Effect of Mooring Lines on the Responses of Spar Platforms

by

Nur Azimah Mohd Zin

Dissertation submitted in partial fulfilment of

the requirements for the

Bachelor of Engineering (Hons)

(Civil Engineering)

JULY2008

Universiti Teknologi PETRONAS Bandar Seri Iskandar 31750 Tronoh Perak Darul Ridzuan

CERTIFICATION OF APPROVAL

Effect Of Mooring Lines On The Responses Of Spar Platform

by

Nur Azimah Mohd Zin

A project dissertation submitted to the

Civil Engineering Programme

Universiti Teknologi PETRONAS

in partial fulfilment of the requirement for the

BACHELOR OF ENGINEERING (Hons)

(CIVIL ENGINEERING)

Approved by,

(Assoc. Prof. Dr. Kurian V. John) Dr Kurian V. John Associate P'rQfesaor Civn fil9lnMring ~-•ln!l.,..onot UnivOISl!l T8llnolotl PETRl:!HAi -So<! .......... 3t1~ T"""'h Perrrlt Darul A~wan, M,'~L-§\Y51A

UNIVERSITI TEKNOLOGI PETRONAS

TRONOH, PERAK

July 2008

CERTIFICATION OF ORIGINALITY

This is to certify that I am responsible for the work submitted in this project, that the

original work is my own except as specified in the references and acknowledgement,

and that the original work contained herein have not been undertaken or done by

unspecified sources or persons

(NUR AZIMAH BINTI MOHD ZIN)

ii

ABSTRACT

Spar platform, a competitive alternative structure for deepwater oil field development

is modelled as a rigid body with six degree -of-freedom, connected to the sea floor

by multi-component catenary mooring lines, which are attached to the spar platform

at the fairleads. Since this spar platform is quite new in deepwater exploration, a lot

of studies and researches still need to be done. Therefore in this project, the different

type of spar platforms as well as the dynamic responses of spar platform such as

surge, heave and pitch are being analyzed and compared by using comparison

method based on its different mooring lines configurations. The mathematical results

by using Linear Airy Wave Theory, Pierson-Moskowitz Spectrum, Morison Equation

and Motion Response Spectrum have been conducted. The frequency domain

analysis and time domain analysis have been performed by choosing frequency

within 0.05 - 0.3Hz and time series within 0 - 100 seconds. For Neptnne Spar

Platform, the maximum profile obtained were 1.9 - 2m for surge, 0.78m for heave

and 0.065radian for pitch. These values are within the permissible limits for offshore

operations. Also, parametric studies have been made by using different number of

mooring lines. It is shows that there is no significant effect on the surge and heave

responses even though the stiffness increases as the number of mooring lines

increases.

iii

ACKNOWLEDGEMENT

In the name of ALLAH S.W.T. The Most Gracious and The Most Merciful for the

blessings and strength to complete this project.

First and foremost, I would like to acknowledge my deepest gratitude to my inspired

supervisor, Assoc. Prof. Dr. Kurian V. John for his extent guidance, constant

attention, valuable suggestion and enthusiastic support as well as personal concern

during one year oftime completing this Final Year Project.

An enormous appreciation to Assoc. Prof. Ir Dr Hj Muhd Fadhil Nuruddin, the

Programme Head of Civil Engineering Department for facilities and equipment

provided in order to complete my project. Special thanks once again to Final Year

Project Coordinators, Mr. Kalaikumar all Vallyutham and Ms. Niraku Rosmawati

Ahmad for their excellent guidance to the Final Year students. Not to forget, an

infinite gratitude to my internship supervisor, Ir. Abd Khalid Jaafar for his support

and motivation that inspired me to complete this project.

Last but not least, special thanks to both of my beloved parents; Hj Mohd Zin Ismail

and Hjh Samiah Hj Hasan and supportive brother, Khairul Anwar Hj Mohd Zin for

being there all the time, giving continuous aspiration, encouragement and support for

me to proceed with my Final Year Project.

iv

TABLE OF CONTENTS

CERTIFICATION OF APPROVAL .................•.............•........................................ i

CERTIFICATION OF ORIGINALITY ................................................................. ii

ABSTRACT ..•.......•..............•...........................................................•....•.......•........... iii

ACKNOWLEDGEMENT ..............•.•............•..•...........•.•......•..........•.•••.................• iv

TABLE OF CONTENTS ..........•.........•............•...........................•.........•....•....•........• v

LIST OF FIGURES ..........•...........................•..•..................................•..................... vi

LIST OF TABLE ...........•..............•.•..•.•....•.•.......•....•..•.•.•..•.•....................•....•....•.... vii

ABBREVIATIONS & NOMENCLATURES ..•.........•.................•.........•.........•.•. viii

CHAPTER 1- INTRODUCTION .•......................••....•..........................•....•............. 1

1.1 BACKGROUND OF STUDY ....................................................... 1

1.2 PROBLEM STATEMENT .............................................................................. 7

1.3 OBJECTIVES .................................................................................................. 7

1.4 SCOPE OF STUDY. ........................................................................................ 8

CHAPTER 2 -LITERATURE REVIEW ............................................................... 9

2.1 SPAR PLATFORM ......................................................................................... 9

2.2 MOORlNG LINES ......................................................................................... 12

2.3 THEORY ............................................................................... 14

CHAPTER 3- METHODOLOGY ...•....•...••...•........•.........•...••.•.•...•....••............•... 19

3.1 PROCEDURE ................................................................................................ 19

3.2 SOFTWAREREQUIRED .............................................................................. 21

3.3 HEALTH, SAFETY & ENVIRONMENT (HSE) ANAL YSIS ...................... 22

CHAPTER 4- RESULTS & DISCUSSIONS .•...•.......•.•............•.......................... 23

4.1 RESEARCH & DATA GATHER1NG ........................................................... 23

4.2 ANALYSIS ............................................................................. 26

v

4.3 PARAMETRIC STUDY (MOORING LINES) .................................. 35

CHAPTER 5- CONCLUSIONS & RECOMMENDATIONS ........................... 38

5.1 CONCLUSIONS ............................................................................................ 38

5.2 RECOMMENDATIONS ............................................................ 39

REFERENCES ......................................................................................................... 40

APPENDICES .......................................................................................................... 43

vi

LIST OF FIGURES

Figure 1.1 : Floating Production and Subsea Systems ................................... 2

Figure 1.2: (a) Classic Spar, (b) Truss Spar, (c) Cell Spar ....................................... 3

Figure 1.3 : Typical Spar Components ..................................................................... 4

Figure 1.4 : List of Spar Platform available in the world (Technip Offshore) ......... 5

Figure 1.5 : Kikeh Spar Platfrom (Technip Offshore) .............................................. 6

Figure 2.1 : Sample of Mooring Lines used for Offshore Platform ......................... 13

Figure 2.2: Sample of Taut Mooring configuration ......................................... 13

Figure 2.3 : Sample of Layout of Mooring Lines and Risers and Environmental

Orientation .......................................................................................... 13

Figure 2.4: Wave Theory ....................................................................................... 14

Figure 2.5 : Orbital motion under linear waves ...................................................... 15

Figure 2.6 : Motion of a particle in an ocean wave .................................... 16

Figure 3.1 : Steps of conducting analysis ......................................................... 21

Figure 4.1 : Neptune Spar Platform Diagram ......................................................... 25

Figure 4.2: Wave-Particle Velocity ...................................................... 26

Figure 4.3 : Wave Spectrum ...................................................................... 27

Figure 4.4 : Wave Profile .................................................................................... 28

Figure 4.5 : Total Horizontal Forces ............................................................... 29

Figure 4.6 : Surge Response Spectrum ............................................................ 30

Figure 4. 7 : Surge Profile ............................................................................ 31

Figure 4.8 : Heave Response Spectrum ........................................................... 32

Figure 4.9 : Heave Profile ................................................................................ 33

Figure 4.10 : Pitch Response Spectrum ............................................................ 34

Figure 4.11 : Pitch Profile ........................................................................... 35

Figure 4.12: Mooring Lines Configuration .............................................................. 36

vii

Figure 4.13 : Surge Stiffness ........................................................................ 36

Figure 4.14 : Heave Stiffness ....................................................................... 36

Figure 4.15: Surge Response Spectrum .......................................................... 36

Figure 4.16: Heave Response Spectrum ....................................................... 36

Figure 4.17: Surge Profile .......................................................................... 37

Figure 4.18: Heave Profile ......................................................................... 37

viii

LIST OF TABLE

Table 4.1 : Details of Neptune Spar Platform ....................................................... 23

Table 4.2 : General Natural Period for spar platform .............................................. 24

Table 4.3 : Wave Height (H(f)) for each frequency ............................................... 28

Table 5.1 : Maximum Responses for Surge, Heave and Pitch ................................ 38

ix

CB

CG

FPS

FPSO

FYPl

FYP2

GoM

HAZID

HAZOP

HSA

HSE

HSEM

PCSB

PPE

RAO

SACS

TADU

TLP

ABBREVIATIONS & NOMENCLATURES

Center of Buoyancy

Center of Gravity

Floating Production System

Floating Production, Storage and Offloading

Final Year Project 1

F ina! Year Project 2

Gulf of Mexico

Hazard Identification

Hazard and Operability Study

Health Risk Assessment

Health, Safety and Enviromnent

Health, Safety and Enviromnent Manual

PETRONAS Carigali Sdn Bhd

Personal Protective Equipment

Response Amplitude Operations

Structural Analysis Computer System

Tender Assisted Drilling Unit

Tension Leg Platform

X