Introduction to Floating Structure

INTRODUCTION TO

FLOATING STRUCTURE

Sekretariat IA ITB, Jakarta –

20 November 2010

KULIAH UMUM

Indratmo Jaring Prasojo([email protected])

AGENDAAGENDAAGENDAAGENDA

1.Main Ideas

2.Basic Concepts

3.Type and Function of Floaters

4.Semi-Submersible

3.Type and Function of Floaters

4.Semi-Submersible

5.Tension Leg Platform

6.Spar

7.FPSO

8.Conclusion

Main Ideas

Limitations on Fixed Structure (cont’d)

Fixed platforms are economically feasible for installation in water depths

up to about 1,700 ft (400 m)

COMPLIANT TOWERtypically used in water depths ranging from 1,500 to 3,000 feet (400 to 550 m)

More than 400 meter?

Main Ideas

Compliant Towers

Main Idea

• Tall structures result in resonant wave response(structural natural period close to wave period)

• Increase in base shear and overturning moments(stronger structure increases costs)

Limitations on Fixed Structure (cont’d)

(stronger structure increases costs)

• Limitation on transportation barges

• Limitation on lifting barges capabilities

Basic Concepts

1. Buoyancy must equal weight plus any external vertical forces

Buoyancy = weight + vertical loads Buoyancy < weight + vertical loads

Vertical loads include:

Basic Concepts

Archimedes Principle

Where:

B = Buoyancy Force

ρ = fluid density ρ = fluid density

Vdisp = Displaced volume (volume terendam)

g = gravitational acceleration

Basic Concepts

2. The weight shall be positioned such that the hull will not tip over

T

y

p

h

T

L

P

h

o

o

n

S

e

a

s

t

a

rHurricane Rita, September 2005

Due to Hurricane Rita, the sea star TLP lost its tether. Without tether the TLP had unbalanced weight distribution which made it tip over

Basic Concepts

3. There should be enough Reserve Buoyancy to maintain balance and stability

even with tanks flooded

Basic Concepts

Study CasesP-36 Semi-submersibleRoncador Field off the coast of Brazil

There was deck hull

acting as reserve

buoyancy in

Thuderhorse which

saved it. No reserve

bouyancy available in

P-36.

Thunderhorse Semi-submersibleUS$ 5 Billion, 150 miles offshore of Texas, GoM

HURRICANE DENNISJune 2005 EXPLOSIONMarch 2001

Basic Concepts

4. The platform should stably support the deck above the highest wave crest

Basic Concepts

SHIP NOMENCLATURE

Basic Concepts

SHIP GEOMETRYMoving forward

Basic Concepts

STABILITYStability is the ability of a system to return to its undisturbed position after an

external force is removed (KrishThiagarajan – Handbook of Offshore Str)

Stability

Static

Dynamic

Due to steady wind force

When a sudden gust blows along with steady wind

Basic Concepts

STABILITY1. Transverse Stability

Positively Stable Negatively Stable = Unstable

Basic Concepts

STABILITYMetacenter Point (M)

K = Keel Point

G = Centre of Gravity

B = Centre of Buoyancy

M = Intersection between B and

centerline

GM = Distance between G andGM = Distance between G and

M → Metacenter Height

STABLE, GM > 0

Basic Concepts

STABILITYMetacenter Height (GM)

GM = KB + BM - KG

Second moment of waterplane area about x-axis

Submerged volume

Basic Concepts

STABILITY2. Longitudinal Stability

GMl = KB + BMl - KG

Basic Concepts

STABILITYDYNAMIC Stability

The dynamic stability criteria for a ship or FPSO are set based on the stability requirement to

withstand a sudden environmental change, e.g. a gust of wind. Vessels that are intact are

required under the ABS certification to be

able to withstand a 100-knot (51 m/s) wind in a storm impact condition.

In a damaged condition, the vessel should have sufficient stability to withstand a 50-knot

(25.7 m/s) wind.

Type &function of Floaters

FUNCTIONS1. Exploratory Drilling: Drillships, semi-submersible, Jack-ups, barges2. Production and Drilling: Semi-submersibles, Spars, TLs3. Production and Storage: Ship conversions, Newbuild ship & barges4. Pipelaying: Barges, semi-submersibles5. Construction/Derrick Vessels: barges, semi-submersibles5. Construction/Derrick Vessels: barges, semi-submersibles

PARAMETERS TO SELECT FLOATER TYPE

1. Water Depth2. Environment3. Function4. Export by pipeline or tanker

Platform drilling or MODU drilling

Wet or dry tree


WET & DRY TREESReservoir drivers


HULL SELECTION CRITERIA

Semi-submersibles

HISTORY

Submersible Semi-Submersible

Before 1971Before 1971

Lack of Consistency in design

Sedco 135 RigPentagone Rig

Semi-submersibles

HISTORY


Between 1971-1980Between 1971-1980

Most Common Rigs today

Twin hulls

High mobility

Standardization

MODU Classification rules

Aker H3 Production Semi-submersible

Semi-submersibles

HISTORY



Twin Hulls

Well designed bracings

Hull type superstructure

Odyssey

Semi-submersibles

HISTORY



Larger

Deepwater

Harsh Environment

Marine 700

Semi-submersibles

HISTORY


Between 1999 - 2009Between 1999 - 2009

Ultra Deepwater

Transocean Deepwater Nautilus

Semi-submersibles

HISTORY


Between 2010 - …..Between 2010 - …..

Ultra Deepwater

Petro Rig 1 – Sembcorp Marine

Semi-submersibles

FUNCTIONSProduction, Drilling &Workover

CAPABILITIESWaterdepth: 80 – 3,000 mWaterdepth: 80 – 3,000 m

Process capacity is up to 180,000 bpd

CURRENT PRESENCENorth Sea, Brazil, Asia, Gulf of Mexico (GoM)

Semi-submersibles

Semi-submersibles

Semi-submersibles

DESIGN PRINCIPLES1 Consist of deck, multiple columns, pontoon and space frame bracings

2 Centre of gravity (cog) is above the centre of buoyancy (cob)

SPAR � stability is achieved by positioning cog* below cob*

TLP � stability is derived from the tendons

3 Main Functions of Semis:

a. To stably support a payload above the highest waves

b. To minimally respond to waves

Number, size, spacing of stability columns

Height of the deck

)* cog = centre of gravity; cob = centre of buoyancy

Tension Leg Platform (TLP)

TERMINOLOGY

APIRP2T


RESPONSE CHARACTERISTICS

TLP TLP

More RigidMore Rigid

(More Fixed)(More Fixed) More CompliantMore Compliant

0 5 10 15 20 25 30

Wave Period (s)

TLP TLP

(heave, roll, (heave, roll,

pitch)pitch)

SemiSemi

Energ

yE

nerg

y

SparSpar


FUNCTIONSProduction, Drilling, Workover& Wellhead Support

Waterdepth: 150 – 1,500 mCAPABILITIES


North Sea, West Africa, Gulf of Mexico (GoM)CURRENT PRESENCE


FLOATERS INSTALLED & UNDER CONSTRUCTION

35000

40000

45000

Thunder Horse

AugerUrsa At lant is

Current TLP Depth Limit

0

5000

10000

15000

20000

25000

30000

0 1000 2000 3000 4000 5000 6000 7000

Water Depth, ft.

To

ps

ide

s W

eig

ht,

to

ns Spars

Semis

Mini-TLPs

TLPs

Genesis

Diana

Nept une

Boomvang/ Nansen

Horn Mtn.

Morpeth

Typhoon Mat t erhorn

Devils Tower

Allegheny

Kizomba (E-TLP)

Mars

Ram,/ Powell

Auger

Jolliet

Mar lin

Medusa

Holst ein

MadDog

Gunnison

Marco Polo

Magnolia

Pr ince

Red Hawk

West Senu

Na Kika

Front runner

Minimal Facilities Market

Large Topside

Wet Tree Market


TLP DEVELOPMENT (since 1983 = 25 TLPs)


TYPES OF TLP1. CONVENTIONAL

Shell’s Ram Powell TLP is located in 3,214ft of water at Viosca Knoll, block 956, in the Gulf Of Mexico

Shell’s Brutus TLP during topsides installation in Corpus Christi, TX, in 2001.


TYPES OF TLP2. E-TLP

• Reason for leg extensions

– Wider tendon base for greater pitch

stiffness (stability)stiffness (stability)

– Smaller spacing of deck supports for

more efficient structure

– Lower rotational inertia for hull and

deck for lower pitch natural period

• Approximately 40 percent lighter hull than

for a comparable, conventional TLP.

• A large moonpool can accommodate

conventional top tension risers.

• De-coupling of tendon porch separation

distance from the topsides deck design

produces maximum design flexibility.ABB


TYPES OF TLP3. MODEC MOSES

• Key points of the TLP design– minimal impact of wave loading– minimum tendon tension to obtain required platform response. – Low-cost tendon design with standard mill run tubulars, threaded

casing couplings and low cost top and bottom tendon connectors. – A well and riser system with standard 9 5/8" casing– short stroke riser tensioner. – a lighter deck structure. – Well drilling or workover capability utilizing leased compact,

lightweight, platform rigs. – A flexible installation method using SSDV, Multi-Service Vessels, or

derrick barge


TYPES OF TLP4. MINI TLP

SEA STAR

• Monocolumn Hull– Stiffened plate construction– Standard mild-grade,thin-plate steels– Fabricated in small modules– Assembled as complete unit at

quayside– No ballasting required during operation– Compartmentalized hull prevents

flooding– Hull can be lengthened to increase

payload– All compartments are accessible for

inspection

• Tendons– Tubular steel elements– Multiple,mechanically coupled sections– Design fatigue life typically exceeds

1000years, (API-requirement 200 years)– Tendon pairs have redundancy– Tendons are neutrally buoyant to minimize

payload and hull displacement– Fairings are installed on the tendons to

preventvortex-induced vibrations.


DESIGN DRIVERS

o Heave and pitch natural periods less than 4 seconds.

o Minimizing bending loads on TLP deck structure

o Minimizing (pitch-induced) tether tensionso Minimizing (pitch-induced) tether tensions

o Acceptable offset and setdown

o Installation stability


PURPOSE OF TETHERS

• Stationkeeping – vessel offset kept to prescribed

limits (~5% of WD)

• Vertical stiffness – reduce heave, pitch and roll • Vertical stiffness – reduce heave, pitch and roll

motions to accommodate rigid vertical risers with

dry trees

• Lateral stiffness – minimize surge, sway and yaw

slow drift motions


INSTALLATION• Conventional TLPs are

stable with deck load and

may be towed into position.may be towed into position.

• Mini-TLPs and ETLP may not

be stable and require

derrick barge or external

temporary buoyancy for

installation

• This factor should be

considered in design

SPAR

FUNCTIONSProduction, Drilling, Workover, Wellhead Support & Oil Storage



Malaysia, Gulf of Mexico (GoM)CURRENT PRESENCE

SPAR

Basic Parts:

SPAR

HARD TANK STRUCTURAL ARRANGEMENT

SPAR

Progression of SPAR

SPAR

TRANSPORTATION & INSTALLATION

SPAR


Truss Spar Wet Tow

SPAR


Truss Spar Upending

SPAR


Truss Spar Upended

SPAR


Add solid ballast

SPAR


Topside Lifting

SPAR


Topside Floatover Installation

FPSO

FUNCTIONSProduction, Storage & Offloading



North Sea, North Atlantic, Canada, Mediterranian, Africa, Brazil, AsiaCURRENT PRESENCE

Storage is up to 2 mmbbl

FPSO

TYPICAL CONFIGURATION OF NEW-BUILD FPSO

Typical Tanker Based FPSO

FPSO

FEATURES & ATTRACTIONS

FPSO

TYPICAL SIZE OF FPSO

FPSO

TYPICAL SIZE OF FPSO

FPSO

FPSO

MOORING SYSTEM1. Turret Moored

INTERNAL

EXTERNAL

2. Spread Mooring

FPSO

MOORING SYSTEM1. Turret Moored

•All mooring lines are attached to turret• All risers routed through turret• Suitable for harsh environment• Disconnection possible• Disconnection possible• Current presence: North Sea, North Atlantic

FPSO

MOORING SYSTEM2. Spread Moorings

• Mooring Lines are routed to optimum position on vessel• Risers are routed alongside of vessel• Suitable for moderate environment• Current presence: Brazil, West Africa • Current presence: Brazil, West Africa

CONCLUSION

Existing Function of Floaters

CONCLUSION

Rules of Thumb for Configuration Sizing

CONCLUSION

Rules of Thumb for Configuration Sizing

REFERENCES

1 Lecture Slides on Design of Floating Structure course – National

University of Singapore

• Dr. John Halkyard

• Prof. KrishThiagarajan

• Guest Lecture from SBM Offshore

2 Handbook of Offshore Engineering• Dr. John Halkyard

• Prof. KrishThiagarajan

3 Handbook of Offshore Engineering

4 www.offshore-technology.com

5 Other websites

Documents

Introduction to Floating Structure