Disconnectable Turret Mooring Systems for Deep Water

2006 ISOPE San Francisco, California

May 30, 2006

Arun Duggal, Sam Ryu, and Caspar Heyl

R&D, FMC Technologies Floating Systems

2/29

Co-authors at FMC Floating Systems

Arun Duggal

Sam Ryu

Caspar Heyl

3/29

Hurricane Katrina

With the large number of hurricanes in the GOM the DTM concept is being looked at with strong interest

Source: World Oil / Nov. 2005

4/29

1. Buoy Disconnect3. Buoy Reconnect

2. Disconnected

5/29

Introduction

• Disconnectable turret mooring systems being in use since late 1980’s offshore Australia and SE Asia

• Two disconnectable systems off the Grand Banks to avoid Icebergs.

• Excellent history of performance in both SC sea and Australia

• JHN system installed in 1993 has disconnected over 20 times

• MODEC/FMC currently building the first deepwater disconnectable system for Stybarrow

6/29

Existing Disconnectable Turret Mooring Systems

• JHN Lufeng 13-1, South China Sea

• 20 disconnects in 13 yrs

• Terra NovaCanada

• Santos Ltd – MV11Mutineer-Exeter Australia

• 5 disconnects in year 2006

7/29

Cyclones around Australia

Research has shown that cyclones in the Australian region exhibit more erratic paths than cyclones in other parts of the world. A tropical cyclone can last for a few days or up to two or three weeks. Movement in any direction is possible including sharp turns and even loops.

Reference: Australian Government, Bureau of Meteorology http://www.bom.gov.au/info/cyclone/#severity

Stybarrow Field

MV11 @ Mutineer/Exeter Field

8/29

Cyclones over Mutineer/Exeter Field

Name Period Max Category

• Clare Jan 7-10 2006 3

• Daryl Jan 18-23 2006 2

• Emma Feb 27-28 2006 1

• Floyd March 21-26 2006 4

• Glenda March 27-31 2006 5

• Hubert April 6-7 2006 2

9/29

Cyclone Phase Boundaries

M = (K + N) x V

Example) A category 3 cyclone moving at 10 knots,time required to sail to safe area is 12 hours.M = ( 20 + 12 ) x 10 = 320

Blue = 1.5 M = 480 nautical miles = 890kmYellow = 1.25 M = 400 nautical miles = 740kmRed = 0.75 M = 240 nautical miles = 440km

245

224

203

162

121

10Tropical Low

KCategory

Blue

YellowRed

1.5M

1.25M

0.75M

FPSO

10/29

Emergency Procedures

• BlueA plan for preparation for disconnection

A ballast plan

A plan for evacuating non-essential personnel

• YellowShutdown production

Prepare to disconnect from DTM

Proceed with ballast plan

• RedDisconnect from DTM

11/29

Safety Case

• A 12 hour period for shutting down production and preparing the FPSO is included in the definition of Cyclone / Storm alert phases.

• Preparations for disconnect commence when a Yellow AlertYellow Alert is declared. Notwithstanding this, the OIM may raise alerts and implement relevant alert procedures at any time.

• The decision to disconnect is made by the Master / Operations Supervisor.

12/29

Clare

2AM Jan 8 Shut-in production

9PM Jan 8 Lowered all risers

2AM Jan 9 Disconnected

Jan 10 Back to Field

7AM Jan 11 Picked up Spider Buoy line3PM Jan 11 Commenced Riser pickup4PM Jan 12 Started production

Under Construction: Boundary radii and sail-away course to be informed by MV11

13/29

Stybarrow FPSO SystemDisconnectable Turret Mooring System

14/29

• BHP Billiton Petroleum Pty. Ltd. (Client

• Stybarrow Field, Southern CarnarvonBasin, Australia

• 150,000 dwt FPSO Stybarrow Venture MV16

• Water depth 2,706-feet (825m)

• Installaltion planned for 2008

Stybarrow Venture MV16 Disconnectable Internal Turret Mooring

15/29

Global Analysis Basic Design Basis

• FPSO to disconnect from mooring and risers to avoid cyclones

• FPSO to stay on station during the 100-year non Cyclonic (winter) storm

• 12 risers and umbilicals

• 15 year design Life

• Mooring system design– maintain adequate offsets for riser system

– optimize mooring, riser and spider buoy system to meet spider buoy and turret requirements

16/29

Stybarrow FPSO Vessel Particulars

PROFILE

F.S . : 800 W.S . : 4800

B .L.

(11.20 m) (34.40 m) (43 .20 m) (50.00 m) (83 .60 m) (117.20 m) (150.80 m)

FR76+0.4

(184 .40 m) (218.00 m) (251.60 m) (264.00 m)

W.S . : 4800 F.S . : 800

F.W.T.(P& S)S TEE RINGGEA R RM.

A.P.T.(C)R.T.

S .L.W.L.

ENGINE ROOM

P UMPROOME NT.

PUMP ROOM

SLOP T. (P&S)

NO.6 W. B. T. (P

&S)

NO.6 C.O.T.(P&S)

NO.5 W. B

. T. (P&S)

NO.5 C.O.T.(P&S)

NO.4 W. B

. T. (P&S)

NO.4 C.O.T.(P&S)

NO.3 W. B

. T. (P&S)

NO.3 C.O.T.(P&S)

NO.2 W. B

. T. (P&S)

NO.2 C.O.T.(P&S)

NO.1 W. B

. T. (P&S)

F.P.T.

(C)

C.L.

S .L.W.L.NO.1 C.O.T.(P&S)

C.W.T. (C)

B .L.

11200 23200 4000 4800 6800

F.S . :850

W.S . :3400

33600 33600 33600 33600 33600 33600 12400

Cofferdam(P

&S)

VOID(C)

M.D.O.T.(P&S)

B .W.

B/S &S tandby .F.P.R.

F.P.120110100959080 857570656040 50302010A .P.

63m≈

264m

• Newbuild vessel

– LBP = 264m, Beam = 48m, Depth = 23.2m

– Maximum Displacement = 181,000 MT

• Turret Location:110m forward of midship

• Bilge Keels: 115m long, 0.8 m wide

• Main Propulsion and Rudder

• Stern thruster for heading control during some operations

17/29

Turret Structure

• Swivel Access Structure

• Swivel Stack

• Manifold Piping

• Upper Turret Structure

• Riser Deck

• Bearing

• Turret Shaft

• Chain Support Assembly

• Anchor Legs

18/29

Things to be considered…

• Buoy Disconnect from FPSO

• Disconnected Buoy Motions

• Buoy Reconnect Analysis

19/29

Design Environmental Criteria• FPSO Connected

– 100-year non cyclonic (winter storm): contour – governing seas

– Cyclone environment: Hs=6m with associated wind and current

– Maximum Offloading Seastate: Hs=3.5m with associated wind and waves

• Maximum Disconnect Environment– Cyclonic storm: Hs=6m, Tp=11.3 sec, Vw=19.5m/s,

Vc=0.8m/s

• Maximum Reconnect Seastate– Hs = 3.0m with associated wind and waves

• Disconnected Buoy – Design: 100-year Cyclonic Storm: Hs=12.6m, Tp=14.1sec

– Survival: 10,000-year Cyclonic Storm: Hs=17.3m, Tp=16.5 s

20/29

Spider Buoy Particulars• Maximum Diameter: 14 m

• Height: ~14.7 m

• Estimated Displacement

• Estimated Weight

• Design Net Buoyancy (mooring and risers)

– Riser Payload

– Mooring Payload

– Total MG load included in above

– Spider Buoy MG load

• Water Ballast System for controlling net buoyancy

• Design Depth Static (to top of buoy) = 30 m

• Maximum Design Depth (bottom) = 90 m

21/29

Spider Buoy Drop Test

22/29

Drop Test Results (Experiment vs. Calculation)

Two model scale tests:

1:351:81

23/29

Spider Buoy Motion Characteristics (Cd & Cm)

• disconnected buoy design– 100-year cyclonic storm

– Hs=12.6m

– Tp=14.1sec

• regular wave case:– 100yr cyclonic collinear

– H=20.9 m

– T=12.9 sec

– Vc=2.1 m/s (current)

24/29

Spider Buoy Motion Characteristics (Cd & Cm)

• inertia and drag coeffs.

– Cd_n=1.0

– Cd_a=0.9

– Cm=0.60

25/29

Simulation of Buoy Pull-in Loads

OrcaFlex 8.6a: sb027.sim (modified 7:45 AM on 10/18/2005 by OrcaFlex

Time (s)6004002000

FPSO

X (m

)

-125

-130

-135

-140

-145

-150

-155

OrcaFlex 8.6a: sb027.sim (modified 7:45 AM on 10/18/2005 by OrcaFlex

Time (s)6004002000

Upd

ated

Spide

r Buo

y Z (m

)

-10

-15

-20

-25

-30

-35

OrcaFlex 8.6a: sb027.sim (modified 7:45 AM on 10/18/2005 by OrcaFlex

Time (s)6004002000

fender Effective Te

nsion (kN) at End A

2500

2000

1500

1000

500

0

26/29

1. Buoy Disconnect3. Buoy Reconnect

2. Disconnected

27/29

Final Remarks (1/2)

• Disconnectable Turret Moorings are proven technology for mooring FPSOs in Hurricane environments

• DTMs in Deepwater have a number of challenges

• Trade-off between buoyancy on riser system and spider buoy

• Spider Buoy ballasting analysis / design along with riser model/installation plans

• Riser contents density variations have large impact on spider buoy payload requires SB with adjustable buoyancy (+/- 30% of average load)

28/29

Final Remarks (2/2)

• Can also be mitigated by adopting hybrid tower risers with individual support buoys

• Presentation showed ability of analysis to model complex operations like disconnect, disconnected buoy response in 100-year typhoon seas, and reconnection

• Design of riser system cannot be independent of turret – in fact riser design needs to be optimized with turret for best overall solution.

29/29

Disconnectable Turret Mooring Systems for Deep Water

Arun Duggal, Sam Ryu, and Caspar Heyl

[arun.duggal, sam.ryu, caspar.heyl]@fmcti.com

R&D, FMC Technologies Floating Systems