Integrated Design Development

of a Low Motion

Semisubmersible Hull Form

Contents

• The Semisubmersible as a Deepwater Concept

• Hull Form Development and Optimization

• Hull Motion and Structural Verification

• Platform Features

– Hull

– Topsides

– Mooring and Riser System

• Conclusions

The Semisubmersible as a Deepwater Concept

• System components adaptable to ultra-deep water • Concept supports wide range of topside payloads • Track record of proven design and fabrication and methods • Proven offshore installation methods with minimal risk • Quayside Hook-up and Commissioning

Advantages

Limitations

• Currently, the concept is limited to applications with subsea wells

Hull Form Development

CONSTRUCTION TRANSPORTATION INSTALLATION OPERATION

-

Functional Requirements

Practical Aspects

Hull Form Optimization

Design Verification

TOPSIDES DRILLING PAYLOAD RISERS HULL

-

OPTIMIZED MOTIONS AND STEEL WEIGHT -

ANALYSIS MODEL TESTING

-

Work Flow Path

Functional Requirements

Basis Range of Application Location Gulf of Mexico Adaptable to other regions

Water Depth 1830 m > 3000 m

Topsides 100 KBOPD 150 MMSCFD Drilling 26,000 Tonnes

Can be re-configured for larger topsides (>40,000 Tonnes)

Riser System Steel Catenary Risers: 6 Production 2 Test 2 Water Injection 2 Export 18-inch Maximum Dia. 4,500 Tonnes vertical load

Flexibility to accommodate additional risers and/or larger diameter

Basic Requirements

Practical Considerations

Draft Limitation Operating Draft (Max.) = 27.5m

• Structural efficiency • Stability / tow-out draft • Deck Installation

Column Configuration Four-column and Six-Column configurations studied Six-column solution selected:

• Structural benefit from reduced deck span • Improved rectangular deck layout (safety, piping, etc.) • Increased flexibility for deck construction

Ring Pontoon Omni Directional Motion Response

Transit Draft (Min.) = 12m • Flexibility for Deck Integration • Access to yards

Hull Form Optimization

Variables • Draft • Columns (number, size,

spacing, shape, inclination)

• Pontoon (length, aspect ratio, bilge radius, shape)

• Cross bracing / ring pontoon configuration

Constraints • Target motion RAOs • Heave natural period • Motion/Acceleration at Riser

Attachment • Minimum GM • Deck area requirement • Minimum trimming ballast • Pontoon span / depth ratio • Maximum Draft • Transit draft

SOLVER

HULL WEIGHT MODEL

MOTION RESPONSE

MODEL

Cycle III-Operating

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0 5 10 15 20 25 30 35 40

Period (sec)

Ang

ular

Mot

ion

(rad

/ m

)

Pitch, Hdg=0Roll, Hdg=90

Cycle III-Operating

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 5 10 15 20 25 30 35 40

Period (sec)

Hea

ve (m

/m)

CG, Hdg=0CG, Hdg=90

Pontoon Weight Coefficients

Pontoon Aspect Ratio

Volu

met

ric W

eigh

t Coe

ff. (

t/m3)

Draft = 22.5 mDraft = 27.5 mDraft = 32.5 m

OPTIMIZED HULL

Hull Form Optimization

• Morison Element formulation for heave pitch and roll motion

• Added mass and inertia (wave) forces calculated assuming hull as an assembly of slender Morison elements

• Closed-form equations for pre-integrated forces along longitudinal, transverse and vertical slender members

• Motions are de-coupled by calculating angular motions about an estimated center of rotation

• Special treatment (added mass corrections) at connections between elements and element ends to obtain reasonable correlation with results from 3-D radiation / diffraction analysis

h_toc

H_taper * (draft_r - Hp) draft_r

Hp

Wpo

Xpon_Ytrans * Yi

Yi

Xsp + Dco

Db_Dt * Dco Db_Dt * Dci

Cant

rad_col * Dcorad_col * Dci

Xsp

Xsp/3 Xsp/3

Ysp/2

Wpi

Dco

Wpx

pon_Xtrans * XspDci

Motion Response Model

Example of Hull Idealization

Pontoon Weight Coefficients

Pontoon Aspect Ratio

Volu

met

ric W

eigh

t Coe

ff. (

t/m3)

Draft = 22.5 mDraft = 27.5 mDraft = 32.5 m

Hull Form Optimization

Pontoon Aspect Ratio

a/b = 2 a/b = 3

Volu

met

ric W

eigh

t Coe

ffici

ent

Increasing Draft

• Steel Weights defined on a volumetric basis

• Correlated to actual and preliminary designs

• Adjustments for draft / column (tank vent) height

• Adjustments for pontoon height and aspect ratio

Steel Weight Calculation:

Hull Motion And Structural Verification

• Motion Response Prediction • Comparison to Production Semi’s and MODU’s • Model Testing • Structural Verification

Hull Form - Key Features

• Six-columns • Ring Pontoon • Pontoon Shaped to Reduce

Motion and Provide Omni-directional Response

• Enlarged Center Column and Pontoon Section

• Pontoon Aspect Ratio Maximizes Added Mass Contribution

• Pontoons Consist Entirely of Flat Plate Construction

• Columns Rounded to Reduce Wave Run-up

Motion Characteristics

Heave Rao Pitch / Roll Rao

0.0000

0.0010

0.0020

0.0030

0.0040

0.0050

0.0060

0.0070

0.0080

0.0090

0.0100

0 5 10 15 20 25 30

Period (seconds)

Rol

l/Pitc

h A

mpl

itude

(rad

/ m

)

Roll (Beam Seas)Pitch (Head Seas)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

0 5 10 15 20 25 30Period (seconds)

Hea

ve A

mpl

itude

(m/m

)

0 deg (Head) 45 deg (Quartering)

90 deg (Beam)

Motion Performance Comparison

HEAVE MOTION @ CG, Hdg=90 (Beam Seas)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

5 6 7 8 9 10 11 12 13

Tz (sec)

Sig.

Hea

ve /

Hs

(m/m

)

KBR Drilling and Production Semi

Production Semi 2

5th Generation Drilling Semi

Production Semi 1

Heave Rao Heave Response

100-YR HURRICANE

Heave RAO, Hdg = 90 (Beam Seas)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 5 10 15 20 25 30

Period (sec)

Hea

ve (m

/m)

KBR Drilling and Production Semi

Production Sem 2

Typical 5th Generation Drilling Semi

Production Semi 1

Motion Performance Comparison

Roll Rao Pitch Rao Pitch RAO, Hdg = 0 (Head Seas)

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0 5 10 15 20 25 30

Period (sec)

Pitc

h (ra

d/m

)

KBR Drilling and Production SemiTypical Production Semi5th Generation Drilling Semi

Roll RAO, Hdg = 90 (Beam Seas)

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0 5 10 15 20 25 30

Period (sec)

Rol

l (ra

d/m

)

KBR Drilling and Production SemiTypical Production Semi5th Generation Drilling Semi

Motion Performance Comparison

Heave Acceleration at Riser Porch #2, Hdg=45

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

5 7 9 11 13

Tz (sec)

Sig.

Hea

ve.A

cc'n

/ H

s [

(m/s

^2)/m

]

Production Semi #1

Production Semi #2

KBR Drilling and Production Semi

Vertical Acceleration At Riser Porch Locations

Heave Acceleration at Riser Porch #1, Hdg=45

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

5 7 9 11 13

Tz (sec)

Sig.

Hea

ve.A

cc'n

/ H

s [

(m/s

^2)/m

]

Production Semi #1

Production Semi #2

KBR Drilling and Production Semi

Model Test Verification

Heave Rao Correlation

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0 5 10 15 20 25 30

Period (sec)

Hea

ve A

mpl

itude

(m/m

)

DIFFRACTION ANALYSISModel Test (soft mooring)Model Test (full mooring)

Structural Design Process

Hull Framing and Scantling Calculations

Global Hull FE Model (Patran): •Shell & Bulkhead Plating •Pontoon & Column Web Frames •Column Deck Flat Plating & Girders •Shell and Bulkhead Stiffeners (“Lumped”) •“Dummy” Members for Risers Porches, Fairleads, etc.

Static and Mooring/Riser Loads (Patran): •Hull Dead Weight and Operational Loads, including Ballast

•Topsides Dead Weight and Operational Loads

•Mooring Line & Riser Tensions

Global Topsides Model (Patran): •Primary Transverse Trusses •Primary Longitudinal Trusses •Primary Deck Girders and Plating

Hydrodynamic Analysis (WADAM)

•Various Wave Headings & Periods •Map Wave Pressures and Inertial Loads onto Global FE Model

Determine Design Waves

•“Squeeze-Pry” Load between the Pontoons •Global Torsional Moment •Longitudinal Shear Force between Pontoons

Global Strength Analysis (SESAM) •Stillwater + Hydrodynamic Loads •Yield Checks •Buckling Checks (SESAM-Platework)

Fatigue Analysis (SESAM)

•“Screening” Level Stochastic Fatigue Analysis using a Blanket SCF and one or more S-N Curves with G.o.M Scatter Diagram •Detailed Fatigue Analysis of Critical Areas using Refined FE Models (e.g. “t” x “t”)

123,239

210,135

262,672

368,602360,927

322,958

Hull Structure

Web Frames

Transv. Bhd. Plating, Stiff & Girders

Shell Plating & Stiff.

Long. Bhd. Plating & Stiff.

Typical Pontoon Framing • Scantlings in accordance with Class Rules (confirmed by Global Strength and Fatigue Analysis).

• Shell Plate Thickness Limited to 22 mm, except 30 mm in way of cross pontoon connections.

• Plate thickness and stiffener size variations minimized (8 plates sizes and 7 stiffener sizes, excluding local reinforcement at foundations).

• Option for bulb or angle stiffeners. • Frame Spacing: 2400 - 2950 mm. • Stiffener Spacing: 640-750 mm. • 355 MPa (50 ksi) Materials.

Hull Structural Design

Global Structural Model

• Hull design has adequate strength and meets stress/buckling criteria using reasonable plating and stiffener sizes

• All areas have fatigue in excess of 200 years (based on Gulf of Mexico Criteria)

• Castings used in “corner” region to provide sufficient fatigue life Casting Detail

Moorings

Risers

Drilling Derrick

Accommodation & Utilities

Platform Configuration

TOPSIDES

Process Capacity: 100 KBOPD 150 MMSCFD Dimensions 60 x 96 x 14m Number of Decks: 2 Operating Weight: 26,000 tonnes

HULL Overall Length………...112 m Overall Breadth………..95.2 m Height (t.o. column)…..43.4 m Draft……………………..27.5 m Air Gap (to deck)..…….18.3 m

Process Facility

PF1CVOID

PF1BBALLAST

PF1ABALLAST

PF2ABALLAST

PF4BBASE OIL

PF3ABALLAST

PF5BBALLAST

PF4ADRILL

WATER

PF5ABALLAST

PF6ABALLAST

ACCESS SHAFTW.T.DOOR

SF1CVOID

SF1BBALLAST

SF1ABALLAST

SF2ABALLAST

SF4BBALLAST

SF3ABALLAST

SF4ABALLAST

SF5ABALLAST

SF6ABALLAST

ACCESS SHAFTW.T.

DOOR

CF1DVOID

PA1CVOID

PA1BBALLAST

PA1ABALLAST

PA2ABALLAST

PA4BBALLAST

PA3ABALLAST

PA5BBALLAST

PA4ABALLAST

PA5ABALLAST

PA6ABALLAST

ACCESS SHAFT

ACCESS SHAFTELEV.SHAFT

P6BBALLAST

S6BBALLAST

SF2BBALLAST

PF2BFUEL OIL

PA2BBALLAST

PUMPROOM

UTIL.SHAFT

ELEV.SHAFT

PUMPROOM

UTIL.SHAFT

ELEV.SHAFT

PUMPROOM

UTIL.SHAFT

ELEV.SHAFT

PUMPROOM

UTIL.SHAFT

SA1ABALLAST

SA2ABALLAST

SA4ABALLAST

SA3ABALLAST

SA5ABALLAST

SA6ABALLAST

SA1BBALLAST

SA2BFUEL OIL

SA4BBASE OIL

SA5BBALLAST

SA1CVOID

CA1DVOID

SF5BBALLAST

Lower Hull Plan

CROSS PONTOONS (VOID TANKS)

PUMP ROOM (TYP)

ACCESS TUNNELS

FLUID STORAGE TANKS (TYP)

Transverse Section At Corner Columns

ACCESS SHAFT

BALLAST TANK

PUMP ROOM

VOID

VOID

EQPT ROOM

CHAIN JACK

FAIRLEAD

VOID

PIPING/UTILITY CHASE

CROSS PONTOON

CHAIN LOCKERS

CHAIN PIPES

Transverse Section At Center Column

ACCESS TUNNEL

VOID VOID

BALLAST TANK

BALLAST TANK

BULK TANKS

CHEMICAL STORAGE

MUD TANKS DRILLING

FLUID STORAGE

COLUMN STORAGE CAPACITIES

Barite/Bentonite…………425 m3 (15,000 ft3)

Cement……………………340 m3 (12,000 ft3)

Liquid Mud……………….4,000 bbls

Drilling Fluid (Brine)……4,000 bbls

Chemical Storage……….4,500 bbls

Topsides Configuration Alternatives

• Integrated Deck – Stiffened Plate “Box” Deck – Floatover or Lifted Construction

• Modular Deck – Truss Structure – Lifted in 4,000 ton modules or

larger

INTEGRATED “BOX” DECK

MODULAR DECK

Modular Deck Configuration

PROCESS MODULE

UPPER DECK

LOWER DECK

MEZZANINE DECK

PROCESS MODULE

Topsides - Upper (Weather) Deck

QUARTERS

RISER RACK

PIPE RACK

PIPE RACK SUBSTRUCT.

POWER GEN.

GAS COMPRESSION

CEMENTING/ SACK STORAGE

DERRICK

FLARE

16.8 m 16.8 m 19.75 m 19.75 m 22.1 m

96 m

60 m

LAYDOWN/ UTILITIES

FLASH GAS

BOOSTER PUMPS

Topsides - Lower (Production) Deck

QUARTERS

MUD PITS

MUD PUMPS

UTILITIES

MANIFOLD

OIL PROCESS

AREA

WATER TREAMENT

UTILITIES

MCC/ SWITCHGEAR

GAS TREATMENT

Hull - Deck Interface

BOX BEAM

FE Model

Modular Deck Construction

Mooring And Riser System

EXPORT RISERS

PRODUCTION, INJECTION & TEST RISERS

MOORINGS

UMBILICALS

RISER PORCHES

Mooring System

SCR Interface - Production Lines

SCR FLEX JOINT/BASKET

CLEAR DECK AREA FOR VERTICAL ACCESS

FIXED PIPING

TO MANIFOLD

CHAIN JACK

CHAIN BASKET

MESSENGER CHAIN

TOPSIDES

SCR LAYOUT CONCEPT

INSTALLATION SET-UP

Summary

• The semisubmersible hull form provides low motion characteristics within normal draft limits and using a relatively simple hull geometry.

• Motion response verified by analysis and model testing

• Structural design and analysis to verify hull weight and construction.

• Efficient and functional deck layout.

• Flexibility to accommodate alternative deck construction methods.

• Flexibility to accommodate riser system

Integrated Design Development

of a Low Motion

Semisubmersible Hull Form

Thank You

Contacts

For further information on our designs and services please contact: Singapore Office: 39, Pandan Road, Singapore. 609281 Tel.: +65 91093201 +65 68539106 Malaysia Office: 11, Jalan 14/2, Taman Tar, Ampang, Salangor, Kuala Lumpur. 68000 Tel.: +60 342665601 Mob.: +60 123210824 +60 178810807 Irvine Engineering Pte Ltd - Registered Address: 60 Paya Lebar Road, #08-43 Paya Lebar Square, Singapore. 409051 Tel.: +65 68539106

Dubai Office: Jumeirah Lake Towers, P.O. Box: 643593, Cluster C, Goldcrest Executive Tower Office 706, Dubai. UAE. Tel.: + 971 4 447 0897 Fax: + 971 4 447 0896 Mob.: + 971 567451923 (Main Company Contact)

enquiries@irvineeng.com