1. School of Energy, Environment and
Agrifood
April 2015
The development of a Floating
Production Vessel for an Ultra-
Deepwater Field
Offshore and Ocean Technology
Group Project
2. Authors
Abubakar Sadiq Abubakar
Biweri Kainga
Chukwunonso Ndububa Okereke
Jordan Jayne Brown
Myles Asota
Tolulope Emiola – Sadiq
Enyioma Iwuoha
Offshore and Ocean Technology MSc Group Project 2014-2015
Key Words
Floating production system, SPAR, mooring system, export, risers, met-ocean, reservoir
.
Research Contractors
Institute for Energy & Resource Technology,
School of Energy, Environment and Agrifood,
Cranfield University, Cranfield,
Bedfordshire, United Kingdom.
MK43 0AL
3. Executive Summary
The project was designed in collaboration with JE & P Associates to consider offshore oil
and gas exploration in the Gulf of Mexico, a geography region of the offshore industry
which are not normally considered in English projects. The objective of the project was
to design a floating production system for an ultra-deep water field in the Gulf of Mexico,
however as there are three different floating production vessels (FPSO, Semi-
submersibles and SPARS) which could have been used to produce a design concept this
project. Therefore firstly a screeningprocess including research into the environment was
conducted to make an initial design choice of which floating production vessel would be
most suitable for the environment. With the support of Dr John Preedy from JE &P
Associates, the group decided the best option would be a SPAR floating production
platform. The concept of a SPAR floating production vessel was taken step-step through
each design stage; SPAR body, topside processing, mooringsystem, risers, export options.
At each stage design concepts and research was transformed into final ideas with
justifications for each design decision was portrayed throughout the project. The
outcome of the project was a realistic functional SPAR floating production system which
would be suitable for the environment and all objectives of the project was met.
4. Acknowledgements
Dr Fuat Kara
The group would like to acknowledge Dr Fuat Kara for his continuous efforts to
challenge the group on the depth and understanding of the project constantly
improving the groups’ knowledge of offshore floating production vessels. Dr kara has
helped the group improve the key concepts within report and presentation work
through feedback and helped the group to understand the requirements needed to
achieve good team work.
Dr John Preedy
The group would like to acknowledge Dr John Preedy for transferring his understanding
and knowledge of the subject area to the group. Dr John Preedy was dedicated to
helping the group further develop the knowledge within offshore floating production
vessels and topside processing and provided a brilliant project to simulate the mind of
each individual.
7. 3
TABLE OF CONTENTS
LIST OF FIGURES..................................................................................................................... 7
LIST OF TABLES....................................................................................................................... 9
LIST OF EQUATIONS............................................................................................................. 10
1 INTRODUCTION ........................................................................................................... 11
1.1 Project synopsis.................................................................................................... 11
2 REGIONAL INFORMATION........................................................................................... 14
2.1 Offshore governing bodies and regulations........................................................ 14
2.1.1 Bureau of Ocean Energy Management ....................................................... 15
2.1.2 Bureau of Safety and Environmental Enforcement.................................... 15
2.2 Met ocean............................................................................................................. 16
2.2.1 Overview of the met-ocean ......................................................................... 16
2.2.2 Sea Temperature .......................................................................................... 17
2.2.3 Wind .............................................................................................................. 18
2.2.4 Waves............................................................................................................ 19
2.2.5 Currents......................................................................................................... 20
2.2.6 Hurricanes..................................................................................................... 21
2.3 Overview of reservoir data .................................................................................. 25
3 SCREENING PROCESS .................................................................................................. 26
3.1.1 FPSO .............................................................................................................. 26
3.2 Semi-Submersibles............................................................................................... 28
3.3 SPAR ...................................................................................................................... 29
3.4 Selection of floating production vessel............................................................... 31
4 SPAR BODY................................................................................................................... 33
4.1 Selection of the SPAR body.................................................................................. 33
4.2 Elements of a SPAR body ..................................................................................... 35
4.3 Summary of the design ........................................................................................ 37
5 TOPSIDE ....................................................................................................................... 38
5.1 Layout and equipment......................................................................................... 38
5.2 Topside Utilises..................................................................................................... 43
5.2.1 Modules for topside facilities....................................................................... 43
5.2.2 Venting and flaring module.......................................................................... 43
5.2.3 Power generation system module............................................................... 45
5.2.4 Fuel gas system module ............................................................................... 46
5.2.5 Diesel fuel system......................................................................................... 47
5.2.6 Produced Water Conditioning Module ....................................................... 48
5.2.7 Drain System ................................................................................................. 49
5.2.8 Helideck......................................................................................................... 51
5.2.9 Material handling system module ............................................................... 52
5.2.10 Control and Safety Systems.......................................................................... 53
5.2.11 Firefighting systems:..................................................................................... 54
8. 4
5.2.12 Volatile Organic Compounds (VOC) Recovery............................................. 56
5.2.13 Chemical Injection System ........................................................................... 56
5.2.14 Inert Gas and Nitrogen System.................................................................... 57
5.2.15 Desalination, Potable and Fresh Water System.......................................... 58
5.2.16 Compressed Air System:............................................................................... 59
5.2.17 Heating System ............................................................................................. 60
5.2.18 Cooling System.............................................................................................. 61
5.2.19 HVAC (Heating Ventilation and Air Conditioning) System.......................... 62
5.2.20 Living Quarters/Accommodation Module................................................... 63
5.3 Reservoir Analysis................................................................................................. 64
5.3.1 Production Profile......................................................................................... 65
5.3.2 Composition.................................................................................................. 67
5.3.3 Reservoir Fluid Characteristics and Modelling............................................ 68
5.3.4 Design Basis................................................................................................... 69
5.4 Overview of the Tequila-Sunrise Topside Processing Units............................... 70
5.4.1 Topside Process Description and Modelling ............................................... 71
5.5 Oil Separation Process ......................................................................................... 73
5.5.1 HP, IP and LP Separation Vessels ................................................................. 74
5.5.2 Electrostatic Coalescer ................................................................................. 75
5.5.3 Separation Process ....................................................................................... 77
5.6 Gas processing...................................................................................................... 79
5.6.1 Gas Compression .......................................................................................... 79
5.6.2 Amine sweetening........................................................................................ 83
5.6.3 Gas dehydration............................................................................................ 85
5.6.4 Export option compression unit .................................................................. 87
5.6.5 Power generation unit.................................................................................. 88
6 MOORING SYSTEM DESIGN ........................................................................................ 89
6.1 Overview of mooring systems ............................................................................. 89
6.2 Design Criteria ...................................................................................................... 90
6.3 Design process...................................................................................................... 90
6.3.1 Elements of a typical mooring system......................................................... 91
6.3.2 Material Selection......................................................................................... 92
6.3.3 Mooring Configuration................................................................................. 96
6.3.4 Orcaflex Modelling........................................................................................ 97
6.4 Summary of design............................................................................................... 98
7 RISER DESIGN............................................................................................................. 100
7.1 Overview of Riser Systems and Design ............................................................. 100
7.1.1 Types of risers used for SPARS................................................................... 100
7.2 Design Process.................................................................................................... 102
7.2.1 Material Selection....................................................................................... 103
7.2.2 Burst Pressure............................................................................................. 104
7.2.3 Hoop stress ................................................................................................. 107
7.2.4 Longitudinal Stress...................................................................................... 109
9. 5
7.2.5 Von Mises.................................................................................................... 111
7.2.6 Collapse under external pressure.............................................................. 112
7.2.7 Propagation buckling.................................................................................. 114
7.2.8 Manufacturing tolerances.......................................................................... 116
7.2.9 Orcaflex Modelling...................................................................................... 116
8 EXPORT....................................................................................................................... 118
8.1 Export route........................................................................................................ 118
8.2 New pipeline connection ................................................................................... 120
8.2.1 Design Criteria............................................................................................. 120
8.2.2 Design Process ............................................................................................ 121
8.3 Summary of design............................................................................................. 124
9 COSTING..................................................................................................................... 125
9.1 Methodology ...................................................................................................... 125
9.2 Topside costing................................................................................................... 125
9.3 SPAR Body costing.............................................................................................. 126
9.4 Mooring system costing..................................................................................... 127
9.5 Risers, export and umbilical costing.................................................................. 128
9.6 Summary of total design cost ............................................................................ 129
REFERENCES....................................................................................................................... 130
APPENDICES .....................................................................................................................cxxxv
Appendix A Regional Data ....................................................................................cxxxv
Appendix B Screening Process Analysis................................................................ cxliii
THE SPAR...................................................................................................................... cxlvii
THE MOORING............................................................................................................. cxlvii
The TOPSIDE ................................................................................................................cxlviii
RISERS and EXPORT PLAN ............................................................................................ cxlix
The Independence Hub................................................................................................ cxlix
Hull Design .........................................................................................................................cl
Mooring..............................................................................................................................cl
TOPSIDE.............................................................................................................................cli
RISERS AND EXPORT PLAN ...............................................................................................cli
Appendix C Calculations for Riser Design ...............................................................cliii
Appendix D Topside processing Gas processing.................................................. clviii
1 Material Stream........................................................................................................ clviii
2 Compositions.............................................................................................................. clix
3 Energy ......................................................................................................................... clxi
1 Material Streams....................................................................................................... clxii
2 Compositions............................................................................................................ clxiii
3 Energy Stream ........................................................................................................... clxv
4 Units Ops.................................................................................................................... clxv
1 Material Stream........................................................................................................ clxvi
2 Compositions........................................................................................................... clxvii
3 Energy Stream .........................................................................................................clxviii
10. 6
Amine Sweetening Unit.................................................................................................... clxix
4 Material Stream......................................................................................................... clxx
5 Composition.............................................................................................................. clxxi
6 Energy .......................................................................................................................clxxii
7 Units Ops..................................................................................................................clxxiii
Appendix E Costing basis..........................................................................................clxxiv
Appendix F Safety......................................................................................................clxxv
Appendix G Spar body design...............................................................................clxxvi
11. 7
LIST OF FIGURES
Figure 1-1 - Map to portray the specific field location for the project............................. 12
Figure 1-2 - Diagram to explain the field architecture ..................................................... 13
Figure 2-1 – Effects of Deep water horizon explosion....................................................... 15
Figure 2-2 - Annual sea temperature for Gulf of Mexico .................................................. 17
Figure 2-3 – Wind roses for December and June 2001..................................................... 18
Figure 2-4 – Typical wave report from the Gulf of Mexico ............................................... 19
Figure 2-5 – Currents in the Gulf of Mexico....................................................................... 20
Figure 2-6 – Hurricane paths in the Gulf of Mexico........................................................... 21
Figure 2-7 – Chevron Typhoon Platform before hurricane Rita........................................ 22
Figure 2-8 – Chevron Typhoon Platform after hurricane Rita........................................... 23
Figure 2-9 – Thunder horse before hurricane Dennis ...................................................... 24
Figure 2-10 – Thunder horse after hurricane Dennis........................................................ 24
Figure 3-1 – Schiehallion FPSO............................................................................................ 26
Figure 3-2 – Location of independence hub field.............................................................. 29
Figure 3-3 – Location of independence hub field.............................................................. 30
Figure 4-1 – Types of SPAR Body ........................................................................................ 33
Figure 4-2 – SPARS designed for the Gulf of Mexico ......................................................... 34
Figure 4-3 – Elements of a Truss SPAR Body...................................................................... 36
Figure 5-1 – Topside configuration..................................................................................... 38
Figure 5-2 - Lower Deck Layout of Tequila Sunrise SPAR Topside .................................... 40
Figure 5-3 - Module Deck Layout of Tequila Sunrise SPAR Topside ................................. 41
Figure 5-4 - Module Deck Layout of Tequila Sunrise SPAR Topside ................................. 42
Figure 5-5 – Flaring and venting stack................................................................................ 45
Figure 5-6 – Gas compressor .............................................................................................. 46
Figure 5-7 – Gas System...................................................................................................... 47
Figure 5-8 – Diesel fuel system........................................................................................... 48
Figure 5-9 – Produced water conditioning module ready to deploy................................ 49
Figure 5-10 – Drain System on Platform Topside .............................................................. 50
Figure 5-11 – Helideck......................................................................................................... 51
Figure 5-12 – Basic crane diagram for offshore material handling................................... 52
Figure 5-13 – Control System Module of an offshore platform........................................ 53
Figure 5-14 – Water pump System for Firefighting ........................................................... 55
Figure 5-15 – Chemical Injection system............................................................................ 57
Figure 5-16 – Inert gas and Nitrogen system..................................................................... 58
Figure 5-17 – Potable and Fresh water system.................................................................. 59
Figure 5-18 – Air compressor system................................................................................. 60
Figure 5-19 – Heating System for a typical Topside platform........................................... 61
Figure 5-20 – HVAC system................................................................................................. 63
Figure 5-21 – Accomodation module ................................................................................. 64
Figure 5-22 – Oil forecast.................................................................................................... 66
12. 8
Figure 5-23 – Gas forecast .................................................................................................. 66
Figure 5-24 – Phase envelope............................................................................................. 68
Figure 5-25 – Topside processing ....................................................................................... 70
Figure 5-26 – HYSYS Topside processing............................................................................ 72
Figure 5-27 – Three phase horizontal separator ............................................................... 73
Figure 5-28 – Operational parts for the three-Phase Horizontal Separator (Maurice and
Ken, 2008).................................................................................................................... 75
Figure 5-29 – Typical Electrostatic Coalescer with Internals............................................. 76
Figure 5-30 –Electrostatic Coalescer Fabricated View ...................................................... 77
Figure 5-31 – Schematic of the Flash compressor train.................................................... 80
Figure 5-32 – Vane Pad Gas Scrubber ................................................................................ 81
Figure 5-33 – A Compressor adopted for topside Compression Unit............................... 81
Figure 5-34 - HYSYS Model of Tequila Sunrise Main Compression Unit........................... 82
Figure 5-35 - Typical flow diagram of a gas amine treating process ................................ 84
Figure 5-36 – HYSYS Model of Tequila Sunrise Amine Sweetening Unit .......................... 84
Figure 5-37 – HYSYS Model of Tequila Sunrise Gas Dehydration Unit ............................. 86
Figure 5-38 – HYSYS Model of Tequila Sunrise Gas Export Compression option............. 87
Figure 5-39 – HYSYS Model of Tequila Sunrise Power Generation Unit........................... 88
Figure 6-1 – Catenary and taut-leg mooring system design ............................................. 89
Figure 6-2 – Offshore mooring winch................................................................................. 91
Figure 6-3 – Suction pile anchor for mooring systems...................................................... 92
Figure 6-4 – Studded (left) and studless chain links .......................................................... 93
Figure 6-5 – Types of steel wire rope ................................................................................. 95
Figure 6-6 – Mooring Layout for Tequila-Sunrise using Orcaflex modelling.................... 97
Figure 7-1 – Steel catenary riser system .......................................................................... 101
Figure 7-2 –Riser Arrangement......................................................................................... 102
Figure 7-3 – Example of burst pressure effects on pipelines.......................................... 105
Figure 7-4 – Direction of hoop stress ............................................................................... 107
Figure 7-5 – Direction of longitudinal stress .................................................................... 109
Figure 7-6 – Propagation buckling of a pipe .................................................................... 114
Figure 7-7 – propagation buckling arrestor...................................................................... 115
Figure 7-8 – Orcaflex model of the riser system.............................................................. 117
Figure 8-1 – Pipeline export route................................................................................... 119
Figure 8-2 – Plan of exporting oil from Tequila-Sunrise to a refinery............................. 120
Figure 8-3 – Pipeline with a FBE coating applied............................................................. 122
Figure 8-4 – Deep Blue pipe laying vessel ........................................................................ 123
Figure 8-5 – Comparison of pipe lay vessels capability ................................................... 123
Figure 8-6 – Deep Blue pipe laying vessel ........................................................................ 124
13. 9
LIST OF TABLES
Table 3-1: Platform comparison table summary ............................................................... 31
Table 4-1: Design parameters for Tequila-Sunrise body ................................................... 37
Table 5-1: Information for the SPAR body ......................................................................... 39
Table 5-2: Oil and Gas forecast........................................................................................... 65
Table 5-3: Badolee Reservoir Fluid Composition............................................................... 67
Table 5-4: Badolee Reservoir Fluid Composition ............................................................... 69
Table 5-5: Pressure rating ................................................................................................... 73
Table 5-6: Intermediate separator sizing ........................................................................... 78
Table 5-7: Low separator sizing .......................................................................................... 79
Table 5-8: Compression sizing ............................................................................................ 83
Table 5-9: Amine unit specification .................................................................................... 85
Table 5-10: TEG Dehydration Unit...................................................................................... 86
Table 5-11: Final Gas Compression Unit............................................................................. 87
Table 6-1: Recommended chain type for specific requirements...................................... 94
Table 6-2: Mooring line steel chain specifications............................................................. 94
Table 6-3: Comparison of spiral strand and six strand steel wire rope ............................ 96
Table 6-4: Orcaflex simulation modelling results............................................................... 98
Table 7-1: Riser and environmental input data for calculations..................................... 103
Table 7-2: Material section for riser system .................................................................... 104
Table 7-3: Results from burst pressure calculations........................................................ 106
Table 7-4: Results from hoop stress calculations............................................................. 108
Table 7-5: Results from Longitudinal stress calculations................................................. 110
Table 7-6: Results from von Mises calculations............................................................... 111
Table 7-7: Results from collapse under external pressure calculations ......................... 113
Table 7-8: Results from propagation buckling calculations............................................. 115
Table 7-9: Results from Orcaflex modelling calculations ................................................ 117
Table 9-1 Tequila-Sunrise Topside CAPEX estimate ........................................................ 126
Table 9-2: SPAR Hull Estimation........................................................................................ 127
Table 9-3: Mooring Cost Estimation................................................................................. 127
Table 9-4: Umbilical, Risers and Pipeline costing estimate ............................................. 128
Table 9-5: Tequila-Sunrise total CAPEX estimate............................................................. 129
15. 11
1 INTRODUCTION
Over the past years the demand for oil and gas production systems has continuously
increased with new contracts and new leases signed every year, however with the
constant reminder there is a limit to non-renewable energy resource, this is causing
pressure within the offshore industry. With this in mind the industry has been forced to
venture to place and fields which were once thought as unavailable due to the
environmental issues involved, therefore there has been a need for advances in
technology. The Gulf of Mexico is reflected as one of these areas, even though the Gulf
is considered as one of the world’s leading hydrocarbon producing regions with many
shallow and deep water fields, the offshore industry are well aware there are many more
oil and gas fields to be discovered in the Ultra deep water regions at water depths greater
than 1500m (Cummings et al, 2015). In recent years engineering teams have managed to
conquer some of these fields, and build platforms and vessels suitable for the
environment, making the Gulf of Mexico the worlds’ pioneers for Ultra deep water
exploration and a very interesting subject topic to look at in further detail.
1.1 Project synopsis
In collaboration with JE & P Associates, this study has been conducted with the desired
outcome of designing a floating production vessel in the Gulf of Mexico for a proposed
ultra-deep water field with a field life of 20 years. The area which the proposed field is
situated is currently an undeveloped area therefore specification have been given for the
field; The geographical region of the proposed field is 250km (155miles) directly south of
New Orleans at a water depth of 2850m, as shown by figure 1-1 the location of the field
would be situated in Walker Ridge near Cascade and Chinook fields. The field will be made
up from 3 similar sized reservoirs, which are situated at the points of an equilateral
triangle pattern located 8km apart from each other, with the floating production host
situated in the centre as portrayed by figure 1-2. As the proposed field does not have a
name, the group have decided to call the field; Badolee and the chosen production vessel;
16. 12
Tequila-Sunrise throughout this report. To fulfil the desired outcome, firstly the group
needed to make a decision to which floating production vessel would be most suitable,
therefore a screening process was conducted by researching into the different types of
floating production vessels currently available (FPOS’s, Semi-submersibles and SPARS)
and making an initial decision of which would be most suitable for environment. This
decision was made final through the support of initial research into reservoir data, met
ocean data including hurricanes which have affected the specific field region and health
and safety regulations which apply the Gulf of Mexico. The initial research provided the
group along with the support from Dr John Preedy the choice of which floating production
vessel was the most suitable for the environment. From this decision the designing of the
floating production vessel was conducted, whereby research and decision were made
about; the vessel body, topside processing, mooring systems, riser systems and export
options. This report can be used as a guide and a reference point of all the decisions and
research which was conducted to fulfil the outcome of the project.
Figure 1-1 - Map to portray the specific field location for the project
Source: Offshore energy today online (2011)
Badolee
18. 14
2 REGIONAL INFORMATION
The objective of this section is to acquire the knowledge needed to make the decision
which floating production vessel would be most suitable for the environment through
producing an evaluation of the regional information.
2.1 Offshore governing bodies and regulations
Regulations are one of the most important factors when itcomes to the offshore industry,
one little mistake could cause catastrophic effects to operations, environment and
personnel involved. In April 2010 the Gulf of Mexico fell victim to one of the largest
accident oil spills caused by an explosion involving the deep Water Horizon semi-
submersible as can be seen in figure 3. As a result of the explosion the vessel burned for
36 hours until finally sinking releasing the oil into the Gulf, not only did it effect the
environment and operations but as a result 11 people died and 17 seriously injured and
by the tragedy (Visser, 2011). This caused for serious changes in the safety regulations for
the offshore industry conducting in the GoM, therefore as part of the regulation
reforming in October 2011, the Minerals Management Service (MMS) was replaced by
the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) which
is split into two different departments; the Bureau of Ocean Energy Management and the
Bureau of Safety and Environmental Enforcement (BOEMRE, 2011), for further
information into how the governing bodies reformed please refer to appendix A.
19. 15
Figure 2-1 – Effects of Deep water horizon explosion
Source: Green Valley Space (2011)
2.1.1 Bureau of Ocean Energy Management
BOEM is the governing body for administering the environmental and economic
responsibility for the development of the nations’ offshore resources, the function of the
BOEM is to approval and sales of offshore leases, evaluated current and new resources,
review and conduct oil and gas development plans, renewable energy development
analysis, review and update national environmental policy act (NEPA) and conduct
general environmental studies (BOEMRE, 2011). The BOEM is governed and monitored
by a varied range of laws, regulations and other guidance provided by the offshore
industry. It is the responsibility of the Bureau to enforce compliances with these
regulations and continuously review and evaluate advances in technology and new
information to keep all regulations up-to-date and relevant.
2.1.2 Bureau of Safety and Environmental Enforcement
The BSEE are the governing body for safety and environmental management for all
offshore operation, including permitting and inspections (BOEMRE, 2011). The main role
of BSEE is the development and administration of environmental and safety regulations,
allowing permits for offshore exploration, planning and preforming inspections, the
development of training programmes for offshore regulations and oil spill guidance.
20. 16
2.2 Met ocean
The objective of this section is to research and examine the met-ocean in the Gulf of
Mexico and evaluate how the environment could cause possible challenges for offshore
floating production vessels.
2.2.1 Overview of the met-ocean
The Gulf of Mexico is commonly described as volatile due to the nature of the met-ocean,
the key to designing an efficient functional floating production vessel for this area, is first
understanding the environment. The floating production platform would have to
withstand the forces produced by daily steady environment, but IVAN, KATRINA, RITA and
DENNIS, these are all names familiar to most especially the offshore environment. The
Gulf of Mexico through a combination of currents, sea temperature and winds, is home
to some of the world’s most fearsome hurricanes which leave behind a path of
destruction, but with the right design considerations can these offshore systems weather
the storm or will destruction be their destiny too. The only way the environment can only
truly be evaluated is with regular testing and up-to-date accurate data of the met-ocean.
Another environmental factor to consider is due to floating production vessels not having
a specific fixed placement like that of a fixed structure, the needed to design for the
correct dynamic response to the environment is a necessary factor, the response is
generally caused as an effect of the environment. Therefore when considering a dynamic
response analysis it is valuable to know, the required design loads for a floating systems
are calculated by the extreme conditions which combine all credible loads from the met-
ocean (wind, waves, currents, ect), however an analysis of dynamic response can only be
achieved using an single load component, most analysis commonly uses the wave factor
(Chen, Jan & Colon, 1982).The specific parts of the waves which need to be taken into
consideration are the wave frequency and wave directions as these factor are the most
dominant cause of affect.
21. 17
To be able to make a decision on which floating production vessel will be most suitable
for the environment a full analysis of the possible environmental threats needs to be
investigated. A thorough investigation of the sea temperature, currents, waves, tidal
force, winds and hurricanes has been conducted and historical events which have caused
damage due to the environment have been.
2.2.2 Sea Temperature
Using the NOAA data for the annual surface sea temperature for the Gulf, as portrayed
by figure 2-2, the annual sea temperature in the Gulf between 23°C - 26°C, however data
collection in appendix A.2.1, demonstrates throughout the winter and summer months,
the Gulf generally has a increase and decrease temperature accordingly, with the
summer ranging between 27°C- 29°C and winter between 19°C-21°C.
Figure
2-2 -
Annual
Sea temperature for Gulf of Mexico
Source: National oceanic and atmospheric administration (2014)
22. 18
2.2.3 Wind
In general as portrayed in figure 2-3, the typical direction of the wind in the Gulf of Mexico
is north to north-east in the autumn/winter months at a typical wind speed of less than
15ms-1
and south-east in the spring/summer months at a wind speed of less than 10 ms-
1
. In the summer months is when the hurricanes and tropical cyclones are likely to occur
therefore this would cause an increase in the wind speed from the normal.
Figure 2-3 – Wind roses for December and June 2001
Source: National oceanic and atmospheric administration (2001)
23. 19
2.2.4 Waves
The direction of waves in the Gulf of Mexico are wind driven, if the wind is moving in a
south-east direction then generally the waves will move with the wind. Typically the
waves in the Gulf of Mexico only reach heights of less than 3m in the winter months, and
1.5m in the summer months, figure 2-4 portrays a typical wave report from the NOAA for
the Gulf of Mexico. The main issue with waves in the Gulf is when tropical cyclones are
hurricanes occur, the wave height can become unpredictable reaching heights as high as
28m, like when hurricane Katrina hit the Gulf.
Figure 2-4 – Typical wave report from the Gulf of Mexico
Source: National oceanic and atmospheric administration (2012)
24. 20
2.2.5 Currents
Figure 2-5 – Currents in the Gulf of Mexico
Source: UCAR (2015)
The loop current
The loop current is a strong current which provides passage for warm Caribbean water
through the Yucatan strait, between Mexico and Cuba. As portrayed by figure 2-5, the
current flows north into the gulf, then creates a loop shape south east towards Florida
current and ends just west of the Bahamas. The whole current is approximately 300km
wide with a water depth of 800m reaching current speeds of 0.8ms-1
(Masters, 1990).
The nature and depth of the loop current provides massive energy source, which would
increase the magnitude of a passing hurricane.
25. 21
Loop current eddies
As portrayed by figure 2-5 loop eddy currents, are warm circular currents, up to 500km
in diameter circling in an anti-clockwise direction. Loop current eddies are particularly
influential to the dynamics of the Gulf, because the eddies act as a passage to transport
salt, heat and momentum across the deep water regions.
2.2.6 Hurricanes
Figure 2-6 – Hurricane paths in the Gulf of Mexico
Source: NOAA (2012)
2.2.6.1 Damaged caused by hurricanes to offshore vessels
Between 2004 and 2005, the Gulf of Mexico was subjected to 8 named hurricanes in the
space of a year with 3 of the hurricanes being category 5 (the highest category), therefore
this was a very destructive time for the Gulf and many offshore platforms and floating
production systems were destroyed (Oil rig disasters 2012).
26. 22
Hurricane Rita (2005)
Hurricane Rita caused a substantial amount of damage to various offshore platforms, as
the platforms were subjected to winds 155mph winds and 60ft waves. There was 66
platforms completely destroyed, 32 platforms with extensive damage, 13 moorings broke
on MODU’s and set units adrift, 1 jack-up rig sunk, 7 jack-up rigs with extensively
damaged and 2 semi-submersibles damaged (Oil rig disasters 2012).
Figure 2-7 – Chevron Typhoon Platform before hurricane Rita
Source: Oil rig disasters (2005)
27. 23
Figure 2-8 – Chevron Typhoon Platform after hurricane Rita
Source: Oil rig disasters (2012)
Hurricane Katrina (2005)
Hurricane Katrina ripped through the heart of the Gulf at 175mph, destroying
everything in the path, the damage caused by hurricane Katrina was 47 platforms
completely destroyed, 20 underwent extensive destruction. 6 mooring system were
broken sending the rigs adrift, 3 platform rigs completely destroyed, 1 jack-up rig
submerged and capsized, 5 semi-submersibles underwent extensive destruction and
2 platform rigs damaged (Oil rig disasters 2012).
Hurricane Dennis (2005)
Even though Dennis hit the Gulf of Mexico with winds of 150mph, there is only one
know platform which was damaged during the hurricane and that was the thunder
horse semi-submersible(Oil rig disasters 2012).
28. 24
Figure 2-9 – Thunder horse before hurricane Dennis
Source: Oil rig disasters (2005)
Figure 2-10 – Thunder horse after hurricane Dennis
Source: Oil rig disasters (2005)
29. 25
Hurricane Ivan
Hurricane Ivan blew through the Gulf of Mexico at 164mph, however due to the
path of the storm only seven platforms were completely destroyed, six with major
destruction and five drilling rigs with major damage, including the Ensco 64 (Oil rig
disasters 2012).
2.3 Overview of reservoir data
The reservoir data which was specified in the project brief suggests that the deep water
reservoirs in the field location are in the range of 0.5 to 0.2 sulphur which indicates
there is a variable of sour corrosion present within the reservoir, due to the
specification that any crude with 0.5% sulphur is consider sour and required a for
sulphur removal (oil and gas corrosion, 2015). The oil in the reservoir has an API gravity
of 25 to 32 degree, therefore this suggests that the oil in the reservoir is light and
violate, as stated by Boardman energy partners (2015)
30. 26
3 SCREENING PROCESS
The objective of the screening process is to discover the advantages and challenges
of the different type of floating production systems which are currently in use in the
Gulf of Mexico and make a selection for the most suitable based on the research.
Currently there are three types of floating production systems used for ultra-deep
water; floating production offloading and storage vessels (FPOS’s), semi-submersibles
and SPARS. A floating production vessel is a structure which either the centre of
gravity is lower than the centre of buoyancy like a SPAR or the centre of gravity is
higher than the buoyance like semi-submersibles or FPOS’s, the forces combined give
the structure the desired variable of floating. These facilities are also designed with
limited allowance for six degree of freedom; heave, surge, sway, pitch, roll and yaw
and need to be able to withstand the natural forces and forces caused by
environmental factors.
3.1.1 FPSO
Figure 3-1 – Schiehallion FPSO
Source: KRVE (2015)
31. 27
One of the most common floating production vessels available is an FPSO. Normally when
there is an essential requirement for large storage of oil an FPSO would be the first option
for the company to choose, however this can be a disadvantage as the FPSO can only be
used for oil production field and has no advantages for gas production fields. As stated
in the name the FPSO is a storage and offloading vessel, therefore to export the product
there is no need for costly pipelines as the product is simply offloaded to a shuttle tanker
and shipped to the shore, even though this is still costly, the export for an FPSO is the
most cost effective of all the floating production vessels. There are two ways in which an
FPSO can be built; firstly old vessels can be converted to the requirements of a specific
field which will provide a low initial cost for the system or the FPSO can be a new build
which is built for purpose, however this would produce a large initial cost and would take
time and planning which would delay the system being installed. The ship-shaped design
of an FPSO provides the topside process equipment and production layout a large surface
area to be spread across, the ship-shaped design compared with the other floating
production vessels, the FPSO has one major advantage there is a very fast installation
time. Not only does the ship-shaped design give many advantages for the FPSO, the
design also causes disadvantages due to the motion caused by the waves in the
environment. The motion of the ship-shape when in the water causes a large
displacement of volume between the FPSO and the water line, and the dynamic response
to the waves is substantial, therefore the requirement for stable anchoring system and
riser system must be designed to accommodate the forces caused by the motion,
therefore new developments in riser systems have been produced for FPSO’s. Due to the
developments of riser systems for FPSO’s becoming more flexible, FPSO have been used
more regularly as production platforms in harsh environments such as Schieallion and
Foinaven field which is situated the North Atlantic Ocean (Inglis, 1993). Due these new
advances, reliability and integrity of an operating FPSO in harsh environments has been
proven with the Schiehallion and Foinaven fields and after much consideration on the use
of FPSO in GOM, the first Floating Production Storage and Offloading facility in the Gulf
of Mexico which is the Cascade/Chinook FPSO was approved, an analysis of the
32. 28
Cascade/Chinook design was conducted for further research in the design process, refer
to appendix B for the full analysis.
3.2 Semi-Submersibles
Semi-submersibles are technically specialised marine vessels and the second most
common floating production system used in the Gulf of Mexico, however through the
met-ocean research, it can be stated that the structures are highly affected by the harsh
environment of the Gulf. Even though semi-submersibles are structurally considered to
be the most stable of all the floating production platforms, this stability is affected when
the semi-submersible is subjected to high wind speed, as majority of the semi-
submersible’s body is above the water level and when the high winds hit the whole body
of the semi-sub it is subjected to the full force of the wind, which due to a high movement
of the semi-sub, it could either capsize or the mooring lines will be subjected to loads
which the systems might not withstand. Compared to other floating production vessels
semi-submersibles are known for the little motion induced by waves, therefore in the
Gulf of Mexico this would have been a suitable design as a typical wave is of little height
and a hurricane wave would also barely affect the semi. Another advantage the semi-
submersible have over an FPSO is that semi-subs are proven with long history of Gulf of
Mexico oil exploration in an Ultra deep water field with the independence hub, portrayed
by figure 3-2 being an example.This platform is a state of the Semisubmersible stationed
in about 2,500m of water capable of producing 1bcf of gas daily from a combination of
10 gas fields which were in such challenging location that it would not have been possible
to explore individually. The fields covered an area 48km by 96km with about 352km of
flow lines, 200km of umbilical and 250km of flow line jumper and tieback distance up to
72km. All these needed to serve the gas production from 15 wells across the 10 fields.
The image below is a geographical layout of the field. While further analysis of the Hub
can be found in the appendix
33. 29
.
Figure 3-2 – Location of independence hub field
Source: MST Houston
3.3 SPAR
The SPAR production unit is one that have grown from an era of SPAR Buoy ocean
structures used for research purposes and ocean data collections back in 1961 to today’s
mega offshore structures (that demonstrate low motion response to environmental loads
acting on it) used for oil exploration even in ultra-deep waters. This stability is due to the
SPAR’s centre of gravity laying below its centre of buoyancy because it has a deep-draft
caisson nature with 90% of its structure under water while the centre of gravity can be
further lowered by installing heavy ballast at the lowest part (keel) and stakes can also be
incorporated in the design to manage vortex induced vibrations (horizontal
displacement).
34. 30
Figure 3-3 – Location of independence hub field
Source: OTC 20234
Generally a SPAR is made of four components which are: mooring, risers, hull and
topside and mainly there exist three types of SPAR based on difference in hull types:
Classic, Truss and Cell with each owning a range of variation with respect needed
functionality and operating environment. The Perdio SPAR was adopted for special review
in this project as its ultra-deep water location make it fit for the nature of this project.
The Perdido SPAR hull have a cylindrical upper-section (hard tank), a trussed mid-section
for tubular braces, legs and an octagonal bottom-section (soft-tank) which comprise of
the fixed ballast. It is 170m tall with a draft of 154 and a weight of about 20,000t, strakes
were also introduced round the circumference of the hard tank to control the effect of
horizontal oscillation due to vortex induced vibrations. For further analysis of the SPAR,
this document’s appendix should be referenced.
35. 31
3.4 Selection of floating production vessel
The selection of an oil field development platform is a process that must be carefully
weighed across some prevailing factors and it should be noted that what works for one
field does not necessarily guarantee itself as the best solution in another field. The table
below is intended at focusing the GOM platform’s performance capabilities in summary.
Table 3-1: Platform comparison table summary
FPSO SEMISUBMERSIBLE SPAR
STORAGE
CAPACITY High storage capacity
from 500,000bbl to
2,000,000bbl.
Average storage capacity of
about 500,000bbl.
Average storage
capacity of about
250,000bbl.
WEATHER DOWN
TIME
High down time due
to weather motion
sensitivity. In the
case of hurricane, the
FPSO is
depressurized and its
control is handed
over to a ship’s
captain who sail it
out of the storm’s
path. After the
storm, the FPSO is
sailed back to
location then all
equipment are
cleared of damage
before production is
continued.
Average bad weather down
time. Production must be
stopped during bad weather
due to high motion rate and
in the event of strong wind
e.g. hurricane, the platform
is depressurized and
abandoned. Then checked
for damages afterwards
before work can continue.
Low weather down
time. Due to its stable
nature, production can
continue during bad
weather but when a
hurricane is coming,
the platform is
depressurized and
abandoned then re-
evaluated upon return
before production can
continue.
PROCESS
CAPACITY High processing
capacity up to
300,000blpd.
Can be designed to process
a fairly high amount of
crude, as much as
250,000blpd.
Its processing capacity
is mostly on the low to
average, from
60,000bpld to
150,000bpld.
36. 32
COST High CAPEX less than
a 1billion USD and
can be cheaper when
it is a converted
FPSO.
Low CAPEX around: 1billion
USD.
Average CAPEX rarely
up to
1billionUSD.
TIME TO FIRST
OIL Long Fabrication
time, hence longer
time to first oil.
Average time to first oil with
respect to FPSO.
Quickest time to first
oil.
MOORING &
STABILITY Detachable Turret
mooring system is
the most suitable
mooring design with
respect to the GOM
and chain-wire-chain
as mooring line
combination are
used. This system is
quite expensive
relative to the other
production units and
it has the lowest
stability rating of
them.
The spread Steel Catenary
Mooring System is adopted
in a chain-wire-chain
combination. It would be
design to survive a 100
years storm and would be
expected to remain as
station after being hit by
such a storm. It is cheaper
that the turret system but
still not stable enough to
support some topside
activity.
Same as the
semisubmersible but
very stable so all
intended topside
activity will not be
subject to stability.
Xmas Tree
Location and well
workover
Wet tree installation
is all that can be
installed when an
FPSO is involved
hence its oil recovery
is lower.
This system is also restricted
to wet tree installation and
subsea workover. Low
recovery is a challenge.
This system can
conveniently support
both dry and wet tree,
top side recovery is
possible hence higher
well recovery.
From the above summery, the SPAR present itself as the most suitable for the
expectations of the target field of this project and in further argument to this selection
choice is the SPAR platform’s survival of the various hurricane that have hit the Gulf of
Mexico with no SPAR ever suffering fatal damage.
37. 33
4 SPAR BODY
The objective of this section is to start the design process of the SPAR through selecting
a SPAR body which will be taken through the design stages for Tequila-Sunrise, to
complete this objective current SPAR bodies’ designs have been taken into consideration,
with these ideas in mind the Tequila-Sunrise body has been completely designed for
purpose.
4.1 Selection of the SPAR body
As explained through the research there are three different types of SPAR body which
could be chosen for Tequila-Sunrise, as portrayed in figure 4-1, therefore a judgement
was made that the truss SPAR body would be most suitable for Tequila-Sunrise and the
environment.
Figure 4-1 – Types of SPAR Body
Source: Oil and Gas journal (1998)
38. 34
The truss SPAR was chosen for Tequila-Sunrise because firstly, the truss SPAR is the most
cost effective of all the SPAR bodies due to the mid-section and soft tank requiring less
structural steel to fabricate therefore the costing of the SPAR body would be less. The
truss SPARS total draft is reduced which gives a chance for single piece fabrication and
transport an achievable option, therefore reducing the costing factor of the design and
ease of installation. The met-ocean is one of the reasons the truss SPAR was chosen due
to the drag load which will are caused by loop current in the Gulf would be reduced
through the truss SPAR due to the open bracing of the mid-section and during hurricane
and tropical cyclone the hull would be less vulnerable to vortex induced vibrations
because of the structural design, as the SPAR is designed with the force of weight higher
buoyance force which in turn majority of the SPAR is underwater which when high winds
prevail the SPAR is projected as it is only subjected to a small surface area of the total
SPAR. Finally the regional data suggest that for deep water exploration the truss SPAR is
the most consistently used SPAR in the Gulf of Mexico, as portrayed by figure 4-2.
Figure 4-2 – SPARS designed for the Gulf of Mexico
Source: Oil and Gas journal (1998)
39. 35
4.2 Elements of a SPAR body
A complete SPAR body would design would contain;
Topside
The topside is the structure where process activities are carried out. It is the most
visible part of the SPAR sustained on the hull structure. Weight of the topside is a
significant factor to the design as topsides weighing up to 18,000 tonnes require
a 4 column support system which will be attached to the hard tank at the
intersection of a radial bulkhead with the outer shelf (Chakrabati 2005).
Hard tank
The hard tank is used to provide the SPAR with buoyance required to support the
platform. Hard tanks are designed to withstand hydrostatic pressures, thereby
initiating the concept that usually accommodate five to six levels in between the
SPAR deck and bottom of the hard tank separated by a waterproof
compartments. Plus a further division of four levels between the radial bulkheads
emerging from the corner of the centre well. Finally at the waterline, an added
cofferdam tank which helps in reducing flooded volume in a situation of a possible
penetration of the outer hall by a ship collision (Chakrabati 2005).
Truss
The truss system also commonly known as the deep draft is the area which
extents below the hard tank, used to support the heave plates and provides
desired separation between the hard tank and soft tank. Another design concept
is that the truss help to reduce mooring loads which would be beneficial for
Tequila-Sunrise as the SPAR is situated in an environment with high currents.
40. 36
Soft tank
The soft tank is positioned at the bottom of the hull and is used to give the body
floatation during the installation process when the SPAR is transported
horizontally (Chakrabati 2005). The soft tank provides placement for the fixed
ballast, and guidance to keep the risers centralised and acts as a natural hang off
location for the export pipelines and flow lines.
Figure 4-3 – Elements of a Truss SPAR Body
Source: Offshore Technology Conference (2009)
41. 37
4.3 Summary of the design
The design of the SPAR body for Tequila-Sunrise was developed using existing SPARS
which are situated in the Gulf of Mexico. The main SPARS which were used to help
develop the design was Lucius truss SPAR, Pedido truss SPAR, Neptune cell SPAR and
Medusa truss SPAR, the research into each of these SPARS combined, made a fit for
purpose Tequila-Sunrise SPAR. Tequila-Sunrise SPAR will be fabricated in Technip,
Finland, as Technip are the leading manufacturers in offshore equipment, the SPAR will
be manufactured to the design specification stated in table 4-1.
Table 4-1: Design parameters for Tequila-Sunrise body
Topside deck weight 9,000 tonnes
Diameter 115ft (35.05m)
Length 610ft (965m)
Hard Tank Length 300ft (92m)
Draft 555ft (153m)
Center Well Dimension 46ft x 46ft
Number of Heave Plate 2
Number of Decks 3 (Lower Deck, Module Deck & Drilling Deck)
42. 38
5 TOPSIDE
5.1 Layout and equipment
Figure 5-1 – Topside configuration
The Tequila-Sunrise SPAR has been choosen as the Floating Production host for the
Badolee Oil and Gas field development (which is a combination of three oil fields), located
at 250Km directly south of New Orleans with a 2850m water depth in the Gulf of
Mexico.The SPAR will be positioned at the centre of the three fields, with the main field
which provide 50% of the expected oil while the other two fields contains 25%
respectively. The SPAR have the following dimensional configurations arranged on the
following decks.
Lower deck.
43. 39
Module deck and
Drilling deck
Table 5-1: Information for the SPAR body
TRUSS SPAR (2nd
GENERATION)
HULL INFORMATION
Diameter 115ft
Length 610ft
Hard Tank Length 300ft
Draft 555ft
Center Well Dimension 46ft x 46ft
Number of Heave Plate 2
Number of Decks 3 (Lower Deck, Module Deck & Drilling Deck)
DECK HEIGHT 27ft (average)
TOPSIDE FACILITIES
Oil Production 80,000bdp (peak)
Gas Production 32 MMscf (peak)
Produced Water 100,000 BPD
Types of Separator 3-Phase
Number of Separators 2 (Intermediate Pressure &
Low Pressure vessels)
Number of Compressors 3
Power Generation (kw) 65-80 MW
Number of Generators 3
Accomodation 112
Safety Escape route, Fire Fighting Mechanism, Blast Walls,
Life Boat, Temporary Accomodation.
Helipad Yes (Large enough for 2 helicopters)
SPAR POSITION Direct Vertical Access to Main Reservoir
Lower deck
- Drainage Systems: These are piping systems used to transport waste liquid
from any part of the SPAR to a central collation point from where it is
transferred to the treatment or disposal module. The liquid waste can be
classified into two types based on their source, which could be “the Hazardous
and the Non-hazardous” liquid waste.
44. 40
- Power Generation Module: This module is designed to supply the platform
with sufficient and relatively cheap power. For the Tequila-Sunrise SPAR, the
designed power supply is 65MW consuming about 20MMscf/d and to
increase the module’s reliability, and three power generating system were
installed then an extra back-up generator was also installed to maintain power
supply in the advent of an emergency.
- Water Processing and Injection Module: This module consist of produced and
sea water treatment plant, then a down-hole pumping machine used to
increase well pressure and crude oil recovery.
- Wellhead Modules: This module contains the production wellheads with
control valves and other machines used to standardize the flowrate of oil and
gas coming from the production risers before it is channelled to the processing
module. This module is also used for work-over activities and location for
work-over equipment while water injection wellhead is also stationed here.
- Utility’s Module: This module is the storage area for the SPAR’s consumables
such as firefighting water, drinking and bathing water, diesel, chemicals and
non-hazardous equipment like portable water treatment with pumping plant.
Electricity control and distribution board are also located within this module.
The layout of the lower deck is presented in the diagram below.
Figure 5-2 - Lower Deck Layout of Tequila Sunrise SPAR Topside
45. 41
Module deck
- Oil and Gas Processing Module: This is where all oil and gas processing
equipment are located, these equipment includes separators, compressors,
electrostatic coalescer, amine sweetener and other processing equipment. This
module is considered highly hazardous and special care need to be taken in its
set up to ensure safety is not compromised while additional measure like the
construction of blast wall to protect other modules and safety routes on this
deck from any blast when the module is compromised.
- Control Room: This module is considered the brain of the operation where all
activities are controlled from while equipment functions and monitoring
sensors are also installed here to help the SPAR’s operators remain in control
of the production process.
The layout of the module deck is presented in the diagram below
Figure 5-3 - Module Deck Layout of Tequila Sunrise SPAR Topside
46. 42
Drilling deck
- Accommodation and Helideck: The accommodation module is designed to
conveniently house all required personnel without compromising their safety
and comfort while the helideck is the landing pad for helicopters mainly used
for the constant in and out flow of operating staffs. Other notable features of
this module are; Temporary accommodation which is meant to protect the
personnel in the advent of any disaster while they wait for rescue, life boat
loading area and the life boats so that the personnel will have a quick means of
exiting the SPAR if required.
- Drilling Derrick and Support: Located in this module are equipment for drilling
and maintenance of the reservoir which include; drilling rig, drilling fluids,
drilling tubes/pipes, drill head and some electric facilities.
- Flare Tower: This module is used as a control measure against excess
hydrocarbon gas. The system consist of vent, burner, low and high pressure
header/flare drum set.
The layout of the drilling deck is presented in the diagram below
Figure 5-4 - Module Deck Layout of Tequila Sunrise SPAR Topsid
47. 43
5.2 Topside Utilises
The process facilities and utilities proposed for any floating production system (SPAR)
must meet the following design requirements:
Modularization of the units on separate skids
Process equipment must operate satisfactorily on a constantly moving vessel
Space and Layout considerations
Corrosion considerations, as crude contains CO2 and H2S
5.2.1 Modules for topside facilities
Production modules – riser& flow line inlets and pipeline networks
Process module – separation systems, oil systems, gas systems, gas lift systems,
produced water systems, injection water systems
Utilities modules – oil dispatch, gas compression modules, power generation
modules etc.
Accommodation modules
Safety systems and firefighting modules.
It is important to locate hazardous facilities away from the accommodation module and
from any possible ignition source.
5.2.2 Venting and flaring module
Venting is the controlled release of gas to the atmosphere during any emergency as part
of contingency measures. The high pressure gas being vented out mixes well with air due
to the large pressure difference. The system is equipped with a knock-out drum to
separate liquid particles from the vapour-like mixture and the liquid sent back to the
process stream for recovery.
48. 44
Flaring is a controlled process of burning natural gas from producing well using
atmospheric vents, low pressure or high pressure flare system. The flaring system
consists mainly of a flare stack and pipes for the gas passage. Usually gas is used for fuel
and excess gas gets disposed as flare. In this flaring system, considerations will be given
to have a safe radiation level and also avoid liquid carryover. Since disposal of gas with
high hydrogen Sulphide can be hazardous, it is important to desulphurize the gas before
flaring. For personal safety, maximum radiation level of 250 Btu/hr-ft2 (1420W/m2-K) is
normally considered a safe option.
The flare system used is the elevated flare type and has an approximate height of
100metres. It has the advantage of efficient particle dispersion. The flare system is
designed based on the API RP 521 criteria, considering the residence time and knock out
velocity and based on flare rate, temperature, gas composition and safety.
Regulatory requirements for the particular field with respect to flaring are included in the
Federal Register 30 CFR 250.1160, National Ambient Air Quality Standards, Notice to
Lessees NTL-4A, EPA.
49. 45
Figure 5-5 – flaring and venting stack
Source: http://thumbs.dreamstime.com/x/gas-vent-flare-boom-3067726.jpg
5.2.3 Power generation system module
The major requirement for power on the SPAR is to drive the various process components
like pumps, compressors, motors, material handling system, HVAC, lightning, control
systems, accommodation, heating and cooling and other deck machinery.
The power generation system ideally consists of the main gas turbines, backup
generators, emergency generators, transformers, distribution units, switch station and
control unit. The system is selected on basis of the total power required, peak load
possible, operational load and load factor. It is required for the module to be redundant
and highly reliable.
50. 46
The SPAR for the fields will be required to generate power of between 65MW. The
reasons for the somehow low energy requirements for the SPAR are the following:
Careful matching of generation capacity to a realistic maximum running load
Use of simple systems ,with gravity flow wherever possible
Choice of compact turbine units available for required duty
Judicious choice between central power supply or independent prime movers for
large equipment drives
Use of a 3 X 50% capacity power generation units (maximize redundancy) rather
than, say 2 X 100% units
Use of waste heat recovery system to reduce electrical heating loads.
Since gas is available in abundance it is utilized as fuel to feed the system after it must
have been processed to meet the required fuel specifications.
Figure 5-6 – Gas compressor
Source: http://parat.no/media/2882/off3_580x297.jpg
5.2.4 Fuel gas system module
This is basically for the power generation module. The required power is produced using
a multi-fuel combustion type turbine which can run both on fuel gas and diesel. The
51. 47
turbines run on diesel whenever the availability of the fuel gas is not guaranteed.
However the diesel used is supplied by a supply vessel and used during start-ups or
extreme conditions. The Fuel Gas System consists of fuel metering system, compressor,
heater and filter for the conversion of natural gas to fuel grade specifications for the
turbine. The specifications are given in terms of the calorific value of the fuel (ASTM
D1945 standards), fuel injection temperature/pressure and contaminants.
Figure 5-7 – Gas System
Source: http://www.technicsgrp.com/images/topside_modules/fuel-gas-treatment-system-for-
p-40-fpso.jpg
5.2.5 Diesel fuel system
This is required because the turbines on the SPAR have dual fuel capability. Thus, during
cold start conditions or zero-gas production, the diesel system, which uses diesel supplied
from another vessel, is used. The diesel fuel system uses pumps to discharge fuel and
atomizers to aid combustion. It is important to remove the water content from the diesel
52. 48
using fuel filters, centrifuges or coalescers as the supply vessel might dampen the fuel.
The fuel tank should also be coated from rust that may clog the fuel lines. The diesel fuel
is to follow the required ASTM standards 1D and 2D. The power system should be able to
provide steady power as any fluctuations will adversely affect the various components
present on board. The generators are often rated to 1.25 times the maximum peak load.
There are auxiliary generators which can run using diesel for long hours in case of a power
failure. Fuel tanks are provided to facilitate this rate of power generation.
Figure 5-8 – Diesel fuel system
Source:http://article.wn.com/view/2014/04/25/Worldwide_Power_Products_to_Host_Open_House_for_
Offshore_Tec/)
5.2.6 Produced Water Conditioning Module
The water separated in the separators and surge tanks are piped to the produced water
conditioner where the oil is skimmed off and the clean water, after various treatment,
deoxygenation and conditioning, is jettisoned on the sea or sump. There are various
processes for conditioning produced water and effluent oil water separation such as
53. 49
gravity separation, floatation, coalescing and the use of hydro-cyclones.The
Environmental Protection Agency enacted the National Pollution Discharge Elimination
System (NPDES) general permit, where the required discharge limit for produced water
in the Gulf of Mexico is a daily maximum of 42mg/l and a monthly average of 29mg/l for
oil and grease
Figure 5-9 – Produced water conditioning module ready to deploy
Source:http://www.siemens.com/press/en/pressrelease/?press=/en/pressrelease/2010/industry
_solutions
5.2.7 Drain System
The mezzanine or production deck just above the main deck allows a significant amount
of process equipment to be located above the main (lowest) deck. The main deck is
served by two open-drain systems; one for non-hazardous areas and the other for the
54. 50
hazardous. The non-hazardous open drain system collects fluids that are considered safe
such as rainfall, hydrants, used water etc., while the hazardous one collects from sections
considered unsafe such as oil spilled on board. Both systems drain to a bucket-and –weir
type slop tank located on a central column and then separated physically ,making it
possible to redirect some component to the process stream. The hazardous and non-
hazardous sections are kept as far apart from each other to prevent contamination of
non-hazardous section.
Figure 5-10 – Drain System on Platform Topside
Source:http://www.blucher.co.uk/references/marine/wastewater-treatment-system-for-marine-
applications/
The closed-drain system is served by the oil-surge tank. It functions by redirecting
hydrocarbon liquids back to the process stream for enhanced recovery. With production
separators on the production deck, there is enough head available for gravity drainage.
Regulations and standards to be considered for the drain system are highlighted in Clean
55. 51
Water Act, NPDES permits (National Pollutant Discharge Elimination System), Effluent
Limitation Guidelines (ELG).
5.2.8 Helideck
The helideck in this SPAR is the roof of the quarters building; this is to trade off cost
against vibration isolation. It is noted that the surface area of the helideck exceeds that
of the helicopter rotor diameter for proper ground cushion effect. Also provided are the
landing /departure paths for the helicopter. For safety purposes, all tall objects around
the helicopter landing path are marked with contrasting paints and the flare stack is kept
as far away as possible from the helideck. API RP 2L, Planning, Designing and Constructing
Heliports for Fixed Offshore Platforms.
Figure 5-11 – Helideck
Source:http://www.awamarine.com.au/files/editor_upload/Image/HMS/Helideck%20Monitorin
g.jpg
56. 52
5.2.9 Material handling system module
Sometimes, the SPAR would require heavy equipment handling. Such scenarios include
equipment repair and replacement, maintenance, modifications, supply vessel
offloading. The options available could be a platform crane, derrick crane, overhead
bridge crane, forklifts and small mechanical lifts in workshops. The main function of the
platform crane is to load and off-load material and supplies from boats. The crane is
located on the top deck over the boat landing area. It is recommended that an open
laydown / storage area be located near the crane on each deck level. Loading porches are
to be provided on the lower deck for easier access. The crane is also used for regular
equipment maintenance. They can also be used for the installation of subsea equipment
modules. Guidance and details on offshore crane usage are found in API RP 2D.
Figure 5-12 – Basic crane diagram for offshore material handling
Source: http://www.seatrax.com/cranebasics.html
57. 53
5.2.10 Control and Safety Systems
The control and safety systems on platform facilities generally include:
Local or central operational control systems
Data acquisition systems
Manual operator interface
Local equipment control and shutdown systems
Well control and shutdown systems
Emergency Shut Down (ESD) System
Fire detection systems
Combustible gas monitoring systems
Figure 5-13 – Control System Module of an offshore platform
Source: http://www.intechww.com/products-and-solutions/wellhead-solutions/hydraulic-
wellhead-control-panel/
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5.2.11 Firefighting systems:
Fire protection involves a complex system of sensors and stand-alone automated
response units which activates the sprinklers and deluge systems in the target hazard
region when a fire is detected. Based on the grade of fire the counter measures may vary
from carbon dioxide, chemicals and water (API 14J). At times in case of gas leaks heavy
blowers could be used to ensure the dilution of the gas. The delivery systems such as
extinguishers, fire hydrant hose are useful in small scale fires, whereas automatic systems
are used in regions such as the turbines, process areas. Inert gas system may be used for
emergency purging of compressors and turbines in case of a fire. The system is usually
designed such that it will not be disabled in case of a calamity, and performs its duty in
the most adverse situations. For this the water supply should be from two separate
locations on the SPAR. The controls for the pumps used for this system are independent
and stand-alone systems having maximum redundancy and also self-priming. The valves
and accessories should be of ABS (American Bureau of Shipping) standards. The fire
protection system which includes both the primary and secondary pumps should be able
to provide the maximum probable water requirement, which has been described as
the quantity of water required to fight the single largest fire area on the SPAR, plus
two pressure fire jets of at least 50psi pressure. The ABS provides detailed design
guidelines on the layout of fire hydrant pumps for the fire protection systems. The water
sprinkler systems should be auto-detect and auto-start type and should have a reliable
driving system which complies with the API and ABS standards. The spray systems
should cover the entire area and point upwards at the well heads rather than downwards.
The fuel system for the fire protection system should last for a minimum of 18
hours. Pipelines used for fire hydrant transmission should be protected from corrosion
to avoid clogging and failure of the system. Fire hoses should be able to resist the action
of oil, chemicals, environment and process conditions that may prevail in the process
deck area.
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In case of a fire emergency occurring, there should be at least two emergency response
units from where process shutdown, isolation, control could be performed. These units
should also have secure communication and power backup. Emergency counter-measure
systems should ensure that systems such as Emergency Lighting, alarm, BOP controls,
evacuation guidance, distress signalling is intact. Portable Extinguishers are provided in
accordance to the guidelines existing for the process area. Fire walls and blast walls have
to be provided as a mitigation procedure in case of a fire or explosion. Marshalling areas
made of steel and reinforced plastic should be available at life boat points. There should
be two well-planned escape routes which are well-lit and structurally intact to facilitate
the routing of personnel to the life-boats and helipad. Emergency response utilities such
as fire protection suits, safety mask, goggles and breathing apparatus are to be provided
at strategic locations. Special care should be taken to ensure that critical equipment or
hazardous pipelines should be given extra protective cover to reduce the chance of any
hazard. Regulations regarding fire-fighting systems are issued by the US Coast Guard or
BSEE in the Federal Register 33 CFR 145, 46 CFR Chapter 1.
Figure 5-14 – Water pump System for Firefighting
Source: http://hunger-hydraulik.de/hydraulic-offshore-applications.html
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5.2.12 Volatile Organic Compounds (VOC) Recovery
During loading operations the inert gas used for blanketing will contain as much as 90%
VOC (volatile organic compounds). This means the loss of organic compounds when
considered on an early basis is substantially high and this emission will contribute towards
environmental damage and economical loss. The use of hydrocarbon blanketing will
reduce the problem of emission. During the offloading procedure hydrocarbon gas is
taken from the production stream and is used to replace the offloaded crude in the
storage tankers. This gas is recovered back and put into the processing stream, leading
to total VOC recovery. Enhanced recovery of volatile organic compounds will contribute
economically and towards environmental conservation. VOC recovery systems prevent
the clouding of hydrocarbons during calm weather and reduce the corrosion issues
pertaining with the inert gas generation system.
5.2.13 Chemical Injection System
Various chemicals are injected into well, well heads, tubing’s, separators, process stream.
The chemicals are injected for various purposes such as hydrate inhibition, corrosion
inhibition, wax inhibition, scale inhibition, de-emulsifier. The various chemicals required
for these purposes are supplied by the supply vessel and is stored in the chemical tanks
on the SPAR. A chemical injection system may be a single point or multi-point injection
system. The system basically functions by pumping the chemical from the storage tanks,
filtering and metering it and then injects the chemical at the required pressure to the
target system.
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Figure 5-15 – Chemical Injection system
Source: http://vtechas.com/
5.2.14 Inert Gas and Nitrogen System
Inert gas is used for purging purposes to remove accumulation of hazardous gases in
vessels and pipelines, and for blanketing in storage tanks while cargo offloading. The main
purpose of blanketing is to prevent the formation of any potential hazardous volatile fuel-
air mixture in the cargo storage of the SPAR. This will also prevent any fire accidents in
the cargo bay. Nitrogen is the inert gas for the purging purpose while CO2 and gaseous
hydrocarbons are used as inert gases for blanketing. Compressed air is used for the
generation of nitrogen with the aid of nitrogen – membrane separators. CO2 for
blanketing is recovered after purification and dehydration from the exhaust of the power
turbines. By doing this the emission levels can be considerably brought down.
Hydrocarbon blanketing is done by diverting a part of processed gas from the gas
processing stream and using it for filling space above crude in the cargo tanks. Provision
should be made to isolate the tankers for maintenance or inspection. The inert gas system
should be isolated in such cases to ensure the safety of the crew.
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Figure 5-16 – Inert gas and Nitrogen system
Source: http://www.nauticexpo.com/prod/hamworthy-plc/
5.2.15 Desalination, Potable and Fresh Water System
Potable fresh water is used for general consumption, chemical injection, for closed loop
cooling and heating systems. Using fresh water for closed loop cooling system will help
save the cost of using exotic materials for heat exchangers and supportive accessories,
that would have been used in case of an open loop system. The processing of sea water
to fresh water requires removal of suspended impurities, salinity. The system is usually
based on a series of filters and reverse osmosis equipment. High level of purity should be
maintained to ensure health safety. The storage tanks and pipelines should have
protective coating to prevent rust formation. The materials used should not be toxic.
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Figure 5-17 – Potable and Fresh water system
Source: http://reactive-innovations.com/2014/04
5.2.16 Compressed Air System:
Compressed air is used on a SPAR for various purposes ranging from instrumentation &
pneumatic valve actuating mechanisms, air for power turbines, cleaning purposes,
nitrogen generation for inert gas purging & blanketing. The air has to be purified to
instrument grade before it could be used. This includes removal of suspended dust
particles and dehydration. The system usually consists of a multi-stage reciprocating air
compressor.
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Figure 5-18 – Air compressor system
Source: http://www.vacuum-guide.com/
5.2.17 Heating System
The major heating requirements are for increasing the temperature of process fluids and
to aid glycol recovery. The total heat required on the SPAR is calculated during the design
of the system. The heating of process fluids can be ensured by using a closed loop Waste
Heat Recovery System working in tandem with the power generation unit and air
compressors. The exhaust gas from turbines and compressors are passed through shell
& tube heat exchangers containing water-glycol mixture which has high heat carrying
capacity compared to pure water. A large quantity of heat is transferred to the heat
transfer medium in the heat exchanger. This hot water is then pumped and circulated to
process areas where heating is necessary. The water is depleted of its heat energy once
it has performed the heat transfer function to the target areas. This depleted water is
then passed through an economizer, such as to enable heat transfer with the processed
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water for injection, thereby lowering the temperature of the heat recovery solution. This
will enable a better heat recovery during continuous working cycles.
Figure 5-19 – Heating System for a typical Topside platform
Source: http://gcaptain.com/power-exhaust-gas-paybacks-waste/
5.2.18 Cooling System
The cooling system can either be a closed loop system or an open loop system. While
selecting a cooling system we have to keep in mind the amount of cooling required. An
optimum cooling fluid temperature in the range of 12o
C – 20o
C is considered ideal for
useful for the topside process cooling. A closed loop system has a working fluid mixture
which is continuously circulated to absorb and disperse heat. This fluid transfers the
absorbed heat to the waste heat recovery system and is subsequently cooled by the
cold sea water pumped up from a depth such that it has an optimum temperature of
15o
C.An open loop cooling system consists of cold sea water being pumped in and
circulated after minor treatment to reduce the chloride levels and suspended impurities
which may clog the heat exchangers. Even though the open cycle system offers an
effective better cooling rate, it requires heat exchangers made off exotic materials which
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may increase the cost of the process train. GRP (Glass Fibre Reinforced Plastic)
pipelines may be used but only if it meets the safety regulations.
5.2.19 HVAC (Heating Ventilation and Air Conditioning) System
It is necessary to provide a comfortable environment for the crew and personnel on a
SPAR. This is also essential for the operation of electrical equipment in the control room.
The air conditioning unit that may be used for the accommodation quarters could be a
direct expansion or chilled water type. Direct expansion type air conditioning uses air
handling units with expansion cooling coils, blowers, heaters and humidifiers which
maintain the required temperature and humidity. A small quantity of cold sea water
could be tapped from the cooling water pumped in for the process-cooling purpose,
and used to serve a chiller-humidifier-heater system and thereby avoid a refrigerant
based air conditioning unit. Sea water based cooling systems can be closed type or open
type. In closed type system the sea water undergoes heat exchange with an air
conditioner working fluid, which could be a mixture of water and TEG (Tri-ethylene
Glycol). In open loop system, sea water is used directly across blower but has to be
purified of impurities to prevent corrosion and clogging. Individual stand -alone systems
could be used for the purpose of cold storage for food.
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Figure 5-20 – HVAC system
Source: /www.frigomeccanicagroup.com
5.2.20 Living Quarters/Accommodation Module
Protection from external fires, noise and vibration is needed for the area where personnel
are concentrated. Fire resistant materials are to be used for the apartments. Potential
sources of ignition and gas leaks are to be isolated. Windows facing process areas if they
cannot be eliminated should be minimized. Escape routes are important and exposure to
radiation from potential flame sources should be taken care of. Utilities are to be near
the quarters building to minimize piping and conduit runs and to minimize the external
exposure to the quarters. Proximity to electricity, sewage treatment, heating, ventilation,
air conditioning and potable water are also considered.
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Figure 5-21 – Accomodation module
Source: http://www.labtechmodular.com/epc/
5.3 Reservoir Analysis
The major objective of this section include the determination of the process requirement
and operations of various unit requires to process the well fluids to meet the BS &W
(basic sediment and water) of 0.5% of oil in water and the removal of CO2 and H2S in the
gas so as to meet specification standards. The produced water will also be treated for
reinjection as prescribed by the offshore regulations, guiding the Gulf of Mexico. The
various streams of operations are listed below:
Determine the configuration of topside process
Determine processing requirement for the Tequila-Sunrise topsides
Equipment selection for unit operations
Equipment specification and sizing
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Topside Equipment Layout
Export pipeline sizing and specification
5.3.1 Production Profile
The Tequila sunrise SPAR design is based on the following STP (Stock Tank Profile) for Gas,
Oil and Water. These profile shows the total amount of Reservoir fluid from the
production riser within the period of production.
Table 5-2: Oil and Gas forecast
Year Average production BOPD Average Gas production MMScf
1 2015 65,000 26
2 2016 80,000 32
3 2017 80,000 32
4 2018 80,000 32
5 2019 80,000 32
6 2020 80,000 32
7 2021 77,000 31
8 2022 73,000 29
9 2023 68,000 27
10 2024 61,000 24
11 2025 55,000 22
12 2026 48,000 19
13 2027 42,000 17
14 2028 36,000 14
15 2029 30,000 12
16 2030 25,000 10
17 2031 20,000 8
18 2032 16,000 6
19 2033 12,000 5
20 2034 8,000 3
The peak production of the Badolee Field will be within the second and sixth production
year and the production of the field will start declining yearly from the seventh year until
its twentieth year after which the well will be abandoned and decommissioning operation
will commence.
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Most of the gas produced at the initial stage of this project will be re-injected into the
exploration well and at the later stage when the production will be of less economic value,
the gas will be used for power generation. This method was adopted for this project due
to the low gas produced from the production well and as a result of low GOR (Gas-Oil-
Ratio) of 400, which indicates a relatively low Gas Quantity in the Reservoir. Hence an
export pipeline construction will not be of economic values for this project and also as a
result of the low cost of gas from the Gulf of Mexico.
5.3.2 Composition
The Badolee Field Reservoir Fluid contains a significant percentage of heavy ends (C10+),
due to this fact it has a relatively low Gas Oil Ratio. The process of topside modelling and
design is based on the following composition and export conditions.
Table 5-3: Badolee Reservoir Fluid Composition
BADOLEE FIELD RESERVOIR COMPOSITION
Methane C1 20%
Ethane C2 3.7%
Propane C3 5.1%
Butane C4 3.8%
Pentane C5 3.70%
Hexane C6 3.50%
Heptane C7 3.50%
Octane C8 3.40%
Nonane C9 2.90%
Others C10+ H2O + Bal 48.99%
Hydrogen Sulphide H2S 0.006%
Carbon (IV) oxide CO2 1%
Sulphur S 0.40%
100%
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5.3.3 Reservoir Fluid Characteristics and Modelling
The phase characteristics for the Badolee field reservoir fluid was examined to determine
the optimal process conditions to maximize the recovery of the reservoir fluids. From the
phase envelope and table shown below, the cricondenbar pressure is 107bars while the
cricondentherm temperature is 460.8ºC. Thus, at the speculated well head pressure of
(285 bar, 95C), the reservoir fluid are basically composed of oil with dissolved gas which
is a single phase composition. As the fluid move through the subsea process equipment
and tubing it becomes a multiphase fluid. At the SPAR pressure of 43.15bar.The reservoir
fluid is essentially in the two-phase region.
Figure 5-24 – Phase envlope
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Table 5-4: Badolee Reservoir Fluid Composition
Badolee Export Oil Specification
Flowrate 80,000 BPD max
Temperature 50ᵒ
C
Pressure 10bar
TVP (True Vapour Pressure) 1 bar @ 38ᵒ
C
RVP (Reid Vapour Pressure) 0.85 bar
BS&W 0.45%
H2S Content 0.00%
Total Sulphur 0.00%
C02 Content 0.05mol%
5.3.4 Design Basis
Field Development Data
- Badolee field 250km North of New Orleans
- Production Risers: 1
- Injection Risers: 2
- Oil Production: 80,000 BPD
- Water Injection: 100,000 BPD
Design Requirement
The Badolee field with 1 Truss SPAR will be designed to meet the following requirements.
- Field Production Life: 20 years
- Daily Production: 80,000 BOPD
- Average water depth: 2850m
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5.4 Overview of the Tequila-Sunrise Topside Processing Units
Figure 5-25 – Topside processing
The Schematics above gives a general overview of the Topside processing in the Tequila-
Sunrise platform. The Tequila Sunrise Platform processing will contain the following
modules:
Oil Separation Module
IP Separator ( First Stage Separator)
LP Separator (Second Stage Separator)
Dehydrated oil cooler
LP Flare KO Drums
Electrostatic Coalescer
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Manifolds Module
Gas lift, Water injection Module, Oil/Water Pre Heater, Seawater Chemical
Injection Unit, Hydraulic Power Unit, Well Kill Pump.
Main Compression Module
Main Gas Compression Unit
Inlet Scrubbers
Coolers
Outlet Scrubber
Amine Sweetening Unit
Inlet Cooler
Inlet Scrubbers
TEG Absorber/Contactor
TEG Regeneration Unit
Heat Exchanger
Gas Dehydration Unit
Export Compression Module
Export Oil Pump
5.4.1 Topside Process Description and Modelling
The Topside process modelling was done using the HYSYS simulation software. The fluid
package used was Peng Robinson. H2S and CO2 removal was modelled using the Amine
Package. The evaluation of the reservoir fluid composition was based on oil and gas
product specification. Hence the various process units were selected to process reservoir
fluid to meet export and injection and re-injection conditions.
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The major process that was selected and modelled include:
Oil Processing
Gas Processing which includes ( Gas compression, Amine Sweetening, Gas Dehydration)
Oil Export
The overall HYSYS model for the Tequila Sunrise Platform is shown in the figure below.
The different process units on the topside were modelled in the sub-flow sheet
architecture. The sub-flow sheet is used to simulate and evaluate different conditions of
operations and to determine maximum operating requirement and sizing of equipment
for the various topside process equipment. The HYSYS model was used to determine
Operating parameters (i.e. Temperature and pressure), which will help maximize product
yield, cooling and heating requirement separator sizing, contactor column sizing, pump
and compressor absorbed power. A general overview of the overall process modelling
and simulation are presented in this section.
Figure 5-26 – HYSYS Topside processing
