Offshore Structures Engineering - EF 2006

1

A)INTRODUCTION TO OFFSHORE STRUCTURES

ENGINEERING AND DESIGN

B) QGII JACKETS AND TOPSIDES DESIGN STRATEGY

(QATARGAS OPCO Engineering Forum Oct. 2006)

By: S. M. Salem

2

INTRODUCTION TO OFFSHORE STRUCTURES ENGINEERING AND DESIGN

Elements Influencing the Structural Design of an Offshore Platform

• Water depth

• Environmental forces

• Topsides size and weight

• Seabed Soil formation / geotechnical properties

• Method of Construction

• Hydrostatic pressure

• Field subsidence

• Geographical location and Earthquake effect

3


Types of Offshore Platforms

Fixed

Platform

Compliant

TowerTLP Mini -TLP SPAR FPS FPSO

4


Sequence Of Construction

• Steel jacket installed on seabed

• Piles driven through jacket’s legs

• Piles welded to the top of the jacket

• Transition pieces welded to the piles top

• Deck installed over transition pieces (by

lifting or float over method)

• Deck legs welded to the transition pieces

Fixed Offshore Platforms

5


6


Type of Analyses & Loads Considered in the Design

In-place Conditions

• Static Analysis

- Operating Environmental Loading

- Extreme Environmental Loading

- Dead weight and buoyancy

- Operational Loads

• Dynamic Analysis (for slender structures)

• Spectral Fatigue Analysis

• Earthquake Analysis

7


Construction / Installation Conditions

• Loadout

- Lifted, Skidded

or Wheeled

• Transportation

- Tow stability

- Structural Transportation

• Installation (Jackets)

- Lifting / Launching,

Floatation & Upending

• Installation (Decks)

- Lifting or Float Over

Jacket Upending

Deck Floatover

8

Wave and Current Forces Calculation on Exposed Members

Some Wave Theories frequently used:

Airy wave Theory (Linear)

Stockes’ Fifth order wave Theory (Non-linear)

Stream Function Theory (Non-linear)


||2

1

4

2

uDug

wCF

dt

duD

g

wCF

FFF

DD

mI

DI

9


Environmental Headings Considered in the Design

10

QGII Jackets and Topsides Design Strategy

LNG TRAIN 5EXPANSIONOPTION 1

QATARGAS NFBCOMPLEX

LNG TRAIN 4EXPANSIONBASE CASE

LQPU

WH-2

PRWH-

1

FLARE

WH4 – 63.4 m(12 Slots)

QatargasRas Laffan Industrial City

QGII-AQGII-B

PL434”

(91 km)

Power/Comm5-6 Power/Comm

5-4

QATARGAS NFB COMPLEX

WH6 – 56.1 m(15 Slots)

WH5 - 46 m(15 Slots)

PL5-616”

(800 m)

PL5-416”

(300 m)

Power/CommMain

AppraisalWell

FOCto

Shore

PL638”

(81 km)

FIELD GENERAL LAYOUT

11


FEED STAGE EXECUTION STRATEGY

• Advance WH4 and WH5 Jackets Engineering to the (RFC) stage for early Construction of

Jackets and Temporary Work Decks

• Perform basic Engineering and Design for full field development

• Use of RG Offshore Expansion Project Specifications and design criteria as a goby to

accelerate the Engineering Works

• Preparation of the EPC bid package and cost / Schedule estimate for the IFD and the FFD

(except for WH4, WH5 and WH6 Jackets)

12


SIMILARITIES BETWEEN RG

and QGII PLATFORMS

1. Similar Design Specifications

2. Same environmental Criteria

3. Similar Process

4. Similar Topsides facilities and

arrangement

5. Similarity of water depth between

RG WH5 and QGII WH4 (64.7 m

versus 63.4 m)

DIFFERENCES BETWEEN RG

and QGII PLATFORMS

1. Different Location. i.e. different soil

formation

2. Nine wells in case of RG WH5

versus Twelve wells in case of QGII

WH4

3. Difference in Topsides Equipment

Weight and Pipeline / Riser size

4. Pipeline, Riser and valves size 38”

in case of RG WH7 versus 34” in

case of QGII WH4

13


DESIGN METHODOLOGY FOR QGII WH4 Jacket (First Jacket RFC)

RGWH5 Jacket configuration taken as a start for the design of QGII WH4 Jacket

Conservative Topsides weight (similar to RG WH7) adopted to launch the Jacket

structural analyses

Jacket analyzed with the modeling of the actual Soil Profile at QGII WH4 location

Perform complete set of In-place analyses

Perform Complete set of Construction analyses

Topsides weight as per the weight report compared to the weights used in the structural

analyses to confirm the validity of the design

14


FEED TOPSIDES WEIGHTS (Values in MT)

QGII - WH4 QGII - WH5

Topsides Weight Used for

QGII Final Jacket / Piles

Analyses

4065.0 3795.0

RG – WH5 topsides Weight 3785.0

(Value increased by 160 MT to

account for a future bridge

proposed for QGII – WH4)

3625.0

QGII topsides weight as per

Rev. 00 FEED Weight

Report

3761.0 3658.0

15


• FEED EXECUTION MILESTONES

Date Milestones

Oct. 03 Start of FEED with J. R. McDermott

Mar. 04 WH4 Jacket and TWD Approved for Construction

Apr. 04 WH5 Jacket and TWD Approved for Construction

Apr. 04 Award Construction and Installation for WH4 and WH5 Jackets and TWD,

with an option for W6 Jacket and TWD to J. R. McDermott

Jan. 05 Exercise option of WH6 Jacket and TWD Construction and Installation

Jul. 04 Completion of FEED Stage

Oct. 04 Completion of WH4 Jacket and TWD fabrication and Installation

May. 05 Completion of WH5 Jacket and TWD fabrication and Installation

Nov. 05 Completion of WH6 Jacket and TWD fabrication and Installation

16


WH4 TOPSIDES PERSPECTIVE

17


WH4 JACKET ELEVATIONS & PLAN

18


WH4 Jacket and TWD

19


EPC STAGE

Awarded to NPCC in Abu Dhabi

TOPSIDES WEIGHT MANAGEMENT

A. TENDERING STAGE AND CONTRACT REQUIREMENTS

Topsides “Not To Exceed Weight” and “Management Reserve” set in the Contract

EPC bidders requested to assess the “Not To Exceed Weight” and “Management Reserve” and confirm compliance

Contractor required to model the jacket, including appurtenances and Piles / soil, with the topsides for accurate pile load computation

All Environmental Loading conditions affecting the Jacket & topsides to be considered

Maximum Piles loads calculated during Jacket design not to be exceeded

20


Topsides Not To Exceed Weight and Contractor’s Weight Budget

21


B. EPC ENGINEERING EXECUTION AND WEIGHT MANAGEMENT

Tight weight management program set by EPC Contractor to monitor and alert Engineering disciplines of Topsides weight and COG trends

Structural weight reductions measures

Change of topsides steel material grade from Low and Medium strength to Medium and High strength

Change from pancake secondary steel construction to intercoastal secondary steel construction

Extra refinement of Live loads Calculations

Optimization of analysis and plate girders design

Piles loads calculated during the jackets detailed Engineering not to be exceed

22

WH4 Operating CoG trendOperating Weight

ForecastRev 01

Rev A

FEED

Rev 0

14.000

15.000

16.000

17.000

18.000

19.000

20.000

18.000 19.000 20.000 21.000 22.000

CoG Plan Trend

Envelope +/- 0.5x0.5m

Y

X

5.8

24

CoG Plan

9.952

15.0

14

.0

1.51

B

A

2

15.012.0

CoG

Legs

10.0

10.0

## 385

## 396

## 384

## 472

## 472

0

0

0

0

0

0

3321

255

385

104

2818

215

396

636

2701

173

384

807

2725

152

472

716

2728

139

472

726

4065 4065 4065 4065 4065 4065

2600

2800

3000

3200

3400

3600

3800

4000

4200

FE

ED

Rev

00

Rev

01

Rev

02

Rev

03

Fore

cast

WH4 Future Operating Weight Trend (Tonnes)

Revised Contractors Budget 3255t

FEED Contractors Budget 3865t

Revised Contractors NTE 3650t

MOC increase to Company Contingency

Net Weight

Reported Weight

FEED Not to Exceed 4065t

Weight Contingency

Allowance

X Y Z

FEED Report Rev 00 21.064 17.639 17.432 3961

Report Rev 01 19.962 16.355 17.350 3429

Report Rev 02 19.854 15.865 16.860 3258

Report Rev 03 19.952 15.824 17.106 3349

Report Rev 04 Forecast 20.075 15.750 17.150 3339

Report NumberOpp Reported CoG (m) Rept'd

Wt (t)


Offshore Structures Engineering - EF 2006

Documents