CRANFIELD UNIVERSITY SF Ali TWO PHASE FLOW IN LARGE DIAMETER VERTICAL RISER ...

352 Pages·2009·12.21 MB·English

CRANFIELD UNIVERSITY

S. F. Ali

TWO PHASE FLOW IN LARGE DIAMETER
VERTICAL RISER

SCHOOL OF ENGINEERING

PHD THESIS
CRANFIELD UNIVERSITY

School of Engineering
Department of Process and Systems Engineering

PHD THESIS

Academic Year 2008 - 2009

Shazia Farman Ali

Two phase flow in large diameter vertical riser

Supervisor: Dr. H. Yeung

February 2009

This thesis is submitted in partial fulfilment of the
requirements for the degree of Doctor of Philosophy

© Cranfield University, 2009. All rights reserved. No part of this publication
may be reproduced without the written permission of the copyright holder.

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Abstract
The rapid depletion of hydrocarbon fields around the world has led the industry to search for
these resources in ever increasing water depths. In this context, the large diameter (D >
100mm) vertical riser has become a subject of great interest.
In this research work, a major investigation was undertaken to determine the two phase flow
hydrodynamics in a 254mm vertical riser. Two types of experiments were performed for
range of air-water superficial velocities. The first experimental campaign addresses the issue
of the two gas injector’s performances (conventional vs. novel design gas injector) in the
large diameter vertical riser. The experimental results show that the novel design gas injector
should be the preferential choice.
The second set of the experimental work investigates the two phase flow hydrodynamics in
the vertical riser in detail. The two phase flow patterns and their transitions were identified by
combination of visual observations and statistical features. Based on the results, the
experimental flow regime map was developed and compared with the existing vertical upflow
regime maps/models. None of the flow regime transition models adequately predicted the
flow regimes transitions in large diameter vertical risers as a whole. In this regard, the Taitel
et al. (1980) bubble to slug flow transition model has been modified for large diameter
vertical upflow conditions, based on the physical mechanism observed. The general trends of
modified criteria agreed well with the current and other large diameter experimental results.
The effect of upstream conditions on the vertical riser flow behaviour was also investigated in
detail by two different inlet configurations (i) near riser base injection and (ii) upstream
flowline injection. It was found that no significant differences exist in flow behaviour at low
air-water superficial velocities for both the inlet configuration, at high air-water superficial
velocities, the intermittent flow behavior in flowline influences the riser flow pattern
characteristics and thereby controls the riser dynamics. It is found that liquid slugs from the
flowline naturally dissipate to some extent in the riser as a consequence of compression of
succeeding bubble that rapidly expands and break through the liquid slug preceding it when it
enters the riser. The experimental work corroborates the general consensus that slug flow
does not exist in large diameter vertical upflow condition.
Experimental data has been further compared to increase the confidence on the existing two
phase flow knowledge on large diameter vertical riser: (a) by comparing with other
experimental studies on large diameter vertical upflow in which generally, a good agreement
was found, (b) by assessing the predictive capability of void fraction correlations/pressure
gradient methods. The important implication of this assessment is that the mechanistic
approach based on specific flow regime in determining the void fraction and pressure
gradient is more successful than conventional empirical based approaches. The assessment
also proposes a proposed set a of flow regime specific correlations that recommends void
fraction correlations based on their performances in the individual flow regimes.
Finally, a numerical model to study the hydrodynamic behaviour in the large diameter
horizontal flowline-vertical riser system is developed using multiphase flow simulator
OLGA. The simulated results show satisfactory agreement for the stable flows while
discrepancies were noted for highly intermittent flows. The real time boundary application
was partially successful in qualitatively reproducing the trends. The discrepancies between
the predicted results and experimental data are likely to be related to the incorrect closure
relations used based on incorrect flow regimes predictions. The existence of the multiple
roots in the OLGA code is also reported for the first time.
Keywords: air-water flow, comparison, drift flux, flow pattern, flow pattern transitions, large
diameter, numerical simulation, flowline-riser, OLGA, vertical pipe, two phase, void fraction,
correlations.

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Acknowledgements

First of all I want to express my thanks to my supervisor Dr. Hoi Yeung for his
guidance and support throughout the duration of this work.

A lot of thanks to Prof. Chris Thompson, head of PASE department for his warm
encouragement when it was most needed.

I gratefully acknowledge the financial support provided by the Department of Process
and Systems Engineering.

I wish to express thanks to the entire Process and Systems Engineering Group, all of
you have been very helpful, especially I wish to thanks, Mrs. Linda Whitfield, Mrs.
Sam Skears, Mr. Flemming Nielsen, Mr. John Knopp and all my fellow students.

The assistance received from the staff of Kings Norton Library especially Ms. Anita
Beal and staff of Cranfield Computer Centre during the course of this work is greatly
appreciated.

A special thanks to Mr. Tim Lockett of Scandpower Technology for answering my
OLGA questions.

I would also like to thank Mrs Zoë Hersov, founder of Anne Marie Schimmel
Scholarship, all my teachers at school, college and universities and many many others
who have been a constant source of encouragements.

My deepest gratitude to my husband Nadeem for his love and support and very very
special love thanks to my son Humd, for his cheerful face has been a constant source
of motivation and delight.

Last but not the least, I would like to thank both my parents, brothers and sister who
have been the greatest inspiration through their nobility and fortitude.

To all of you, I humbly dedicate this thesis.

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Table of Contents
Abstract...................................................................................................I
Acknowledgements..............................................................................III
Table of Contents................................................................................. IV
List of Figures................................................................................... VIII
List of Tables ......................................................................................XV
List of Tables ......................................................................................XV
Nomenclature ....................................................................................XVI
Chapter 1................................................................................................1
Introduction............................................................................................................1
1.1 Background.....................................................................................................1
1.2 Objectives.......................................................................................................5
1.3 Thesis outline..................................................................................................6
Chapter 2................................................................................................8
Literature Review...................................................................................................8
2.1 Fundamentals of Two phase flows...................................................................8
2.1.1 Void fraction - The Definition...............................................................8
2.1.2 Pressure gradient - The Definition........................................................9
2.1.3 Gas-Liquid flow pattern........................................................................9
2.1.4 Flow regime maps...............................................................................12
2.1.6 Void phase distribution characteristics in the vertical pipe.................24
2.2 Literature Review on the Large Diameter (D ≥ 100mm) Studies in the Past...28
2.3 Application of Vertical Pipe in Offshore Flowline-Riser system....................41
2.3.1 Unstable cyclic flow............................................................................42
2.3.2 Methods to eliminate/ reduce unstable cyclic flows.............................44
2.3.3 Gas lifting...........................................................................................46
2.4 OLGA – the multiphase flow simulator.........................................................48
2.4.1 Introduction........................................................................................48
2.4.2 OLGA – The code...............................................................................48
2.4.3 Literature Review on OLGA................................................................53
2.4.4 Literature review on horizontal flowline-vertical riser........................56
Chapter 3..............................................................................................59
Experimental Facility, Instrumentation and Data Acquisition...........................59
3.1 Cranfield University’s Large Diameter Experimental Facility........................59
3.1.1 Water supply circuit............................................................................59
3.1.2 Air supply circuit................................................................................61
3.1.3 Test section.........................................................................................61

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3.1.4 Gas injectors.......................................................................................61
3.1.5 Overhead tank & Downcomer.............................................................62
3.2 Instrumentation.............................................................................................64
3.2.1 Flowmeters.........................................................................................64
3.2.2 Pressure Transducers.........................................................................65
3.2.3 Differential Pressure Transducers......................................................65
3.2.4 Temperature Probes............................................................................65
3.2.5 Miscellaneous.....................................................................................65
3.3 Data Acquisition............................................................................................66
3.4 Experiments..................................................................................................69
3.4.1 Experimental configurations...............................................................69
3.4.2 Test Matrix.........................................................................................71
3.4.3 Deduction of Parameters....................................................................73
3.5 Summary.......................................................................................................76
Chapter 4..............................................................................................77
Experimental Results............................................................................................77
Part I – Gas Injectors Characteristics..................................................................77
4.1 Gas Injectors Results.....................................................................................78
4.1.1 Visual flow pattern characterization of the injectors...........................78
4.1.2 Lifted liquid flow characteristics.........................................................87
4.1.3 Total pressure gradient characteristics...............................................91
4.1.4 Void fraction characteristics...............................................................94
4.1.5 Riser base pressure characteristics.....................................................98
4.1.6 Stability characteristics.....................................................................100
4.1.7 Interim Summary..............................................................................109
Part II – Flow Pattern Characterization............................................................110
4.2 Flow Regime...............................................................................................110
4.2.1 Flow regimes classification...............................................................110
4.2.2 Visual observations...........................................................................111
4.2.3 Statistical analysis............................................................................118
4.2.4 Flow regime transitions characteristics............................................124
4.2.5 Interim Summary..............................................................................129
4.3 Effect of Upstream Conditions on Flow Patterns in Vertical Riser Section...129
4.3.1 Near riser base gas injection.............................................................130
4.3.2 Upstream flowline gas injection........................................................132
4.3.3 Interim Summary..............................................................................139
4.4 Flow Regime Maps/ models........................................................................140
4.4.1 Comparison of experimental results with theoretical flow regime maps/
models.......................................................................................................140
4.4.2 Comparison of flow pattern results with other experimental studies
conducted in large diameter vertical pipe..................................................149
4.4.3 Modification to Taitel et al. (1980) bubble to slug transition model for
large diameter application.........................................................................151
4.4.4 Interim Summary..............................................................................157

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Part III - Void Fraction Characterization..........................................................159
4.5 Void Fraction..............................................................................................159
4.5.1 Drift flux model.................................................................................159
4.5.2 Void fraction phase distribution........................................................165
4.5.3 Comparison of experimental results with other studies on large diameter
vertical pipe...............................................................................................170
4.6 Conclusion..................................................................................................173
Chapter 5............................................................................................178
The performance assessment study of the existing void fraction correlations and
pressure gradient models....................................................................................178
5.1 Introduction.................................................................................................178
5.2 Previous Assessments on Void Fraction Correlations and Pressure Gradient
Models..............................................................................................................179
5.3 Void Fraction Correlations..........................................................................181
5.3.1 Homogenous void fraction model......................................................181
5.3.2 Separate flow model..........................................................................182
5.3.3 Miscellaneous correlations...............................................................183
5.4 Pressure Gradient Correlations....................................................................184
5.4.1 Based on Homogenous mixture model...............................................184
5.4.2 Based on Two phase friction multiplier concept................................184
5.4.3 Based on Empirical models...............................................................185
5.5 Experimental Data.......................................................................................185
5.6 Results and Discussion................................................................................186
5.6.1 Correlation based on Homogenous void fraction model....................186
5.6.2 Void fraction correlations based Separate flow model.......................188
5.6.3 Miscellaneous void fraction correlation............................................198
5.6.4 Pressure gradient methods based on Homogenous mixture model.....201
5.6.5 Pressure gradient methods based on friction multiplier concept........204
5.6.6 Pressure gradient methods based on empirical approach..................205
5.7 Summary.....................................................................................................207
Chapter 6............................................................................................215
Numerical simulation of the large diameter horizontal flowline-vertical riser
system..................................................................................................................215
6.1 Introduction.................................................................................................215
6.2 Pipeline-Riser Experiments.........................................................................215
6.2.1 Parameters simulated.......................................................................216
6.2.2 Test matrix description......................................................................217
6.3 The Model Formulation...............................................................................217
6.3.1 Loop Topology..................................................................................217
6.3.2 Piping material.................................................................................219
6.3.3 Assumptions......................................................................................219
6.3.4 PVT file description..........................................................................219
6.3.5 Run time conditions..........................................................................220
6.3.6 Boundary conditions.........................................................................220
6.4 Results – from First Model..........................................................................221

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6.4.1 Case A1............................................................................................222
6.4.2 Case B1............................................................................................224
6.4.3 Case C1............................................................................................228
6.4.4 Special Case - D1.............................................................................232
6.4.5 Case E1............................................................................................237
6.4.6 Discussion on first model predictions................................................238
6.5 Modifications to the First Model..................................................................239
6.6 Results from the Extended Model................................................................244
6.6.1 Case B3............................................................................................245
6.6.2 Case C3............................................................................................245
6.6.3 Case D3............................................................................................247
6.6.4 Case F3............................................................................................247
6.6.5 Case G3............................................................................................249
6.6.6 Case H3............................................................................................251
6.6.7 Case I3.............................................................................................254
6.7 Numerical Experiments...............................................................................259
6.7.1 Effect of Grid density change............................................................259
6.7.2 Effect of Timestep change.................................................................261
6.8 Summary.....................................................................................................262
6.8.1 General Observations.......................................................................263
6.8.2 Recommendations.............................................................................264
Chapter 7............................................................................................266
Conclusions and Future Work............................................................................266
7.1 Summary of the thesis.................................................................................266
7.2 Conclusions.................................................................................................266
7.2 Future work.................................................................................................272
7.2.1 Experimental work............................................................................272
7.2.2 Numerical work................................................................................273
REFERENCES...................................................................................274
APPENDIX A.....................................................................................291
APPENDIX B.....................................................................................295
APPENDIX C.....................................................................................311
APPENDIX D.....................................................................................322

VII
List of Figures
Figure 1.1 Schematic diagram of the Greater Plutonio Development: host FPSO
vessel, riser, flowlines and wellheads (BP Angola, 2004)...........................................3
Figure 1.2 The top and side views of three gas injector inlets (porous annular, porous
slot and nozzle) used by Guet et al. (2003) to study the gaslift efficiency...................5
Figure 2.1 Flow regimes in vertical gas-liquid upflow.............................................10
Figure 2.2 Flow regimes in horizontal gas-liquid flows...........................................11
Figure 2.3 Flow regime map for horizontal flow showing Mandhane et al. (1974) and
Taitel et al. (1976) transitions (Brennen, 2005)........................................................13
Figure 2.4 Flow regimes map for vertical upflow showing Taitel et al. (1980) and
Mishima and Ishii (1984) transitions (Mishima and Ishii, 1984)..............................13
Figure 2.5 Flow regimes map of Weisman and Kang (1981) for vertical upflow
(Brennen, 2005)......................................................................................................14
Figure 2.6 Phase Distribution according to flow regimes in 30mm internal diameter
pipe by Serizawa and Kataoka (1987).....................................................................26
Figure 2.7 Comparison of the injection devices in 72mm diameter pipe (Guet et al.,
2003).......................................................................................................................28
Figure 2.8 Ohnuki and Akimoto (1996) data on Mishima and Ishii (1984) flow map.
...............................................................................................................................33
Figure 2.9 Ohnuki and Akimoto (2000) data on Mishima and Ishii (1984) flow map.
...............................................................................................................................35
Figure 2.10 Comparison of phase distribution according to flow regimes in 38 mm
and 200 mm diameter pipe (Ohnuki and Akimoto, 2001).........................................35
Figure 2.11 The flow patterns in (a) 51.2mm and (b) 200mm diameter pipe taken with
wire mesh tomography (Prasser et al., 2002)...........................................................37
Figure 2.12 The extraction of a large bubble from the signal of the wire-mesh sensor
at j = 1.3 m/s and j = 1 m/s (Prasser et al., 2002)..................................................38
g w
Figure 2.13 Comparison of bubble size distribution in 200 mm and 50 mm
diameter pipe at j of air = 0.53m/s and j = 1m/s (Prasser et al., 2002)....................38
g l
Figure 2.14 Omebere-Iyari et al. (2007) data on (a) Taitel et al. (1980) flow map and
(b) modified bubble to slug transition......................................................................40
Figure 2.15 Omebere-Iyari et al. (2008) data on Taitel et al. (1980) flow map.........41
Figure 2.16 Figure depicting some of the deep water riser shapes............................42
Figure 2.17 Schematic of Severe Slugging in Flowline Riser Systems (Pickering et
al., 2001).................................................................................................................43
Figure 2.18 Pressure oscillations of severe slugging in horizontal flowline-vertical
riser system taken from Schmidt et al. (1980) data along with OLGA predictions...55
Figure 2.19 Schmidt et al. (1980) vertical flow regime map for horizontal flowline-
vertical riser system (Brill et al., 1981)....................................................................57
Figure 2.20 Pots et al. (1987) flow regime map for horizontal flowline-vertical riser
system.....................................................................................................................57
Figure 2.21 (a) Fabre et al. (1990) experimental data points on Taitel and Dukler flow
regime map (b) flowline pressure response in horizontal flowline-vertical riser
system.....................................................................................................................58
Figure 3.1 Schematic of the large diameter riser facility..........................................60
Figure 3.2 (a) The schematic of individual air injectors and (b) the schematic of

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