocity
Vm Total phase velocity
Vo Oil phase superficial velocity
VOF Volume of fluid
Vw Water phase superficial velocity
WC Water cut
Wi Interfacial slip velocity between the liquid phase
F Interfacial friction factor
M Gas to liquid viscosity ratio
h Area fraction occupied by the gas
Xa Absolute measured flow
Xai Input flow rate
αg Void/volume fraction of the gas phase
αo Void/volume fraction of the oil phase
αw Void/volume fraction of the water phase
μeff Efficient viscosity of the multiphase flow
ρeff Efficient density of the multiphase flow
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF STUDY
The expanded industrial application of fluid flow dynamics in pipes has created the need to provide solutions to complex flow systems. To achieve this, nano-engineering research has steered to improve the efficiency of existing operating flow systems, understand the complex phenomenon of multi-phase flow in pipes and introduce new fluid flow models to meet the industrial market demand. For example, recent advancements in the petroleum industries has brought about the application of complex multiphase models to reduce industrial emitted harmful CO2 gas through the transport of two or more fluids for a simultaneous carbon capture sequestration and enhance oil/gas production flow system.
A Multiphase flow involves the simultaneous flow of two or more fluids. The flow structures of a three-phase flow are much more complex than the flow structure of the two-phase flow (Khosla 2012). The different types of multiphase flow in pipes are recognised by the developed patterns of the flow system. The research study by Banwart et al, (2013) showed that the development of certain flow patterns indicates how the phase distributions affect the physical nature of the flow system. Hence, the properties of the fluid materials employed and their flow parameters are some of the basic factors considered in modelling a multiphase flow system (Chung 2007). Depending on the application, recent studies have employed different modelling techniques to identify the nature of flows in pipes, the transition mechanism (criteria) from one to another and general characterisation of the flow phenomenon. These techniques are broadly classified as experimental, empirical, computational and mathematical.
Experimental technique is often the first method employed by researchers to study multiphase flow in pipes. It provides a means of identifying the developed flow patterns and predicting the flow parameters for its transition criterium from one to another of a flow system (Fan 2005). Although the result of the measured input flow parameters of this modelling technique is efficient to provide basic input data for industrial application, it does not provide the basis to analyse the flow characteristics of each phase (Nimwegen et al, (2017).
However, there are other modelling techniques that predict accurate analytical results of a multiphase flow system. Empirical modelling in multiphase flow is usually applied to validate and further analyse past experimental modelling flow data. As fluid properties vary in density and viscosity, the results from the analysis of a multiphase flow system vary with regards to the materials used (Omebere-Iyari et al., 2007). Hence, empirical correlation models of multiphase flow available in literature vary over wide range different fluid properties, flow conditions, and pipe dimensions.
Computational fluid dynamic (CFD) modelling technique is supported with the aid of super-computers simulations of the multiphase flow process. It is capable of simulating experimental scenario that incorporates sets of thermodynamic mathematical equation for governing all types multiphase flows in pipes. The experimental data and results developed can serve as a means to validate the results of these modelling techniques and provide a good understanding of the industrial application of multiphase flow in pipes (Wegmann et al., 2010). However, the identification of the various types of flow pattern in a multiphase flow simulation process is limited despite its graphical visual computer aided advancements.
The mathematical model of the multi-phase flow system is based on proven scientific flow conditions and assumptions that are applied to analyse, validate, and further predict scientific conclusions of a multiphase flow system (Herard 2007). According to Han et al. (2017), it accounts for the local distributions of volume fraction and velocity for each phase as important factors in the identification, modelling and characterisation of flow patterns for three phase flow in pipes. This modelling technique also provide an efficient means of predicting the void fractions and the pressure drop along the pipe of a multiphase flow system
Despite its versatility, the petroleum industrial application of these multiphase flow modelling techniques in pipes is limited to liquid-liquid or gas-liquid upward flow due to the optimization of oil and gas recovery pipe systems to meet its industrial demands. Perhaps more attention should be given to the investigation of introducing a new fluid material in a multiphase process that will lead to the development of new modelling techniques to achieve more than one objectives rather than modification of existing ones. The question remains, though as with other flow processes, can a three-phase downward flow in a vertical pipe provide a more effective means to reduce green gas emission and enhance oil and gas recovery (EOGR) processes simultaneously. Challenges in the petroleum industries are to reduce the atmospheric pollution caused by its operations while optimising production to meet its growing industrial demands.
1.2 STATEMENT OF PROBLEM
Greenhouse gas emission to the environment has resulted to global warming and negative climatic effects to mankind. There have been several research calls and proposals to study the process of carbon capture and sequestration (CCS) underground, and reduce carbon emission from industrial sources such as fossil fuel and power stations (Olusegun 2016). This on-going research provides an opportunity to study and apply the process of CCS in transporting emitted CO2 gas in a multiphase downwards flow in a vertical pipe. The quest to apply a three-phase flow system in an oil and gas reservoir that will enhance the recovery of lighter natural gas and oil production processes simultaneously, while the harmful heavier CO2 gas is captured underground. Thus, the need for an improved and cost-effective, environmental-friendly oil and gas production flow systems to cater for future demands.
The concept of multiphase in pipes is to accurately predict the flow behaviour of complex flow systems, for an economical and safe transportation of the targeted fluids. The homogenous flow models have been employed by researchers to obtain the measured the flow parameters for the visualized flow patterns; while the separate and other mathematical modelling techniques are duly acknowledged to analyse the effect of the flow parameters and properties of each phase on the flow system and predict the transition criterium of the develop the flow pattern maps (Hadzˇiabdic´ and Oliemans, 2007). However, literature available on three phase flow in pipes show that researchers apply one methodical modelling approach to analyse a given multiphase flow system. Although, marked improvements were noticed in the consistence prediction of three-phase upward flow patterns in pipe in the models of Safarri and Dalir (2013) and Han et al. (2017). There is need to employ two or more methodological modelling techniques/approaches for a comprehensive understanding of a three-phase flow in pipe, to establish guiding principle for the fluid materials used for its industrial application that meet the demands of emerging technologies to dominate research in this sector.
The understanding of the flow characteristics such as the pressure drop and the flow patterns developed in multiphase flow in pipes are paramount in the design, control and optimization of a given flow system (Azzopardi, 2006). In a homogenous flow analysis, the volume percentage of a phase inside the pipeline of the mixture is not equal to the input volume fraction due to the density and viscosity differences between the phases. Hence, this modelling approach does not provide a comprehensive analysis of the flow system as the effects of each phase on the pressure drop were not accounted (Rocha et al., 2017). Consequently, improved mathematical techniques have been applied as a convenient modelling approach to further study the flow characteristics of a given flow systems. However, recent research findings focus on the liquid phase flow parameters in a multiphase upward flow in pipes to enhance oil or gas production and meet increasing emerging industrial demands. It is evidently the study for the effect of the gas phase, especially for three-phase downward flow in pipe is limited (Han et al., 2017). Therefore the novelty of introducing CO2 gas as the focus for the analysis of a multiphase gas-liquid-liquid downward flow in vertical pipe will propose a sustainable means to simultaneously optimise industrial natural oil and gas production while reducing greenhouse gas emission from the environment.
1.3 AIM AND OBJECTIVES
The aim of this study is to model a multiphase CO2-kerosene-water downward flow in a vertical pipe. The specific objectives are to:
- Obtain the input flow parameter data of the phases for the identified flow patterns of the experimental set-up to develop the multiphase hydrodynamic homogenous and drift-flux mathematical simulation models of the flow process
- Develop the numerical model for the flow patterns transition criteria
- Develop the flow pattern map of the studied flow system
- Parametric analysis of the effect of the CO2 gas phase on the multiphase flow system using MATLAB R2015a; and
- Comparative analysis of the two developed models, and with that in open literature.
1.4 SCOPE OF STUDY
This study involves the engineering experimental/numerical modelling and analysis the hydrodynamics of three-phase CO2-kerosine-water downward flow in a vertical pipe to identify the flow patterns observed and establish the criterium of transition of the developed flow patterns from one another. The governing laws of continuity and momentum of fluid flow in pipes that applied the necessary flow parameters to further analyse the effect of the gas and develop the physical data for the studied multiphase flow system in a one dimensional, incompressible, energy-constant and steady-state, boundary conditions.
1.5 JUSTIFICATION FOR THE STUDY
The study of flow characteristics of CO2-kerosene-water particularly in a vertical downward pipe is of importance to the process engineers and industrialists especially in the oil and gas sector. It opens a route of knowledge in understanding fluid dynamics and flow characterization of CO2 gas in a multiphase downwards flow in a vertical pipe. Furthermore, the pressure drop and stability characteristics of the three-phase flow in pipes are important for the efficient operation of oil and gas well platforms. Hence, proper understanding of the three-phase phenomena and its applications in industrial natural gas recovery systems is a positive development to enhance gas production (Hanafizadeh et al., 2017). This is achievable through the process of capturing and sequestration of the harmful carbon gas underground which would reduce greenhouse emission synonymous with the conventional gas exploration flaring techniques.
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