Introduction to Floating Structure

KULIAH UMUM Sekretariat IA ITB, Jakarta – 20 November 2010

INTRODUCTION TO FLOATING STRUCTURE

Indratmo Jaring Prasojo ([email protected])

AGENDA 1.Main Ideas 2.Basic Concepts 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) More than 400 meter?

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

Main Ideas Compliant Towers

Main Idea Limitations on Fixed Structure (cont’d) • 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) • 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 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 T y L p P h o o n S e a s t the TLP had Due to Hurricane Rita, the sea star TLP lost its tether. Without tether unbalanced weight distribution which made it tip over a r Hurricane Rita, September 2005

Basic Concepts 3. There should be enough Reserve Buoyancy to maintain balance and stability even with tanks flooded

Basic Concepts Study Cases

P-36 Semi-submersible Roncador Field off the coast of Brazil

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

June 2005 HURRICANE DENNIS

March 2001 EXPLOSION

There was deck hull acting as reserve buoyancy in Thuderhorse which saved it. No reserve bouyancy available in P-36.

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

Basic Concepts SHIP NOMENCLATURE

Basic Concepts SHIP GEOMETRY Moving forward

Basic Concepts STABILITY Stability is the ability of a system to return to its undisturbed position after an external force is removed (KrishThiagarajan – Handbook of Offshore Str)

Static Due to steady wind force

Stability Dynamic When a sudden gust blows along with steady wind

Basic Concepts STABILITY 1. Transverse Stability

Positively Stable

Negatively Stable = Unstable

Basic Concepts STABILITY Metacenter Point (M)

K = Keel Point G = Centre of Gravity B = Centre of Buoyancy M = Intersection between B and centerline GM = Distance between G and M → Metacenter Height

STABLE, GM > 0

Basic Concepts STABILITY Metacenter Height (GM)

GM = KB + BM - KG

Second moment of waterplane area about x-axis Submerged volume

Basic Concepts STABILITY 2. Longitudinal Stability

GMl = KB + BMl - KG

Basic Concepts STABILITY DYNAMIC 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 FUNCTIONS 1. 2. 3. 4. 5.

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

PARAMETERS TO SELECT FLOATER TYPE 1. 2. 3. 4.

Platform drilling or MODU drilling Water Depth Environment Wet or dry tree Function Export by pipeline or tanker

Type &function of Floaters WET & DRY TREES Reservoir drivers

Type &function of Floaters HULL SELECTION CRITERIA

Semi-submersibles HISTORY Submersible

Semi-Submersible Before 1971 Lack of Consistency in design

Pentagone Rig

Sedco 135 Rig

Semi-submersibles HISTORY Submersible

Semi-Submersible Between 1971-1980 Most Common Rigs today Twin hulls High mobility Standardization MODU Classification rules

Aker H3 Production Semi-submersible

Semi-submersibles HISTORY Submersible

Semi-Submersible Between 1981-1984 Twin Hulls Well designed bracings Hull type superstructure

Odyssey

Semi-submersibles HISTORY Submersible

Semi-Submersible Between 1984-1998 Larger Deepwater Harsh Environment

Marine 700

Semi-submersibles HISTORY Submersible

Semi-Submersible Between 1999 - 2009 Ultra Deepwater

Transocean

Deepwater Nautilus

Semi-submersibles HISTORY Submersible

Semi-Submersible Between 2010 - ….. Ultra Deepwater

Petro Rig 1 – Sembcorp Marine

Semi-submersibles FUNCTIONS Production, Drilling &Workover

CAPABILITIES Waterdepth: 80 – 3,000 m Process capacity is up to 180,000 bpd

CURRENT PRESENCE North Sea, Brazil, Asia, Gulf of Mexico (GoM)

Semi-submersibles

Semi-submersibles

Semi-submersibles DESIGN PRINCIPLES 1 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

Tension Leg Platform (TLP) RESPONSE CHARACTERISTICS More Rigid

More Compliant

(More Fixed)

TLP (heave, roll, pitch)

Energy

Spar Semi

0

5

10

15

Wave Period (s)

20

25

30

Tension Leg Platform (TLP) FUNCTIONS

Production, Drilling, Workover& Wellhead Support

CAPABILITIES

Waterdepth: 150 – 1,500 m Process capacity is up to 220,000 bpd

CURRENT PRESENCE

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

Tension Leg Platform (TLP) FLOATERS INSTALLED & UNDER CONSTRUCTION Current TLP Depth Limit

45000 40000

Thunder Horse

Topsides Weight, tons

35000

Ursa

Auger

At lant is

Spars 30000

Holst ein

Semis Mini-TLPs

25000

Large Topside Wet Tree Market

Diana

Mars Ram,/ Powell

TLPs

Na Kika MadDog

20000 Genesis

Kizomba (E-TLP)

15000 Front runner

10000

Gunnison

Nept une West Senu

Horn Mt n. Devils Tower

Marco Polo

Marlin Jolliet

Magnolia

Medusa

5000

Red Hawk

Boomvang/ Nansen Prince

Typhoon

Mat t erhorn Allegheny

Morpet h

0 0

1000

2000

Minimal Facilities Market

3000

4000

Water Depth, ft.

5000

6000

7000

Tension Leg Platform (TLP) TLP DEVELOPMENT (since 1983 = 25 TLPs)

Tension Leg Platform (TLP) TYPES OF TLP 1. CONVENTIONAL

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

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

Tension Leg Platform (TLP) TYPES OF TLP 2. E-TLP •

• • • ABB

Reason for leg extensions – Wider tendon base for greater pitch 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.

Tension Leg Platform (TLP) TYPES OF TLP 3. 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

Tension Leg Platform (TLP) TYPES OF TLP 4. 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.

Tension Leg Platform (TLP) DESIGN DRIVERS o o o o o

Heave and pitch natural periods less than 4 seconds. Minimizing bending loads on TLP deck structure Minimizing (pitch-induced) tether tensions Acceptable offset and setdown Installation stability

Tension Leg Platform (TLP) PURPOSE OF TETHERS • Stationkeeping – vessel offset kept to prescribed limits (~5% of WD) • 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

Tension Leg Platform (TLP) INSTALLATION • Conventional TLPs are stable with deck load and 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 FUNCTIONS

Production, Drilling, Workover, Wellhead Support & Oil Storage

CAPABILITIES

Waterdepth: 150 – 1,500 m Process capacity is up to 220,000 bpd

CURRENT PRESENCE Malaysia, Gulf of Mexico (GoM)

SPAR

Basic Parts:

SPAR HARD TANK STRUCTURAL ARRANGEMENT

SPAR

Progression of SPAR

SPAR TRANSPORTATION & INSTALLATION

SPAR TRANSPORTATION & INSTALLATION

Truss Spar Wet Tow

SPAR TRANSPORTATION & INSTALLATION

Truss Spar Upending

SPAR TRANSPORTATION & INSTALLATION

Truss Spar Upended

SPAR TRANSPORTATION & INSTALLATION

Add solid ballast

SPAR TRANSPORTATION & INSTALLATION

Topside Lifting

SPAR TRANSPORTATION & INSTALLATION

Topside Floatover Installation

FPSO FUNCTIONS

Production, Storage & Offloading

CAPABILITIES

Waterdepth: 30 – 3,000 m Process capacity is up to 200,000 bpd Storage is up to 2 mmbbl

CURRENT PRESENCE

North Sea, North Atlantic, Canada, Mediterranian, Africa, Brazil, Asia

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 SYSTEM 1. Turret Moored

INTERNAL EXTERNAL 2. Spread Mooring

FPSO MOORING SYSTEM 1. Turret Moored •All mooring lines are attached to turret • All risers routed through turret • Suitable for harsh environment • Disconnection possible • Current presence: North Sea, North Atlantic

FPSO MOORING SYSTEM 2. 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

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